Negative electrode active material, negative electrode, sodium ion battery, potassium ion battery, and method for manufacturing negative electrode active material

Abstract

To provide a negative electrode active material that provides a secondary battery with a high discharge capacity, a method for manufacturing the same, a negative electrode including the negative electrode active material, and a sodium ion battery and a potassium ion battery equipped with the negative electrode.SOLUTION: A negative electrode active material includes a carbon material containing graphene, the number of stacked graphene layers is 3.10 to 3.90, and the internal pore diameter measured by small-angle X-ray scattering is 1.25 nm to 1.60 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode active material, a negative electrode, a sodium-ion battery, a potassium-ion battery, and a method for producing a negative electrode active material. [Background technology]

[0002] Currently, high-energy-density secondary batteries are known in which charging and discharging are performed by moving lithium ions, sodium ions, potassium ions, etc., between the positive and negative electrodes.

[0003] In such secondary batteries, generally, layered transition metal composite oxides such as lithium cobalt oxide (LiCoO2) and sodium cobalt oxide (NaCoO2) are used as the positive electrode, and carbon materials capable of intercalating and releasing lithium ions are used as the negative electrode.

[0004] For example, Patent Document 1 proposes "a carbon material used as an electrode material for an energy storage device, wherein the carbon material has a graphene stacked structure, and in the small-angle X-ray scattering spectrum of the carbon material, the slope of the line connecting the point showing the natural logarithm of the scattering intensity when the natural logarithm of the scattering vector LN(q) is -1.5 and the point showing the natural logarithm of the scattering intensity when the natural logarithm of the scattering vector LN(q) is 1.4 is -1.5 or less." [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2021 / 060243 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] There is a growing demand for even higher capacity in secondary batteries.

[0007] The problem that this disclosure aims to solve is to provide a negative electrode active material and a method for producing the same that can yield a secondary battery with a high discharge capacity, a negative electrode containing the negative electrode active material, and a sodium-ion battery and a potassium-ion battery equipped with the negative electrode. [Means for solving the problem]

[0008] The means to solve the above problems include the following: <1> Contains a carbon material containing graphene, The number of layers of the aforementioned graphene is 3.10 to 3.90. A negative electrode active material with an internal pore diameter of 1.25 nm to 1.60 nm, as measured by small-angle X-ray scattering. <2> The number of layers of graphene is 3.20 to 3.50. <1> The negative electrode active material described above. <3> <1> or <2> A negative electrode containing the negative electrode active material described above. <4> <3> A sodium-ion battery equipped with the negative electrode described above. <5> <3> A potassium-ion battery equipped with the negative electrode described above. <6> <1> or <2> A method for producing the negative electrode active material described above, A process for preparing a powder containing organic acid zinc, A method for producing a negative electrode active material, comprising the step of obtaining a carbon material by firing at 1350°C to 1700°C. <7> The aforementioned zinc organic acid includes zinc organic acid A with a formula weight of 400 to 600 and zinc organic acid B with a formula weight of 180 to 220. <6> A method for producing the negative electrode active material described above. <8> The aforementioned zinc organic acid A is at least one selected from the group consisting of zinc gluconate and zinc gluconate hydrate, and the aforementioned zinc organic acid B is at least one selected from the group consisting of zinc acetate and zinc acetate hydrate. <7> A method for producing the negative electrode active material described above. [Effects of the Invention]

[0009] The problem to be solved by the present disclosure is to provide a negative electrode active material capable of obtaining a secondary battery with a high discharge capacity, a method for manufacturing the same, a negative electrode including the negative electrode active material, and a sodium ion battery and a potassium ion battery including the negative electrode.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic diagram showing an example of a sodium ion battery and a potassium ion battery 10 according to the present disclosure.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In this specification, "~" is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value.

[0012] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0013] <Negative electrode active material> The negative electrode active material according to the present disclosure includes a carbon material containing graphene, the number of graphene layers is 3.10 to 3.90, and the internal pore diameter measured by the small angle X-ray scattering method is 1.25 nm to 1.60 nm.

[0014] The negative electrode active material according to the present disclosure becomes a negative electrode active material capable of obtaining a secondary battery with a high discharge capacity due to the above configuration. The reason is presumed as follows.

[0015] The negative electrode active material according to the present disclosure contains a carbon material containing graphene, the number of graphene layers is 3.10 to 3.90, and the internal pore diameter measured by the small-angle X-ray scattering method is 1.25 nm or more, so that more ions (lithium ions, sodium ions, potassium ions, etc.) can be accommodated. In addition, since it is difficult to manufacture those with an internal pore diameter exceeding 1.60 nm, the internal pore diameter is 1.60 nm or less.

[0016] Hereinafter, the negative electrode active material will be described in detail.

[0017] (Carbon material) The negative electrode active material according to the present disclosure contains graphene. And the number of graphene layers is 3.10 to 3.90. Here, graphene refers to a single-layer sheet having the same thickness as the diameter of carbon atoms formed by bonding carbon atoms having sp2 hybrid orbitals.

[0018] Since the negative electrode active material according to the present disclosure contains graphene and the number of graphene layers is 3.10 or more, more ions can be stored in the stacked portion of graphene. Also by setting the number of graphene layers to 3.90 or less, the size of the pores surrounded by graphene changes flexibly, and more ions can be stored. Therefore, it becomes a negative electrode active material capable of obtaining a secondary battery with a high discharge capacity.

[0019] From the viewpoint of discharge capacity, the number of graphene layers is preferably 3.20 to 3.50, and more preferably 3.30 to 3.40.

