Porous carbon, method for producing positive electrode active substance, and lithium ion secondary battery

Abstract

One aspect of the present invention provides porous carbon capable of increasing the amount of supported sulfur. In a state whereby a lid is placed on a container that houses a mixture obtained by mixing a spherical resin, a base and water, modification is carried out by performing a first heat treatment in an inert atmosphere at a temperature of 700°C or higher. Chemical activation, and especially alkali activation, is used as an activation method, and carbonization and alkali activation are carried out by means of the first heat treatment to bring about modification, and specifically particle shrinkage, formation of pores due to gas release inside the particles, cracks on the surface of particles, and the like. The modified carbon (also known as porous carbon) is used as a support body for sulfur that is subsequently blended.

Description

Method for producing porous carbon, positive electrode active material, and lithium-ion secondary battery

[0001] One aspect of the present invention relates to a product, a method, or a method of manufacture; or to a process, a machine, a manufacture, or a composition of matter. Another aspect of the present invention relates to an energy storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a method of manufacturing the same.

[0002] In this specification, "electronic equipment" refers to all devices that have an energy storage device, and all electro-optical devices with an energy storage device, information terminal devices with an energy storage device, etc., are considered electronic equipment.

[0003] Furthermore, in this specification, the term "energy storage device" refers to all elements and devices having an energy 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, there has been a great deal of activity in the development of lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and various energy storage devices. In particular, lithium-ion secondary batteries, which offer high output and high energy density, are seeing a rapid increase in demand in portable information terminals such as mobile phones, smartphones, and notebook computers, as well as portable music players, digital cameras, medical devices, and next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). This demand has also grown rapidly in conjunction with the development of the semiconductor industry, making them an indispensable source of rechargeable energy for today's information society.

[0005] Furthermore, there is a demand for lightweight, high-capacity secondary batteries, and secondary batteries using materials containing sulfur as the positive electrode active material are attracting attention. Sulfur is known to have a high theoretical discharge capacity of approximately 1670 mAh / g and is also promising as a positive electrode active material in terms of energy density (see, for example, Patent Document 1).

[0006] WO2024 / 141882

[0007] In lithium-sulfur batteries, lithium metal is used as an example of the negative electrode active material. During discharge, the lithium metal dissolves in the electrolyte at the negative electrode and Li ＋ As a result, it reacts with sulfur at the positive electrode and is oxidized to form lithium polysulfide (Li) as a reaction intermediate product. ２ S ｎ (2 ≤ n ≤ 8) then lithium sulfide (Li ２ It becomes S.

[0008] One of the challenges of lithium-sulfur batteries is the poor electrical conductivity of the positive electrode, which is composed of lithium and sulfur. To address this challenge, it is expected that the charge and discharge capacity can be improved by supporting sulfur on porous carbon. However, if the pore size (also called pore diameter) of the porous carbon is made too large to support a large amount of sulfur, lithium polysulfide, an intermediate product of the reaction, will leach from the porous carbon into the electrolyte. On the other hand, if the pores of the porous carbon are made smaller to suppress the leaching of lithium polysulfide, the amount of sulfur that can be supported in the pores decreases, resulting in a smaller charge and discharge capacity.

[0009] Therefore, one aspect of the present invention aims to provide porous carbon that can support a large amount of sulfur.

[0010] Furthermore, one aspect of the present invention aims to provide a positive electrode active material in which sulfur is supported on porous carbon with a high sulfur-supporting capacity.

[0011] Furthermore, one aspect of the present invention aims to provide a secondary battery using a positive electrode active material in which sulfur is supported on porous carbon with a high sulfur-supporting capacity.

[0012] Furthermore, one aspect of the present invention aims to provide a high-capacity lithium-ion secondary battery and a method for manufacturing the same. Another aspect of the present invention aims to provide a lightweight and high-capacity lithium-ion secondary battery and a method for manufacturing the same.

[0013] Furthermore, one aspect of the present invention aims to provide a lithium-ion secondary battery with excellent charge-discharge cycle characteristics, and a method for manufacturing the same. Alternatively, one aspect of the present invention aims to provide a secondary battery with a long cycle life and high safety or reliability, and a method for manufacturing the same.

[0014] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims.

[0015] A mixture of spherical resin, base, and water is placed in a sealed container and subjected to a first heat treatment at over 700°C under an inert atmosphere to modify (carbonize and activate) the spherical resin. Chemical activation, particularly alkaline activation, is used as the activation method. Carbonization and alkaline activation are carried out by the first heat treatment, modifying the material, specifically causing shrinkage of particles, formation of pores due to gas release inside the particles, and cracking of the particle surface. The carbon (which can also be called porous carbon) modified from the spherical resin is used as a carrier for the sulfur that is later mixed in. Activation refers to increasing the function or action of a substance, specifically by making the substance porous to increase its adsorption capacity. Furthermore, the substance modified by the above treatment has numerous pores and is called porous carbon.

[0016] The first heat treatment results in porous carbon in which the particle size distribution or resistance of the spherical resin changes. Specifically, the conditions for the first heat treatment are an inert atmosphere, a temperature of 700°C to 1000°C for 1 hour to 40 hours, preferably 750°C to 950°C for 2 hours to 20 hours.

[0017] By heating with the lid on during the first heat treatment, the distribution of pore sizes in the porous carbon can be made sharper. A sharp distribution of pore sizes in the porous carbon means that the variation in the state of sulfur that penetrates the pores in subsequent processes can be reduced.

[0018] If the most frequent pore radius is too large, the specific surface area decreases, and if it is too small, the diffusion of sulfur into the pore becomes difficult. The most frequent pore radius can be determined by analyzing the relationship between nitrogen partial pressure and nitrogen adsorption amount in adsorption measurements using nitrogen gas, using the MP (micropore analysis) method or the BJH (Barrett-Joyner-Halenda) method. Furthermore, the pore volume at each pore size can also be measured using the MP method or the BJH method.

[0019] After the first heat treatment, the obtained substance is mixed with an acidic aqueous solution, washed, and then subjected to a second heat treatment under reduced pressure. After the second heat treatment under reduced pressure, the carbon mass is crushed, and the carbon and sulfur are mixed and subjected to a third heat treatment. The mixture of carbon and sulfur can also be called a sulfur-carbon composite. Porous carbon can adsorb and capture sulfur in the numerous pores present on its surface and inside the particles, making it possible to produce a positive electrode active material that supports a large amount of sulfur.

[0020] Preferably, the proportion of sulfur in the sulfur-carbon composite is 50% or more and less than 70% of the total weight of the sulfur-carbon composite.

[0021] The invention disclosed herein is a porous carbon material that uses spherical resin as a raw material and satisfies the following conditions: the mode of the pore radius distribution analyzed by the MP method is 0.40 nm or more and 1.00 nm or less; and the mode of the pore diameter distribution analyzed by the BJH method is 1.40 nm or more and 2.00 nm or less.

[0022] In the above configuration, the spherical resin is a phenolic resin, and in the particle size distribution measured using a laser diffraction particle size distribution analyzer, D50 is between 3 μm and 12 μm. Since the shape of the resin used as a raw material greatly affects the shape of the porous carbon, spherical resin particles are a suitable shape. Furthermore, it is preferable that (D90 - D10) / D50 is between 0.1 and 1.5. Note that D50 (also called the median diameter) refers to the particle diameter at 50% of the cumulative distribution of particles calculated in the 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.

[0023] Also, in the above configuration, the porous carbon has a BET (Brunauer-Emmett-Teller) specific surface area of 2000 m ２ / g or more and 3000 m ２ / g or less, and the integrated pore volume analyzed by the MP method is 1 cm ３ / g or more, and the integrated pore volume analyzed by the BJH method is 1 cm ３ / g or more.

[0024] <Pore size distribution measurement> In this specification, the gas adsorption method is used as the method for measuring the pore size distribution. The gas adsorption method is a technique for measuring the specific surface area, pore size distribution, integrated pore volume, etc. of a sample by adsorbing gas molecules with a known adsorption occupation area on the surface of the sample as an adsorbate and measuring the amount of adsorbed gas. Pores are classified by their diameter. Pores with a pore diameter of 2 nm or less are called micropores (also referred to as micro pores, micro holes or micro pores), pores with a pore diameter greater than 2 nm and 50 nm or less are called mesopores (also referred to as meso pores), and pores with a pore diameter greater than 50 nm are called macropores (also referred to as macro pores).

