Method for producing secondary battery

Abstract

Provided are: a high-capacity lithium ion secondary battery; and a positive electrode active material that can be used for the same. Also provided is a porous carbon that can be used for a positive electrode active material. The production process can be simplified by performing a carbonization step and an activation step at the same time, and a process with a high production efficiency can be achieved by performing the carbonization step and the activation step in the same process. A positive electrode can thus be advantageously produced on an industrial scale.

Description

Method for manufacturing secondary batteries

[0001] One embodiment of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a 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 article that can be used as a secondary battery and an active material 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 this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, power storage devices using lithium ions (also called lithium ion 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 is an abundant resource and has the advantage of being cheaper than rare metals such as cobalt.

[0007] For example, research has been conducted on sulfur secondary batteries using sulfur and graphene sponge (3DGS) (Non-Patent Document 1). [Prior Art Literature] [Non-Patent Document] [Non-Patent Document 1] 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

[0008] 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 and is oxidized to form the intermediate product lithium polysulfide (Li ２ S ｎ (2<n<8)) and then lithium sulfide (Li ２ S).

[0009] Lithium-sulfur batteries have problems such as the poor electrical conductivity of the positive electrode made of lithium and sulfur, and the elution of lithium polysulfide, a reaction intermediate, into the electrolyte.

[0010] 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.

[0011] Another object of one embodiment of the present invention is to provide a positive electrode that can be used in a lithium-ion battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a porous carbon that can be used for a positive electrode and a manufacturing method thereof.

[0012] 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.

[0013] To solve the above problems, one aspect of the present invention is to support sulfur on activated 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.

[0014] To shorten the production process, the spherical resin is mixed with an alkaline solution and then heated in an inert atmosphere to perform both carbonization and alkali activation. When both carbonization and alkali activation are performed, the shape of the spherical resin is partially changed, resulting in porous carbon. Although some aggregation occurs when both carbonization and alkali activation are performed, a uniform particle size can be achieved by performing an optimal crushing process.

[0015] 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.

[0016] One aspect of the present invention is a method for producing a secondary battery, the method comprising the steps of: preparing porous carbon by mixing a spherical resin, a base, and water, and then performing a first heat treatment in an inert atmosphere at 600° C. to 900° C. for 20 minutes to 3 hours; a first washing step of washing the porous carbon; a step of mixing the porous carbon with an acidic solution and stirring the mixture; a second washing step of washing the porous carbon after mixing; a step of drying the porous carbon by performing a second heat treatment under reduced pressure after the second washing step; a step of crushing the aggregated porous carbon after the second heat treatment; a step of mixing the crushed porous carbon with sulfur and then performing a third heat treatment to prepare a positive electrode active material containing the porous carbon and sulfur; a step of mixing a conductive additive and a binder solution with the positive electrode active material to prepare a slurry; a step of drying the slurry on the surface of a current collector to prepare a positive electrode; and a step of pressing the positive electrode to prepare an electrode for the secondary battery.

[0017] Furthermore, it is preferable to carry out a crushing step after the second heat treatment in the above-mentioned production method. The porous carbon obtained after crushing can be made into a particle powder having a large specific surface area by the BET method. When the particle powder having a large specific surface area is mixed with sulfur, the contact surface between sulfur and carbon becomes large, improving electronic conductivity, and therefore, when used in a positive electrode, it can improve the charge / discharge characteristics of a secondary battery.

[0018] In this specification, the porous carbon and sulfur composite is referred to as the positive electrode active material and is used in the positive electrode of a secondary battery. By applying a slurry to the surface of a current collector and drying it, an electrode can be fabricated in which an electrode mixture layer (also referred to as a positive electrode active material layer) is formed on the current collector. This electrode can function as a secondary battery electrode without a pressing process. Pressing can increase the density of the electrode mixture layer and reduce contact resistance with the current collector.

[0019] In this specification, the positive electrode includes a carbon material carrying at least a sulfur-containing substance, and the sulfur is attached to the surface or inside the pores of the carbon material. The sulfur-containing substance in the positive electrode includes sulfur or a sulfur derivative, such as lithium sulfide or lithium polysulfide.