[0020] The number of graphene layers is a value measured by a powder X-ray diffractometer. The specific procedure for measuring the number of graphene layers is as follows: The number of layers is determined by measuring the crystallite size of the carbon material and the interlayer distance of the graphene using the procedures described below (see "Procedure for measuring the crystallite size of the carbon material" and "Procedure for measuring the interlayer distance of the graphene") and substituting them into the following formula. Formula: (Number of layers) = {(Crystallite size of carbon material) / (Interlayer distance of graphene)} + 1

[0021] From the viewpoint of discharge capacity, the interlayer distance of graphene in the carbon material is preferably 0.37 nm to 0.39 nm, more preferably 0.375 nm to 0.385 nm, and even more preferably 0.377 nm to 0.38 nm.

[0022] • Procedure for measuring the interlayer distance of graphene The interlayer distance of graphene is a value measured by a powder X-ray diffractometer. For example, the powder X-ray diffractometer "SmartLab®" manufactured by Rigaku Corporation can be used. The specific measurement method is as follows: The sample is packed into a glass sample holder, a Cu tube is used as the X-ray source, Kβ rays are attenuated with a Ni filter, the tube voltage is 40kV and the tube current is 45mA, a high-speed one-dimensional detector (product name "D / teX Ultra250", manufactured by Rigaku Corporation) is used as the detector, and measurements are taken in a Bragg-Brentano optical system with a measurement range of 5° to 100° and a step size of 0.02°. Peak fitting is performed on the measured diffraction lines using the curve fitting program fityk. Specifically, first, a straight line connecting two local minima in the diffraction line is used as the background. Next, only the 002 diffraction line is selected and peak fitting is performed to determine the position of the diffraction line. The function used at this time is PseudoVoigt. The interlayer distance is calculated from the peak position of 002 using Bragg's formula.

[0023] From the viewpoint of discharge capacity, the crystallite size of the carbon material is preferably 0.75 nm or more and 1.00 nm or less, more preferably 0.80 nm or more and 0.95 nm or less, and even more preferably 0.85 nm or more and 0.90 nm or less.

[0024] • Procedure for measuring the crystallite size of carbon materials The crystallite size of carbon materials is a value measured using a powder X-ray diffractometer. The specific procedure for measuring the crystallite size of carbon materials is as follows: Crystallite size is measured using a powder X-ray diffractometer (product name "SmartLab®", manufactured by Rigaku Corporation). The measurement method is as follows: The sample is packed into a glass sample holder, a Cu tube is used as the X-ray source, Kβ rays are attenuated with a Ni filter, the tube voltage is 40kV and the tube current is 45mA, a high-speed one-dimensional detector (product name "D / teX Ultra250", manufactured by Rigaku Corporation) is used as the detector, and measurements are taken in a Bragg-Brentano optical system with a measurement range of 5° to 100° and a step size of 0.02° to obtain diffraction lines. Peak fitting is performed on the measured diffraction lines using a curve fitting program (e.g., fityk). Specifically, first, a straight line connecting two local minima in the diffraction line is used as the background. Next, only the 002 diffraction line is selected and peak fitting is performed to determine the position of the 002 diffraction line. The function used at this time is PseudoVoigt. After that, the position of the 002 diffraction line is calculated using Scherrer's formula.

[0025] (Physical properties of the negative electrode active material) -Internal pore diameter- The negative electrode active material relating to this disclosure has an internal pore diameter (hereinafter also simply referred to as "specific internal pore diameter") of 1.25 nm to 1.60 nm, as measured by small-angle X-ray scattering.

[0026] By setting the specific internal pore diameter to 1.25 nm or larger, sufficient capacity is ensured to accommodate more ions. Therefore, it becomes a negative electrode active material that can produce secondary batteries with high discharge capacity. From a manufacturing standpoint, the internal pore diameter is 1.60 nm or less.

[0027] From the viewpoint of discharge capacity and manufacturing, the specific internal pore diameter is preferably 1.35 nm to 1.55 nm, and more preferably 1.40 nm to 1.50 nm.

[0028] The specific internal pore diameter is a value measured by a powder X-ray diffractometer using small-angle X-ray scattering. For example, the powder X-ray diffractometer "SmartLab®" manufactured by Rigaku Corporation can be used. The specific measurement method is as follows: The sample was packed into a borosilicate glass capillary, a Cu tube was used as the X-ray source with a tube voltage of 40kV and a tube current of 45mA, and a scintillation counter (product name "SC-70", manufactured by Rigaku Corporation) was used as the detector with an angular range of 0.06° to 9.98° and a scan speed of 0.33°min. -1 Measurements are taken under the specified conditions. The obtained spectra are fitted using particle size / pore size analysis software (product name "NANO-Solver3.7", manufactured by Rigaku Corporation), and the pore diameter is calculated assuming that the pore shape is spherical.

[0029] <Method for manufacturing negative electrode active material> The method for producing the negative electrode active material according to this disclosure comprises a step of preparing a powder containing an organic acid zinc (preparation step), Preferably, the process includes a step of obtaining a carbon material by firing at 1350°C to 1700°C (firing step).

[0030] (preparation process) The preparation process involves preparing a powder containing zinc organic acid. Zinc organic acids are salts of zinc and organic acids. Organic acids refer to organic compounds that are Arrhenius acids. The organic acid preferably contains at least one selected from the group consisting of a carboxyl group, a sulfo group, a hydroxyl group, and a thiol group, and more preferably contains a carboxyl group.

[0031] Examples of zinc organic acids include zinc gluconate, zinc orotate, zinc glycinate, zinc glutamate, zinc acetate, zinc citrate, zinc malate, zinc benzoate, zinc stearate, and their hydrates.