[0025] As the measurement of the gas adsorption method, using nitrogen as the adsorbate and performing isothermal adsorption measurement at a liquid nitrogen temperature of minus 195.8 °C, in the adsorption isotherm obtained, adsorption in the range where the relative pressure p / p ０ is 0 or more and 0.2 or less can be considered to be due to micropores, adsorption in the range greater than 0.2 and 0.95 or less 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.

[0026] The porous carbon of one aspect of the present invention has a large amount of adsorption in the range where the relative pressure p / p ０ is 0 or more and 0.2 or less in the adsorption isotherm. That is, it can be said that it has many micropores with a pore diameter of 2 nm or less. Note that p in the relative pressure p / p ０ is the measurement pressure, and p ０ is the saturated vapor pressure.

[0027] As a method for analyzing micropores, the MP method is known. The MP method uses the t-plot method and was devised by R. S. Mikhail, S. Brunauer, and E. E. Bodor. By performing analysis using the MP method, the pore volume distribution and cumulative pore volume of micropores can be calculated. When nitrogen is used for measurement by the gas adsorption method, since the size of one nitrogen molecule is 0.354 nm, it is difficult to measure pores smaller than this. Also, since the t-plot method is a technique for analysis using a t-plot in which the adsorption amount is plotted against the adsorption thickness, for example, 0.52 nm is the lower limit value applicable for analysis as the pore diameter calculated by analyzing the nitrogen adsorption isotherm by the MP method.

[0028] Also, as a method for analyzing the range of pore diameters from 1 nm to 100 nm including a part of the micropores, the BJH method is known, and the pore volume distribution and cumulative pore volume in the range of pore diameters from 1 nm to 100 nm can be calculated.

[0029] Also, by performing analysis using the BET method, it is possible to calculate the specific surface area. The specific surface area calculated by the BET method may be referred to as the BET specific surface area.

[0030] Also, a method for producing a positive electrode active material is also one of the present inventions, and its configuration is to store a mixture of a spherical resin, a base that is 1.0 times or more and 2.0 times or less the weight of the spherical resin, and water in a container with a lid, and with the lid on, set the range in an inert atmosphere to 700°C or more and 1000°C or less, perform a first heat treatment for 1 hour or more and 20 hours or less to produce porous carbon, wash the porous carbon, mix the porous carbon and an acidic aqueous solution and stir, after washing the porous carbon, perform a second heat treatment under reduced pressure, crush the porous carbon, mix the porous carbon and sulfur, and perform a third heat treatment in an inert atmosphere.

[0031] In the above production method, the spherical resin is a phenol resin and the base is sodium hydroxide.

[0032] In the above production method, the weight ratio of sulfur to the total of the weight of sulfur and the weight of porous carbon is 50% or more and less than 70%.

[0033] In the above manufacturing method, the second heat treatment is performed at a temperature of 60°C to 300°C for 5 hours to 20 hours, and the third heat treatment is performed at a temperature of 120°C to 160°C for 1 hour to 10 hours.

[0034] One aspect of the present invention provides porous carbon that can support a large amount of sulfur. Furthermore, by heating with a lid on, the distribution of pore sizes can be made sharper. A sharp distribution of pore sizes reduces the variation in the state of solidified sulfur after impregnation of the pores with liquid sulfur in a later process.

[0035] Figure 1A is a flowchart illustrating an example of a method for producing porous carbon. Figure 1B is a graph illustrating the temperature conditions for the heating process. Figure 2A is a flowchart illustrating an example of a method for producing a positive electrode active material. Figure 2B is a flowchart illustrating an example of a method for producing a positive electrode. Figure 3 is a flowchart illustrating an example of a method for producing porous carbon. Figure 4A is an exploded perspective view of a coin-type secondary battery, Figure 4B is a perspective view of a coin-type secondary battery, and Figure 4C is a cross-sectional perspective view thereof. Figures 5A, 5B, 5C, and 5D illustrate an example of electronic equipment. Figures 6A, 6B, and 6C illustrate an example of electronic equipment. Figures 7A, 7B, and 7C illustrate an example of a vehicle. Figures 8A and 8B illustrate an example of an electric bicycle. Figures 9A and 9B are perspective views showing an example of an aircraft. Figures 10A and 10B are graphs showing the pore radius distribution with differential pore volume on the vertical axis. Figures 11A and 11B are graphs showing the pore diameter distribution with differential pore volume on the vertical axis. Figure 12 is a graph showing the XRD pattern. Figure 13 is a graph showing the results of the charge-discharge cycle test. Figures 14A and 14B are graphs showing the results of the charge-discharge cycle test. Figures 15A and 15B are graphs showing the results of the charge-discharge cycle test.

[0036] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0037] In this specification, the terms "first" and "second" may be used for convenience to understand the technical content or to identify each component. Therefore, the terms "first" and "second" do not limit the number of each component. Nor do the terms "first" and "second" limit the order of each component. Furthermore, the terms "first" and "second" or identification codes used in this specification may not correspond to the terms or identification codes in the claims of this patent.

[0038] (Embodiment 1) In this embodiment, a method for producing porous carbon that can be used in a lithium-sulfur battery according to one aspect of the present invention, and a method for producing porous carbon that can be used in a positive electrode active material layer will be explained with reference to Figures 1A to 2B.

[0039] <Method for producing porous carbon> A method for producing porous carbon by activating resin particles will be described. Activation refers to increasing the function or action of a substance, specifically by making the substance porous to increase its adsorption capacity. First, in step S21, alkaline activation using an alkali as the activating agent is performed, and a base and water are prepared. For example, sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, etc. can be used as the base. In this embodiment, sodium hydroxide will be used.

[0040] Next, in step S11, spherical resin particles are prepared. The resin material is not particularly limited, but it is preferable to use a phenolic resin which has a three-dimensional network structure containing a six-membered carbon ring and is relatively inexpensive. Phenolic resin is also preferable because it has a high carbon content and a high carbon residue rate in the carbonization process. The spherical phenolic resin is synthesized by a condensation reaction between phenols containing polyhydric phenols and aldehydes, and then obtained by separating and recovering the phenolic resin.

[0041] Since the shape of the resin used here greatly influences the shape of the porous carbon, spherical resin particles are a suitable shape. Furthermore, as for the particle size distribution of the resin particles, D50 (also called the median diameter) is preferably 3 μm to 50 μm, more preferably 3 μm to 12 μm, and even more preferably 6 μm to 10 μm. Also, (D90 - D10) / D50 is preferably 0.1 to 1.5. 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, by a laser diffraction particle size distribution analyzer.

[0042] In this embodiment, as the spherical phenolic resin, Marilyn HF-008 manufactured by Gun-ei Chemical Industry Co., Ltd. is used, in which the particle size distribution measured using a laser diffraction particle size distribution analyzer shows a D50 of 7.92 μm and a (D90-D10) / D50 of 0.435.

[0043] Next, the base and water are mixed and stirred to prepare an alkaline solution (aqueous sodium hydroxide solution), then the spherical phenolic resin is mixed in, and the mixture is 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 the mixture is stirred at 600 rpm for 30 minutes using a stirring bar and a magnetic stirrer. After that, the mixture is transferred from the beaker to a petri dish, and the heating temperature during stirring is set to 100°C to 120°C, and the mixture is stirred at 40 rpm for 4 to 6 hours using a stirring bar and a magnetic stirrer. 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.

[0044] Furthermore, regarding the amount of sodium hydroxide aqueous solution mixed with the spherical phenolic resin, it is preferable that the weight of sodium hydroxide contained in the sodium hydroxide aqueous solution is 1.0 to 2.0 times the weight of the phenolic resin, and more preferably 1.3 to 1.8 times.

