Method for producing positive electrode active material, method for producing secondary battery, method for producing porous carbon, positive electrode active material, and secondary battery

Abstract

Provided are a high-capacity lithium-ion secondary battery, and a positive electrode active material used for the same. Also provided is a porous carbon that can be used in the positive electrode active material. Provided is a method for producing a positive electrode active material, in which a porous carbon and sulfur are mixed and subjected to a heat treatment at from 120°C to 160°C for from 1 to 10 hours. The porous carbon is obtained by: mixing a spherical resin, a base having a weight of from 1.0 to 2.0 times a weight of the spherical resin, and water; subjecting the mixture to a first heat treatment performed in an inert atmosphere at from 700°C to 1000°C for from 1 to 20 hours; and then washing, performing a treatment with an acidic solution, washing, and crushing. The volume of pores of the porous carbon having a pore diameter of 2.0 nm or less as calculated by an MP method is from 0.70 to 1.2 cm3 / g.

Description

Method for producing positive electrode active material, method for producing secondary battery, method for producing porous carbon, positive electrode active material, and secondary battery

[0001] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof. Another embodiment of the present invention relates to an object that can be used as a secondary battery and an active material included therein, or a manufacturing method thereof.

[0002] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like.

[0003] In addition, in this specification, the term "energy storage device" refers to elements and devices in general that have a power storage function, and includes, for example, lithium ion secondary battery energy storage devices (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors.

[0004] In recent years, the development of various power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, has been actively pursued. Demand for high-power, high-energy-density lithium-ion secondary batteries has been rapidly expanding in modern society, along with the development of portable information terminals (PDAs) such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, next-generation clean-energy automobiles (CEs) such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and the semiconductor industry. These batteries have become indispensable to modern society as a rechargeable energy source.

[0005] In addition, lightweight, high-capacity secondary batteries are desired, and lithium-ion secondary batteries (also called lithium-sulfur batteries or Li-S batteries) that use sulfur-containing materials as the positive electrode have attracted attention. Sulfur has a high theoretical capacity of approximately 1670 mAh / g and is known to be a promising positive electrode material in terms of energy density.

[0006] Furthermore, sulfur has the advantage of being abundant as a resource and being cheaper than rare metals such as cobalt.

[0007] For example, research is being conducted on sulfur-based secondary batteries using sulfur and graphene sponge (3DGS) (Non-Patent Document 1).

[0008] Chao Lin et al. , “A facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles for flexible Li-S cathodes”, Phys. Chem. Chem. Phys. ,2016,18,22146-22153

[0009] In lithium-sulfur batteries, lithium metal is used as an example of a negative electrode active material. During discharge, lithium metal dissolves in the electrolyte at the negative electrode to form Li ＋ This reacts with sulfur at the positive electrode to produce the intermediate product lithium polysulfide (Li ２ S ｎ (2<n<8)) and then lithium sulfide (Li ２ S).

[0010] One of the challenges of lithium-sulfur batteries is the poor electrical conductivity of their sulfur-based cathodes. To address this challenge, porous carbon can be loaded with sulfur, which is expected to improve charge-discharge capacity. However, if the pore diameter of the porous carbon is too large to load a large amount of sulfur, lithium polysulfides, a reaction intermediate, will leach from the porous carbon into the electrolyte. Furthermore, if the pores of the porous carbon are made smaller to prevent the leach-out of lithium polysulfides, the amount of sulfur that can be loaded in the pores will decrease, resulting in a lower charge-discharge capacity.

[0011] Therefore, an object of one embodiment of the present invention is to provide porous carbon capable of supporting a large amount of sulfur. Another object of another embodiment of the present invention is to provide porous carbon having pores with a diameter of 2.0 nm or less. Another embodiment of the present invention is to provide porous carbon having pores with a diameter of 2.0 nm or less and a volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide porous carbon having a molecular weight of 1 / g or less.

[0012] An object of one embodiment of the present invention is to provide a positive electrode active material in which a large amount of sulfur is supported on porous carbon. Another object of another embodiment of the present invention is to provide a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less. Another embodiment of the present invention is to provide a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide a positive electrode active material in which sulfur is supported on porous carbon having a capacitance of 1 / g or less.

[0013] An object of one embodiment of the present invention is to provide a secondary battery using a positive electrode active material in which a large amount of sulfur is supported on porous carbon. Another object of another embodiment of the present invention is to provide a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less. Another object of one embodiment of the present invention is to provide a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a capacitance of 1 / g or less.

[0014] Another object of one embodiment of the present invention is to provide a method for manufacturing porous carbon that can increase the amount of sulfur supported. Another object of another embodiment of the present invention is to provide a method for manufacturing porous carbon having pores with a diameter of 2.0 nm or less. Another object of one embodiment of the present invention is to provide a method for manufacturing porous carbon having pores with a diameter of 2.0 nm or less and a volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide a method for producing porous carbon having a surface roughness of 1 / g or less.

[0015] An object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material in which a large amount of sulfur is supported on porous carbon.Another object of another embodiment of the present invention is to provide a method for manufacturing a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less.Another object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide a method for manufacturing a positive electrode active material in which sulfur is supported on porous carbon having a specific surface area of ​​1 / g or less.

[0016] An object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery using a positive electrode active material in which a large amount of sulfur is supported on porous carbon.Another object of another embodiment of the present invention is to provide a method for manufacturing a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less.Another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ An object of the present invention is to provide a method for manufacturing a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a solubility of 0.1% or less.

[0017] An object of one embodiment of the present invention is to provide a high-capacity lithium-ion secondary battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a lithium-ion secondary battery with excellent charge-discharge cycle characteristics and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a secondary battery with long cycle life and high safety or reliability and a manufacturing method thereof.

[0018] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims.

[0019] To solve the above problems, one aspect of the present invention is to support sulfur on porous carbon and use it in the positive electrode of a lithium-sulfur battery. The porous carbon is made of spherical resin and activated by chemical activation, particularly alkaline activation.

[0020] After mixing the spherical resin with an alkaline solution, the mixture is heated in an inert atmosphere to perform both carbonization and alkaline activation. When both carbonization and alkaline activation are performed, the shape of the spherical resin is partially changed to form porous carbon. The porous carbon has an integrated pore volume of 0.70 cm3 for pores with a diameter of 2.0 nm or less, as calculated by the MP method. ３ / g or more 1.2cm ３ / g or less is preferable.

[0021] The spherical resin is a phenolic resin, has a D50 of 3 μm or more and 12 μm or less, and (D90−D10) / D50 of 0.1 or more and 1.5 or less.

[0022] (1) One aspect of the present invention is a method for producing a positive electrode active material, comprising: mixing a spherical resin, a base in an amount 1.0 to 2.0 times the weight of the spherical resin, and water; performing a first heat treatment in an inert atmosphere at 700°C to 1000°C for 1 hour to 20 hours; washing the porous carbon; mixing and stirring the porous carbon with an acidic solution; washing the porous carbon; performing a second heat treatment under reduced pressure; crushing the porous carbon; mixing the porous carbon with sulfur; and performing a third heat treatment.

[0023] (2) In the above (1), it is preferable that the spherical resin is a phenolic resin and the base is sodium hydroxide.

[0024] (3) In the above (2), the phenolic resin preferably has a particle size distribution measured using a laser diffraction particle size distribution analyzer, in which D50 is 3 μm or more and 12 μm or less, and (D90−D10) / D50 is 0.1 or more and 1.5 or less.

[0025] (4) In the above (1), the weight of sulfur is preferably 1.0 to 1.5 times the weight of the porous carbon.

[0026] (5) In the above (1), the second heat treatment is preferably performed at 60° C. or higher and 300° C. or lower for 1 hour or longer and 20 hours or shorter, and the third heat treatment is preferably performed at 120° C. or higher and 160° C. or lower for 1 hour or longer and 10 hours or shorter.

[0027] (6) In the above (1) to (5), it is preferable that the first heat treatment is performed by heating at a first temperature for 30 minutes to 10 hours, and then heating at a second temperature higher than the first temperature for 30 minutes to 10 hours.

[0028] (7) In the above (6), it is preferable that the first temperature is 700°C or higher and 850°C or lower, and the second temperature is 800°C or higher and 1000°C or lower.

[0029] (8) Alternatively, one aspect of the present invention is a method for producing a secondary battery, the method including: preparing a positive electrode active material by any one of the above-described methods; mixing the positive electrode active material with a conductive material and a binder solution to prepare a slurry; applying the slurry to a surface of a positive electrode current collector and drying the slurry to prepare a positive electrode; preparing an electrolyte solution containing lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate; and assembling the positive electrode and the electrolyte solution.

[0030] (9) Alternatively, one embodiment of the present invention is a method for manufacturing a secondary battery, the method including: preparing a positive electrode active material by any one of the above-described methods; mixing the positive electrode active material with a conductive material and a binder solution to prepare a slurry; applying the slurry to a surface of a positive electrode current collector and drying the slurry to prepare a positive electrode; preparing an electrolyte solution containing lithium bis(trifluoromethane)sulfonimide, sulfolane, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; and assembling the positive electrode and the electrolyte solution.

[0031] (10) Alternatively, in one embodiment of the present invention, the pore volume at pore diameters of 2.0 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ / g or less and sulfur are mixed, and the mixture is subjected to a heat treatment at 120° C. or more and 160° C. or less for 1 hour or more and 10 hours or less.

[0032] (11) Alternatively, one aspect of the present invention is a method for producing porous carbon, comprising mixing spherical phenolic resin with sodium hydroxide in an amount 1.3 to 1.8 times the weight of the spherical phenolic resin and water, and carrying out a heat treatment in an inert atmosphere at 750°C to 950°C for 1 hour to 20 hours, washing the porous carbon, mixing the porous carbon with an acidic solution and stirring the mixture, washing the porous carbon, and then carrying out a heat treatment under reduced pressure at 60°C to 300°C for 5 hours to 20 hours, thereby crushing the porous carbon.

[0033] (12) Alternatively, one aspect of the present invention is a method for producing porous carbon, comprising mixing spherical phenolic resin, sodium hydroxide in an amount 1.0 to 2.0 times the weight of the spherical phenolic resin, and water, and carrying out a heat treatment in an inert atmosphere at 780°C to 820°C for 30 minutes to 1.5 hours, and a heat treatment at 830°C to 870°C for 30 minutes to 1.5 hours, to produce porous carbon, washing the porous carbon, mixing the porous carbon with an acidic solution and stirring, washing the porous carbon, and then carrying out a heat treatment under reduced pressure at 60°C to 300°C for 5 hours to 20 hours, to disintegrate the porous carbon.