[0032] The zinc organic acid preferably contains zinc organic acid A with a formula weight of 400 to 600 and zinc organic acid B with a formula weight of 180 to 220. The presence of both Zinc Organic Acid A and Zinc Organic Acid B in the zinc organic acid mixture tends to increase the amount of zinc in the powder containing the zinc organic acid mixture. Since zinc forms pores in the negative electrode active material, an increase in the amount of zinc makes it easier for pores to form in the negative electrode active material. Therefore, the presence of both Zinc Organic Acid A and Zinc Organic Acid B in the zinc organic acid mixture tends to result in a specific internal pore diameter of 1.25 nm to 1.60 nm in the negative electrode active material.

[0033] From the viewpoint of discharge capacity, the molecular weight of zinc organic acid A is more preferably 400 to 650, and even more preferably 450 to 500. From the viewpoint of discharge capacity, the molecular weight of zinc organic acid B is more preferably 180 to 210, and even more preferably 180 to 200.

[0034] Here, the formula weights of zinc organic acid A and zinc organic acid B do not include the formula weight of water molecules if zinc organic acid A and zinc organic acid B exist as hydrates. Specifically, Zinc organic acid A is zinc(II) gluconate hydrate (composition formula: C 12 H 22 0 14 If the product is Zn·2H2O (formula weight 492), the formula weight of organic acid zinc A is the sum of the formula weights of the two water molecules (i.e., formula weight 18 × 2 = 36) minus the formula weight of zinc(II) gluconate hydrate (i.e., formula weight 492), which is 456.

[0035] Examples of organic zinc acid A include zinc gluconate, zinc citrate, and their hydrates. Examples of organic zinc acid B include zinc glycinate, zinc glutamate, zinc acetate, zinc acrylate, and their hydrates. From the viewpoint of discharge capacity and solubility, it is preferable that organic acid zinc A is at least one selected from the group consisting of zinc gluconate and zinc gluconate hydrate, and that organic acid zinc B is at least one selected from the group consisting of zinc acetate and zinc acetate hydrate.

[0036] The molar ratio of zinc organic acid A to zinc organic acid B (zinc organic acid A / zinc organic acid B) is preferably 1 or more and 5 or less, more preferably 2 or more and 4 or less, and even more preferably 3.

[0037] The method for preparing the powder containing zinc organic acid is not particularly limited, but it is preferable to, for example, mix zinc organic acid with water to obtain an aqueous solution, freeze this aqueous solution, and then sublimate the water under reduced pressure, i.e., freeze-dry it, and then pulverize the freeze-dried product obtained by freeze-drying.

[0038] Freeze-drying is performed, for example, using a freeze-drying apparatus manufactured by Tokyo Rikakikai Co., Ltd. (product name "FDU-1100"), 10 3 Pa~10 4 It is performed at a pressure of Pa. The method for grinding the freeze-dried material is not particularly limited, and known grinding methods can be used.

[0039] (Firing process) The calcination process involves calcining the powder containing zinc organic acid obtained in the preparation process or the precursor obtained in the other processes described below at 1350°C to 1700°C to obtain a carbon material.

[0040] This process is preferably carried out under an inert gas atmosphere. Examples of inert gases include nitrogen gas and argon gas. The flow rate of the inert gas is preferably 50 mL / min to 300 mL / min.

[0041] The firing method is not particularly limited and can be carried out using, for example, a tubular furnace. The firing temperature is preferably 1350°C to 1700°C, and more preferably 1400°C to 1600°C. It is believed that by firing at a temperature of 1350°C to 1700°C, the structure of the carbon material becomes more suitable for ion storage. The rate of temperature rise to the final temperature is preferably 5°C / min to 20°C / min. The firing time after reaching the final temperature is preferably 30 minutes to 2 hours.

[0042] After firing, it is preferable to allow the material to cool to room temperature and then pulverize the fired material obtained by firing. The pulverized fired material may be used as is as the negative electrode active material, or a mixture of the fired material and additives may be used as the negative electrode active material. The pulverization method is not particularly limited, and known pulverization methods can be used.

[0043] (Other processes) The method for producing a negative electrode active material according to this disclosure may include steps other than the preparation step and the calcination step described above.

[0044] Specifically, it is preferable that the process further includes, between the above preparation step and the above firing step, a heat treatment step in which the material is heat-treated at 500°C to 800°C, a washing step in which the heat-treated material obtained by the heat treatment is washed with acid, and a drying step in which the acid-treated material obtained by washing is dried to obtain a precursor.

[0045] The heat treatment process is preferably carried out under an inert gas atmosphere. Examples of inert gases include nitrogen gas and argon gas. The flow rate of the inert gas is preferably 50 mL / min to 300 mL / min.

[0046] The heat treatment method is not particularly limited and can be carried out using, for example, a tubular furnace. The heat treatment temperature is preferably 500°C to 800°C, more preferably 500°C to 700°C, and even more preferably 550°C to 650°C. It is believed that pre-heating the powder containing organic zinc acid and then firing it results in a carbon material structure that is more suitable for ion storage. The rate of temperature rise to the final temperature is preferably 5°C / min to 20°C / min. The heat treatment time after reaching the final temperature is preferably 30 minutes to 2 hours.

[0047] After heat treatment, it is preferable to allow the material to cool to room temperature and then pulverize the heat-treated product obtained by the heat treatment. The pulverization method is not particularly limited, and known pulverization methods can be used.

[0048] In the washing process, the type of acid is not particularly limited, but hydrochloric acid is preferred from the viewpoint of ease of handling. The concentration of hydrochloric acid is preferably 0.5 mol / L to 2 mol / L from the viewpoint of washing efficiency.

[0049] The cleaning method is not particularly limited, and known methods can be used. From the viewpoint of cleaning efficiency, it is preferable to clean while applying ultrasonic vibrations to the acidic solution, which is the cleaning solution.

[0050] There is no specific time limit for the cleaning process; for example, it could be between 30 minutes and 2 hours.

