Secondary battery, electronic device, vehicle, ship, method for producing secondary battery, method for producing positive electrode active material, and method for producing activated spherical porous carbon

Abstract

Provided is a method for producing a high-capacity lithium-ion secondary battery. This method comprises: a step for mixing activated spherical porous carbon and sulfur to produce activated spherical porous carbon in which sulfur is supported; a step for mixing a binder solution with the activated spherical porous carbon that supports the sulfur to produce a slurry; a step for applying the slurry to the surface of a current collector and drying the slurry; and a step for carrying out a pressing treatment to produce an electrode for a secondary battery. The pressing treatment is preferably performed under heating.

Description

Secondary battery, electronic device, vehicle, ship, method for producing secondary battery, method for producing positive electrode active material, and method for producing activated spherical porous carbon

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

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

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

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

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

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

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

[0008] Also, image processing software such as ImageJ (Non-Patent Documents 2 to 4) is known. By using this software, for example, the shape of a positive electrode active material or the like can be analyzed.

[0009] Chao Lin et al. , “A facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles for flexible Li-S cathodes”, Phys. Chem. Chem. Phys. , 2016, 18, 22146-22153 Rasband, W. S. , ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, http: / / rsb. info. nih. gov / ij / , 1997-2012. Schneider, C. A. , Rasband, W. S. , Eliceiri, K. W. “NIH Image to ImageJ: 25 years of image analysis”. Nature Methods 9, 671-675, 2012. Abramoff, M. D. , Magelhaes, P. J. , Ram, S. J. "Image Processing with ImageJ". Biophotonics International, volume 11, issue 7, pp. 36-42, 2004.

[0010] In lithium-sulfur batteries, metallic lithium is used as an example of a negative electrode active material. During discharge, metallic lithium dissolves in the electrolyte at the negative electrode to form Li ＋ This reacts with sulfur at the positive electrode and is oxidized to form the intermediate product lithium polysulfide (Li２ S Ｘ , X is 2 or more and 8 or less), and then lithium sulfide (Li ２ S).

[0011] Lithium-sulfur batteries have problems such as the poor electrical conductivity of the positive electrode active material made of lithium and sulfur, and the elution of lithium polysulfide, a reaction intermediate, into the electrolyte.

[0012] An object of one embodiment of the present invention is to provide a high-capacity lithium-ion secondary battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a lithium-ion secondary battery with excellent charge-discharge cycle characteristics and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a secondary battery with long cycle life and high safety or reliability and a manufacturing method thereof.

[0013] Another object of one embodiment of the present invention is to provide a positive electrode active material that can be used in a lithium-ion battery and a manufacturing method thereof.Another object of one embodiment of the present invention is to provide porous carbon that can be used as a positive electrode active material and a manufacturing method thereof.

[0014] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims.

[0015] In order to solve the above problems, one aspect of the present invention is to support sulfur on activated spherical porous carbon and use it as a positive electrode active material for lithium-sulfur batteries. The spherical porous carbon is made of spherical phenolic resin, and chemical activation, particularly alkaline activation, is used as the activation method.

[0016] One aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, in which the positive electrode has a positive electrode active material containing sulfur and carbon, and in a cross-sectional SEM image of the positive electrode, at least a portion of the positive electrode active material has a cross-sectional diameter of 5 μm or more and 50 μm or less, and when cross-sectional SEM-EDX point analysis of the positive electrode is performed, sulfur and carbon are detected inside the positive electrode active material, but nitrogen is not detected.

[0017] In the above, when a cross-sectional SEM-EDX point analysis of the positive electrode is performed, the sulfur / carbon (mass ratio) detected inside the positive electrode active material is preferably 0.01 or more and 2.5 or less.

[0018] In the above, when the positive electrode active material is analyzed by powder X-ray diffraction using CuKα radiation, it is preferable that the XRD pattern has at least a broad peak with a full width at half maximum of 3° or more in the 2θ range of 15° or more and 35° or less, and does not have a signal with a width three times or more the average noise width in the 2θ ranges of 23.02° or more and 23.22° or less and 27.64° or more and 27.84° or less.