[0045] Next, in step S23, the mixture of spherical phenolic resin and alkaline solution is transferred from the petri dish to a container that can be covered, and the mixture is heated with the lid on. However, if the container is completely sealed by covering it with a lid, the gas inside the container cannot be released, so some gas exchange should occur through the gap between the container and the lid. Heating is preferably carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating furnace is not particularly limited, but for example, a tubular furnace, muffle furnace, rotary kiln, roller hearth kiln, etc. can be used. As the container for holding the resin particles, for example, a crucible or sheath that can be covered with a lid can be used, and the materials for these can be graphite, aluminum oxide, or an oxide having aluminum and silicon. Alternatively, the mixture may be placed in a graphite crucible, the crucible placed in an alumina sheath, and heated with an alumina lid (lid of the alumina sheath). The heating temperature is preferably 700°C to 1000°C, and more preferably 750°C to 950°C. The heating time is preferably between 2 hours and 40 hours.

[0046] In addition, for the heating in step S23, a one-step heating method can be used in which heating is performed for a predetermined time without changing the temperature within the above heating temperature range. However, the heating in step S23 may also be performed using the two-step heating method shown in Figure 1B.

[0047] Figure 1B illustrates a two-step heating method in which heating is performed at a first temperature T1, followed by heating at a second temperature T2. The second temperature T2 is preferably higher than the first temperature T1. Specifically, it is preferable that the first temperature T1 is between 700°C and 850°C, and the second temperature T2 is between 800°C and 1000°C. It is even more preferable that the first temperature T1 is between 750°C and 850°C, and the second temperature T2 is between 850°C and 950°C.

[0048] As shown in Figure 1B, in the two-step heating method, the heating time can be as follows: heating at the first temperature T1 is performed for (t2-t1) time, and heating at the second temperature T2 is performed for (t4-t3) time. The first heating time is preferably 30 minutes to 20 hours, and more preferably 1 hour to 10 hours. The second heating time is preferably 1 hour to 20 hours, and more preferably 1 hour to 10 hours.

[0049] Next, in step S24, the heated material is washed. The washing method is not particularly limited, but it is preferable to wash it with pure water and repeat the process until the solution becomes neutral.

[0050] Next, in steps S25 and S26, it is preferable to mix and stir an acidic aqueous solution. For example, hydrochloric acid can be used as the acidic aqueous solution. For example, 1 mol / L hydrochloric acid can be used. Even if basic components remain in the porous carbon after step S24, these basic components can be removed by treatment with the acidic aqueous solution, and porous carbon with fewer impurities can be obtained.

[0051] Next, as step S27, it is preferable to wash again. The method can be described in step S24.

[0052] Next, in step S28, the washed material is dried. The drying method is not particularly limited, but for example, it can be dried under reduced pressure. Vacuum drying is a heat treatment under reduced pressure, at a temperature of 60°C to 300°C for 5 hours to 20 hours, and in this embodiment, it is 120°C for 10 hours.

[0053] Next, in steps S29 and S30, it is preferable to crush the dried material and sift it. The crushing method is not particularly limited as long as it can crush the aggregated porous carbon, but a mortar and pestle, ball mill, or bead mill can be used. Agate balls, aluminum oxide balls, or zirconium oxide balls are preferred as the grinding media. Zirconium oxide balls are preferred because they produce less impurity. When using a ball mill or bead mill, it is preferable to set the rotation speed to 100 rpm or more and 400 rpm or less in order to suppress contamination from the media. In this embodiment, a 45 ml container is used, 50 g of zirconium oxide balls (1 mm in diameter) are used, and the process is carried out at a rotation speed of 250 rpm for 1 hour. After crushing using a ball mill, the material is passed through a separation sieve with a mesh opening of 300 μm (step S30).

[0054] Porous carbon can be produced through the above process (step S31).

[0055] The porous carbon obtained through the process described in this embodiment satisfies the following conditions: the most frequent value of the pore radius distribution analyzed by the MP method is 0.40 nm or more and 1 nm or less; and the most frequent value of the pore diameter distribution analyzed by the BJH method is 1.4 nm or more and 2 nm or less. Furthermore, the BET specific surface area is 2000 m². ２ / g or more 3000m ２ It is less than or equal to / g.

[0056] The apparatus and conditions for pore size distribution measurement are not particularly limited. For example, measurements can be taken using the following apparatus and conditions: [Measurement Apparatus] Apparatus: Tristar II 3020, manufactured by Micromerities [Measurement Conditions] Measurement Method: Isothermal adsorption measurement Measurement Range: Relative pressure p / p ０ = 0.01~1.0 Measurement temperature: -195.8℃ Adsorbate: Nitrogen Pretreatment method: Vacuum drying at 300℃ 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 or BJH method Reference t curve: Harkins and Jura (t = [13.99 / (0.034 - log(p / p0))] ０．５) Applicable range (pore radius range) for the MP method: 0.25 nm to 1.0 nm (the pore diameter value is twice the pore radius value) Applicable range (pore diameter range) for the BJH method: 1.0 nm to 100 nm

[0057] <Method for preparing positive electrode active material> Next, an example of a method for preparing positive electrode active material will be explained using the flowchart in Figure 2A.

[0058] First, in step S41, sulfur and the porous carbon described above are prepared. The sulfur is preferably of high purity, for example, a purity of 99.5% or higher is preferred, and a purity of 99.999% or higher is more preferred. The sulfur is preferably crushed and sieved. This process is carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere.

[0059] Next, in step S42, the sulfur and porous carbon are mixed. This step is carried out in an inert atmosphere. The mixing method is not particularly limited, but for example, a ball mill can be used. If the mixing ratio S / (S+C) of sulfur (S) to porous carbon (C) is too small, the charge / discharge capacity will decrease, but if it is too large, there is a risk that a large amount of sulfur will not be able to 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% or more and 75% or less by weight, more preferably 50% or more and less than 70%, and more preferably 50% or more and 67% or less.

[0060] Furthermore, by using porous carbon formed at the mode of the pore radius distribution and the mode of the pore diameter distribution analyzed by the BJH method, and by using the sulfur (S) mixing ratio described above, the amount of sulfur that does not fit into the pores of the porous carbon can be reduced, thereby suppressing the elution of lithium polysulfide when used in a secondary battery.

[0061] Next, in step S43, the mixture of sulfur and porous carbon is sealed in a container and the container is heated. For example, a sealed cylindrical metal container can be used. To prevent sulfur that has not compounded with carbon from adhering to the container, it is preferable to wrap the mixture in resin-coated metal foil, such as silicone-coated aluminum foil, before placing it in the container. The sealing is carried out in an inert atmosphere.

[0062] The heating temperature in step S43 is preferably 120°C to 160°C, and the heating time is preferably 1 hour to 10 hours. The atmosphere at this time is an inert atmosphere, and an argon atmosphere is particularly preferred.

[0063] In step S44, it is preferable to sift the heated material. If necessary, it may be crushed using an agate mortar and pestle or the like.

[0064] Through the above process, a positive electrode active material can be produced in which sulfur is supported on porous carbon (step S45).

[0065] Furthermore, it is preferable that the sulfur in the positive electrode active material exists in an amorphous state. The amorphous state of sulfur indicates that the sulfur and carbon are sufficiently compounded. Therefore, when porous carbon or a positive electrode active material layer or secondary battery containing it is analyzed by diffraction methods such as X-ray diffraction (XRD), sulfur crystals (S ８ It is preferable that no peaks originating from ) are observed.

[0066] Therefore, when analyzed by X-ray diffraction using CuKα rays, for example, the XRD pattern shows that sulfur crystals (S) are present in the ranges of 2θ = 23.12 ± 0.1° (23.02° to 23.22°) and 27.74° ± 0.1° (27.64° to 27.84°). ８ It is preferable that the sample does not have a distinct peak derived from ).

[0067] Furthermore, it is preferable that the carbon in the positive electrode active material has low crystallinity. Lower carbon crystallinity results in a larger specific surface area, which is advantageous for the compounding of sulfur and carbon. Therefore, hydrogen and oxygen may be detected along with carbon in the elemental analysis of the positive electrode active material. Also, when the positive electrode active material or a positive electrode or secondary battery containing it is analyzed by diffraction, it is preferable that the peak originating from carbon is broad.

[0068] For example, when analyzed by X-ray diffraction using CuKα rays, 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 where 2θ is 15° or more and 35° or less.