[0034] (13) Alternatively, in one embodiment of the present invention, the pore volume at pore diameters of 2.0 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ / g or less.

[0035] (14) Alternatively, in one embodiment of the present invention, the pore volume at pore diameters of 2.0 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ The positive electrode active material comprises porous carbon having a densitometric value of 0.15 to 0.25 wt % or less and sulfur.

[0036] (15) Alternatively, one embodiment of the present invention is a secondary battery including a positive electrode having the positive electrode active material described in (14) above, a negative electrode, and an electrolyte solution, in which the negative electrode includes lithium metal, and the electrolyte solution includes lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate.

[0037] (16) Alternatively, one embodiment of the present invention is a secondary battery including a positive electrode having the positive electrode active material described in (14), a negative electrode, and an electrolyte solution, in which the negative electrode includes lithium metal, lithium bis(trifluoromethane)sulfonimide, sulfolane, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0038] One aspect of the present invention can provide porous carbon with a high sulfur loading. Another aspect of the present invention can provide porous carbon having pores with a diameter of 2.0 nm or less. Another aspect of the present invention can provide porous carbon having pores with a diameter of 2.0 nm or less and a volume of 0.70 cm or less. ３ / g or more 1.2cm ３ / g or less.

[0039] One embodiment of the present invention provides a cathode active material in which sulfur is supported on porous carbon with a high sulfur loading. Another embodiment of the present invention provides a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less. Another embodiment of the present invention provides a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ It is possible to provide a positive electrode active material in which sulfur is supported on porous carbon having a SiO 2 content of 0.1g or less.

[0040] One embodiment of the present invention can provide a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a high sulfur content. Another embodiment of the present invention can provide a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less. Another embodiment of the present invention can provide a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ Therefore, a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a specific surface area of ​​0.1 μm or less can be provided.

[0041] Another aspect of the present invention provides a method for producing porous carbon having a high sulfur loading. Another aspect of the present invention provides a method for producing porous carbon having pores with a diameter of 2.0 nm or less. Another aspect of the present invention provides a method for producing porous carbon having pores with a diameter of 2.0 nm or less and a volume of 0.70 cm or less. ３ / g or more 1.2cm ３ / g or less.

[0042] One embodiment of the present invention provides a method for producing a cathode active material in which sulfur is supported on porous carbon with a high sulfur content. Another embodiment of the present invention provides a method for producing a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less. Another embodiment of the present invention provides a method for producing a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ The present invention provides a method for producing a positive electrode active material in which sulfur is supported on porous carbon having a SiO 2 content of 0.1g or less.

[0043] One embodiment of the present invention can provide a method for manufacturing a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a high sulfur content. Another embodiment of the present invention can provide a method for manufacturing a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less. Another embodiment of the present invention can provide a method for manufacturing a secondary battery using a cathode active material in which sulfur is supported on porous carbon with a pore diameter of 2.0 nm or less and a pore volume of 0.70 cm or less. ３ / g or more 1.2cm ３ It is possible to provide a method for producing a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon having a specific surface area of ​​0.1 μm or less.

[0044] According to one embodiment of the present invention, a high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a lithium-ion secondary battery with excellent charge / discharge characteristics and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a secondary battery with long cycle life and high safety or reliability and a manufacturing method thereof can be provided.

[0045] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0046] FIG. 1A is a flowchart showing an example of a method for producing porous carbon. FIG. 1B is a graph illustrating temperature conditions in a heating step. FIG. 2A is a flowchart showing an example of a method for producing a positive electrode active material. FIG. 2B is a flowchart showing an example of a method for producing a positive electrode. FIG. 3 is a flowchart showing an example of a method for producing porous carbon. FIG. 4A is an exploded perspective view of a coin-type secondary battery, FIG. 4B is a perspective view of the coin-type secondary battery, and FIG. 4C is a cross-sectional perspective view thereof. FIGS. 5A, 5B, 5C, and 5D are diagrams illustrating an example of an electronic device. FIGS. 6A, 6B, and 6C are diagrams illustrating an example of an electronic device. FIGS. 7A, 7B, and 7C are diagrams illustrating an example of a vehicle. FIGS. 8A and 8B are diagrams illustrating an example of an electric bicycle. FIGS. 9A and 9B are perspective views showing an example of an aircraft. FIG. 10 is a graph showing the cumulative pore volume. FIGS. 11A and 11B are graphs showing the pore diameter distribution. FIG. 12 is a graph showing an XRD pattern. FIG. 13 is a graph showing an XRD pattern. Fig. 14 is a graph showing an XRD pattern. Fig. 15 is a graph showing an XRD pattern. Fig. 16 is a graph showing the results of a charge-discharge cycle test. Fig. 17 is a graph showing the results of a charge-discharge cycle test. Fig. 18 is a graph showing the results of a charge-discharge cycle test.

[0047] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0048] In this specification, the words "first" and "second" are used for the convenience of understanding the technical content or to identify each component. Therefore, the words "first" and "second" do not limit the number of each component. Furthermore, the words "first" and "second" do not limit the order of each component. Furthermore, the words "first" and "second" or identifying symbols used in this specification may not match the words or identifying symbols in the claims.

[0049] Embodiment 1 In this embodiment, a method for manufacturing a positive electrode active material that can be used in a lithium-sulfur battery according to one embodiment of the present invention, porous carbon that can be used for the positive electrode active material, and a method for manufacturing the porous carbon will be described with reference to FIGS. 1A to 2B .

[0050] <Method of Producing Porous Carbon> A method of producing porous carbon by activating resin particles will be described. Activation refers to a reaction or operation that generates nanometer-sized pores inside a carbon material. First, in step S21, a base and water are prepared for alkaline activation, which uses an alkali as an activating agent. Examples of bases that can be used include sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate. In this embodiment, sodium hydroxide is used.

[0051] Next, in step S11, spherical resin particles are prepared. While the resin material is not particularly limited, it is preferable to use a phenolic resin, which has a three-dimensional network structure containing six-membered carbon rings and is relatively inexpensive. Phenolic resins are also preferable because they have a high carbon content and a high carbon residue rate in the carbonization process. Spherical phenolic resins are synthesized by a condensation reaction between phenols, including polyhydric phenols, and aldehydes, followed by separation and recovery of the phenolic resin.

[0052] Since the shape of the resin used here significantly affects the shape of the porous carbon, spherical resin particles are a preferred shape. Furthermore, as the particle size distribution of the resin particles, D50 (also referred to as median diameter) is preferably 3 μm or more and 50 μm or less, more preferably 3 μm or more and 12 μm or less, and even more preferably 6 μm or more and 10 μm or less. Furthermore, (D90-D10) / D50 is preferably 0.1 or more and 1.5 or less. Note that D50 refers to the particle diameter at 50% of the cumulative distribution of particles calculated in particle size distribution measurement, D90 refers to the particle diameter at 90% of the cumulative distribution, and D10 refers to the particle diameter at 10% of the cumulative distribution. The particle size distribution can be measured, for example, using a laser diffraction particle size distribution analyzer.

[0053] As the laser diffraction particle size distribution analyzer, for example, an apparatus such as the SALD-2200 manufactured by Shimadzu Corporation can be used. Furthermore, measurement conditions can be set as follows: measurement range: 0.03 to 1000 μm, refractive index: 1.70-0.20i, dispersant: sodium hexametaphosphate. The laser diffraction particle size distribution analyzer is not limited to the above, but it is preferable to use an apparatus having measurement performance equivalent to or better than the above.

[0054] In this embodiment, the spherical phenolic resin used is Marilyn HF-008 manufactured by Gun-ei Chemical Industry Co., Ltd., which has a D50 of 7.92 μm and a (D90-D10) / D50 ratio of 0.435 in the particle size distribution measured using a laser diffraction particle size distribution analyzer.

[0055] Next, the base and water are mixed and stirred to prepare an alkaline solution (aqueous sodium hydroxide solution), after which spherical phenolic resin is mixed and stirred in step S22. The stirring conditions in step S22 are not particularly limited, but in this embodiment, the heating temperature during stirring is set to 50°C, and stirring is performed at 600 rpm using a stirrer and magnetic stirrer for 30 minutes. The mixture is then transferred from the beaker to a petri dish, and the heating temperature during stirring is set to between 100°C and 120°C, and stirring is performed at 40 rpm using a stirrer and magnetic stirrer for 4 hours. The reason for setting the heating temperature during stirring within the above range and stirring is to uniformly mix the sodium hydroxide and phenolic resin and evaporate the water.

[0056] As for the amount of aqueous sodium hydroxide solution to be mixed with the spherical phenolic resin, for example, the weight of sodium hydroxide contained in the aqueous sodium hydroxide solution is preferably 1.0 to 2.0 times the weight of the phenolic resin, and more preferably 1.3 to 1.8 times.

[0057] Next, in step S23, the mixture of spherical phenolic resin and alkaline solution is transferred from the petri dish to a graphite container (hereinafter referred to as a graphite crucible) and heated. Heating is preferably performed in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating furnace is not particularly limited, but examples thereof include a tubular furnace, a muffle furnace, a rotary kiln, and a roller hearth kiln. Examples of containers that can be used to hold the resin particles include crucibles and sheaths, and these can be made of graphite, aluminum oxide, or an oxide containing aluminum and silicon. The heating temperature is preferably 700°C or higher and 1000°C or lower, more preferably 750°C or higher and 950°C or lower. The heating time is preferably 1 hour or higher and 20 hours or lower.

[0058] The heating in step S23 can be a one-step heating method in which heating is performed for a predetermined time without changing the temperature at a temperature within the above-mentioned heating temperature range, but the heating in step S23 may also be performed using a two-step heating method shown in FIG. 1B.

[0059] 1B is a diagram illustrating a two-step heating method in which heating is performed at a first temperature T1 and then at a second temperature T2. The second temperature T2 is preferably higher than the first temperature T1. Specifically, the first temperature T1 is preferably 700°C or higher and 850°C or lower, and the second temperature T2 is preferably 800°C or higher and 1000°C or lower. It is more preferable that the first temperature T1 is 780°C or higher and 820°C or lower, and the second temperature T2 is 830°C or higher and 870°C or lower.