[0019] In the above, the negative electrode is preferably metallic lithium.

[0020] In the above, the secondary battery has an electrolyte and a separator, and the electrolyte preferably contains lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate, and the separator preferably contains glass fiber.

[0021] Another embodiment of the present invention is an electronic device including any of the above secondary batteries.

[0022] Another embodiment of the present invention is a vehicle including the above-described secondary battery.

[0023] Another embodiment of the present invention is a ship including the above-described secondary battery.

[0024] Another aspect of the present invention is a method for producing activated spherical porous carbon, comprising the steps of: subjecting spherical resin having a D50 of 3 μm or more and 12 μm or less and a (D90-D10) / D50 of 0.1 or more and 1.5 or less to a first heat treatment at 500°C or more and 800°C or less for 1 hour or more and 10 hours or less in an inert atmosphere to produce spherical porous carbon; and mixing the spherical porous carbon with an alkaline solution, followed by a second heat treatment at 600°C or more and 900°C or less for 20 minutes to 3 hours in an inert atmosphere to produce activated spherical porous carbon.

[0025] In the above, the spherical resin is preferably a phenolic resin.

[0026] In the above, the alkaline solution is a sodium hydroxide aqueous solution, and the sodium hydroxide aqueous solution is preferably prepared by dissolving sodium hydroxide in water in an amount (weight ratio) that is 2 to 4 times the amount of the spherical resin.

[0027] Another embodiment of the present invention is a method for producing a positive electrode active material, the method including the steps of mixing activated spherical porous carbon and sulfur, sealing the mixture in a container, and performing a third heat treatment at 120°C to 160°C inclusive for 1 hour to 10 hours inclusive in an inert atmosphere to produce a positive electrode active material, wherein the activated spherical porous carbon has a D50 of 3 μm to 12 μm inclusive, a (D90−D10) / D50 of 0.1 to 1.5 inclusive, and a mode of pore radius of 0.30 nm to 0.40 nm inclusive in a differential pore volume distribution measured by gas adsorption method.

[0028] Another aspect of the present invention is a method for producing a secondary battery, the method including the steps of: mixing activated spherical porous carbon with sulfur to produce a sulfur-loaded cathode active material; mixing the sulfur-loaded cathode active material with a binder solution to produce a slurry; applying the slurry to a surface of a current collector and drying it to produce a cathode; and pressing the cathode to produce an electrode for the secondary battery.

[0029] In this specification, activated spherical porous carbon can be referred to as a lithium-carrying material, and the lithium-carrying material is used as an electrode material in the positive electrode of a secondary battery. By applying a slurry to the surface of a current collector and drying it, an electrode can be produced in which an electrode mixture layer (also referred to as a positive electrode active material layer) is formed on the current collector, and the electrode can function as an electrode for a secondary battery without a pressing process. Pressing can increase the density of the electrode mixture layer and reduce contact resistance with the current collector.

[0030] In this specification, the positive electrode may comprise at least a carbon material carrying an active material, the active material being attached to the surface or inside the pores of the carbon material. The positive electrode contains sulfur or a sulfur derivative, such as lithium sulfide or lithium polysulfide, as the active material.

[0031] By using activated spherical porous carbon loaded with sulfur as the positive electrode and metallic lithium as the negative electrode, a lightweight, high-capacity secondary battery can be realized, which also has high charge / discharge efficiency and improved lifespan.

[0032] According to one embodiment of the present invention, a high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a lithium-ion secondary battery with excellent charge-discharge cycle characteristics and a manufacturing method thereof can be provided. According to another embodiment of the present invention, a secondary battery with long cycle life and high safety or reliability and a manufacturing method thereof can be provided.

[0033] According to another embodiment of the present invention, a positive electrode active material that can be used in a lithium-ion battery and a manufacturing method thereof can be provided. Furthermore, according to another embodiment of the present invention, a porous carbon that can be used in a positive electrode and a manufacturing method thereof can be provided.