[0020] Furthermore, when a cross-sectional SEM-EDX point analysis is performed on the positive electrode obtained by the above-described fabrication method, the sulfur / carbon (mass ratio) detected inside the positive electrode active material layer is preferably 0.01 or more and 1 or less. Here, SEM refers to a scanning electron microscope, and EDX refers to energy dispersive X-ray spectroscopy.

[0021] Among EDX measurements, EDX area analysis is the measurement performed while scanning an area and evaluating the area two-dimensionally. Linear analysis is the measurement performed while scanning linearly and evaluating the distribution of atomic concentration within the positive electrode active material. Linear analysis can also be used to refer to data extracted from an arbitrary area of ​​EDX area analysis using analysis software. For EDX measurement of the surface layer of the positive electrode active material, a magnification that can obtain sufficient information within a few nanometers from the surface is preferable. For example, a magnification that allows the electron beam scanning pitch of EDX area analysis to be approximately 0.3 nm, or a measurement magnification of approximately 160,000 times (doubled to 320,000 times on the screen for drift correction), is preferable.

[0022] Furthermore, when the positive electrode active material layer obtained by the above-described production method is analyzed by powder X-ray diffraction using CuKα radiation, the XRD pattern preferably has at least a broad peak with a full width at half maximum of 3° or more in the 2θ range of 15° or more and 35° or less, and does not have a signal with a width three times or more than the average noise width in the 2θ ranges of 23.02° or more and 23.22° or less and 27.64° or more and 27.84° or less.

[0023] Since the carbonization step and the activation step are carried out simultaneously, the spherical resin is partially deformed to obtain porous carbon having dents on the surface. In addition, the porous carbon can be made into a particle powder with a large specific surface area by the BET method.

[0024] By performing the carbonization step and the activation step at the same time, the manufacturing process can be simplified, and by performing the carbonization step and the activation step in the same process, the manufacturing process can be made highly efficient, and therefore, positive electrodes can be manufactured advantageously on an industrial scale.

[0025] Furthermore, by performing the carbonization step and the activation step at the same time, the number of steps can be reduced, and the efficiency of material recovery can be increased.

[0026] This process can increase the specific surface area of ​​the porous carbon, increasing the contact area with sulfur. Increasing the contact area with sulfur improves the electronic conductivity of sulfur, leading to improved charge-discharge characteristics of secondary batteries.

[0027] By using sulfur-loaded porous carbon as the positive electrode and lithium metal as the negative electrode, a lightweight, high-capacity secondary battery can be realized. In addition, the secondary battery has high charge / discharge efficiency and an improved lifespan.

[0028] 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.

[0029] According to another embodiment of the present invention, a positive electrode that can be used in a lithium-ion battery and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a porous carbon that can be used for a positive electrode and a manufacturing method thereof can be provided.

[0030] FIG. 1 is a flowchart showing an example of a method for producing porous carbon. FIG. 2A is a flowchart showing an example of a method for producing a positive electrode active material layer. 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 a coin-type secondary battery. FIG. 4C is a cross-sectional perspective view thereof. FIGS. 5A to 5D are views illustrating an example of an electronic device. FIGS. 6A to 6C are views illustrating an example of an electronic device. FIGS. 7A to 7C are views illustrating an example of a vehicle. FIGS. 8A and 8B are views illustrating an example of an electric bicycle. FIGS. 9A and 9B are SEM images of porous carbon.

[0031] 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.

[0032] 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.

[0033] Embodiment 1 In this embodiment, a method for manufacturing a positive electrode active material layer 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 layer, and a method for manufacturing the porous carbon will be described with reference to FIGS. 1 to 2B .

[0034] First, in step S21, a base and water are prepared for alkaline activation using an alkali as an activation 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.

[0035] 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.