[0051] After washing with acid, it is preferable to wash the acid-washed mixture with deionized water. It is preferable to continue washing with deionized water until the electrical conductivity of the water discharged by washing is 0.2 mS / m or less.

[0052] It is preferable to obtain a precursor by drying the acid-treated product obtained by washing with deionized water. Drying is carried out under reduced pressure, for example, at a pressure of 1000 Pa to 20000 Pa. The drying temperature is, for example, 80°C to 120°C.

[0053] <Negative electrode> The negative electrode relating to this disclosure includes the negative electrode active material relating to this disclosure. Examples of negative electrodes include those made of the negative electrode active material and those having a current collector and a negative electrode active material layer formed on the surface of the current collector, wherein the negative electrode active material layer contains the negative electrode active material and additives. Examples of additives include conductive agents and binders.

[0054] The following describes a negative electrode having a current collector and a negative electrode active material layer formed on the surface of the current collector, wherein the negative electrode active material layer contains a negative electrode active material and additives.

[0055] -Current collector- Examples of current collectors include foils, meshes, expanded grids (expanded metals), and punched metals made from conductive materials such as nickel, aluminum, and stainless steel (SUS). The mesh opening, wire diameter, and number of meshes are not particularly limited. Aluminum current collectors are preferred.

[0056] -Conductive agent- Examples of conductive materials include carbon black, graphite, carbon nanotubes (CNTs), and vapor-grown carbon fibers (VGCFs).

[0057] Examples of carbon black include acetylene black, oil furnace, and Ketjen black. Of these, from the viewpoint of conductivity, it is preferable to use at least one selected from the group consisting of acetylene black and Ketjen black, and more preferably acetylene black or Ketjen black.

[0058] The conductive agent may be used alone or in combination of two or more types. The content of the conductive agent in the negative electrode active material layer is not particularly limited, but is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, and even more preferably 3% to 10% by mass, relative to the total mass of the negative electrode active material layer. Within the above range, a negative electrode with higher output can be obtained, and the durability of the negative electrode is also excellent.

[0059] -Binding agent- The binder is not particularly limited, and known binders can be used, such as polymer compounds. Specific examples of polymer compounds include fluororesins, polyolefin resins, rubbery polymers, polyamides, polyimides, polyamide-imides, glutamic acid, starch, cellulose compounds, polyacrylic acid, sodium polyacrylate, and polyacrylonitrile.

[0060] Examples of fluororesins include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber).

[0061] Examples of polyolefin resins include polyethylene, syndiotactic-1,2-polybutadiene, ethylene-vinyl acetate copolymer, and propylene-α-olefin (2-12 carbon atoms) copolymer.

[0062] Examples of rubbery polymers include styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer and its hydrogenated products, styrene-ethylene-butadiene-styrene copolymer, and styrene-isoprene-styrene block copolymer and its hydrogenated products.

[0063] Examples of cellulosic compounds include cellulose, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylhydroxyethylcellulose, and nitrocellulose.

[0064] In particular, sodium polyacrylate is preferred as the binder because it can be used with water as a dispersion medium and has excellent binding strength.

[0065] The binder may be used alone or in combination of two or more types. The binder content in the negative electrode active material layer is not particularly limited, but is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, and even more preferably 5% to 15% by mass, relative to the total mass of the negative electrode active material layer. Within the above range, the moldability and durability of the negative electrode are excellent.

[0066] -Method for manufacturing a negative electrode- The method for manufacturing a negative electrode having a current collector and a negative electrode active material layer formed on the surface of the current collector is not particularly limited. For example, it may be a method of mixing the negative electrode active material with a conductive additive and a binder and performing pressure molding, or it may be a method of preparing a slurry as described later, coating it onto the current collector, and drying it.

[0067] In a method for manufacturing a negative electrode having a current collector and a negative electrode active material layer formed on the surface of the current collector, if the method involves preparing a slurry, coating it onto the current collector, and drying it, the slurry preferably contains a negative electrode active material, a conductive additive, a binder, and a solvent. Examples of solvents include amines such as N,N-dimethylaminopropylamine and diethyltriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone; and water.

[0068] Methods for coating a slurry onto a current collector include, for example, slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0069] The shape and size of the negative electrode relating to this disclosure are not particularly limited and may be adjusted to match the shape and size of the battery used.

[0070] The negative electrode according to this disclosure may contain only one type of negative electrode active material, or it may contain two or more types. The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but it is preferably 80% to 95% by mass.

[0071] <Sodium-ion batteries and potassium-ion batteries> The sodium-ion battery relating to this disclosure is a sodium-ion battery equipped with the negative electrode relating to this disclosure. The potassium-ion battery relating to this disclosure is a potassium-ion battery equipped with the negative electrode relating to this disclosure. The sodium-ion battery and potassium-ion battery according to this disclosure can be suitably used as a sodium-ion secondary battery and a potassium-ion secondary battery.

[0072] The sodium-ion battery and potassium-ion battery according to this disclosure preferably include a positive electrode and an electrolyte in addition to the negative electrode, and more preferably include a positive electrode, an electrolyte and a separator in addition to the negative electrode.

[0073] The sodium-ion battery and potassium-ion battery relating to this disclosure may be equipped with various known materials used in lithium-ion batteries, such as battery cases, spacers, gaskets, and springs.

[0074] The methods for manufacturing sodium-ion batteries and potassium-ion batteries according to this disclosure are not particularly limited and can be carried out according to known methods. The shape of the manufactured batteries is not particularly limited and can be various shapes such as cylindrical, prismatic, or coin-shaped.

[0075] (positive electrode) The sodium-ion battery and potassium-ion battery according to this disclosure preferably include a positive electrode. The positive electrode preferably contains a positive electrode active material. The positive electrode may also contain other compounds besides the positive electrode active material.