[0034] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0035] FIG. 1 is a schematic cross-sectional view of a positive electrode having a positive electrode active material. FIG. 2 is a flowchart illustrating an example of a method for preparing activated spherical porous carbon. FIG. 3A is a flowchart illustrating an example of a method for preparing a positive electrode active material. FIG. 3B is a flowchart illustrating an example of a method for preparing a positive electrode. FIG. 4A is an exploded perspective view of a coin-type secondary battery, FIG. 4B is a perspective view of the coin-type secondary battery, and FIG. 4C is a cross-sectional perspective view thereof. FIGS. 5A and 5B are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 6A to 6D are diagrams illustrating a lithium-ion battery and a power storage system of one embodiment of the present invention. FIGS. 7A to 7C are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 8A to 8C are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 9A to 9C are diagrams illustrating an electric vehicle of one embodiment of the present invention. FIGS. 10A to 10D are diagrams illustrating a transportation vehicle and a ship of one embodiment of the present invention. FIGS. 11A to 11C are diagrams illustrating a motorcycle or the like of one embodiment of the present invention. FIGS. 12A to 12D are diagrams illustrating an electronic device or the like according to one embodiment of the present invention. FIGS. 13A to 13C are diagrams illustrating an electronic device according to one embodiment of the present invention. FIGS. 14A to 14D are diagrams illustrating an example of a space device. FIG. 15 is a graph showing particle size distribution. FIG. 16 is a graph showing BET specific surface area. FIG. 17 is a graph showing differential pore volume distribution of spherical porous carbon. FIG. 18 is a graph showing differential pore volume distribution of activated spherical porous carbon. FIG. 19 is a graph showing differential pore volume distribution of activated spherical porous carbon. FIG. 20 is a graph showing differential pore volume distribution of activated spherical porous carbon. FIG. 21 is an XRD pattern of a positive electrode active material. FIG. 22 is an XRD pattern of a positive electrode active material. FIG. 23A is a cross-sectional SEM image of a positive electrode. FIG. 23B is a characteristic X-ray spectrum obtained by SEM-EDX. FIGS. 24A to 24E are SEM-EDX mapping images. Fig. 25A is a cross-sectional SEM image showing the analyzed area. Fig. 25B is a characteristic X-ray spectrum of SEM-EDX. Figs. 26A to 26C are characteristic X-ray spectra of SEM-EDX. Figs. 27A and 27B are graphs showing charge / discharge curves of a secondary battery. Figs. 28A and 28B are graphs showing charge / discharge curves of a secondary battery.29A and 29B are graphs showing charge / discharge curves of a secondary battery. FIGS. 30A to 30C are graphs showing charge / discharge cycle characteristics for the discharge capacity of a secondary battery. FIGS. 31A to 31C are graphs showing charge / discharge cycle characteristics for the discharge capacity of a secondary battery. FIGS. 32A to 32C are graphs showing charge / discharge cycle characteristics for the charge / discharge efficiency of a secondary battery. FIG. 33A is a graph showing the second charge / discharge curve of a half cell using spherical porous carbon, and FIG. 33B is a graph showing the second charge / discharge curve of a half cell using activated spherical porous carbon. FIG. 34 shows the energy density (mWh / cm) per electrode layer volume with and without heat pressing. ３ ) is a graph showing the change in

[0036] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0037] In this specification and the like, when simply referring to a positive electrode active material, there are cases where the description refers to multiple positive electrode active material particles and cases where the description refers to a single positive electrode active material particle, depending on the analytical method, etc. For example, in the case of descriptions relating to scanning transmission electron microscope-energy dispersive X-ray fluorescence detector (STEM-EDX) line analysis, STEM-electron energy loss spectroscopy (STEM-EELS), and electron diffraction, the description refers to a single positive electrode active material particle unless otherwise specified. On the other hand, in the case of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), scanning electron microscope-energy dispersive X-ray detector (SEM-EDX), various mass analyses, etc., the description refers to multiple positive electrode active material particles unless otherwise specified.