[0060] 1B, the heating time in the two-step heating method is (t2-t1) for heating at the first temperature T1, and (t4-t3) for heating at the second temperature T2. The first heating time is preferably, for example, 30 minutes to 10 hours, and more preferably 30 minutes to 1.5 hours. The second heating time is preferably, for example, 30 minutes to 10 hours, and more preferably 30 minutes to 1.5 hours.

[0061] Next, in step S24, the heated product is washed. The washing method is not particularly limited, but it is preferable to wash with pure water, for example, and repeat the washing until the solution becomes neutral.

[0062] Next, in steps S25 and S26, it is preferable to mix and stir an acidic solution. For example, hydrochloric acid can be used as the acidic solution. For example, 1 mol / L hydrochloric acid can be used as the hydrochloric acid. Even if basic components remain in the porous carbon after step S24, the basic components can be removed by treating with the acidic solution, and porous carbon with few impurities can be obtained.

[0063] Next, in step S27, it is preferable to wash again, as described in step S24.

[0064] Next, in step S28, the washed product is dried. The drying method is not particularly limited, but for example, reduced-pressure drying can be used. Reduced-pressure drying is a heat treatment under reduced pressure, and is performed at 60° C. to 300° C. for 5 hours to 20 hours. In this embodiment, the reduced-pressure drying is performed at 120° C. for 10 hours.

[0065] Next, in steps S29 and S30, the dried material is preferably crushed and sieved. As long as the aggregated porous carbon can be crushed, the crushing means is not particularly limited, but a mortar, ball mill, bead mill, or the like can be used. Agate balls, aluminum oxide balls, or zirconium oxide balls are preferably used as the grinding media. Zirconium oxide balls are preferred because they emit less impurities. Furthermore, when using a ball mill or bead mill, the rotation speed is preferably set to 100 rpm or more and 400 rpm or less to suppress contamination from the media. In this embodiment, a 45 ml container is used, zirconium oxide balls (diameter 1 mm) weighing 50 g are used, and the rotation speed is set to 250 rpm for 1 hour. After crushing using the ball mill, the material is passed through a separation sieve with a mesh size of 300 μm.

[0066] Through the above steps, porous carbon can be produced (step S31).

[0067] <Pore Distribution Measurement> The characteristics of porous carbon can be clarified by measuring the pore distribution. Gas adsorption can be used as a method for measuring the pore distribution. Gas adsorption is a technique in which gas molecules with a known adsorption area are adsorbed onto the surface of a sample as an adsorbate, the amount of adsorbed gas is measured, and the resulting isothermal adsorption curve is analyzed to calculate the specific surface area, pore distribution, cumulative pore volume, etc. of the sample. Pores are classified by their diameter: pores with a pore diameter of 2 nm or less are called micropores (also called micropores, micropores, or micropores), pores with a pore diameter of more than 2 nm but not more than 50 nm are called mesopores (also called mesopores), and pores with a pore diameter of more than 50 nm are called macropores (also called macropores).

[0068] In the gas adsorption method, nitrogen is used as the adsorbate, and the relative pressure p / p ０ Adsorption in the range of 0 to 0.2 can be considered to be due to micropores, adsorption in the range of greater than 0.2 to 0.95 can be considered to be due to mesopores, and adsorption in the range greater than 0.95 can be considered to be due to macropores.

[0069] In one embodiment of the porous carbon of the present invention, the relative pressure p / p ０ In other words, it can be said that there are many micropores with a pore diameter of 2 nm or less. ０ where p is the measured pressure, p ０ is the saturated vapor pressure.

[0070] The MP (micropore analysis) method is known as a method for analyzing micropores. The MP method is an analysis method devised by R. S. Mikhail, S. Brunauer, and E. E. Bodor using the t-plot method, and analysis using the MP method can calculate the pore volume distribution and cumulative pore volume of micropores. When nitrogen is used for measurement by gas adsorption, the size of one nitrogen molecule is 0.354 nm, making it difficult to measure pores smaller than this size. Furthermore, the t-plot method is a method of analysis using a t-plot in which the adsorption amount is plotted against the adsorption thickness. Therefore, the pore diameter calculated by analyzing the adsorption isotherm using nitrogen using the MP method is, for example, 0.52 nm, which is the lower limit of the pores that can be analyzed.

[0071] In addition, the BJH (Barrett-Joyner-Halenda) method is known as a method for analyzing pores with diameters in the range of 1 nm to 100 nm, which includes some micropores, and can calculate the pore volume distribution and cumulative pore volume in the range of pore diameters in the range of 1 nm to 100 nm.

[0072] Furthermore, the specific surface area can be calculated by performing analysis using the Brunauer-Emmett-Teller (BET) method. The specific surface area calculated by the BET method is sometimes called the BET specific surface area.

[0073] The porous carbon that has undergone the process described in this embodiment has a pore volume of 0.70 cm3 at pore diameters of 2.0 nm or less calculated by the MP method. ３ / g or more 1.2cm ３ / g or less, and ３ / g or more 1.20cm ３ Further, with reference to the lower limit of the pore diameter that can be calculated by the MP method, the porous carbon that has undergone the steps described in this embodiment has a pore volume of 0.70 cm3 or less at pore diameters of 0.52 nm or more and 2.0 nm or less, as calculated by the MP method. ３ / g or more 1.2cm ３ / g or less, and ３ / g or more 1.20cm ３It can also be said that it is more preferable that the pore size is 1 / g or less.

[0074] Alternatively, when the pore volume at pore diameters of 2.0 nm or less is calculated by the MP method, if the maximum pore diameter output is 1.72 nm, the pore volume at pore diameters of 1.72 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ / g or less, and ３ / g or more 1.20cm ３ / g or less, or the pore volume in the pore diameter range of 0.52 nm or more and 1.72 nm or less calculated by the MP method is more preferably 0.70 cm ３ / g or more 1.2cm ３ / g or less, and ３ / g or more 1.20cm ３ By using porous carbon having such an cumulative pore volume distribution, it is possible to obtain a positive electrode active material supporting a larger amount of sulfur by mixing with sulfur and heating, which will be described later.

[0075] The apparatus and conditions for measuring the pore size distribution are not particularly limited. For example, the measurement can be performed using the apparatus and conditions as follows. [Measurement apparatus] Apparatus: Tristar II 3020, manufactured by Micromeritics [Measurement conditions] Measurement method: Isothermal adsorption measurement Measurement range: Relative pressure p / p ０ = 0.01~1.0 Measurement temperature: -195.8°C Adsorbate: Nitrogen Pretreatment method: Vacuum drying at 300°C for 10 hours [Analysis conditions] Analysis method: BET method Analysis range: p / p0 = 0.05 or more and 0.16 or less Analysis method: MP method Standard t curve: Harkins and Jura(t=[13.99 / (0.034-log(p / p0))] ０．５ ) Applicable range (pore radius range): 0.25 to 1.0 nm (pore diameter value is twice the pore radius value)

[0076] <Method for Producing Positive Electrode Active Material> Next, an example of a method for producing a positive electrode active material will be described with reference to the flowchart of FIG. 2A.

[0077] First, in step S41, sulfur and the porous carbon described above are prepared. The sulfur is preferably of high purity, for example, 99.5% or higher purity is preferable, and 99.999% or higher purity is more preferable. The sulfur is preferably pulverized and sieved. This step is performed in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere.

[0078] Next, in step S42, sulfur and porous carbon are mixed. This step is performed in an inert atmosphere. The mixing method is not particularly limited, but a ball mill, for example, can be used. If the mixing ratio S / C of sulfur (S) to porous carbon (C) is too small, the charge / discharge capacity decreases, but if it is too large, there is a risk that too much sulfur will not fit into the pores of the porous carbon. Therefore, the mixing ratio S / (S+C) of sulfur (S) in the mixture of sulfur (S) and porous carbon (C) is preferably 30% to 75% by weight, more preferably 50% to 70%, and even more preferably 50% to 67%.

[0079] In addition, in relation to the cumulative pore volume distribution, the pore volume for pore diameters of 0.52 nm or more and 2.0 nm or less is 0.70 cm ３ / g or more 1.0cm ３ In the case of porous carbon having a pore volume of less than 1.0 cm3 / g, the mixing ratio S / (S+C) is preferably 30% or more and 60% or less. ３ / g or more 1.2cm ３ In the case of porous carbon having a pore volume and a mixing ratio of 50% to 70% by weight, the pore volume and the mixing ratio are preferably 50% to 70% by weight, respectively. By setting the pore volume and the mixing ratio as described above, the amount of sulfur that does not enter the pores of the porous carbon can be reduced, and it becomes possible to suppress the elution of lithium polysulfides when the porous carbon is made into a secondary battery.

[0080] Next, in step S43, the mixture of sulfur and porous carbon is sealed in a container and heated together with the container. For example, a sealable cylindrical metal container can be used as the container. To prevent sulfur that has not been composited with carbon from adhering to the container, it is preferable to wrap the mixture in resin-coated metal foil, for example, silicone-coated aluminum foil, before placing it in the container. Sealing is performed in an inert atmosphere.

[0081] The heating temperature in step S43 is preferably 120° C. to 160° C., and the heating time is preferably 1 hour to 10 hours, and the atmosphere is preferably an inert atmosphere, particularly an argon atmosphere.

[0082] In step S44, the heated material is preferably sieved. If necessary, it may be crushed using an agate mortar or the like.

[0083] Through the above steps, a positive electrode active material in which sulfur is supported on porous carbon can be produced (step S45).

[0084] The sulfur contained in the positive electrode active material is preferably present in an amorphous state. The fact that the sulfur is in an amorphous state indicates that sulfur and carbon are sufficiently composited. Therefore, when the positive electrode active material or the positive electrode or secondary battery having the same is analyzed by a diffraction method such as X-ray diffraction (XRD: x-ray-diffractometers), sulfur crystals (S ８ It is preferable that no peaks derived from the above-mentioned amine group are observed.

[0085] Therefore, when analyzed by X-ray diffraction using, for example, CuKα radiation, the XRD pattern shows that sulfur crystals (S) are present at least in the range of 2θ of 23.12±0.1° (23.02° or more and 23.22° or less) and 27.74°±0.1° (27.64° or more and 27.84° or less). ８ ) is preferably free of peaks derived from

[0086] Furthermore, the carbon contained in the positive electrode active material preferably has low crystallinity. Low crystallinity carbon has a large specific surface area, which is advantageous for the composite formation of sulfur and carbon. Therefore, hydrogen and oxygen may be detected along with carbon in elemental analysis of the positive electrode active material. Furthermore, when analyzing the positive electrode active material or a positive electrode or secondary battery containing the same by diffraction, it is preferable that the peak derived from carbon be broad.