[0036] Since the shape of the resin used here greatly affects the shape of the porous carbon, spherical resin particles are a suitable shape. Therefore, D50 is preferably 5 μm or more and 50 μm or less, more preferably 5 μm or more and 20 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 size at 50% of the calculated cumulative distribution of particles, D90 refers to the particle size at 90% of the cumulative distribution, and D10 refers to the particle size at 10% of the cumulative distribution.

[0037] 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.

[0038] Next, the base and water are mixed and stirred to prepare an alkaline 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 with a stirrer and magnetic stirrer for 30 minutes. The mixture is then transferred from the beaker to a petri dish, where the heating temperature during stirring is set to 120°C, and stirring is performed at 40 rpm with a stirrer and magnetic stirrer for 4 hours. The heating temperature during stirring is set to 120°C and stirring is performed in order to uniformly mix the sodium hydroxide and phenolic resin and evaporate the water.

[0039] 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 muffle furnace, a rotary kiln, and a roller hearth kiln. To prevent leakage of the mixture from the graphite crucible, a container for containing the spherical resin particles can be, for example, a crucible or a sheath. Materials such as aluminum oxide and oxides containing aluminum and silicon can be used. The heating temperature is preferably 600°C or higher and 900°C or lower, more preferably 700°C or higher and 850°C or lower. The heating time is preferably 20 minutes to 3 hours.

[0040] 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.

[0041] Next, in steps S25 and S26, an acidic solution is preferably mixed and stirred. For example, hydrochloric acid can be used as the acidic solution.

[0042] Next, in step S27, it is preferable to wash again, as described in step S24.

[0043] 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.

[0044] Next, in steps S29 and S30, the dried material is preferably crushed and sieved. The crushing means is not particularly limited, but a ball mill, a bead mill, or the like can be used. 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, a bead mill, or the like, 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 separating sieve with a mesh size of 300 μm.

[0045] Through the above steps, porous carbon can be produced (step S31).

[0046] <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.

[0047] First, in step S41, sulfur and the porous carbon described above are prepared. High-purity sulfur is preferred, with a purity of 99.999% or higher. The sulfur is preferably in powder form. This step is carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere.

[0048] 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 an agate mortar can be used, for example. 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 be able to be composited with carbon. Therefore, when S / C (weight ratio) = x:1, x is preferably 0.5 to 2.5, and more preferably 1 to 2.

[0049] 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 silicone-coated aluminum foil before placing it in the container. Sealing is performed in an inert atmosphere.

[0050] 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.

[0051] In step S44, the heated material is preferably sieved. If necessary, it may be crushed using an agate mortar or the like.

[0052] Through the above steps, a positive electrode active material in which sulfur is supported on porous carbon can be produced (step S45).

[0053] <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.

[0054] First, in step S51, the positive electrode active material, conductive material, and binder solution prepared above are prepared.

[0055] 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, graphite, etc.). In this embodiment, acetylene black (AB) is used as the conductive material.

[0056] As the binder, it is preferable to use materials 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, polyvinylpyrrolidone, or the like.

[0057] 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, ethylene-propylene-diene copolymer, etc. As the binder, fluororubber can also be used.

[0058] 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.

[0059] The solvent may be N-methylpyrrolidone (NMP) or acetone, or may be a mixture of water, alcohol (methanol, ethanol, propanol, butanol, isopropyl alcohol, etc.).

[0060] In this embodiment, a PVDF solution using NMP as a solvent is prepared as the binder solution.

[0061] Next, in step S52, these are mixed and kneaded while adjusting the amount of binder solution to obtain a desired viscosity.

[0062] Next, in step S53, a binder solution and a solvent are added to prepare a slurry containing the positive electrode active material, the conductive material, and the binder in a desired ratio. The viscosity of the slurry is preferably adjusted appropriately by adjusting the amount of solvent, the reaction temperature, or the reaction time. It is preferable to perform degassing as needed.

[0063] 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.