[0038] Furthermore, when describing the characteristics of particles of a positive electrode active material, it is not necessary for all particles to have the characteristics. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected particles of a positive electrode active material have the preferred characteristics described below, it can be said that the positive electrode active material and the secondary battery having the same are sufficiently effective in improving their properties.

[0039] The distribution of a certain element refers to a region in which the element is continuously detected within a range that is not a noise by a certain continuous analytical method. A region in which the element is continuously detected within a range that is not a noise can also be referred to as a region in which the element is always detected when the analysis is performed multiple times.

[0040] Unless otherwise specified, the materials (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) contained in secondary batteries are described in their pre-degradation state. Note that a decrease in discharge capacity due to aging and burn-in treatments during secondary battery manufacturing is not considered to be degradation. For example, a lithium-ion secondary cell or lithium-ion secondary battery pack (hereinafter referred to as a lithium-ion secondary battery) can be said to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. For lithium-ion secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to not only the above JIS standard but also various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0041] In this specification and the like, the state of the materials of a secondary battery before deterioration is sometimes referred to as an initial product or initial state, and the state after deterioration (the state when the secondary battery has a discharge capacity of less than 97% of the rated capacity) is sometimes referred to as a product in use or in use state, or a used product or used state.

[0042] Embodiment 1 In this embodiment, a positive electrode active material 100 that can be used in a lithium-sulfur battery of one embodiment of the present invention will be described with reference to FIG.

[0043] FIG. 1 is a schematic diagram of a cross-sectional SEM image of a positive electrode 201 having a positive electrode active material 100. The cross-sectional portion is shown hatched. The non-hatched portion represents the surface other than the cross section. As shown in FIG. 1, the particles of the positive electrode active material 100 are preferably spherical, and therefore the cross section is preferably circular. The arrow in FIG. 1 indicates the diameter of the cross section of the positive electrode active material 100. It is preferable that at least a portion of the positive electrode active material 100 has a cross-sectional diameter of 5 μm or more and 50 μm or less.

[0044] Spherical particles with the above-described particle size and particle size distribution are preferred because they have high mechanical strength and are easy to maintain their spherical shape. Furthermore, they are less likely to form aggregates during slurry formation, making them easy to coat. Furthermore, particle breakage is suppressed during the pressing process performed during the formation of the positive electrode active material layer. Therefore, they are suitable as positive electrode active materials for secondary batteries.

[0045] Furthermore, the positive electrode active material 100 preferably contains sulfur and carbon, particularly sulfur present not only near the surface but also deep within the particles. Therefore, when elemental analysis is performed on the positive electrode active material 100, it is preferable to detect sulfur and carbon, particularly from the interior. The "interior" of the particle refers to, for example, a region 10 nm or deeper vertically from the surface. The "surface" here refers to the spherical surface of the positive electrode active material 100 that can be observed using an SEM or the like. The "near-surface" refers to the area that can be analyzed using standard X-ray photoelectron spectroscopy (XPS) using AlKα radiation. Most pores too large to be observed with an SEM and areas that cannot be analyzed with standard XPS are included within the interior. Elemental analysis of the interior of particles can be performed using, for example, cross-sectional SEM-EDX analysis and STEM-EDX analysis, cross-sectional electron probe microanalyzer (EPMA), depth-direction XPS analysis combined with ion sputtering, and secondary ion mass spectrometry (SIMS).

[0046] It is also preferable that sulfur is sufficiently supported inside the positive electrode active material 100. Therefore, when a cross-sectional SEM-EDX point analysis of the positive electrode active material 100 is performed, the sulfur / carbon (mass ratio) detected inside the positive electrode active material is preferably 0.01 or more and 2.5 or less, and more preferably 0.02 or more and 2 or less.

[0047] Furthermore, the positive electrode active material 100 preferably does not contain nitrogen.