[0076] As other compounds, there is no particular limitation, and known additives used in the production of the positive electrode of the battery can be used. Examples of the additives include a conductive agent, a binder, and a current collector. As the conductive agent, the binder, and the current collector, those described above can be used.

[0077] The shape and size of the positive electrode according to the present disclosure are not particularly limited, and can be set to desired shapes and sizes according to the shape and size of the battery to be used.

[0078] There is no particular limitation on the positive electrode active material, and a known positive electrode active material for a sodium ion battery or a known positive electrode active material for a potassium ion battery can be used. From the viewpoints of charge-discharge capacity and output characteristics, the positive electrode active material for a sodium ion battery is preferably a sodium-containing compound, and more preferably a sodium-transition metal composite oxide. Examples of the sodium-transition metal composite oxide include NaMn2O4, NaNiO2, NaCoO2, NaFeO2, NaNi 0.5 Mn 0.5 O2, and NaNi 0.5 Ti 0.5 O2. The positive electrode active material for a potassium ion battery includes potassium salts of KxMy[Fe(CN)6]z (where M represents Fe, Mn, Co, Ni, Cr, or Cu, x represents a number of 0 or more and 2 or less, y represents a number of 0.5 or more and 1.5 or less, and z represents a number of 0.5 or more and 1.5 or less), KFeSO4F, potassium iron phosphate compounds, potassium vanadium phosphate compounds, activated carbon, α-FePO4, K 0.3 MnO2, anhydrous perylene, and the like.

[0079] (Electrolyte) As the electrolyte used in the sodium ion battery and the potassium ion battery according to the present disclosure, either an electrolytic solution or a solid electrolyte can be used.

[0080] In the case of sodium-ion batteries, the electrolyte is not particularly limited as long as it has a sodium salt as the main electrolyte. Examples of sodium salts in aqueous electrolytes include NaClO4, NaPF6, NaNO3, NaOH, NaCl, Na2SO4, and Na2S.

[0081] Furthermore, examples of sodium salts for non-aqueous electrolytes include NaPF6, NaBF4, CF3SO3Na, NaAsF6, NaB(C6H5)4, CH3SO3Na, NaN(SO2CF3)2, NaN(SO2C2F5)2, NaC(SO2CF3)3, and NaN(SO3CF3)2). These sodium salts may be used individually or in combination of two or more. Among these, NaPF6 is preferred.

[0082] In the case of potassium-ion batteries, the electrolyte is not particularly limited as long as it uses potassium salts as the main electrolyte. Examples of potassium salts used in aqueous electrolytes include KClO4, KPF6, KNO3, KOH, KCl, K2SO4, and K2S. These potassium salts can be used individually or in combination of two or more. As potassium salts, in the case of non-aqueous electrolytes, for example, electrolytes (e.g., KPF6, KBF4, CF3SO3K, KAsF6, KB(C6H5)4, CH3SO3K, KN(SO2CF3)2, KN(SO2C2F5)2, KC(SO2CF3)3, KN(SO3CF3)2, etc.) can be used as an electrolyte containing a solvent, such as propylene carbonate (PC). In addition, solutions dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), or solutions dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC), can also be used as the electrolyte. Among these, KPF6 is preferred as the potassium salt.

[0083] The electrolyte preferably contains a sodium salt or potassium salt and a solvent. Suitable solvents include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, fluoroethylene carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane. Ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; Esters such as methyl formate, methyl acetate, and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N,N-dimethylformamide and N,N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidone; Examples include sulfur-containing compounds such as sulfolanes, dimethyl sulfoxides, and 1,3-propanesaltones; and compounds obtained by substituting hydrogen atoms with fluorine atoms in the above compounds.

[0084] The solvent may be used alone or as a mixture of two or more, but it is preferable to use a mixture of two or more.

[0085] In particular, the solvent is preferably at least one solvent selected from the group consisting of propylene carbonate, ethylene carbonate, and diethyl carbonate, and more preferably a mixed solvent of at least two solvents selected from the group consisting of propylene carbonate, ethylene carbonate, and diethyl carbonate.

[0086] In the case of sodium-ion batteries, the concentration of sodium salt in the electrolyte is not particularly limited, but is preferably 0.1 mol / L or more and 2 mol / L or less, and more preferably 0.5 mol / L or more and 1.5 mol / L or less. In the case of potassium-ion batteries, the concentration of potassium salt in the electrolyte is not particularly limited, but is preferably 0.1 mol / L or more and 2 mol / L or less, and more preferably 0.5 mol / L or more and 1.5 mol / L or less.

[0087] As the solid electrolyte, known solid electrolytes can be used. For example, organic solid electrolytes such as polyethylene oxide-based polymer compounds, polymer compounds containing at least one of polyorganosiloxane chains or polyoxyalkylene chains can be used. In addition, so-called gel-type electrolytes, in which a non-aqueous electrolyte solution is held in a polymer compound, can also be used.

[0088] (Separator) The sodium-ion battery and potassium-ion battery according to this disclosure preferably include a separator.

[0089] A separator physically separates the positive and negative electrodes, preventing internal short circuits. The separator is made of a porous material, and the voids within it are impregnated with an electrolyte. To ensure the battery reaction, it is ion-permeable (in particular, at least sodium ion permeability or potassium ion permeability).

[0090] Examples of separators include porous membranes made of resin and nonwoven fabrics. The separator may be a single layer consisting of a layer of porous membrane or a layer of nonwoven fabric, or it may be a laminate consisting of multiple layers. Examples of laminates include a laminate having multiple layers of porous membranes with different compositions, and a laminate having a layer of porous membrane and a layer of nonwoven fabric.