[0064] Next, in step S55, the solvent 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 it is preferable to perform drying under reduced pressure. Pressing may be performed if necessary. Pressing increases the capacity per volume and improves the energy density. Furthermore, since sulfur is distributed inside the carbon material in porous carbon, the influence of heat during pressing can be suppressed. On the other hand, in the case of unactivated carbon, sulfur is distributed outside the carbon material, so there is a risk that the sulfur will melt due to the heat during pressing and leak from the electrode surface. The pressing conditions using a roll press machine should be 20°C or higher and 60°C or lower, and a linear pressure of, for example, 500 kN / m or less, preferably 300 kN / m or less, and more preferably 250 kN / m or less.

[0065] Through the above steps, the positive electrode can be produced (step S56).

[0066] In addition, Fig. 1 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.

[0067] 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.

[0068] 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.

[0069] The steps from step S22 onwards are the same as those in FIG. 1, and therefore detailed description thereof will be omitted here.

[0070] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0071] 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.

[0072] A secondary battery has at least a positive electrode, an electrolyte, a separator, and a negative electrode.

[0073] [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.

[0074] 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.

[0075] The organic solvent that is liquid at room temperature is preferably an aprotic organic solvent, and 1,3-dioxolane (DOL) or 1,2-dimethoxyethane (DME) can be used as an ether-based organic solvent. Sulfolane (SL) can also be used as an organic solvent. 1,1,2,2-tetrafluoroethyl (TTE) or bis(2,2,2-trifluoromethyl)ethyl (BTFE) can also be used as a fluorine-based ether-based organic solvent. Glymes (ethyl monoglyme, butyl diglyme, triglyme, tetraglyme, etc.) can also be used as an organic solvent.

[0076] The lithium salt to be dissolved in the organic solvent is not particularly limited, and may be any salt that can be used in known lithium-sulfur batteries, such as LiCl, LiPF ６ , LiSCN, and lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0077] <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.

[0078] [Separator] The secondary battery preferably has a separator. Examples of separators that can be used include those made of paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0079] 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).

[0080] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging 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-based materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0081] 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.

[0082] 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.

[0083] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector.

[0084] [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. In addition, graphite, silicon-based materials (Si or SiO Ｘ ), or lithium-doped graphite, lithium-doped silicon can also be used.

[0085] [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.

[0086] [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 perspective view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0087] 4A is a schematic diagram showing the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 4A and 4B are not completely corresponding views.

[0088] 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.

[0089] 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 .

[0090] FIG. 4B is a perspective view of the completed coin-type secondary battery.

[0091] 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.

[0092] Note that the positive electrode 201 and the negative electrode 207 used in the coin-type secondary battery 200 each only need to have an active material layer formed on one side.

[0093] 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.

[0094] 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 producing a coin-shaped secondary battery 200.

[0095] By having the above-described configuration, the coin-type secondary battery 200 can have a high discharge capacity and excellent cycle characteristics.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0105] 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.

[0106] FIG. 5B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0123] Embodiment 4 In this embodiment, an example in which a secondary battery of one embodiment of the present invention is mounted on a vehicle will be described.

[0124] 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.

[0125] 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).

[0126] 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.

[0127] The automobile 8500 shown in FIG. 7B can charge its secondary battery by receiving power from an external charging facility using a plug-in method and / or a wireless power supply method. 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 method, 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.

[0128] 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, a solar cell can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped and / or moving. For such contactless power supply, an electromagnetic induction method and / or a magnetic field resonance method can be used.

[0129] 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.

[0130] 7C, the secondary battery 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0131] 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.

[0132] 8A illustrates 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 illustrated 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.

[0133] 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.

[0134] 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.

[0135] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0136] In this example, porous carbon was produced and its characteristics were analyzed. Note that the present invention is not limited to the following examples.

[0137] A method for producing porous carbon will be described with reference to Figure 1. First, in step S11, 8 g of spherical phenolic resin (product name Marilyn HF-008, manufactured by Gun-ei Chemical Industry Co., Ltd.) was prepared. In step S21, 12 g of sodium hydroxide was prepared as a base, and 30 ml of pure water was prepared as water. Each component was weighed so that the weight ratio of spherical phenolic resin to sodium hydroxide was 2:3.