[0087] For example, when analyzed by X-ray diffraction using CuKα radiation, the XRD pattern preferably has a broad peak with a full width at half maximum of 1° or more, more preferably 3° or more, in the range of 2θ of 15° or more and 35° or less.

[0088] <XRD> The XRD measurement device and conditions are not particularly limited. For example, the measurement can be performed using the following device and conditions. XRD device: D8 ADVANCE manufactured by Bruker X-ray source: Cu Output: 40 kV, 40 mA Divergence slit: 0.6 mm Detector: LYNXEYE XE-T Scan method: 2θ / θ continuous scan Measurement range (2θ): 5° to 60° Step width (2θ): 0.01° setting Counting time: 0.5 seconds / step Sample stage rotation: 5 rpm

[0089] If the measurement sample is a powder, it can be placed in a glass sample holder or sprinkled on a greased silicone anti-reflective plate. If the measurement sample is a positive electrode rather than a powder, the positive electrode can be attached to a substrate of appropriate thickness with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device. If the positive electrode active material layer is higher than the measurement surface required by the device, the diffraction pattern will be shifted overall to higher angles; if it is lower, the diffraction pattern will be shifted overall to lower angles. In this case, it is preferable to correct the diffraction pattern shift using crystal structure analysis software or similar.

[0090] In this specification, the term "spherical particles" refers to particles in which, when the cross sections of a plurality of particles are observed, the cross sections of the majority of the particles are circular. In this case, the number of particles is preferably 5 or more. Furthermore, the circular shape is not limited to a perfect circle.

[0091] <Method for Producing Positive Electrode> Next, an example of a method for producing a positive electrode will be described with reference to the flowchart of FIG. 2B.

[0092] First, in step S51, the positive electrode active material, conductive material, and binder solution prepared above were prepared.

[0093] The conductive material may be one or more selected from carbon, copper, tin, zinc, silver, and nickel. Typical carbon materials used as the conductive material include carbon black (particulate carbon such as furnace black and acetylene black), carbon nanotubes, graphene, and carbon fibers. In this embodiment, acetylene black (AB) is used as the conductive material.

[0094] As the binder, it is preferable to use a material such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, or polyvinylpyrrolidone.

[0095] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. As the binder, fluororubber can also be used.

[0096] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0097] The solvent may be N-methylpyrrolidone (NMP) or acetone, or may be a mixture of water, alcohol (methanol, ethanol, propanol, butanol, isopropyl alcohol, etc.).

[0098] In this embodiment, a PVDF solution using NMP as a solvent is prepared as the binder solution.

[0099] Next, in step S52, the positive electrode active material, the conductive material, and the binder are mixed and kneaded while adjusting the amount of the binder solution so as to obtain a desired viscosity.

[0100] Next, in step S53, a binder solution of the same type as the binder solution prepared in step S51 and a solvent are added to prepare a slurry so that the positive electrode active material, conductive material, and binder are mixed in any desired ratio. The viscosity of the slurry is preferably adjusted appropriately by the amount of solvent, reaction temperature, or reaction time. It is preferable to degas the slurry as needed.

[0101] Next, in step S54, the slurry is applied onto a positive electrode current collector, which is preferably made of carbon-coated aluminum foil to improve conductivity.

[0102] Next, in step S55, the slurry coated on the positive electrode current collector is dried. The drying method is not particularly limited, and can be performed by methods such as ventilation drying or reduced-pressure (vacuum) drying, but reduced pressure drying is preferred. Furthermore, to prevent sulfur melting and sublimation, drying is preferably performed at a low temperature sufficient to evaporate the solvent. Pressing may be performed if necessary. Pressing increases the capacity per volume and improves the energy density. Furthermore, in spherical porous carbon, sulfur is distributed inside the carbon material, thereby reducing the effects of heat during pressing. On the other hand, in the case of unactivated spherical porous carbon, sulfur is distributed outside the carbon material, so the heat during pressing can cause sulfur to melt and leak from the electrode surface. The pressing conditions using a roll press can be 20°C to 60°C, for example, at a linear pressure of 500 kN / m or less, preferably 300 kN / m or less, and more preferably 250 kN / m or less.

[0103] Through the above steps, the positive electrode can be produced (step S56).

[0104] 1A shows an example in which the base and water are mixed together and then the spherical resin is mixed in, but this is not particularly limited, and the process shown in Fig. 3 may also be used. Fig. 3 shows an example in which dispersion is performed using ultrasonic waves.

[0105] 3, in step S12, the spherical resin is mixed with water and ultrasonically treated to thoroughly disperse the spherical resin in water to obtain a dispersion. Then, in step S21, the dispersion is mixed with a mixture of base and water, and stirring is performed in step S22.

[0106] By preparing the dispersion liquid first, a sufficiently stirred mixture can be obtained in a short time, and therefore the stirring time in step S22 can also be shortened.

[0107] The steps from step S22 onwards are the same as those in FIGS. 1A and 1B, and therefore detailed description thereof will be omitted here.

[0108] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0109] Second Embodiment An example of fabricating a secondary battery using the mixture of sulfur and porous carbon obtained in the first embodiment as a positive electrode will be described below.

[0110] A secondary battery has at least a positive electrode, an electrolyte, a separator, and a negative electrode.

[0111] [Electrolyte] The secondary battery has an electrolyte containing carrier ions. In this specification and the like, the electrolyte is not limited to an electrolyte containing an organic solvent that is liquid at room temperature, but also includes a solid electrolyte, and also includes an electrolyte containing both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature (semi-solid electrolyte). Note that a lithium salt dissolved in an organic solvent that is liquid at room temperature may be referred to as an electrolyte solution.

[0112] One of the issues with secondary batteries using sulfur is that the battery performance is significantly affected by the formation and elution of lithium polysulfides. ２ S ｎ (2<n<8)) is generated, and the liquid lithium polysulfides dissolve into the electrolyte, reducing the capacity. Furthermore, lithium polysulfides undergo shuttle reactions during charging, significantly reducing charge-discharge efficiency. Furthermore, many organic solvents react with lithium polysulfides.

[0113] The organic solvent that is liquid at room temperature is preferably an aprotic organic solvent, and 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), or sulfolane (SL) can be used as an ether-based electrolyte.In addition, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (abbreviated as TTE or HFE) or bis(2,2,2-trifluoromethyl)ethyl (BTFE) can be used as a fluorine-based ether-based electrolyte.In addition, glymes (ethyl monoglyme, butyl diglyme, triglyme, tetraglyme, etc.) can be used as an electrolyte.

[0114] The lithium salt to be dissolved in the organic solvent is not particularly limited, and any known lithium salt that can be used in lithium-sulfur batteries may be used, such as LiCl, LiPF６ , LiSCN, lithium bis(trifluoromethane)sulfonimide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0115] <Additives> The organic solvent may contain additives. Examples of additives include lithium nitrate, imide salts, sulfonated compounds, aromatic compounds, halogen-substituted compounds thereof, and Li ２ S ６ , P ２ S ５ etc. can be used.

[0116] <Example 1 of Electrolyte Solution> As a combination of the above organic solvent, lithium salt, and additive, for example, an electrolyte solution containing LiTFSI, DOL, DME, and lithium nitrate can be used. In the above combination, it is preferable to use an electrolyte solution obtained by mixing LiTFSI in an amount of 1 mol / L with a mixed solvent obtained by mixing DOL and DME in a volume ratio of 1:1, and further mixing lithium nitrate in an amount of 0.1 mol / L.

[0117] <Electrolyte Solution Example 2> Alternatively, as an example of a combination different from the above, an electrolyte solution containing LiTFSI, SL, and TTE can be used. In the above combination, it is preferable to use an electrolyte solution obtained by mixing the components in a molar ratio of LiTFSI:SL:TTE = 1:2:2. Since this electrolyte solution contains SL, and the elution of lithium polysulfide into the electrolyte solution is suppressed, it is preferable to combine it with a positive electrode active material that supports a large amount of sulfur.

[0118] [Separator] The secondary battery preferably has a separator. Examples of the separator include a porous film made of paper, nonwoven fabric, glass fiber, ceramics, nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyimide, polyolefin, or polyurethane. The separator may be processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0119] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0120] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0121] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0122] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the discharge capacity per volume of the secondary battery can be increased.

[0123] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector.

[0124] [Negative Electrode Active Material] As the negative electrode active material, for example, lithium metal or an alloy material (alloy with copper, tin, or cobalt) can be used.

[0125] [Negative Electrode Current Collector] For the negative electrode current collector, in addition to copper, the same materials as those for the positive electrode current collector can be used.

[0126] When lithium metal is used as the negative electrode active material, a film for uniforming lithium deposition may be provided on the lithium metal. For example, a solid electrolyte having lithium ion conductivity can be used as the film for uniforming lithium deposition. Examples of solid electrolytes that can be used include sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes. Furthermore, for example, a metal film that forms an alloy with lithium can be used as the film for uniforming lithium deposition. For example, a magnesium metal film can be used as the metal film that forms an alloy with lithium. Because lithium and magnesium form a solid solution over a wide range of compositions, this film is suitable as a film for uniforming lithium deposition.

[0127] [Coin-type secondary battery] Fig. 4A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 4B is an external view, and Fig. 4C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0128] 4A is a schematic diagram that allows the overlapping of components (upper and lower relationships and positional relationships) to be seen, and therefore, FIGS. 4A and 4B are not completely identical corresponding views.

[0129] In Fig. 4A, a positive electrode 201, a separator 210, a negative electrode 207, a spacer 222, and a washer 212 are stacked. These are sealed with a negative electrode can 202, a positive electrode can 204, and a gasket. Note that the gasket for sealing is not shown in Fig. 4A. The spacer 222 and the washer 212 are used to protect the inside or to fix the position inside the can when the positive electrode can 204 and the negative electrode can 202 are crimped together. The spacer 222 and the washer 212 are made of stainless steel or an insulating material.

[0130] The positive electrode 201 has a laminated structure in which a positive electrode active material layer 206 is formed on a positive electrode current collector 205 .

[0131] FIG. 4B is a perspective view of the completed coin-type secondary battery.

[0132] In the coin-type secondary battery 200, a positive electrode can 204, which also serves as a positive electrode terminal, and a negative electrode can 202, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 203 made of polypropylene or the like. The positive electrode 201 is formed of a positive electrode current collector 205 and a positive electrode active material layer 206 provided in contact with the positive electrode current collector. The negative electrode 207 is formed of a negative electrode current collector 208 and a negative electrode active material layer 209 provided in contact with the negative electrode current collector. The negative electrode 207 is not limited to a laminated structure, and may be made of lithium metal foil or a lithium-aluminum alloy foil.