[0069] <XRD> The equipment and conditions for XRD measurement are not particularly limited. For example, measurements can be performed with the following equipment and conditions: XRD equipment: Bruker D8 ADVANCE X-ray source: Cu Output: 40kV, 40mA Divergent slit: 0.6mm Detector: LynxEye XE-T Scanning method: 2θ / θ continuous scan Measurement range (2θ): 5° to 60° Step width (2θ): 0.01° Setting counting time: 0.5s / step Sample stage rotation: 5rpm

[0070] If the sample to be measured is a powder, it can be set up by placing it in a glass sample holder or by sprinkling the sample onto a grease-coated silicone anti-reflective plate. If the sample to be measured is a positive electrode, the positive electrode can be attached to a substrate with double-sided tape, and the positive electrode active material layer can be set up to match the measurement surface required by the device.

[0071] In this specification, a spherical particle refers to a particle in which, when the cross-sections of multiple particles are observed, the majority of the cross-sections are circular. In this case, the number of particles is preferably five or more. Furthermore, the circular shape is not limited to a perfect circle.

[0072] <Method for Manufacturing a Positive Electrode> Next, an example of a method for manufacturing a positive electrode will be explained using the flowchart in Figure 2B.

[0073] First, in step S51, the positive electrode active material, conductive material, and binder solution prepared as described above were prepared.

[0074] One or more conductive materials selected from carbon, copper, tin, zinc, silver, and nickel can be used. Typical carbon materials used as conductive materials include carbon black (such as furnace black and acetylene black, as well as other particulate carbon), carbon nanotubes, graphene, and carbon fibers. In this embodiment, acetylene black (AB) will be used as the conductive material.

[0075] It is preferable to use materials such as polystyrene, methyl polyacrylate, 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 as the binder.

[0076] Furthermore, as a binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluororubber can also be used as a binder.

[0077] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. One or more polysaccharides can be used from among cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0078] As a solvent, NMP (N-methylpyrrolidone) or acetone can be used. Water, alcohol (methanol, ethanol, propanol, butanol, or isopropyl alcohol, etc.) can also be used. These may be mixed and used together.

[0079] In this embodiment, a PVDF solution using NMP as the solvent was prepared as the binder solution.

[0080] Next, in step S52, the positive electrode active material, the conductive material, and the binder are mixed and kneaded while adjusting the amount of binder solution to achieve a desirable viscosity.

[0081] Next, in step S53, the same type of binder solution and solvent prepared in step S51 are added to prepare a slurry so that the positive electrode active material, conductive material, and binder are in any proportion. The viscosity of the slurry is preferably adjusted as appropriate by the amount of solvent, reaction temperature, or reaction time. Degassing is preferably performed as necessary.

[0082] Next, in step S54, the slurry is coated onto the positive electrode current collector. It is preferable to use carbon-coated aluminum foil for the positive electrode current collector in order to improve adhesion or reduce interfacial resistance.

[0083] 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 carried out by methods such as forced-air drying or reduced-pressure (vacuum) drying, but it is preferable to dry under reduced pressure. In addition, in order to suppress the melting and sublimation of sulfur, it is preferable to dry at a low temperature that allows the solvent to evaporate. If necessary, pressing may be performed. Pressing increases the volume per unit area and improves the energy density. Furthermore, in the case of spherical porous carbon, the sulfur is distributed on the inside of the carbon material, so the effect of heat during pressing can be suppressed. On the other hand, in the case of unactivated spherical porous carbon, the sulfur is distributed on the outside of 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. Pressing conditions using a roll press machine can be 20°C to 60°C, for example, a linear pressure of 500 kN / m or less, preferably a linear pressure of 300 kN / m or less, and more preferably a linear pressure of 250 kN / m or less.

[0084] The positive electrode can be manufactured through the above process (step S56).

[0085] Furthermore, while Figure 1A shows an example where the base and water are mixed first, followed by the addition of spherical resin, the procedure is not limited to this, and the steps shown in Figure 3 may also be used. Figure 3 shows an example of dispersion using ultrasound.

[0086] In Figure 3, in step S12, the spherical resin and water are mixed and ultrasonically treated to thoroughly disperse the spherical resin in the water and obtain a dispersion. Then, in step S21, the mixture of base and water is mixed with the dispersion, and in step S22, stirring is performed.

[0087] By preparing the dispersion beforehand, a well-mixed solution can be obtained in a short time. Therefore, the stirring time in step S22 can also be shortened.

[0088] Since the steps from step S22 onward are the same as those in Figures 1A and 1B, a detailed explanation is omitted here.

[0089] This embodiment can be implemented in appropriate combination with other embodiments.

[0090] (Embodiment 2) An example of fabricating a secondary battery using the mixture of sulfur and porous carbon obtained in Embodiment 1 as the positive electrode is shown below.

[0091] A secondary battery comprises at least a positive electrode, an electrolyte, a separator, and a negative electrode.

[0092] [Electrolyte] A secondary battery has an electrolyte containing carrier ions. In this specification, the electrolyte is not limited to one containing an organic solvent that is liquid at room temperature, but also includes solid electrolytes, and electrolytes containing both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature (semi-solid electrolytes) are also included. Note that a solution in which lithium salt is dissolved in an organic solvent that is liquid at room temperature is sometimes called an electrolyte solution.

[0093] A challenge with sulfur-based secondary batteries is that their performance is greatly affected by the formation and dissolution of lithium polysulfide. ２ S ｎ (2 ≤ n ≤ 8) is generated, and the liquid lithium polysulfide dissolves into the electrolyte, reducing the capacity. In addition, lithium polysulfide undergoes a shuttle reaction during charging, significantly reducing the charge and discharge efficiency. Furthermore, many organic solvents react with lithium polysulfide.

[0094] The organic solvent, which is liquid at room temperature, is preferably an aprotic organic solvent. As an ether-based electrolyte, 1,3-dioxolane (DOL) or 1,2-dimethoxyethane (DME) can be used. Sulfolane (SL) can also be used as an electrolyte. As a fluorine-based ether, 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. Glymes (butyl diglyme, triglyme, tetraglyme, etc.) can also be used as electrolytes.

[0095] Furthermore, the lithium salt to be dissolved in the above organic solvent is not particularly limited, and any known lithium salt usable in lithium-sulfur batteries may be used, for example, LiCl, LiPF ６ Examples include LiSCN, bis(trifluoromethane)sulfonimide lithium (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0096] <Additives> The above organic solvent may contain additives. Possible additives include lithium nitrate, imide salts, sulfonated compounds, aromatic compounds, halogen-substituted versions thereof, Li ２ S ６ , P ２ S ５ These can be used.

[0097] <Example of Electrolyte 1> As a combination of the above organic solvent, lithium salt, and additive, an electrolyte containing LiTFSI, DOL, DME, and lithium nitrate can be used. In the above combination, it is preferable to use an electrolyte obtained by mixing a mixed solvent of DOL and DME in a volume ratio of 1:1, adding an amount of LiTFSI to make up 1 mol / L, and then adding an amount of lithium nitrate to make up 0.1 mol / L.

[0098] <Example of Electrolyte 2> Alternatively, as an example of a different combination than the above, an electrolyte containing LiTFSI, SL, and TTE can be used. In the above combination, it is preferable to use an electrolyte obtained by mixing LiTFSI:SL:TTE in a molar ratio of 1:2:2. Since this electrolyte contains SL, the elution of lithium polysulfide into the electrolyte is suppressed, so it is preferable to combine it with a positive electrode active material that supports a large amount of sulfur.

[0099] [Separator] A secondary battery preferably has a separator. As the separator, for example, one made of paper, nonwoven fabric, glass fiber, ceramics, nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, polyimide, acrylic, polyolefin, or synthetic fiber using polyurethane can be used. The separator may be processed into an envelope shape and arranged to enclose either the positive or negative electrode.

[0100] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0101] 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 facilitates better adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thereby enhancing the safety of secondary batteries.

[0102] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0103] By using a multilayer separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the discharge capacity per unit volume of the secondary battery.

[0104] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector.

[0105] [Negative electrode active material] For example, lithium metal or alloy materials (alloys with copper, tin, or cobalt) can be used as the negative electrode active material.

[0106] [Negative electrode current collector] In addition to copper, the same materials as those used for the positive electrode current collector can be used for the negative electrode current collector.

[0107] When lithium metal is used as the negative electrode active material, a film may be provided on the lithium metal to homogenize the deposition of lithium. As a film to homogenize the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. Alternatively, as a film to homogenize the deposition of lithium, for example, a metal film that forms an alloy with lithium can be used. As a metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Since lithium and magnesium form a solid solution over a wide composition range, magnesium is suitable as a film to homogenize the deposition of lithium.