[0091] The material of the separator can be selected considering conditions such as the operating temperature of the battery and the composition of the electrolyte. Examples of resins included in the fibers that form the porous membrane and nonwoven fabric include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyphenylene sulfide resins such as polyphenylene sulfide and polyphenylene sulfide ketone; polyamide resins such as aromatic polyamide resins; and polyimide resins. These resins may be used individually or in combination of two or more. The fibers that form the nonwoven fabric may also be inorganic fibers such as glass fibers.

[0092] The separator is preferably made of at least one material selected from the group consisting of glass, polyolefin resin, polyamide resin, and polyphenylene sulfide resin. Among these, a glass fiber filter is preferred as the separator.

[0093] The separator may contain an inorganic filler. Examples of inorganic fillers include ceramics (e.g., silica, alumina, zeolite, and titania), talc, mica, and wollastonite. The inorganic filler is preferably in particulate or fibrous form.

[0094] The inorganic filler content in the separator is preferably 10% to 90% by mass, and more preferably 20% to 80% by mass.

[0095] The shape and size of the separator are not particularly limited and should be selected appropriately to match the desired battery shape.

[0096] Figure 1 is a schematic diagram showing an example of the configuration of a sodium-ion battery and a potassium-ion battery 10 according to the present disclosure. However, the sodium-ion battery and potassium-ion battery according to the present disclosure are not limited to this. The sodium-ion battery and potassium-ion battery 10 shown in Figure 1 are coin-type batteries and include a battery case 12, a gasket 14, a negative electrode 16, a separator 18, a positive electrode 20, a spacer 22, a spring 24, and a battery case 26 on the positive electrode side. The separator 18 is impregnated with an electrolyte (not shown). [Examples]

[0097] The following examples will provide further details, but the disclosure is not limited to these examples unless it exceeds the spirit of the disclosure.

[0098] <Preparation of negative electrode active material> (Example 1) -Preparation process- In a flask, 7.1 mmol of zinc(II) gluconate dihydrate (manufactured by Tokyo Chemical Industry Co., Ltd., formula weight 456) as zinc organic acid A, 2.4 mmol of zinc(II) acetate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., formula weight 183) as zinc organic acid B, and 60 mL of water were added and stirred for 10 minutes to mix. Next, the mixture was freeze-dried for 12 hours under a pressure of 6 Pa using a freeze-drying apparatus (product name "FDU-1100", manufactured by Tokyo Rikakikai Co., Ltd.). The freeze-dried material was pulverized using an agate mortar to obtain a powder containing zinc organic acid.

[0099] - Heat treatment process (other processes) - The powder obtained in the preparation step was heat-treated in a tubular furnace at 600°C for 1 hour under an argon gas atmosphere. The gas flow rate was 200 mL / min, and the rate of temperature rise to the final temperature (600°C) was 10°C / min. After heat treatment, it was allowed to cool to room temperature. The resulting heat-treated material was pulverized using an agate mortar.

[0100] -Cleaning process (other processes)- The pulverized material obtained from the heat treatment process was cleaned with 1 mol / L hydrochloric acid using an ultrasonic cleaning device (product name "ASU CLEANER ASU-3M", manufactured by AS ONE Corporation) while applying ultrasonic vibrations. The acid-cleaned material was then washed with deionized water, and it was confirmed that the electrical conductivity of the water discharged by the cleaning process was 0.2 mS / m or less.

[0101] -Drying process (other processes)- The acid-treated material obtained in the washing process was dried at 110°C for more than 24 hours under a pressure of 2000 Pa to obtain a precursor.

[0102] - Firing process - The precursor obtained in the drying process was heat-treated in a tubular furnace at 1400°C for 1 hour under an argon gas atmosphere. The gas flow rate was 200 mL / min, and the rate of temperature rise to the final temperature (1400°C) was 10°C / min. After calcination, it was allowed to cool to room temperature. The resulting calcined material was crushed using an agate mortar to obtain the negative electrode active material.

[0103] (Example 2) The negative electrode active material was obtained in the same manner as in Example 1, except that the preparation steps were as follows. -Preparation process- 8.1 mmol of zinc(II) gluconate dihydrate (manufactured by Tokyo Chemical Industry Co., Ltd., formula weight 456) and 60 mL of water were added to a flask and stirred for 10 minutes to mix. Next, the mixture was freeze-dried for 12 hours under a pressure of 6 Pa using a freeze-drying apparatus (product name "FDU-1100", manufactured by Tokyo Rikakikai Co., Ltd.). The freeze-dried material was pulverized using an agate mortar to obtain a powder containing zinc organic acid.

[0104] (Comparative Example 1) The negative electrode active material was obtained in the same manner as in Example 1, except that the preparation steps were as follows. -Preparation process- 8.9 mmol of magnesium(II) gluconate dihydrate (manufactured by Tokyo Chemical Industry Co., Ltd., formula weight 414.6) and 60 mL of water were added to a flask and stirred for 10 minutes to mix. Next, the mixture was freeze-dried for 24 hours under a pressure of 6 Pa using a freeze-drying apparatus (product name "FDU-1100", manufactured by Tokyo Rikakikai Co., Ltd.). The freeze-dried material was pulverized using an agate mortar to obtain a powder containing organic magnesium.

[0105] (Comparative Example 2) -Preparation process- 10 mmol of D-glucose (manufactured by Kanto Chemical Co., Ltd., molecular weight 180.16) and 100 mL of water were added to a flask and stirred for 10 minutes to mix. Next, the mixture was freeze-dried for 12 hours under a pressure of 6 Pa using a freeze-drying apparatus (product name "FDU-1100", manufactured by Tokyo Rikakikai Co., Ltd.). The freeze-dried material was ground using an agate mortar to obtain a powder.