[0133] Note that the positive electrode 201 and the negative electrode 207 used in the coin-type secondary battery 200 can each have an active material layer formed on only one surface.

[0134] The positive electrode can 204 and the negative electrode can 202 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, or the like. The positive electrode can 204 is electrically connected to the positive electrode 201, and the negative electrode can 202 is electrically connected to the negative electrode 207.

[0135] These negative electrode 207, positive electrode 201, and separator 210 are immersed in an electrolyte solution, and as shown in FIG. 4C , the positive electrode 201, separator 210, negative electrode 207, and negative electrode can 202 are stacked in this order with the positive electrode can 204 facing downward, and the positive electrode can 204 and the negative electrode can 202 are crimped together via a gasket 203, thereby assembling a coin-type secondary battery 200.

[0136] With the above configuration, the coin-type secondary battery 200 can have a high capacity, a high discharge capacity, and excellent cycle characteristics.

[0137] Embodiment 3 In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS. 5A to 6C. FIG.

[0138] 5A shows an example of a wearable device. Wearable devices use high-capacity, lightweight secondary batteries as a power source. Furthermore, in order to enhance splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging, with an exposed connector.

[0139] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 5A . The eyeglasses-type device 4000 includes a frame 4000 a and a display unit 4000 b. Mounting the secondary battery on the temples of the curved frame 4000 a makes it possible to provide the eyeglasses-type device 4000 with a lightweight design, a good weight balance, and a long continuous use time. The inclusion of the secondary battery of one embodiment of the present invention allows for a space-saving configuration that can be achieved by miniaturizing the housing.

[0140] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A high-capacity, lightweight secondary battery can be provided in the flexible pipe 4001b and / or the earphone unit 4001c. By including the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a smaller housing can be realized.

[0141] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A high-capacity and lightweight secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0142] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A high-capacity and lightweight secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By including the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0143] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and a high-capacity, lightweight secondary battery can be mounted inside the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0144] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and a high-capacity, lightweight secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0145] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0146] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0147] FIG. 5B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0148] 5C shows a side view of the display portion 4005. Fig. 5C shows that the display portion 4005 has a built-in secondary battery 913. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0149] 5D shows an example of a wireless earphone, which is shown here as having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0150] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0151] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0152] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played back on the main units 4100a and 4100b. If the main units 4100a and 4100b have microphones, the sound picked up by the microphones can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the devices to be used as, for example, translation devices.

[0153] The secondary battery 4103 included in the main body 4100a can be charged from the secondary battery 4111 included in the case 4110. A coin-type secondary battery, a cylindrical secondary battery, or the like can be used as the secondary battery 4111 and the secondary battery 4103. The secondary battery obtained in Embodiment 1 is lightweight and has a high energy density. Using the secondary battery 4103 and the secondary battery 4111 can contribute to space saving and weight reduction associated with miniaturization of the wireless earphone.

[0154] 6A shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0155] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the weight of the cleaning robot 6300 can be reduced, and therefore the cleaning robot 6300 can be an electronic device with a long operating time.

[0156] Fig. 6B shows an example of a robot. A robot 6400 shown in Fig. 6B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0157] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0158] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0159] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. Furthermore, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0160] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component inside the robot 6400. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the weight of the entire robot 6400 can be reduced, and the robot 6400 can be an electronic device with a long operating time.

[0161] 6C shows an example of an air vehicle (also called a drone). The air vehicle 6500 shown in FIG. 6C includes a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has the function of flying autonomously.

[0162] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of obstacles during movement. Furthermore, the electronic component 6504 can estimate the remaining battery charge from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention therein. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the secondary battery is lightweight and has a high capacity, and therefore the flying object 6500 can be made lighter overall and have a longer operating time.

[0163] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0164] Fourth Embodiment When a secondary battery is installed in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs) can be realized.

[0165] 7A to 7C illustrate examples of vehicles using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 7A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery 8402. For example, modules of the secondary battery 8402 can be arranged on the floor of the interior of the vehicle. The secondary battery 8402 not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0166] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0167] The automobile 8500 shown in FIG. 7B can charge its secondary battery by receiving power from an external charging facility using a plug-in system and / or a wireless power supply system. FIG. 7B shows a state in which a ground-mounted charging device 8021 charges a secondary battery 8024 mounted on the automobile 8500 via a cable 8022. The charging method and connector specifications may be determined as appropriate using a predetermined system, such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device, such as an AC-DC converter.

[0168] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into the road and / or exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped and / or moving. Electromagnetic induction and / or magnetic resonance methods can be used for such contactless power supply.

[0169] 7C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 7C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0170] 7C is capable of storing a secondary battery 8602 in under-seat storage 8604. Even if under-seat storage 8604 is small, secondary battery 8602 can be stored in under-seat storage 8604. Secondary battery 8602 is removable, and when charging, secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0171] According to one aspect of the present invention, the secondary battery can be made lighter and the discharge capacity of the secondary battery can be increased. Therefore, the capacity per unit weight can be increased, allowing the secondary battery itself to be made smaller and lighter. Reducing the size and weight of the secondary battery itself contributes to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery mounted on the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand periods. Avoiding the use of a commercial power source during peak power demand periods can contribute to energy conservation and the reduction of carbon dioxide emissions.

[0172] 8A is an example of an electric bicycle using the secondary battery of one embodiment of the present invention. The secondary battery of one embodiment of the present invention can be applied to the electric bicycle 8700 shown in FIG. 8A. The power storage device of one embodiment of the present invention includes, for example, a plurality of secondary batteries and a charge / discharge control unit.

[0173] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor (electric unit) that assists the rider. The power storage device 8702 is portable and is shown removed from the bicycle in FIG. 8B, where it corresponds to a secondary battery unit. The power storage device 8702 also includes a plurality of built-in batteries 8701, and a display unit 8703 can display the remaining battery charge. The remaining charge is also displayed on the display unit 8703. The power storage device 8702 also includes a charge / discharge control unit 8704 that can control charging or detect abnormalities of the secondary battery. The charge / discharge control unit 8704 is electrically connected to the positive and negative electrodes of the battery 8701. The electric vehicle main unit of the electric bicycle 8700 also includes an operation unit 8712 provided in the handle portion. The operation unit 8712 includes a display unit 8713, a power switch 8714, and a power storage device 8711.

[0174] Since the secondary battery of one embodiment of the present invention is made of inexpensive materials, the cost of the electric bicycle 8700 can be significantly reduced.

[0175] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0176] Fifth Embodiment In this embodiment, an application example of a lithium ion secondary battery will be described.

[0177] Fig. 9A is a perspective view showing an example of an aircraft, and Fig. 9B is a perspective view illustrating the inside of the main wing of Fig. 9A.

[0178] 9A includes a main wing section 8901, a propeller 8902, a vertical tail section 8903, a horizontal tail section 8904, a control device 8905, and a solar panel 8906. The solar panel may be called a solar cell module.

[0179] The flying object 8900 may have a skid. The skid may be attached, for example, to the underside of the main wing 8901. Wheels may also be attached to the bottom of the skid.

[0180] Furthermore, as shown in Fig. 9B , flying vehicle 8900 has lithium ion secondary batteries 8907 inside main wing section 8901. Fig. 9B shows an example in which a plurality of lithium ion secondary batteries 8907 having a generally rectangular upper surface shape are arranged inside main wing section 8901. Fig. 9B shows a state in which a plurality of lithium ion secondary batteries 8907 are arranged in a row inside main wing section 8901, but a plurality of lithium ion secondary batteries 8907 may be arranged in multiple rows. Furthermore, the upper surface shape of lithium ion secondary battery 8907 is not limited to a rectangle, and may take various shapes, such as a polygon other than a rectangle, a polygon with rounded corners, a circle, an ellipse, an L-shape, etc.

[0181] In addition, in the flying object 8900, charging of the lithium ion secondary battery 8907 with the electricity generated by the solar panel 8906 and supply of electricity from the lithium ion secondary battery 8907 to the propeller 8902 may occur simultaneously.

[0182] The flying object 8900 also has an antenna. The flying object 8900 has a function of performing wireless communication using the antenna. A plurality of antennas may be provided in the flying object 8900. For example, a multi-beam antenna can be used as the antenna.

[0183] The air vehicle 8900 can function as, for example, a radio base station.

[0184] For example, the air vehicle 8900 can fly in the stratosphere and provide a stratospheric platform. The air vehicle 8900 can also communicate with a base station installed on the ground. Alternatively, multiple air vehicles 8900 may each form a base station. In such a case, it is preferable for communication to occur between multiple air vehicles. The air vehicle 8900 may also have the function of transmitting and receiving signals with an artificial satellite. The air vehicle 8900 can provide wireless communication services to a user terminal on the ground from the stratospheric platform. Here, the user terminal is, for example, a smartphone. The air vehicle 8900 may circle above the target area for which the wireless communication service is provided. As a communication protocol or communication technology, a communication standard specification such as LTE (Long Term Evolution), GSM (Global System for Mobile Communication: registered trademark), EDGE (Enhanced Data Rates for GSM Evolution), CDMA2000 (Code Division Multiple Access 2000), W-CDMA (registered trademark), etc. Also, a third generation mobile communication system (3G), a fourth generation mobile communication system (4G), or a fifth generation mobile communication system (5G) defined by the International Telecommunication Union (ITU) can be used.

[0185] The control device 8905 may include an imaging device. The flying object 8900 can take pictures of the air, ground, or sky while flying using the imaging device.

[0186] The control device 8905 may have sensors (including the ability to measure force, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemicals, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared).

[0187] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0188] In this example, porous carbon was prepared and its characteristics were analyzed. Furthermore, a positive electrode active material was prepared using the prepared porous carbon and sulfur. It should be noted that the present invention is not limited to the following examples.

[0189] <Preparation of Porous Carbon> A method for preparing porous carbon will be described with reference to Fig. 1A. Six porous carbons (Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, and Sample 6) were prepared under different preparation conditions.

[0190] [Sample 1] First, 8 g of spherical phenolic resin (product name Marilyn HF-008, manufactured by Gun-ei Chemical Industry Co., Ltd.) was prepared, corresponding to step S11 in Fig. 1A. Also, 4 g of sodium hydroxide was prepared as a base, and 30 ml of pure water was prepared as water, corresponding to step S21. The weight ratio of spherical phenolic resin to sodium hydroxide was 2:1.