[0048] Furthermore, the sulfur contained in the positive electrode active material 100 is preferably present in an amorphous state. The fact that the sulfur is in an amorphous state suggests that sulfur and carbon are sufficiently composited. Therefore, when the positive electrode active material 100 or a positive electrode or secondary battery having the same is analyzed by a diffraction method such as X-ray diffraction (XRD), sulfur crystals (S ８ It is preferable that no peaks derived from the above-mentioned amine group are observed.

[0049] Therefore, when analyzed by powder X-ray diffraction using, for example, CuKα radiation, it is preferable that the XRD pattern does not have signals that are three times or more the average noise width at least in the 2θ ranges of 23.12±0.1° (23.02° or more and 23.22° or less) and 27.74°±0.1° (27.64° or more and 27.84° or less).

[0050] Furthermore, it is preferable that the carbon contained in the positive electrode active material 100 has low crystallinity. Low crystallinity carbon has a large specific surface area, which is advantageous for compounding sulfur and carbon. Therefore, hydrogen and oxygen may be detected along with carbon in elemental analysis of the positive electrode active material 100. Furthermore, when the positive electrode active material 100 or a positive electrode or secondary battery containing the same is analyzed by a diffraction method, it is preferable that the peak derived from carbon be broad.

[0051] For example, when analyzed by powder X-ray diffraction using CuKα radiation, the XRD pattern preferably has a broad peak with a full width at half maximum of 1° or more, more preferably 3° or more, in the range of 2θ of 15° or more and 35° or less.

[0052] The XRD measurement apparatus and conditions are not particularly limited. For example, the measurement can be performed using the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: Cu Output: 40 kV, 40 mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 10° to 60° Step width (2θ): 0.01° setting Counting time: 0.5 s / step Sample stage rotation: 5 rpm

[0053] If the measurement sample is a powder, it can be set by placing it in a glass sample holder, or by sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.

[0054] In this specification, spherical particles refer to particles in which, when the cross sections of a plurality of particles are observed, the cross sections of the majority of the particles are circular. In this case, the number of particles is preferably five or more. Furthermore, the circular shape does not necessarily have to be mathematically strict.

[0055] <<Shape Analysis Using Cross-Sectional SEM Image of Positive Electrode>> For example, when a cross-sectional SEM image is analyzed using ImageJ by the following method, if the circularity (4π × (area) / (square of perimeter)) of the cross sections of the majority of particles is 0.8 or more, the particles can be said to be spherical.

[0056] First, an analysis region is cut out from the acquired cross-sectional SEM image. A range having a sufficient area for image analysis can be cut out, for example, a range of 50 μm or more × 100 μm or more, but this is not limited thereto. Depending on factors such as the size of the positive electrode active material, a smaller or larger area may be cut out.

[0057] The cross-sectional SEM image may be cut out using a function of image processing software, for example, the crop function of ImageJ.

[0058] Next, the cut-out first image is binarized using image processing software, and particle analysis is performed.

[0059] The binarization process is explained below. A first image shown in 256 grayscale levels is used as a frequency graph excluding black (value 0) and white (value 255), and the low-value side (HWHM_L) and high-value side (HWHM_H) are determined as the half-width at half maximum (HWHM) of the maximum peak in the frequency graph. Next, a minimum value a in the range twice the width of HWHM_L on the low-value side from the value that is the peak top (maximum frequency) of the maximum peak, and a maximum value b in the range twice the width of HWHM_H on the high-value side are determined.

[0060] Next, binarization is performed so that values ​​less than a are white, values ​​greater than a and less than b are black, and values ​​greater than b are white. Specifically, the threshold function of ImageJ is used to perform binarization as Threshold (a, b). After that, random bright spots thought to be caused by the conductive material are removed using the Gray Morphology (radius = 3, operator = open, type = circle) and Gray Morphology (radius = 1, operator = close, type = circle) conditions, and a second image can be obtained.