[0106] -Cleaning process (other processes)- The powder obtained in the preparation step was cleaned with 1 mol / L hydrochloric acid using an ultrasonic cleaning device (product name "ASU CLEANER ASU-3M", manufactured by AS ONE Corporation) while applying ultrasonic vibrations. The acid-cleaned material was then washed with deionized water, and it was confirmed that the electrical conductivity of the water discharged by the cleaning was 0.2 mS / m or less.

[0107] -Drying process (other processes)- The acid-treated material obtained in the washing process was dried at 110°C for more than 24 hours under a pressure of 2000 Pa to obtain a precursor.

[0108] - Firing process - The precursor obtained in the drying process was heat-treated in a tubular furnace at 1500°C for 1 hour under an argon gas atmosphere. The gas flow rate was 200 mL / min, and the rate of temperature rise to the final temperature (1500°C) was 10°C / min. After calcination, it was allowed to cool to room temperature. The resulting calcined material was crushed using an agate mortar to obtain the negative electrode active material.

[0109] (Comparative Example 3) The negative electrode active material was obtained in the same manner as in Example 1, except that the preparation steps were as follows. -Preparation process- 4.5 mmol of calcium(II) gluconate monohydrate (manufactured by Tokyo Chemical Industry Co., Ltd., formula weight 430.39) was heat-treated in a tubular furnace under an argon gas atmosphere at 600°C for 1 hour. The gas flow rate was 200 mL / min, and the rate of temperature rise to the final temperature (600°C) was 10°C / min. After calcination, it was allowed to cool to room temperature. The resulting calcined material was crushed using an agate mortar to obtain a powder containing organic calcium acid.

[0110] (Comparative Example 4) -Preparation process- 8.2% by mass of a pore-forming agent (PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether)) was added to the raw material, liquid Resol-type phenolic resin. Next, formalin was added as a crosslinking agent and maleic acid as a catalyst. This mixture was poured into a block-shaped mold made of synthetic resin and cured at 60°C for 16 hours to obtain a cured product. The cured product was removed from the mold, washed with water to remove PFA and unreacted materials, and dried. This method yielded a block of yellow porous phenolic resin in which interconnected macropores formed a three-dimensional network.

[0111] - Heat treatment process (other processes) - The starting material, porous phenolic resin, was placed in an alumina boat and carbonized in a tubular furnace under an argon atmosphere at 800°C for 1 hour. The gas flow rate was 100°C / min and the heating rate was 5°C / min. The resulting carbonized material was pulverized using an agate mortar.

[0112] -Cleaning process (other processes)- The pulverized material obtained from the heat treatment process was cleaned with 1 mol / L hydrochloric acid using an ultrasonic cleaning device (product name "ASU CLEANER ASU-3M", manufactured by AS ONE Corporation) while applying ultrasonic vibrations. The acid-cleaned material was then washed with deionized water, and it was confirmed that the electrical conductivity of the water discharged by the cleaning process was 0.2 mS / m or less.

[0113] -Drying process (other processes)- The acid-treated material obtained in the washing process was dried at 110°C for more than 24 hours under a pressure of 2000 Pa to obtain a precursor.

[0114] - Firing process - The precursor obtained in the drying process was heat-treated in a tubular furnace at 1500°C for 1 hour under an argon gas atmosphere. The gas flow rate was 100 mL / min, and the rate of temperature rise to the final temperature (1500°C) was 5°C / min. After calcination, it was allowed to cool to room temperature. The resulting calcined material was crushed using an agate mortar to obtain the negative electrode active material.

[0115] <Fabrication of the negative electrode> The prepared negative electrode active material, acetylene black (product name "Li-400", manufactured by Denka Co., Ltd.) as a conductive agent, and sodium polyacrylate (manufactured by Kishida Chemical Co., Ltd.) as a binder were weighed in a weight ratio of 85:5:10 and mixed with water as a solvent to obtain a slurry. The obtained slurry was coated onto a current collector (aluminum foil, manufactured by Hosen Co., Ltd., thickness 0.017 mm) using a doctor blade. The coated material was dried in a dryer at 80°C for 2 hours, and then vacuum dried at 150°C for 12 hours to obtain an electrode sheet. The electrode sheet was punched out into a 10 mm diameter circle using an electrode punching machine to be used as the negative electrode.

[0116] <Fabrication of sodium-ion batteries> (Fabrication of the positive electrode) The positive electrode was made by punching out a circular shape with a diameter of 10-12 mm from sodium metal (manufactured by Kanto Chemical Co., Ltd.) using an electrode punching machine.

[0117] (Preparation of electrolyte solution) An electrolyte solution was prepared by dissolving 1 molar sodium hexafluoride phosphate (manufactured by Kishida Chemical Co., Ltd.) in a solution of ethylene carbonate and diethyl carbonate mixed in a volume ratio of 1:1.

[0118] (Construction of sodium-ion batteries) In this embodiment, a negative electrode was fabricated using a negative electrode active material, and sodium metal was used as the positive electrode to evaluate the negative electrode characteristics of a sodium-ion battery as a half-cell. The sodium-ion battery was fabricated in a glove box under an argon gas atmosphere. The fabricated negative electrode, separator (product name "GB-100R", 380 μm thick, 1.8 cm diameter circular glass fiber filter paper), and fabricated positive electrode were stacked in this order. This was placed in a SUS battery case, and the prepared electrolyte was injected. A polypropylene gasket (product name "CR2032", manufactured by Hosen Co., Ltd.), a spacer (material: SUS, diameter 16 mm x height 0.5 mm, manufactured by Hosen Co., Ltd.), and a leaf spring (material: SUS, inner diameter 10 mm, height 2.0 mm, thickness 0.25 mm, washer manufactured by Hosen Co., Ltd.) were used to seal the battery and obtain a sodium-ion battery (half-cell). The amount of electrolyte injected was enough to completely fill the separator (200 μl).