[0191] Next, sodium hydroxide and water were mixed to prepare an alkaline solution, which was then stirred with a stirrer at 300 rpm for 10 minutes.

[0192] Next, the alkaline solution and the spherical phenolic resin were mixed and stirred in step S22. The heating temperature during stirring was set to 50°C, and stirring was performed for 30 minutes at 600 rpm using a stirring bar and a magnetic stirrer. Thereafter, the mixture was transferred from the beaker to a petri dish, and the heating temperature during stirring was set to 120°C, and stirring was performed for 2 hours at 30 rpm using a stirring bar and a magnetic stirrer.

[0193] Next, in step S23, the mixture of spherical phenolic resin and alkaline solution was transferred from the petri dish to a graphite crucible and heated. The uncovered crucible was placed in a muffle furnace and heated at 800°C for 1 hour. In the heating treatment in step S23, the temperature was increased and decreased by 200°C per hour. Nitrogen gas was flowed into the furnace at a flow rate of 5 L / min to create an inert atmosphere, and the heating treatment was performed in a nitrogen atmosphere.

[0194] Next, in step S24, pure water was added, and the mixture was suction filtered and washed (step S24). This was repeated until the filtrate became neutral.

[0195] Next, 600 ml of 1 mol / L hydrochloric acid was prepared as an acidic solution in step S25. The hydrochloric acid was mixed with the material washed in step S24, and the mixture was stirred with a stirrer at 600 rpm for 1 hour (step S26).

[0196] Thereafter, in step S27, the acidic solution was filtered by suction, and then washed with pure water in the same manner as in step S24 (step S27).

[0197] Next, in step S28, the substrate was dried by heating under reduced pressure at 120° C. for 10 hours.

[0198] The dried product was crushed in an agate mortar (step S29), passed through a sieve with 53 μm openings (step S30), and then crushed in a ball mill to obtain porous carbon (step S31). This was designated as Sample 1.

[0199] [Sample 2] Sample 2 was a porous carbon prepared in the same manner as Sample 1, except that the heating in step S23 in FIG. 1A was performed in two steps (FIG. 1B) of heating at 800°C for 1 hour and then at 850°C for 1 hour.

[0200] [Sample 3] Sample 3 was a porous carbon prepared in the same manner as Sample 1, except that in steps S21 and S22 of FIG. 1A, the spherical phenolic resin and sodium hydroxide were weighed out so that the weight ratio was 2:2.

[0201] [Sample 4] Sample 4 was a porous carbon prepared in the same manner as Sample 3, except that the heating in step S23 in FIG. 1A was performed in two steps (FIG. 1B) of heating at 800°C for 1 hour and then at 850°C for 1 hour.

[0202] [Sample 5] Sample 5 was a porous carbon prepared in the same manner as Sample 1, except that in steps S21 and S22 of FIG. 1A, the spherical phenolic resin and sodium hydroxide were weighed out so that the weight ratio was 2:3.

[0203] [Sample 6] Sample 6 was a porous carbon prepared in the same manner as Sample 5, except that the heating in step S23 in FIG. 1A was performed in two steps (FIG. 1B) of heating at 800°C for 1 hour and then at 850°C for 1 hour.

[0204] In this manner, six porous carbons (sample 1, sample 2, sample 3, sample 4, sample 5, and sample 6) were prepared under different preparation conditions.

[0205] <Pore Distribution Measurement> Pore distribution measurement was carried out on the six porous carbons (samples 1, 2, 3, 4, 5, and 6) prepared above.

[0206] The pore size distribution measurement was performed using the following equipment and conditions: [Measurement equipment] Equipment: Tristar II 3020, manufactured by Micromeritics [Measurement conditions] Measurement method: Isothermal adsorption measurement Measurement range: Relative pressure p / p ０ = 0.01 to 1.0 Measurement temperature: -195.8°C Adsorbate: Nitrogen (G1 grade, purity > 99.99995 vol.%) Pretreatment method: 300°C, 10 hours of vacuum drying Degassing conditions: Degassing by vacuum evacuation, 1.0 mmHg or less Options used: isothermal jacket, filler rod [Analysis conditions] Analysis method: MP method Reference t curve: Harkins and Jura (t = [13.99 / (0.034-log(p / p0))] ０．５ ) Applicable range (pore radius range): 0.25 to 1.0 nm (pore diameter value is twice the pore radius value)

[0207] The results of the pore distribution measurement are shown in Figures 10, 11A, 11B and Table 1. Figure 10 is a graph showing the cumulative pore volume distribution of Samples 1 to 6, Figure 11A is a graph showing the pore distribution of Samples 1 to 3, and Figure 11B is a graph showing the pore distribution of Samples 4 to 6. The graph in Figure 10 shows pore diameter on the horizontal axis and cumulative pore volume on the vertical axis, and is called a cumulative pore volume graph. The graphs in Figures 11A and 11B show pore diameter on the horizontal axis and differential pore volume obtained by differentiating the cumulative pore volume with pore diameter on the vertical axis, and are also called pore diameter distribution graphs.

[0208]

[0209] In Table 1, the first column shows the sample name, the second column shows the cumulative pore volume calculated by the MP method with a pore diameter of 0.52 nm or more and 1.0 nm or less, the third column shows the cumulative pore volume of a pore diameter of 0.52 nm or more and 1.52 nm or less, and the fourth column shows the cumulative pore volume of a pore diameter of 0.52 nm or more and 1.72 nm or less. In this analysis, the maximum value of the pore diameter output when the pore volume at a pore diameter of 2.0 nm or less was calculated by the MP method was 1.72 nm. In addition, in Table 1, the fifth column shows the maximum value (also called the peak) of the differential pore volume in the range of pore diameters of 0.60 nm or more, and the sixth column shows the value of the pore diameter corresponding to the maximum value. A large value in the sixth column indicates a large proportion of large pores.

[0210] As shown in Table 1, in Samples 4, 5, and 6, the pore volume at pore diameters of 1.72 nm or less calculated by the MP method was 0.70 cm ３ In addition, in sample 6, the pore volume at pore diameters of 1.72 nm or less calculated by the MP method was 1.00 cm ３ In addition, in all samples, the pore volume at pore diameters of 1.72 nm or less calculated by the MP method was 1.20 cm ３ / g or less.

[0211] As shown in Figures 10, 11A, 11B and Table 1, the cumulative pore volumes increase in the order of Sample 1, Sample 2, Sample 3, Sample 4, Sample 5 and Sample 6. This difference is thought to be due to the fact that in the samples with larger cumulative pore volumes, activation of the spherical phenolic resin progressed due to the inclusion of a process with a higher heating temperature. Furthermore, comparing Samples 2, 4 and 6, which were heated under the same conditions, Sample 6 had the largest cumulative pore volume and the largest position (pore diameter) at which the differential pore volume reached its maximum value. This difference is thought to be due to the fact that in the samples with larger cumulative pore volumes, activation progressed more even under the same heating conditions due to the higher proportion of activator.

[0212] Furthermore, in Samples 2, 4, and 6, which were subjected to two-step heating as the heating in step S23, the spherical phenolic resin reacted with sodium hydroxide to produce sodium carbonate during heating at 800°C for 1 hour, and this sodium carbonate functioned as an activator during heating at 850°C for 1 hour, which is thought to have resulted in more advanced activation than in Samples 1, 3, and 5, which were not subjected to two-step heating.

[0213] From the above results, it can be seen that samples 3, 4, 5, and 6, which were prepared by mixing spherical resin with a base in an amount 1.0 to 2.0 times the weight of the spherical resin and water, and then heat-treating them in an inert atmosphere at 700°C to 1000°C for 1 to 20 hours, had a pore volume of 0.50 cm3 at pore diameters of 2.0 nm or less calculated by the MP method. ３ / g or more 1.2cm ３ Furthermore, in Samples 4 and 6, which were subjected to two-step heating in the heat treatment, the pore volume at pore diameters of 2.0 nm or less calculated by the MP method was in the range of 0.70 cm ３ / g or more 1.2cm ３ In addition, in Samples 5 and 6, which were mixed with a base in an amount 1.5 times the weight of the spherical resin, the pore volume at pore diameters of 2.0 nm or less calculated by the MP method was 0.70 cm ３ / g or more 1.2cm ３In addition, Sample 6, which was mixed with a base in an amount 1.5 times the weight of the spherical resin and was subjected to two-step heating in the heat treatment, had a pore volume of 1.00 cm3 for pores with a diameter of 2.0 nm or less calculated by the MP method. ３ / g or more 1.2cm ３ / g or less.

[0214] 2A , sulfur (5N, manufactured by Strem Chem) was crushed in an argon atmosphere glove box and passed through a 53 μm sieve to prepare a plurality of positive electrode active materials (Sample 3A, Sample 4A, Sample 5A, and Sample 6A) by combining this sulfur with each of the porous carbons of Samples 3 to 6 prepared above.

[0215] 2A, sulfur and Sample 3 were weighed in a glove box under an argon atmosphere so that the weight of sulfur (S) / (S+C) relative to the total weight of sulfur (S) and porous carbon (C) was 50% (i.e., S:C = 1:1). Mixing was then performed using a ball mill at a rotation speed of 150 rpm with zirconium oxide balls having a diameter of 1 mm for 1 hour. After mixing using the ball mill, the mixture was passed through a separating sieve with a mesh size of 300 μm.

[0216] Next, in step S43, the mixture was wrapped in silicone-coated aluminum foil (Cookpar (registered trademark) frying pan foil, manufactured by Asahi Kasei Corporation) in an argon atmosphere glove box and sealed in a cylindrical container. The cylindrical container was then heated. The heating in step S43 was performed at 155°C for 6 hours in an argon atmosphere. The argon flow rate was 0.2 L / min. The temperature-raising process involved raising the temperature from 25°C to 120°C over 30 minutes, and then raising the temperature to 155°C over 1 hour. By raising the temperature in this stepwise manner, the temperature could be raised without significantly deviating from the set temperature. After heating at 155°C for 6 hours, the mixture was allowed to cool naturally in an argon atmosphere.

[0217] The heated material was sieved through a sieve with 53 μm openings in a dry room (step S44), to obtain a positive electrode active material (step S45). If the material did not pass through the sieve, it was lightly crushed in an agate mortar and then sieved.

[0218] The positive electrode active material obtained by subjecting Sample 3 to the above steps was designated Sample 3A.