[0108] [Coin-type rechargeable battery] Figure 4A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 4B is an external view, and Figure 4C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

[0109] Note that Figure 4A is a schematic diagram to show the overlapping of the components (up / down relationship and positional relationship). Therefore, Figures 4A and 4B are not perfectly identical corresponding diagrams.

[0110] In Figure 4A, the positive electrode 201, separator 210, negative electrode 207, spacer 222, and 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 Figure 4A. The spacer 222 and washer 212 are used to protect the inside or fix the position within the can when the positive electrode can 204 and negative electrode can 202 are pressed together. The spacer 222 and washer 212 are made of stainless steel or an insulating material.

[0111] The positive electrode 201 is a laminated structure in which a positive electrode active material layer 206 is formed on a positive electrode current collector 205.

[0112] Figure 4B is a perspective view of the completed coin-type rechargeable battery.

[0113] The coin-type secondary battery 200 has a positive electrode casing 204, which also serves as the positive electrode terminal, and a negative electrode casing 202, which also serves as the negative electrode terminal, which are insulated and sealed by a gasket 203 made of polypropylene or the like. The positive electrode 201 is formed by a positive electrode current collector 205 and a positive electrode active material layer 206 provided in contact with it. The negative electrode 207 is formed by a negative electrode current collector 208 and a negative electrode active material layer 209 provided in contact with it. Furthermore, the negative electrode 207 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0114] Furthermore, the positive electrode 201 and negative electrode 207 used in the coin-type secondary battery 200 can each have the active material layer formed on only one side.

[0115] The positive electrode can 204 and the negative electrode can 202 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel or aluminum to prevent corrosion caused by the electrolyte. 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.

[0116] The negative electrode 207, positive electrode 201, and separator 210 are immersed in the electrolyte, and as shown in Figure 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 at the bottom, and the positive electrode can 204 and negative electrode can 202 are crimped together via the gasket 203 to assemble a coin-type secondary battery 200.

[0117] The above configuration makes it possible to create a coin-type secondary battery 200 with high capacity and excellent cycle characteristics.

[0118] This embodiment can be implemented in appropriate combination with other embodiments.

[0119] (Embodiment 3) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device will be described with reference to Figures 5A to 6C.

[0120] Figure 5A shows an example of a wearable device. Wearable devices use high-capacity, lightweight rechargeable batteries as a power source. Furthermore, in order to enhance splash-proof, water-resistant, or dustproof performance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0121] For example, a secondary battery according to one aspect of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 5A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 with good weight balance and a long continuous usage time can be made. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0122] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. A high-capacity and lightweight secondary battery can be provided in the flexible pipe 4001b and / or in the earphone section 4001c. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0123] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in a device 4002 that can be directly attached to the body. A high-capacity and lightweight secondary battery 4002b can be provided within the thin housing 4002a of the device 4002. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0124] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on the device 4003, which can be attached to clothing. A high-capacity and lightweight secondary battery 4003b can be provided within the thin housing 4003a of the device 4003. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0125] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply and receiving portion 4006b, and a high-capacity and lightweight secondary battery can be mounted inside the belt portion 4006a. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0126] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and a high-capacity and lightweight secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0127] The display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0128] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0129] Figure 5B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0130] A side view is also shown in Figure 5C. Figure 5C shows the internal structure with a secondary battery 913. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, and is small and lightweight.

[0131] Figure 5D shows an example of wireless earphones. Here, wireless earphones having a pair of main units 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0132] The main units 4100a and 4100b have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. Preferably, they also have a circuit board on which a wireless IC or the like is mounted, charging terminals, etc. They may also have a microphone.

[0133] The case 4110 contains a secondary battery 4111. Preferably, it also has a circuit board on which circuits such as a wireless IC and a charging control IC are mounted, and charging terminals. It may also have a display unit, buttons, etc.

[0134] The main units 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. This allows them to play back audio data sent from other electronic devices. Furthermore, if the main units 4100a and 4100b have microphones, they can send sound acquired by the microphones to other electronic devices, process the audio data, and then send it back to the main units 4100a and 4100b for playback. This allows them to be used, for example, as a translation device.

[0135] Furthermore, the secondary battery 4103 in the main unit 4100a can be charged from the secondary battery 4111 in the case 4110. Coin-type secondary batteries, cylindrical secondary batteries, etc., can be used as the secondary batteries 4111 and 4103. The secondary batteries obtained in Embodiment 1 are lightweight and have high energy density, and by using them in the secondary batteries 4103 and 4111, they can contribute to space saving and weight reduction associated with the miniaturization of wireless earphones.

[0136] Figure 6A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0137] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that may become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one aspect of the present invention and a semiconductor device or electronic components inside. By using the secondary battery 6306 according to one aspect of the present invention in the cleaning robot 6300, the weight is reduced, making the cleaning robot 6300 an electronic device with a long operating time.

[0138] Figure 6B shows an example of a robot. The robot 6400 shown in Figure 6B is equipped with 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 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0139] The microphone 6402 has the function of detecting the user's voice and ambient sounds. The speaker 6404 has the function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and speaker 6404.

[0140] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the 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, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0141] The upper camera 6403 and the lower camera 6406 have the function of imaging the area around the robot 6400. In addition, 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 its surrounding environment and move safely using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407.

[0142] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components inside. By using the secondary battery according to one aspect of the present invention in the robot 6400, the entire robot 6400 can be made lighter and an electronic device with a longer operating time.

[0143] Figure 6C shows an example of an aircraft (also called a drone). The aircraft 6500 shown in Figure 6C has a propeller 6501, a camera 6502, and a secondary battery 6503, and has the ability to fly autonomously.

[0144] For example, image data captured by camera 6502 is stored in electronic component 6504. Electronic component 6504 can analyze the image data and detect the presence or absence of obstacles during movement. Furthermore, electronic component 6504 can estimate the remaining battery level from the change in the storage capacity of secondary battery 6503. The aircraft 6500 is equipped with a secondary battery 6503 according to one aspect of the present invention. By using a secondary battery according to one aspect of the present invention in the aircraft 6500, the secondary battery is lightweight and has a high capacity, so the aircraft 6500 as a whole can be made lighter, and the aircraft 6500 can have a longer operating time.

[0145] This embodiment can be implemented in appropriate combination with other embodiments.

[0146] (Embodiment 4) By installing a secondary battery in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized.

[0147] Figures 7A to 7C illustrate a vehicle using a secondary battery according to one aspect of the present invention. The automobile 8400 shown in Figure 7A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. By using one aspect of the present invention, a vehicle with a long driving range can be realized. The automobile 8400 also has a secondary battery 8402. For example, modules of the secondary battery 8402 can be arranged and used in the floor area inside the vehicle. The secondary battery 8402 can not only drive the electric motor 8406 but also supply power to light-emitting devices such as headlights 8401 and room lights (not shown).

[0148] Furthermore, the secondary battery can supply power to display devices such as the speedometer and tachometer of the automobile 8400. The secondary battery can also supply power to semiconductor devices such as the navigation system of the automobile 8400.

[0149] The automobile 8500 shown in Figure 7B can be charged by receiving power from an external charging facility via a plug-in method and / or a contactless power supply method to the secondary battery of the automobile 8500. Figure 7B shows the state in which the secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector specifications may be carried out as appropriate using a prescribed method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility, or it may be a household power supply. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ADC converter.

[0150] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road and / or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between vehicles. In addition, solar cells can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and / or in motion. For such wireless power supply, electromagnetic induction and / or magnetic resonance methods can be used.

[0151] Furthermore, Figure 7C shows an example of a two-wheeled vehicle using a secondary battery according to one embodiment of the present invention. The scooter 8600 shown in Figure 7C is equipped with 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.

[0152] Furthermore, the scooter 8600 shown in Figure 7C can store a secondary battery 8602 in the under-seat storage compartment 8604. The secondary battery 8602 can be stored in the under-seat storage compartment 8604 even if the compartment is small. The secondary battery 8602 is removable, so when charging, it can be carried indoors, charged, and then stored before driving.