[0061] Next, using the second image, the particle size (projected area) was determined to be 0.5 μm using the Analyze Particles function of ImageJ. ２ 700 μm or more ２ The following particles are detected and the area of ​​each particle is obtained. Next, the circularity of each particle is calculated based on the area of ​​each particle. The diameter of each particle can also be calculated based on the area.

[0062] In this way, the circularity and diameter of the particles can be calculated from the cross-sectional SEM image. Performing the above analysis is called performing particle shape analysis using a cross-sectional SEM image of the positive electrode.

[0063] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0064] Embodiment 2 In this embodiment, a method for manufacturing a positive electrode active material 100 that can be used in a lithium-sulfur battery according to one embodiment of the present invention, activated spherical porous carbon that can be used for the positive electrode active material 100, and a method for manufacturing the activated spherical porous carbon will be described with reference to FIGS. 2 and 3 .

[0065] <Method for Producing Activated Spherical Porous Carbon> First, an example of a method for producing activated spherical porous carbon will be described with reference to the flow chart of FIG.

[0066] First, in step S11, spherical resin particles are prepared. While the resin material is not particularly limited, it is preferable to use a phenolic resin, which has a three-dimensional network structure containing six-membered carbon rings and is relatively inexpensive. Phenolic resins are also preferable because they have a high carbon content and a high carbon residue rate in the carbonization process. Spherical phenolic resins are synthesized by a condensation reaction between phenols, including polyhydric phenols, and aldehydes, followed by separation and recovery of the phenolic resin.

[0067] Since the shape of the resin used here greatly affects the shape of the activated spherical porous carbon and the positive electrode active material, it is preferable that the spherical resin particles have a shape suitable for the positive electrode active material. Therefore, D50 is preferably 5 μm or more and 50 μm or less, more preferably 5 μm or more and 20 μm or less, and even more preferably 6 μm or more and 10 μm or less. In addition, it is preferable that (D90 - D10) / D50 is 0.1 or more and 1.5 or less. Note that D50 refers to the particle diameter at 50% of the calculated cumulative distribution of particles, 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.

[0068] In this embodiment, the spherical phenolic resin used is Marilyn HF-008 manufactured by Gun-ei Chemical Industry Co., Ltd., which has a D50 of 7.92 μm and a (D90−D10) / D50 ratio of 0.435.

[0069] Next, in step S12, the spherical resin particles prepared in step S11 are heated. Heating is preferably performed in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating furnace is not particularly limited, and examples thereof include a muffle furnace, a rotary kiln, and a roller hearth kiln. A crucible, a sheath, or the like can be used as a container for containing the spherical resin particles, and materials such as aluminum oxide and oxides containing aluminum and silicon can be used. Heating is preferably performed with a lid made of a similar material. The heating conditions are such that the spherical resin particles become porous carbon, but the crystallinity of the carbon does not become too high. For example, the heating temperature is preferably 500°C or higher and 800°C or lower, more preferably 600°C or higher and 700°C or lower, and the heating time is preferably 1 hour or higher and 10 hours or lower.

[0070] In this embodiment, the spherical phenolic resin is placed in an aluminum oxide crucible, which is then covered with an aluminum oxide lid and placed in a muffle furnace, where it is heated in a nitrogen atmosphere at 650°C for 4 hours. The temperature is increased and decreased at a rate of 200°C per hour.

[0071] Next, in steps S13 and S14, the heated material is preferably crushed and sieved. The crushing means is not particularly limited, but an agate mortar or the like can be used.

[0072] Through the above steps, spherical porous carbon can be produced (step S15).

[0073] Next, the spherical porous carbon is activated. Chemical activation or gas activation can be used as the activation method. In this embodiment, among chemical activation methods, alkaline activation is performed using an alkali as the activation agent. Examples of bases that can be used include sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate. In this embodiment, sodium hydroxide is used.