[0219] [Sample 4A] Sample 4A was a positive electrode active material prepared in the same manner as Sample 3A, except that Sample 4 was used instead of Sample 3 in step S42 of FIG. 2A.

[0220] [Sample 5A] Sample 5A was a positive electrode active material prepared in the same manner as Sample 3A, except that Sample 5 was used instead of Sample 3 in Step S42 of FIG. 2A.

[0221] [Sample 6A] Sample 6A was a positive electrode active material prepared in the same manner as Sample 3A, except that Sample 6 was used instead of Sample 3 in Step S42 of FIG. 2A.

[0222] [Sample 3B] Sample 3B was a positive electrode active material prepared in the same manner as Sample 3A, except that in step S42 of FIG. 2A , sulfur (S) and porous carbon (C) were mixed so that the weight ratio of sulfur (S / (S+C)) was 40% with respect to the total weight of sulfur.

[0223] [Sample 4C] Sample 4C was a positive electrode active material prepared in the same manner as Sample 4A, except that in step S42 of FIG. 2A , sulfur (S) and porous carbon (C) were mixed so that the weight ratio of sulfur (S / (S+C)) relative to the total weight of sulfur was 60%.

[0224] [Sample 5C] Sample 5C was a positive electrode active material prepared in the same manner as Sample 5A, except that in step S42 of FIG. 2A , sulfur (S) and porous carbon (C) were mixed so that the weight ratio of sulfur (S / (S+C)) relative to the total weight of sulfur was 60%.

[0225] [Sample 6C] Sample 6C was a positive electrode active material prepared in the same manner as Sample 6A, except that in step S42 of FIG. 2A , sulfur (S) and porous carbon (C) were mixed so that the weight ratio of sulfur (S / (S+C)) relative to the total weight of sulfur was 60%.

[0226] [Sample 6D] Sample 6D was a positive electrode active material prepared in the same manner as Sample 6A, except that in step S42 of FIG. 2A , sulfur (S) and porous carbon (C) were mixed so that the weight ratio of sulfur (S / (S+C)) relative to the total weight of sulfur was 70%.

[0227] <XRD> The positive electrode active material prepared above was subjected to XRD analysis. The apparatus and conditions were as follows: XRD apparatus: D8 ADVANCE manufactured by Bruker Corporation; X-ray source: Cu; Output: 40 kV, 40 mA; Divergence slit: 0.6 mm; Detector: LynxEye XE-T; Scanning method: 2θ / θ continuous scan; Measurement range (2θ): 5° to 60°; Step width (2θ): 0.01° setting; Counting time: 0.5 seconds / step; Sample stage rotation: 5 rpm

[0228] 12 to 15 show the obtained XRD patterns. The XRD patterns are relative intensities normalized by the maximum intensity in the range of 2θ between 15° and 60°, and the background and CuKa ２ For comparison, the sulfur (S ８ ) is also shown.

[0229] As shown in FIG. 12 , in the positive electrode active material using Sample 3, no peak derived from sulfur crystals was observed in Sample 3B, which was prepared so that the sulfur content was 40%, but a peak derived from sulfur crystals was observed in Sample 3A, which was prepared so that the sulfur content was 50%.

[0230] Furthermore, as shown in FIG. 13 , in the positive electrode active material using Sample 4, no peak derived from sulfur crystals was observed in Sample 4A, which was prepared so that sulfur was 50%, but a peak derived from sulfur crystals was observed in Sample 4C, which was prepared so that sulfur was 60%.

[0231] 14, in the positive electrode active material using Sample 5, no peak derived from sulfur crystals was observed in Sample 5A, which was prepared so that sulfur was 50%, but a peak derived from sulfur crystals was observed in Sample 5C, which was prepared so that sulfur was 60%. Note that the peak derived from sulfur crystals observed in Sample 5C was smaller than that observed in Sample 4C.

[0232] Furthermore, as shown in FIG. 15 , in the positive electrode active material using Sample 6, no peak derived from sulfur crystals was observed in Sample 6A prepared so that sulfur was 50%, no peak derived from sulfur crystals was observed in Sample 6C prepared so that sulfur was 60%, and a peak derived from sulfur crystals was observed in Sample 6D prepared so that sulfur was 70%.

[0233] Table 2 shows the positive electrode active material samples that were subjected to XRD analysis.

[0234]

[0235] 12 to 15 and Table 1, it was revealed that the smaller the cumulative pore volume, the more likely a sulfur crystal peak is detected at a lower sulfur ratio S / (S+C). Furthermore, in order to prevent the detection of a sulfur crystal peak in a positive electrode active material having a sulfur ratio exceeding 50%, it is preferable that the cumulative pore volume of the porous carbon used to prepare the positive electrode active material is approximately 0.7 or more. Furthermore, in order to prevent the detection of a sulfur crystal peak in a positive electrode active material having a high sulfur ratio, for example, a sulfur ratio exceeding 60%, it is preferable that the cumulative pore volume of the porous carbon used to prepare the positive electrode active material is approximately 1.0 or more.

[0236] <Preparation of Positive Electrode> A method for preparing a positive electrode will be described with reference to FIG. 2B . First, in step S51, the positive electrode active materials (Sample 3A, Sample 4A, Sample 5A, and Sample 6A) prepared above were used, and a 5% PVDF solution (manufactured by Solvay, product name Solef 5130) using acetylene black (Denka Black, manufactured by Denka) as a conductive material and NMP as a solvent was prepared as a binder solution. In step S52, these were mixed while adjusting the amount of the 5% PVDF solution to achieve a desired viscosity, and the mixture was kneaded using a planetary mixer (Thinky Mixer). Next, in step S53, the 5% PVDF solution and solvent were added to prepare a slurry with a final ratio of positive electrode active material:acetylene black:PVDF of 8:1:1 (by weight).

[0237] Next, in step S54, the slurry was applied to a positive electrode current collector. Carbon-coated aluminum foil (SDX-PM, manufactured by Showa Denko Packaging Co., Ltd.) was used as the positive electrode current collector. The amount of the positive electrode active material carried and the electrode density are shown in Table 3. This was dried (step S55) to obtain a positive electrode (step S56). The dried positive electrode was cut into a width of 4 cm and then subjected to a roll press treatment under conditions of a roll gap of 20 μm and 20° C.

[0238] As described above, the positive electrode fabricated using Sample 3A as the positive electrode active material is referred to as Positive Electrode 3A. Similarly, the positive electrodes fabricated using Sample 4A, Sample 5A, and Sample 6A are referred to as Positive Electrode 4A, Positive Electrode 5A, and Positive Electrode 6A, respectively.

[0239] <Preparation of Secondary Battery> A coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) was prepared using the above-described positive electrode. An aluminum clad positive electrode can was used. Note that an aluminum clad positive electrode can has an aluminum coating on the inside. An aluminum clad positive electrode can is used when there is a risk that the material of the housing, such as the positive electrode can, may chemically react with the electrolyte, and can prevent corrosion by the electrolyte.

[0240] A lithium metal foil was used as the negative electrode. A glass fiber (GF / C manufactured by Whatman) was used as the separator. The electrolyte solution was prepared by mixing LiTFSI to a mixed solvent of DOL and DME in a volume ratio of 1:1 to make a 1 mol / L solution, and then adding lithium nitrate to make a 0.1 mol / L solution.

[0241] Coin cells were fabricated by assembling the positive electrode, negative electrode, and electrolyte solution described above inside a glove box. The coin cell fabricated using positive electrode 3A is referred to as cell 3A. Similarly, coin cells fabricated using positive electrode 4A, positive electrode 5A, and positive electrode 6A are referred to as cells 4A, 5A, and 6A, respectively.

[0242] <Charge-Discharge Cycle Test> A charge-discharge cycle test was performed on Cells 3A to 6A prepared as described above. A rest period of at least 6 hours was allowed between the completion of secondary battery fabrication and the start of the charge-discharge cycle test. The conditions for the charge-discharge cycle test were discharge: CC (current: 200 mA / g, end voltage: 1.4 V), charge: CC (current: 200 mA / g, end voltage: 2.8 V), and an ambient temperature of 25°C. The cells were placed in the charge-discharge cycle tester and allowed to stand for 6 hours before the cycle test. A 10-minute pause was provided between each charge and discharge. The above values ​​represent current values ​​per weight of sulfur in the positive electrode active material. The weight of sulfur in the positive electrode active material was calculated assuming that the sulfur content did not change during the mixing and calcination processes. However, the above description does not imply that the sulfur content does not change at all during the actual process.

[0243] The results of the charge-discharge cycle test for cells 3A to 6A are shown in Figure 16 and Table 3. In the graph of Figure 16, the horizontal axis represents the number of charge-discharge cycles (number of cycles), and the vertical axis represents the discharge capacity at each cycle.

[0244]

[0245] According to the results of the charge-discharge cycle test shown in FIG. 16 and Table 3, the cumulative pore volume was 0.70 cm ３ Cell 3A, which has porous carbon less than 0.70 cm3 / g, has an integrated pore volume of 0.70 cm3. ３It was revealed that the discharge capacity of Cell 3A was significantly lower than that of Cell 4A, Cell 5A, and Cell 6A, which had porous carbon of 0.1 / g or more. This is thought to be because sulfur is present outside the porous carbon in the positive electrode active material of Cell 3A, and therefore the proportion of sulfur that can come into contact with carbon with high electronic conductivity and allow lithium ions to enter and exit is low.

[0246] On the other hand, Cell 4A, Cell 5A, and Cell 6A had a large maximum discharge capacity of 600 mA / g or more, and the cells using porous carbon with a larger cumulative pore volume obtained a larger discharge capacity. The cumulative pore volume of the porous carbon used in these cells with a large discharge capacity was 0.70 cm ３ / g or more 1.2cm ３ / g or less, and no peaks derived from sulfur crystals were detected in XRD analysis. In other words, it can be considered that the positive electrode active material used in these cells was able to maintain a large discharge capacity and a high discharge capacity after 50 cycles because there was almost no sulfur that did not fit into the pores of the porous carbon, even though the sulfur mixing ratio S / (S+C) was 50%.

[0247] Secondary batteries were fabricated using the positive electrode active materials of Samples 4C, 6C, and 6D fabricated in Example 1, and a charge-discharge cycle test was carried out.

[0248] <Preparation of Positive Electrode> Positive electrodes having the positive electrode active materials of Sample 4C, Sample 6C, and Sample 6D were prepared in the same manner as in Example 1. The prepared positive electrodes are referred to as Positive Electrode 4C, Positive Electrode 6C, and Positive Electrode 6D, respectively.