[0153] According to one aspect of the present invention, the secondary battery can be made lighter and its discharge capacity can be increased. Therefore, since the capacity per unit weight can be increased, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to the weight reduction of the vehicle, and thus the driving range can be improved. In addition, the secondary battery installed in the vehicle can be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using commercial power during peak power demand. If the use of commercial power during peak power demand can be avoided, it will contribute to energy saving and the reduction of carbon dioxide emissions.

[0154] Furthermore, Figure 8A shows an example of an electric bicycle using a secondary battery according to one embodiment of the present invention. The secondary battery according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 8A. The energy storage device according to one embodiment of the present invention includes, for example, a plurality of secondary batteries and a charge / discharge control unit.

[0155] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to the motor (electric unit) that assists the rider. The power storage device 8702 is portable and is shown detached from the bicycle in Figure 8B, and corresponds to a secondary battery unit. The power storage device 8702 also has multiple batteries 8701 built in, and the remaining battery level can be displayed on the display unit 8703. The remaining level is displayed on the display unit 8703. The power storage device 8702 also has a charge / discharge control unit 8704 that can control the charging of the secondary battery or detect abnormalities. The charge / discharge control unit 8704 is electrically connected to the positive and negative electrodes of the battery 8701. The electric vehicle body unit of the electric bicycle 8700 is equipped with an operation unit 8712 on the handlebars. The operation unit 8712 has a display unit 8713, a power switch 8714, and a power storage device 8711.

[0156] Because the secondary battery according to one aspect of the present invention uses inexpensive materials, it is possible to significantly reduce the cost of the electric bicycle 8700.

[0157] This embodiment can be implemented in appropriate combination with other embodiments.

[0158] (Embodiment 5) This embodiment describes an example of an application of a lithium-ion secondary battery.

[0159] Figure 9A is a perspective view showing an example of an aircraft. Figure 9B is a perspective view illustrating the interior of the main wing section shown in Figure 9A.

[0160] The aircraft 8900 shown in Figure 9A has a main wing section 8901, a propeller 8902, a vertical stabilizer section 8903, a horizontal stabilizer section 8904, a control device 8905, and a solar panel 8906. The solar panel is sometimes called a solar cell module.

[0161] The aircraft 8900 may have skids. The skids can be attached, for example, to the underside of the main wing section 8901. Wheels may also be attached to the underside of the skids.

[0162] Furthermore, as shown in Figure 9B, the aircraft 8900 has lithium-ion secondary batteries 8907 inside the main wing section 8901. Figure 9B shows an example in which multiple lithium-ion secondary batteries 8907, each having a roughly rectangular upper surface shape, are arranged inside the main wing section 8901. In Figure 9B, multiple lithium-ion secondary batteries 8907 are shown arranged in a single row inside the main wing section 8901, but multiple lithium-ion secondary batteries 8907 may be arranged in multiple rows. Also, the upper surface shape of the lithium-ion secondary battery 8907 is not limited to a rectangle, and can take various shapes such as polygons other than rectangles, polygons with rounded corners, circles, ellipses, L-shapes, etc.

[0163] In addition, in the aircraft 8900, the charging of the lithium-ion secondary battery 8907 with electricity generated by the solar panel 8906 and the supply of power from the lithium-ion secondary battery 8907 to the propeller 8902 may occur simultaneously.

[0164] Furthermore, the aircraft 8900 has an antenna. The aircraft 8900 has the function of performing wireless communication using the antenna. Multiple antennas may be provided on the aircraft 8900. For example, a multi-beam antenna can be used as the antenna.

[0165] For example, the aircraft 8900 can function as a radio base station.

[0166] The aircraft 8900 can, for example, fly in the stratosphere and provide a stratospheric platform. The aircraft 8900 can also communicate with base stations installed on the ground. Furthermore, multiple aircraft 8900s may each form a base station. In such cases, communication between multiple aircraft is preferable. The aircraft 8900 may also have the function of sending and receiving signals with artificial satellites. The aircraft 8900 can provide wireless communication services from the stratospheric platform to user terminals on the ground. Here, a user terminal is, for example, a smartphone. The aircraft 8900 may orbit above the area where wireless communication services are to be provided. Standardized communication protocols or technologies 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), and W-CDMA (registered trademark) can be used. Furthermore, third-generation mobile communication systems (3G), fourth-generation mobile communication systems (4G), or fifth-generation mobile communication systems (5G) as defined by the International Telecommunication Union (ITU) can also be used.

[0167] The control device 8905 may have an imaging device. The aircraft 8900 can use the imaging device to photograph the air, ground, or sky while flying.

[0168] The control device 8905 may have sensors (including those with functions to measure force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared radiation).

[0169] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0170] In this embodiment, porous carbon was prepared and its characteristics were analyzed. Furthermore, a slurry was prepared by mixing the prepared porous carbon with sulfur, and a positive electrode active material layer was fabricated. It should be noted that the present invention is not limited to the following embodiments.

[0171] <Preparation of Porous Carbon> The method for preparing porous carbon will be explained with reference to Figure 1A. Four types of porous carbon (Sample 1, Sample 2, Sample 3, and Sample 4) were prepared under different preparation conditions.

[0172] [Sample 1] First, 8 g of spherical phenolic resin (manufactured by Gun-ei Chemical Industry Co., Ltd.: product name Marilyn HF-008) was prepared in accordance with step S11 in Figure 1A. Also, 12 g of sodium hydroxide was prepared as the base and 30 ml of pure water was prepared in accordance with step S21. The weight ratio of spherical phenolic resin to sodium hydroxide was weighed to be 2:3.

[0173] Next, sodium hydroxide and pure water were mixed to prepare an alkaline solution. This alkaline solution was stirred with a stirring bar at 300 rpm for 10 minutes.

[0174] Next, the alkaline solution and spherical phenolic resin were mixed and stirred as step S22. The heating temperature during stirring was set to 50°C, and the mixture was stirred at 600 rpm for 30 minutes using a stirring bar and a magnetic stirrer. After that, the mixture was transferred from the beaker to a petri dish, and the heating temperature during stirring was set to 100°C, and the mixture was stirred at 40 rpm for 5 hours using a stirring bar and a magnetic stirrer.

[0175] Next, in step S23, the mixture of spherical phenolic resin and alkaline solution was transferred from the petri dish to a graphite container (hereinafter referred to as a graphite crucible), and then placed in an alumina scabbard, and heated. The graphite crucible was placed in a muffle furnace without a lid and heated at 850°C for 2 hours. In the heating process of step S23, the heating and cooling processes were performed at 200°C per hour, and nitrogen gas was flowed into the furnace at a flow rate of 5 L / min to create an inert atmosphere, and the heating process was performed in a nitrogen atmosphere.

[0176] Next, in step S24, pure water was added and the mixture was filtered by suction to wash it (step S24). This process was repeated until the filtrate was neutral (pH within the range of 6.0 to 8.0).

[0177] Next, 600 ml of 1 mol / L hydrochloric acid was prepared as the acidic aqueous solution for step S25. The hydrochloric acid was mixed with the material washed in step S24, and the mixture was stirred with a stirring bar at 600 rpm for 1 hour (step S26).

[0178] Subsequently, in step S27, the acidic aqueous solution was filtered by suction and then washed with pure water in the same manner as in step S24 (step S27).

[0179] Next, in step S28, the material was dried by heating under reduced pressure at 120°C for 10 hours.

[0180] The dried material was crushed in an agate mortar (Step S29), passed through a sieve with a mesh size of 53 μm (Step S30), and then crushed in a ball mill to obtain porous carbon (Step S31). This was designated as Sample 1.

[0181] [Sample 2] Sample 2 was made using the same method as Sample 1, except that the heating in step S23 of Figure 1A was done at 850°C for 10 hours.

[0182] [Sample 3] Sample 3 was prepared using the same method as Sample 1, except that, as part of step S23 in Figure 1A, a graphite crucible was placed in an alumina pod, the lid of the alumina pod was closed, and the crucible was placed in a muffle furnace and heated at 850°C for 2 hours.

[0183] [Sample 4] Sample 4 was prepared using the same method as Sample 1, except that, as part of the heating in step S23 of Figure 1A, a graphite crucible was placed in an alumina pod, the lid of the alumina pod was closed, and the crucible was placed in a muffle furnace and heated at 850°C for 10 hours.