[0074] If the amount of sodium hydroxide used for activation is too small, a sufficient effect will not be obtained, but if it is too large, the pore diameter may become too large. If the pore diameter is too large, there is a risk that the sulfur supported in the pores will separate from the carbon during charging and discharging. Specifically, when the pore radius of the activated spherical porous carbon is plotted as a frequency graph in increments of 0.02 nm, the mode is preferably 0.30 nm or more and 0.40 nm or less. The pore radius can be determined by a gas adsorption method. As a method for analyzing the pore distribution in the gas adsorption method, the MP method (micropore analysis method), the t-plot method, the BJH (Barrett-Joyner-Halenda) method, or the DFT (density functional theory) method can be selected and used depending on the pore diameter.

[0075] In order to set the pore radius within the above range, it is preferable to use sodium hydroxide in an amount of from 2 to 5 times (weight ratio) the amount of the spherical porous carbon, and it is more preferable to use sodium hydroxide in an amount of from 2 to 4 times (weight ratio).

[0076] In this embodiment, sodium hydroxide in an amount (weight ratio) three times the amount of spherical porous carbon and 45 ml of water are prepared as the base in step S21.

[0077] Next, in step S22, a base and water are mixed to prepare an alkaline solution. The spherical porous carbon obtained in step S15 is mixed with the alkaline solution and stirred. Although the stirring conditions are not particularly limited, in this embodiment, the mixture is stirred at 800 rpm using a stirring bar and a magnetic stirrer for 1 hour.

[0078] Next, in step S23, the mixture of spherical porous carbon and alkaline solution is heated. Heating is preferably carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. The description of step S12 can be referred to for the heating furnace and container. The heating temperature is preferably 600°C or higher and 900°C or lower, more preferably 700°C or higher and 850°C or lower. The heating time is preferably 20 minutes or higher and 3 hours or lower.

[0079] Next, in step S24, the heated product is washed. The washing method is not particularly limited, but it is preferable to wash with pure water, for example, and repeat the washing until the solution becomes neutral.

[0080] Next, in steps S25 and S26, an acidic solution is preferably mixed and stirred. For example, hydrochloric acid can be used as the acidic solution.

[0081] Next, in step S27, it is preferable to wash again, as described in step S24.

[0082] Next, in step S28, the washed product is dried. The drying method is not particularly limited, but vacuum drying can be used, for example.

[0083] Next, in steps S29 and S30, the dried material is preferably crushed and sieved. The method can be based on the description of steps S13 and S14.

[0084] Through the above steps, activated spherical porous carbon can be produced (step S31).

[0085] By using the above process, it is possible to produce activated spherical porous carbon having a D50 of 3 μm or more and 12 μm or less, a (D90−D10) / D50 of 0.1 or more and 1.5 or less, and a mode of pore radius of 0.30 nm or more and 0.40 nm or less in a differential pore volume distribution determined by gas adsorption method.

[0086] <Method for Producing Positive Electrode Active Material> Next, an example of a method for producing a positive electrode active material will be described with reference to the flowchart of FIG. 3A.

[0087] First, in step S41, sulfur and the activated spherical porous carbon described above are prepared. High-purity sulfur is preferred, with a purity of 99.999% or higher. The sulfur is preferably pulverized and sieved. This step is carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere.

[0088] Next, in step S42, sulfur and activated spherical porous carbon are mixed. This step is performed in an inert atmosphere. The mixing method is not particularly limited, but an agate mortar can be used, for example. If the mixing ratio S / C of sulfur (S) to activated spherical porous carbon (C) is too small, the charge / discharge capacity decreases, but if it is too large, there is a risk that too much sulfur will not be able to be composited with carbon. Therefore, when S / C (weight ratio) = x:1, x is preferably 0.5 to 2.5, more preferably 1 to 2, and most preferably 1.5.

[0089] Next, in step S43, the mixture of sulfur and activated spherical porous carbon is sealed in a container and heated together with the container. The container can be, for example, a sealable cylindrical metal container. To prevent sulfur that has not been composited with carbon from adhering to the container, it is preferable to wrap the mixture in silicone-coated aluminum foil before placing it in the container. Sealing is performed in an inert atmosphere.