[0249] <Preparation of Secondary Battery> A coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) was prepared using the above positive electrode.

[0250] Secondary batteries having positive electrodes 4C, 6C, and 6D were fabricated in the same manner as in Example 1. These secondary batteries are referred to as cell 4C, cell 6C, and cell 6D.

[0251] Secondary batteries having positive electrodes 4C, 6C, and 6D were fabricated in the same manner as in Example 1, except that electrolytic solution 2 obtained by mixing LiTFSI:SL:TTE in a molar ratio of 1:2:2 was used instead of electrolytic solution 1 used in fabricating the secondary battery described above. These secondary batteries are referred to as cell 4Cs, cell 6Cs, and cell 6Ds.

[0252] <Charge-Discharge Cycle Test> Coin cells were fabricated by assembling the positive electrode, negative electrode, and electrolyte solution described above inside a glove box. A charge-discharge cycle test was performed on the fabricated cells 4C, 6C, 6D, 4Cs, 6Cs, and 6Ds. The charge-discharge cycle test was performed under the same conditions as those described in Example 1.

[0253] The results of the charge-discharge cycle tests for cells 4C, 6C, and 6D are shown in Figure 17. The results of the charge-discharge cycle tests for cells 4Cs, 6Cs, and 6Ds are shown in Figure 18. The results of the charge-discharge cycle tests shown in Figures 17 and 18 are shown in Table 4.

[0254]

[0255] According to the results of the charge-discharge cycle test shown in Figures 17 and 18 and Table 4, among the cells containing electrolyte solution 1, Cell 4C and Cell 6D did not achieve as large a discharge capacity as Cell 6C. This is thought to be because, in the positive electrode active material of Cell 4C and Cell 6D, sulfur is present outside the porous carbon, and therefore the proportion of sulfur that can come into contact with the highly electronically conductive carbon and allow lithium ions to enter and exit is relatively low. On the other hand, in Cell 6C, most of the sulfur contained in the positive electrode active material was able to come into contact with the carbon and contribute to charge and discharge.

[0256] 17, 18, and Table 4, all of the cells containing electrolyte 2 achieved a large capacity exceeding 1000 mAh / g in the initial charging / discharging cycle. Note that cell 6Cs exceeded the theoretical capacity of sulfur, which was 1672 mAh / g. This is presumably due to the effects of side reactions, such as the formation of a coating film and decomposition of the electrolyte, other than the chemical reaction between sulfur and lithium, during charging and discharging.

[0257] On the other hand, Cell 4Cs, Cell 5Cs, and Cell 6Cs each exhibited different charge-discharge cycle characteristics. For example, Cell 4Cs had a large initial discharge capacity, but the discharge capacity significantly decreased after several cycles. Cell 5Cs' discharge capacity decreased to the 900 mAh / g range after the second cycle, but maintained a relatively large discharge capacity until the end of the charge-discharge cycle test. Cell 6Cs' discharge capacity significantly decreased after the second cycle, but then gradually recovered over approximately 30 cycles.

[0258] As described above, excellent charge-discharge cycle characteristics were obtained for Cell 6C containing Electrolyte Solution 1 and Cell 6Cs containing Electrolyte Solution 2. The positive electrode active material used in both Cell 6C and Cell 6Cs was a material having an integrated pore volume of 1.0 cm3 for pores with a pore diameter of 1.72 nm or less calculated by the MP method. ３ / g or more 1.2cm ３ / g or less, and sample 6C was used, which was prepared so that the weight ratio of sulfur to porous carbon was 1.0 to 1.5 times. In other words, it can be considered that excellent charge-discharge cycle characteristics can be obtained by using a positive electrode active material that satisfies the above conditions.

[0259] 200: secondary battery, 201: positive electrode, 202: negative electrode can, 203: gasket, 204: positive electrode can, 205: positive electrode current collector, 206: positive electrode active material layer, 207: negative electrode, 208: negative electrode current collector, 209: negative electrode active material layer, 210: separator, 212: washer, 222: spacer, 913: secondary battery, 4000: eyeglass-type device, 4000a: frame, 4000b: display unit, 4001: headset-type device, 4001a: microphone unit, 4001b: flexible pipe, 4001c: earphone unit, 400 2: device, 4002a: housing, 4002b: secondary battery, 4003: device, 4003a: housing, 4003b: secondary battery, 4005: wristwatch type device, 4005a: display unit, 4005b: belt unit, 4006: belt type device, 4006a: belt unit, 4006b: wireless power supply receiving unit, 4100a: main body, 4100b: main body, 4101: driver unit, 4102: antenna, 4103: secondary battery, 4104: display unit, 4110: case, 4111: secondary battery, 6300: cleaning robot 6301: housing, 6302: display unit, 6303: camera, 6304: brush, 6305: operation button, 6306: secondary battery, 6310: dust, 6400: robot, 6401: illuminance sensor, 6402: microphone, 6403: upper camera, 6404: speaker, 6405: display unit, 6406: lower camera, 6407: obstacle sensor, 6408: moving mechanism, 6409: secondary battery, 6500: flying object, 6501: propeller, 6502: camera, 6503: secondary battery, 6504: electronic component, 802 1: charging device, 8022: cable, 8024: secondary battery, 8400: automobile, 8401: headlight, 8402: secondary battery, 8406: electric motor, 8500: automobile, 8600: scooter, 8601: side mirror, 8602: secondary battery, 8603: turn signal light, 8604: under-seat storage, 8700: electric bicycle, 8701: battery, 8702: power storage device, 8703: display unit, 8704: charge / discharge control unit, 8711: power storage device, 8712: operation unit, 8713: display unit, 8714: power switch

Claims

a spherical resin, a base in an amount 1.0 to 2.0 times the weight of the spherical resin, and water are mixed, and the mixture is subjected to a first heat treatment in an inert atmosphere at 700°C to 1000°C for 1 hour to 20 hours to prepare porous carbon; washing the porous carbon; The porous carbon and the acidic solution are mixed and stirred, After washing the porous carbon, the porous carbon is subjected to a second heat treatment under reduced pressure; crushing the porous carbon; mixing the porous carbon with sulfur and performing a third heat treatment; A method for producing a positive electrode active material. 　 In claim 1, the spherical resin is a phenolic resin, The base is sodium hydroxide. A method for producing a positive electrode active material. 　 In claim 2, The phenolic resin is In the particle size distribution measured using a laser diffraction particle size distribution analyzer, D50 is 3 μm or more and 12 μm or less, and (D90−D10) / D50 is 0.1 or more and 1.5 or less. A method for producing a positive electrode active material. 　 In claim 1, a ratio of the weight of the sulfur to the total weight of the sulfur and the porous carbon is 50% or more and 70% or less; A method for producing a positive electrode active material. 　 In claim 1, the second heat treatment is performed at a temperature of 60° C. or higher and 300° C. or lower for 5 hours or higher and 20 hours or lower; The third heat treatment is performed at a temperature of 120° C. or higher and 160° C. or lower for 1 hour or higher and 10 hours or lower. A method for producing a positive electrode active material. 　 In any one of claims 1 to 5, The first heat treatment includes heating at a first temperature for 30 minutes to 10 hours, and then heating at a second temperature higher than the first temperature for 30 minutes to 10 hours. A method for producing a positive electrode active material. 　 In claim 6, The first temperature is 700°C or higher and 850°C or lower, and the second temperature is 800°C or higher and 1000°C or lower. A method for producing a positive electrode active material. 　 a step of preparing a positive electrode active material according to the method of claim 1; mixing the positive electrode active material with a conductive material and a binder solution to prepare a slurry; a step of applying the slurry to a surface of a positive electrode current collector and drying the slurry to prepare a positive electrode; preparing an electrolyte solution having lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate; and assembling the positive electrode and the electrolyte solution. 　 a step of preparing a positive electrode active material according to the method of claim 1; mixing the positive electrode active material with a conductive material and a binder solution to prepare a slurry; a step of applying the slurry to a surface of a positive electrode current collector and drying the slurry to prepare a positive electrode; preparing an electrolyte solution having lithium bis(trifluoromethane)sulfonimide, sulfolane, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; and assembling the positive electrode and the electrolyte solution. 　 The pore volume at pore diameters of 2.0 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ / g or less porous carbon and sulfur are mixed, Heat treatment is performed at 120°C or higher and 160°C or lower for 1 hour or higher and 10 hours or lower. A method for producing a positive electrode active material. 　 a spherical phenolic resin, sodium hydroxide in an amount 1.3 to 1.8 times the weight of the spherical phenolic resin, and water are mixed, and the mixture is subjected to a heat treatment in an inert atmosphere at 750°C to 950°C for 1 hour to 20 hours to prepare porous carbon; washing the porous carbon; The porous carbon and the acidic solution are mixed and stirred, After washing the porous carbon, the porous carbon is subjected to a heat treatment under reduced pressure at 60° C. or higher and 300° C. or lower for 5 hours or higher and 20 hours or lower; crushing the porous carbon; Methods for preparing porous carbon. 　 a method for producing porous carbon by mixing a spherical phenolic resin with sodium hydroxide in an amount 1.0 to 2.0 times the weight of the spherical phenolic resin and water, and then subjecting the mixture to a heat treatment in an inert atmosphere at 780°C to 820°C for 30 minutes to 1.5 hours, and a heat treatment in an inert atmosphere at 830°C to 870°C for 30 minutes to 1.5 hours; washing the porous carbon; The porous carbon and the acidic solution are mixed and stirred, After washing the porous carbon, the porous carbon is subjected to a heat treatment under reduced pressure at 60° C. or higher and 300° C. or lower for 5 hours or higher and 20 hours or lower; crushing the porous carbon; Methods for preparing porous carbon. 　 The pore volume at pore diameters of 2.0 nm or less calculated by the MP method is 0.70 cm ３ / g or more 1.2cm ３ / g or less porous carbon and sulfur, a ratio of the weight of the sulfur to the total weight of the sulfur and the porous carbon is 50% or more and 70% or less; Cathode active material. 　 A battery comprising a positive electrode having the positive electrode active material according to claim 13, a negative electrode, and an electrolyte solution, the negative electrode comprises lithium metal; The electrolyte solution contains lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate. Secondary battery. 　 A battery comprising a positive electrode having the positive electrode active material according to claim 13, a negative electrode, and an electrolyte solution, the negative electrode comprises lithium metal; Lithium bis(trifluoromethane)sulfonimide, sulfolane, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; Secondary battery.

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