[0184] In this way, four porous carbon samples (Sample 1, Sample 2, Sample 3, and Sample 4) were prepared under different manufacturing conditions.

[0185] [Comparative Example] In addition, a sample was prepared as a comparative example by preparing 5 g of spherical phenolic resin (manufactured by Gun-ei Chemical Industry Co., Ltd.: product name Marilyn HF-008) and heat-treating it at 650°C for 4 hours under a nitrogen atmosphere.

[0186] <Pore Distribution Measurement> The pore distribution was measured for the four porous carbon samples (Sample 1, Sample 2, Sample 3, and Sample 4) prepared as described above.

[0187] The equipment and conditions for pore size distribution measurement were as follows: [Measurement Equipment] Equipment: Tristar II 3020, manufactured by Micromeritics [Measurement Conditions] Measurement Method: Isothermal adsorption measurement Measurement Range: Relative pressure p / p ０ = 0.01~1.0 Measurement temperature: -195.8℃ Adsorbate: Nitrogen Pretreatment method: Vacuum drying at 300℃ for 10 hours [Analysis conditions] Analysis method: MP method or BJH method Reference t curve: Harkins and Jura (t = [13.99 / (0.034 - log(p / p0))] ０．５ ) Applicable range for the MP method (pore radius range): 0.25 to 1.0 nm (the pore diameter value is twice the pore radius value) Applicable range for the BJH method (pore diameter range): 1.0 to 100 nm

[0188] Furthermore, specific surface area can also be measured using the BET method with the TriStar II 3020 automatic specific surface area measuring device.

[0189] The results of pore distribution measurements and other tests are shown in Figures 10A, 10B, 11A, 11B, and Table 1.

[0190]

[0191] In Table 1, Sample 2 and Sample 4 satisfy the condition that the most frequent value of the pore radius distribution analyzed by the MP method is between 0.40 nm and 1.00 nm, and the most frequent value of the pore diameter distribution analyzed by the BJH method is between 1.40 nm and 2.00 nm. Furthermore, Sample 2 and Sample 4 have a BET specific surface area of ​​2000 m². ２ / g or more 3000m ２ The concentration was less than / g, and the cumulative pore volume analyzed by the MP method was 1 cm³. ３ The pore volume must be greater than or equal to 1 cm³ / g, and the cumulative pore volume analyzed by the BJH method must be 1 cm³ or less. ３ The ratio is 1 / g or more. Furthermore, for samples 1 and 3, the most frequent value of the pore radius distribution analyzed by the MP method is 0.35 nm to 1.00 nm, and the most frequent value of the pore diameter distribution analyzed by the BJH method is 1.20 nm to 2.00 nm. Therefore, for samples 1 to 4, the most frequent value of the pore radius distribution analyzed by the MP method is 0.35 nm to 1.00 nm, and the most frequent value of the pore diameter distribution analyzed by the BJH method is 1.20 nm to 2.00 nm. On the other hand, the comparative example has a BET specific surface area of ​​588 m². ２ The concentration was / g, and the cumulative pore volume analyzed by the MP method was 0.27 cm³. ３ The cumulative pore volume analyzed by the BJH method was 0.06 cm³ / g. ３ It was / g.

[0192] In step S23, when the alumina lid is not used, the gas directly hits the mass of spherical resin and base and water mixture placed in the graphite crucible, which is thought to cause a large difference in the surrounding atmosphere due to the spherical resin. Conversely, when the alumina lid is used, the gas is retained inside the lid, and the atmosphere around each spherical resin is thought to become relatively uniform. Therefore, when comparing samples with the same heat treatment time, sample 3, synthesized with the alumina lid, has a sharper pore size distribution than sample 1, and sample 4 has a sharper pore size distribution than sample 2.

[0193] Using the porous carbon samples 1, 2, 3, and 4 prepared in Example 1, positive electrodes were fabricated, and secondary batteries with these positive electrodes were constructed and subjected to charge-discharge cycle tests.

[0194] <Preparation of Cathode Active Materials> As step S41 in Figure 2A, sulfur (manufactured by Strem Chemicals, 5N) was pulverized in a glove box under an argon atmosphere and sieved through a 53 μm sieve. This sulfur was combined with each of the porous carbon samples 1 to 4 prepared above to produce several types of cathode active materials (Sample 1A, Sample 2A, Sample 3A, and Sample 4A).

[0195] [Sample 1A] As step S42 in Figure 2A, sulfur (S) and Sample 1 were weighed in a glove box under an argon atmosphere so that the weight ratio of sulfur to the total weight of porous carbon (C), S / (S+C), was 60% (i.e., S:C = 60:40). Then, mixing was carried out using a ball mill at a rotation speed of 150 rpm, with a zirconium oxide ball diameter of 1 mm, for 1 hour. After mixing with the ball mill, the mixture was passed through a separation sieve with a mesh size of 300 μm to obtain a mixture of sulfur and porous carbon (Sample 1).

[0196] Next, in step S43, the mixture was wrapped in silicone-coated aluminum foil (Asahi Kasei Corporation's Cookper® frying pan foil) in a glove box under an argon atmosphere and sealed in a cylindrical container. The cylindrical container was then heated. The heating in step S43 was performed in a tubular furnace under an argon atmosphere at 155°C for 6 hours. The argon flow rate was 0.2 L / min. The heating process involved raising the temperature from 25°C to 120°C in 30 minutes, and then raising it to 155°C over 1 hour. By raising the temperature in this stepwise manner, the temperature could be raised without deviating significantly from the set temperature. After heating at 155°C for 6 hours, it was allowed to cool naturally under an argon atmosphere.

[0197] The heated material was passed through a 53 μm sieve in a dry room (Step S44) to obtain the positive electrode active material (Step S45). If the material did not pass through the sieve, it was lightly crushed in an agate mortar before being passed through the sieve again.

[0198] Sample 1A was defined as the positive electrode active material obtained by the above process for Sample 1.

[0199] [Sample 2A] Sample 2A was prepared using the same method as Sample 1A, except that in step S42 of Figure 2A, Sample 2 was used instead of Sample 1.

[0200] [Sample 3A] Sample 3A was prepared using the same method as Sample 1A, except that in step S42 of Figure 2A, Sample 3 was used instead of Sample 1.

[0201] [Sample 4A] Sample 4A was prepared using the same method as Sample 1A, except that in step S42 of Figure 2A, Sample 4 was used instead of Sample 1.

[0202] <XRD> XRD analysis was performed on the cathode active material prepared as described above. The apparatus and conditions were as follows: A Bruker silicon non-reflective sample holder, model number C79298A3244B249, was used for sampling. A thin layer of Apiezon Grease N was applied to the Si portion of the silicon non-reflective sample holder, and the cathode active material powder was lightly sprinkled on it. Excess powder was brushed off to prepare the measurement sample. XRD apparatus: Bruker, D8 ADVANCE X-ray source: Cu Output: 40kV, 40mA Divergent slit: 0.6mm 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

[0203] Figure 12 shows the obtained XRD pattern. The XRD pattern is a relative intensity normalized by the maximum intensity in the range where 2θ is between 15° and 60°, and includes background and CuKα ２ The lines have not been removed. For comparison, sulfur (S) was used as a raw material. ８ The XRD patterns of the individual sulfur molecules are also shown. As shown in Figure 12, in all samples, no peaks originating from the sulfur crystal structure were observed in the ranges of 2θ = 23.12 ± 0.1° (23.02° to 23.22°) and 27.74° ± 0.1° (27.64° to 27.84°).

[0204] <Preparation of the positive electrode> The method for preparing the positive electrode will be explained with reference to Figure 2B. First, in step S51, each of the positive electrode active materials prepared above (Sample 1A, Sample 2A, Sample 3A, and Sample 4A) was used to prepare a 5% concentration solution by dissolving acetylene black (manufactured by Denka, trade name DENKA BLACK Li-100) as a conductive material and PVDF (manufactured by Solvay, trade name SOREF 5130) as a binder solution in NMP. In step S52, these were mixed while adjusting the amount of PVDF solution to achieve a desirable viscosity, and kneaded using a rotation-orbit mixer (Awatori Rentaro, manufactured by THINKY). Next, in step S53, the PVDF solution and solvent were added, and a slurry was prepared with a final ratio of positive electrode active material:acetylene black:PVDF of 8:1:1 (by weight).