[0119] <Making a potassium-ion battery> (Fabrication of the positive electrode) The positive electrode was made by punching out a circular shape with a diameter of 10-12 mm from potassium metal (manufactured by Kanto Chemical Co., Ltd.) using an electrode punching machine.

[0120] (Preparation of electrolyte solution) An electrolyte solution was prepared by dissolving 1 molar potassium bis(fluorosulfonyl)amide (KFSA) (manufactured by SOLVIONIC SA) in a solution of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1.

[0121] (Making a potassium-ion battery) In this example, a negative electrode was fabricated using a negative electrode active material, and potassium metal was used as the positive electrode to evaluate the negative electrode characteristics of a potassium-ion battery as a half-cell. The potassium ion battery was fabricated in a glove box under an argon gas atmosphere. The fabricated negative electrode, separator (product name "GB-100R", 380 μm thick, 1.8 cm diameter circular glass fiber filter paper), and fabricated positive electrode were stacked in this order. This was placed in a SUS battery case, and the prepared electrolyte was injected. A polypropylene gasket (product name "CR2032", manufactured by Hosen Co., Ltd.), a spacer (material: SUS, diameter 16 mm x height 0.5 mm, manufactured by Hosen Co., Ltd.), and a leaf spring (material: SUS, inner diameter 10 mm, height 2.0 mm, thickness 0.25 mm, Hosen Co., Ltd. washer) were used to seal the battery and obtain a potassium ion battery (half-cell). The amount of electrolyte injected was enough to completely fill the separator (200 μl).

[0122] Furthermore, potassium-ion batteries were only fabricated using the following methods: a potassium-ion battery equipped with a negative electrode containing the negative electrode active substance obtained in Example 1, a potassium-ion battery equipped with a negative electrode containing the negative electrode active substance obtained in Example 2, a potassium-ion battery equipped with a negative electrode containing the negative electrode active substance obtained in Comparative Example 1, and a potassium-ion battery equipped with a negative electrode containing the negative electrode active substance obtained in Comparative Example 3.

[0123] <Charge / Discharge Test> Using the fabricated sodium-ion and potassium-ion batteries, charge-discharge tests were conducted under the following conditions: current density of 25 mA / g, charge termination voltage of 0.002 V (held at the termination voltage for 8 hours after reaching it (only Comparative Example 4 was held at the termination voltage for 14 hours)), 5-minute rest period after charging, discharge termination voltage of 2 V, and 5-minute rest period after discharge. The charge capacity and discharge capacity were measured. A charge-discharge test apparatus (product name "TOSCAT-3100", manufactured by Toyo System Co., Ltd.) was used for the charge-discharge tests. Furthermore, the initial charge-discharge efficiency (discharge capacity ÷ charge capacity × 100) was calculated from the measured charge and discharge capacity values.

[0124] [Table 1]

[0125] The following explains the information contained in Table 1. • "Organic acid zinc A" and "Organic acid zinc B" The specific compounds of organic zinc A and organic zinc B used in the preparation steps for each example are shown below. The abbreviations for the compound names are as follows. The numbers in parentheses below the abbreviations for the compound names represent the formula weights of organic zinc A and organic zinc B used in the preparation steps for each example. Zn Glu: This refers to zinc(II) gluconate dihydrate. Zn Ace: This refers to zinc(II) acetate dihydrate. ·"others" In each example, if a different compound is used instead of zinc organic acid in the production of the negative electrode active material, that compound is indicated. Mg Glu means magnesium(II) gluconate dihydrate. Glc means D-glucose. Ca Glu means calcium(II) gluconate monohydrate.

[0126] • "Number of layers" This refers to the number of layers of graphene. • "Interlayer distance" This refers to the average interlayer distance of graphene in carbon materials. · "Crystallite size" This refers to the crystallite size of carbon materials.

[0127] From the above results, it can be seen that the negative electrode active material in this embodiment is a negative electrode active material that can produce a secondary battery with a high discharge capacity. [Explanation of Symbols]

[0128] 10: Sodium-ion battery and potassium-ion battery, 12: Battery case (negative electrode side), 14: Gasket, 16: Negative electrode, 18: Separator, 20: Positive electrode, 22: Spacer, 24: Leaf spring, 26: Battery case (positive electrode side)

Claims

1. Contains a carbon material containing graphene, The number of layers of the aforementioned graphene is 3.10 to 3.

90. A negative electrode active material with an internal pore diameter of 1.25 nm to 1.60 nm, as measured by small-angle X-ray scattering.

2. The negative electrode active material according to claim 1, wherein the number of layers of graphene is 3.20 to 3.

50.

3. A negative electrode comprising the negative electrode active material according to claim 1 or claim 2.

4. A sodium-ion battery comprising the negative electrode described in claim 3.

5. A potassium-ion battery comprising the negative electrode described in claim 3.

6. A method for producing a negative electrode active material according to claim 1 or claim 2, A process for preparing a powder containing organic acid zinc, A method for producing a negative electrode active material, comprising the step of obtaining a carbon material by firing at 1350°C to 1700°C.

7. The method for producing a negative electrode active material according to claim 6, wherein the zinc organic acid comprises zinc organic acid A having a formula weight of 400 to 600 and zinc organic acid B having a formula weight of 180 to 220.

8. The method for producing a negative electrode active material according to claim 7, wherein the zinc organic acid A is at least one selected from the group consisting of zinc gluconate and zinc gluconate hydrate, and the zinc organic acid B is at least one selected from the group consisting of zinc acetate and zinc acetate hydrate.

Images