[0138] 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.

[0139] 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.

[0140] Next, in step S23, the mixture of porous carbon and alkaline solution was transferred from the petri dish to a graphite crucible and heated. The crucible was then placed in a muffle furnace with a lid on and heated at 800°C for 1 hour. In the heating treatment of step S23, the temperature was increased and decreased at 200°C per hour, and nitrogen gas was flowed at 5 L / min to create an inert atmosphere.

[0141] Next, in step S24, pure water was added and the mixture was suction filtered and washed. This was repeated until the filtrate became neutral.

[0142] Next, 600 ml of 1 M 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).

[0143] Thereafter, the substrate was washed with pure water in the same manner as in step S24 (step S27).

[0144] Next, in step S28, the substrate was dried by heating under reduced pressure at 60° C. for 10 hours.

[0145] The dried material was crushed in an agate mortar (step S29) and passed through a sieve with 53 μm openings (step S30) to obtain porous carbon (step S31). This was designated Sample 1. An SEM image of Sample 1 is shown in FIG. 9A.

[0146] Before the treatment, the spherical phenolic resin particles were nearly spherical, but after the carbonization and activation processes were carried out simultaneously, it was observed that part of the surface of the porous carbon was deformed and had dents on the surface, as shown in Figure 9A. By undergoing this process, the number of particles that were not spherical increased.

[0147] Furthermore, in step S41 corresponding to FIG. 2A, sulfur (5N, manufactured by Strem Chem) was pulverized in a glove box under an argon atmosphere and passed through a 53 μm sieve to prepare sulfur.

[0148] Next, in step S42, sulfur (S) and porous carbon (C) were weighed in a glove box under an argon atmosphere so that the weight ratio was 5 / 5, and mixed in an agate mortar. Mixing using a ball mill was then performed at a rotation speed of 150 rpm with zirconium oxide balls of 1 mm diameter for 1 hour. After mixing using the ball mill, the mixture was passed through a separating sieve with 300 μm openings.

[0149] 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.

[0150] 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.

[0151] The sample that underwent the above steps for sample 1 is called sample 2, and its SEM image is shown in FIG. 9B.

[0152] In sample 2, mixing was performed using a ball mill, but like sample 1, part of the surface of the porous carbon was deformed and had dents on the surface.

[0153] In this example, porous carbon was produced according to the flow chart of FIG. 3, and the effects of the crushing conditions and specific surface area of ​​S29 were investigated.

[0154] A method for producing porous carbon will be described with reference to Fig. 3. First, 8 g of spherical phenolic resin (manufactured by Gun-ei Chemical Industry Co., Ltd.: product name Marilyn HF-008) and 15 ml of pure water were prepared.

[0155] After mixing the spherical phenolic resin with pure water, ultrasonic waves were applied for 5 minutes to prepare a dispersion liquid, which corresponds to step S12.

[0156] In addition, in step S21, 12 g of sodium hydroxide was prepared as a base, and 15 ml of pure water was prepared as water. Each was weighed so that the weight ratio of the spherical phenolic resin to the sodium hydroxide was 2:3. After mixing the sodium hydroxide and the pure water to prepare an alkaline solution, the alkaline solution was stirred with a stirrer at 300 rpm for 10 minutes.

[0157] Next, the dispersion liquid and the alkaline solution 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 4 hours at 30 rpm using a stirring bar and a magnetic stirrer.

[0158] Next, in step S23, the mixture of porous carbon and alkaline solution was transferred from the petri dish to a graphite crucible and heated. The mixture was placed in a muffle furnace and heated at 800°C for 1 hour. In the heat treatment of step S23, the temperature increase and decrease were performed at 200°C per hour, and nitrogen gas was flowed at 5 L / min to create an inert atmosphere.

[0159] Next, in step S24, pure water was added and the mixture was suction filtered and washed. This was repeated until the filtrate became neutral.

[0160] Next, 600 ml of 1 M 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).

[0161] Thereafter, the substrate was washed with pure water in the same manner as in step S24 (step S27).