[0205] Next, in step S54, the slurry was coated onto the positive electrode current collector to form a positive electrode active material layer. A carbon-coated aluminum foil (SDX-PM, manufactured by Showa Denko Packaging Co., Ltd.) was used as the positive electrode current collector. This was dried (step S55) to obtain the positive electrode (step S56). After drying, the positive electrode was cut into 4 cm widths and then roll-pressed under conditions of a roll gap of 20 μm and a roll temperature of 20°C. The amount of positive electrode active material supported was 2 mg / cm². ２ 3mg / cm or more ２ The electrode density is 0.9 g / cm³. ３ 1.3g / cm or more ３ It was as follows:

[0206] As described above, the positive electrode prepared using sample 1A for the positive electrode active material layer is called positive electrode 1A. Similarly, the positive electrodes prepared using samples 2A, 3A, and 4A are called positive electrode 2A, positive electrode 3A, and positive electrode 4A, respectively.

[0207] <Fabrication of a Secondary Battery> Using the positive electrode described above, a coin cell (CR2032 type, 20 mm in diameter, 3.2 mm in height) was fabricated. Aluminum cladding was used for the positive electrode casing. Aluminum cladding refers to a positive electrode casing whose inside surface is coated with aluminum. Aluminum cladding is used when there is a risk of the housing material, such as the positive electrode casing, reacting chemically with the electrolyte, thereby preventing corrosion by the electrolyte.

[0208] A lithium metal foil was used as the negative electrode. A porous polypropylene (PP) film was used as the separator. The electrolyte was a mixture of LiTFSI, sulfolane (SL), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) in a molar ratio of 1:2:2.

[0209] The coin cells were assembled inside the glove box using the positive electrode, negative electrode, and electrolyte described above. The coin cells produced using positive electrode 1A are referred to as cell 1A. Similarly, the coin cells produced using positive electrode 2A, positive electrode 3A, and positive electrode 4A are referred to as cell 2A, cell 3A, and cell 4A, respectively.

[0210] <Charge-Discharge Cycle Test> Charge-discharge cycle tests were performed on cells 1A to 4A prepared as described above. A standing period of at least 6 hours was allowed between the completion of secondary battery preparation and the start of the charge-discharge cycle test. The conditions for the charge-discharge cycle test were: discharge: CC (current: 120 mA / g, termination voltage: 1.4 V), charge: CC (current: 120 mA / g, termination voltage: 2.8 V), ambient temperature 25°C. A waiting period of 6 hours was allowed after the cells were placed in the charge-discharge cycle test machine before the cycle test was performed. A 10-minute break was provided between each charge and discharge cycle. The current values ​​above are current values ​​per unit weight of positive electrode active material. The discharge capacity is shown per unit weight of positive electrode active material, not per unit weight of sulfur.

[0211] The results of the charge-discharge cycle tests for cells 1A through 4A are shown in Figures 13, 14, and 15. In the graph in Figure 13, the vertical axis shows the discharge capacity (mAh / g) and the horizontal axis shows the number of cycles.

[0212] Figure 14A shows the charge-discharge cycle test results for cell 1A, and Figure 14B shows the charge-discharge cycle test results for cell 2A. Figure 15A shows the charge-discharge characteristics of cell 3A, and Figure 15B shows the charge-discharge characteristics of cell 4A. The results for the first, second, and fifth cycles of each cell are shown.

[0213] Figures 14 and 15 show the cycle characteristics of the discharge capacity of cells 1A, 2A, 3A, and 4A. The discharge capacity in the first cycle is approximately 1000 mA / g for all cells. In the second cycle, the discharge capacity is largest in the order of cell 2A, cell 4A, cell 1A, and cell 3A. This corresponds to the order of the most frequent values ​​of pore radius obtained by analyzing the porous carbon used in each cell using the MP method. It is thought that the larger the pore diameter, the larger the contact area between the electrolyte and sulfur, resulting in a larger discharge capacity. Conversely, if the pore diameter is too large, the discharge capacity is large in the initial stages of the charge-discharge cycle, but sulfur or sulfur compounds are more likely to dissolve from inside to outside the pores, and the discharge capacity tends to decrease as the cycle progresses.

[0214] Furthermore, the cycle count and discharge capacity values ​​for each sample are shown in Table 2 below.

[0215]

[0216] Furthermore, the cumulative pore volume of the porous carbon used in the cells that obtained these large discharge capacities was 1 cm³. ３ The concentration was above 1 / g, and no peaks originating from sulfur crystals were detected in the XRD analysis. This suggests that even with a sulfur mixing ratio S / (S+C) of 60%, the positive electrode active material used in these cells had almost no sulfur that could not be contained within the pores of the porous carbon, thus enabling the maintenance of a high discharge capacity.

[0217] 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: Glasses-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: Two 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 unit, 4100b: Main unit, 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 N, 6306: Rechargeable battery, 6310: Garbage, 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: Rechargeable battery, 6500: Aircraft, 6501: Propeller, 6502: Camera, 6503: Rechargeable battery, 6504: Electronic component, 8021: Charging device, 8022: Cable, 8024: Rechargeable battery, 8400: Automobile, 8401: Headlight, 8402: Rechargeable battery, 8406: Electric motor - 8500: automobile, 8600: scooter, 8601: side mirror, 8602: secondary battery, 8603: turn signal, 8604: under-seat storage, 8700: electric bicycle, 8701: battery, 8702: energy storage device, 8703: display unit, 8704: charge / discharge control unit, 8711: energy storage device, 8712: control unit, 8713: display unit, 8714: power switch, 8900: aircraft, 8901: main wing section, 8902: propeller, 8903: vertical stabilizer section, 8904: horizontal stabilizer section, 8905: control device, 8906: solar panel, 8907: lithium-ion secondary battery,

Claims

A porous carbon material made from spherical resin, satisfying the following conditions: the most frequent value of the pore radius distribution analyzed by the MP method is between 0.40 nm and 1.00 nm, and the most frequent value of the pore diameter distribution analyzed by the BJH method is between 1.40 nm and 2.00 nm. 　 The spherical resin is a phenolic resin, and the porous carbon is such that, 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. 　 In claim 1, the porous carbon has a BET specific surface area of ​​2000 m². ２ / g or more 3000m ２ / g or less, The cumulative pore volume analyzed by the MP method was 1 cm ３ The pore volume must be greater than or equal to 1 cm³ / g, and the cumulative pore volume analyzed by the BJH method must be 1 cm³ or less. ３ Porous carbon with a weight of 1 / g or more. 　 A lithium-ion secondary battery comprising the porous carbon described in claim 1, a positive electrode having sulfur in the pores, a negative electrode, and an electrolyte. 　 A mixture of spherical resin, a base in an amount of 1.0 to 2.0 times the weight of the spherical resin, and water is placed in a container with a lid, and with the lid still on, a first heat treatment is performed in an inert atmosphere at a temperature of 700°C to 1000°C for 1 to 20 hours to produce porous carbon. The porous carbon is washed, The porous carbon and the acidic aqueous solution are mixed and stirred. After washing the porous carbon, a second heat treatment is performed under reduced pressure. The porous carbon is crushed, The porous carbon and sulfur are mixed and subjected to a third heat treatment in an inert atmosphere. Method for preparing positive electrode active material. 　 In claim 5, the spherical resin is a phenolic resin, A method for preparing a positive electrode active material, wherein the base is sodium hydroxide. 　 A method for producing a positive electrode active material according to claim 6, wherein the phenol resin has a particle size distribution measured using a laser diffraction particle size distribution analyzer, in which (D90 - D10) / D50 is 0.1 or more and 1.5 or less, and D50 is 3 μm or more and 12 μm or less. 　 A method for producing a positive electrode active material according to claim 5, wherein the weight ratio of the sulfur to the sum of the weight of the sulfur and the weight of the porous carbon is 50% or more and less than 70%. 　 In claim 5, the second heat treatment is performed at a temperature of 60°C or higher and 300°C or lower, and for a period of 5 hours or higher and 20 hours or lower. A method for producing a positive electrode active material, wherein the third heat treatment is performed at a temperature of 120°C or higher and 160°C or lower, and for 1 hour or higher and 10 hours or lower.

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