[0162] Next, in step S28, the substrate was dried by heating under reduced pressure at 120° C. for 10 hours.

[0163] The dried material was crushed in an agate mortar (step S29), and passed through a sieve with 53 μm openings (step S30) to obtain porous carbon (step S31). This was designated as Sample A.

[0164] Sample A was then crushed using a ball mill at a rotation speed of 150 rpm with zirconium oxide balls of 1 mm diameter for 1 hour. After crushing using the ball mill, the sample was sieved through a separation sieve with 300 μm openings. The sample thus obtained is referred to as Sample B.

[0165] Sample B was then crushed using a ball mill at a rotation speed of 250 rpm with zirconium oxide balls of 1 mm diameter for 1 hour. After crushing using the ball mill, the sample was sieved through a separation sieve with 300 μm openings. The sample thus obtained is referred to as Sample C.

[0166] Sample C was then crushed using a ball mill at a rotation speed of 350 rpm with zirconium oxide balls of 1 mm diameter for 1 hour. After crushing using the ball mill, the sample was sieved through a separation sieve with 300 μm openings. The sample thus obtained is referred to as Sample D.

[0167] The results of measuring the BET specific surface area of ​​samples A, B, C, and D are shown in Table 1. For samples B, C, and D, the results of measurements were taken at two points.

[0168]

[0169] The BET specific surface area measurement device, conditions, and pretreatment were as follows: Pretreatment: Vacuum drying at 300°C for 10 hours or more Measurement device: Automatic specific surface area measurement device Tristar II 3020 Gas used: Nitrogen Measurement temperature: -195.8°C

[0170] Table 1 also shows the particle size distribution of each sample measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-2200), and the D50 value and (D90-D10) / D50 value. D50 refers to the particle diameter at 50% of the calculated cumulative distribution, 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 smaller the (D90-D10) / D50 value, the sharper the particle size distribution and the more uniform the particle diameters.

[0171] As shown in Table 1, the porous carbon obtained in this example had a relatively large specific surface area. The maximum specific surface area was 1789 cm ２ Sample A, which was not subjected to ball mill crushing, had a specific surface area of ​​1731 cm ２ / g, the D50 value was large at 14.5 μm, and the (D90−D10) / D50 value was also large at 1.5. In contrast, Samples B, C, and D, which were subjected to ball mill crushing, were able to maintain a relatively large specific surface area while reducing the particle size and sharpening the particle size distribution by crushing with a ball mill.

[0172] 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, 4002 : 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: Aircraft, 6501: Propeller, 6502: Camera, 6503: Secondary battery, 6504: Electronic component, 8021 : 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 step of preparing porous carbon by mixing a spherical resin, a base, and water, and then performing a first heat treatment in an inert atmosphere at a temperature of 600° C. to 900° C. for 20 minutes to 3 hours; a first cleaning step of cleaning the porous carbon; mixing and stirring the porous carbon with an acidic solution; a second washing step of washing the porous carbon after the mixing; a step of drying the substrate by performing a second heat treatment under reduced pressure after the second cleaning step; a step of crushing the aggregated porous carbon after the second heat treatment; a step of mixing the crushed porous carbon with sulfur, and then performing a third heat treatment to prepare a positive electrode active material containing the porous carbon and the sulfur; mixing the positive electrode active material with a conductive additive and a binder solution to prepare a slurry; a step of drying the slurry on a surface of a current collector to form a positive electrode; a step of performing a press treatment on the positive electrode to prepare an electrode for a secondary battery; A method for producing a secondary battery having the above structure.

2. The method for producing a secondary battery according to claim 1, wherein the D50 of the spherical resin is 3 μm or more and 12 μm or less, and (D90−D10) / D50 is 0.1 or more and 1.5 or less.

2. The method for manufacturing a secondary battery according to claim 1, wherein the second heat treatment is performed at a temperature of 60° C. or higher and 300° C. or lower.

2. The method for producing a secondary battery according to claim 1, wherein the second heat treatment is carried out in a graphite container.

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