[0090] The heating temperature in step S43 is preferably 120° C. to 160° C., and the heating time is preferably 1 hour to 10 hours, and the atmosphere is preferably an inert atmosphere, particularly an argon atmosphere.

[0091] In step S44, the heated material is preferably sieved. If necessary, it may be crushed using an agate mortar or the like.

[0092] Through the above steps, a positive electrode active material in which sulfur is supported on activated spherical porous carbon can be produced (step S45).

[0093] <Method for Producing Positive Electrode> Next, an example of a method for producing a positive electrode active material will be described with reference to the flowchart of FIG. 3B.

[0094] First, in step S51, the positive electrode active material, conductive material, and binder solution prepared above were prepared.

[0095] The conductive material may be one or more selected from carbon, copper, tin, zinc, silver, and nickel. Typical carbon materials used as the conductive material include carbon black (particulate carbon such as furnace black and acetylene black, graphite, etc.). In this embodiment, acetylene black (AB) is used as the conductive material.

[0096] As the binder, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, polyvinylpyrrolidone, or the like.

[0097] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. As the binder, fluororubber can also be used.

[0098] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0099] The solvent may be N-methylpyrrolidone (NMP) or acetone, or may be a mixture of water, alcohol (methanol, ethanol, propanol, butanol, isopropyl alcohol, etc.).

[0100] In this embodiment, a PVDF solution using NMP as a solvent is prepared as the binder solution.

[0101] Next, in step S52, these are mixed and kneaded while adjusting the amount of binder solution to obtain a desired viscosity.

[0102] Next, in step S53, a binder solution and a solvent are added to prepare a slurry containing the positive electrode active material, the conductive material, and the binder in a desired ratio. The viscosity of the slurry is preferably adjusted appropriately by adjusting the amount of solvent, the reaction temperature, or the reaction time. It is preferable to perform degassing as needed.

[0103] Next, in step S54, the slurry is applied onto a positive electrode current collector, which is preferably made of carbon-coated aluminum foil to improve conductivity.

[0104] Next, in step S55, the solvent is dried. The drying method is not particularly limited, and can be performed by methods such as ventilation drying or reduced-pressure (vacuum) drying, but reduced pressure drying is preferred. Pressing may be performed if necessary. Pressing increases the capacity per volume and improves the energy density. Furthermore, since sulfur is distributed inside the activated spherical porous carbon, the influence of heat during pressing can be suppressed. On the other hand, in the case of unactivated spherical porous carbon, sulfur is distributed outside the carbon material, so the heat during pressing can cause sulfur to melt and leak from the electrode surface. The pressing conditions using a roll press can be 20°C to 130°C, for example, with a linear pressure of 500 kN / m or less, preferably 300 kN / m or less, and more preferably 250 kN / m or less. When PVDF is used as the binder, since PVDF is a resin with a melting point in the range of 134°C to 169°C, the heat treatment temperature is preferably 130°C or less.

[0105] Through the above steps, the positive electrode can be produced (step S56).

[0106] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0107] Embodiment 3 An example of manufacturing a secondary battery using the positive electrode described in the above embodiment will be described below.

[0108] A secondary battery has at least a positive electrode, an electrolyte, a separator, and a negative electrode.

[0109] [Electrolyte] The secondary battery has an electrolyte containing carrier ions. In this specification and the like, the electrolyte is not limited to an electrolyte containing an organic solvent that is liquid at room temperature, but also includes a solid electrolyte, and also includes an electrolyte containing both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature (semi-solid electrolyte). Note that a lithium salt dissolved in an organic solvent that is liquid at room temperature may be referred to as an electrolyte solution.

[0110] One of the issues with secondary batteries using sulfur is that the battery performance is significantly affected by the formation and elution of lithium polysulfides. ２ S Ｘ , where X is 2 or more and 8 or less) is generated, reducing the capacity. Furthermore, lithium polysulfides undergo shuttle reactions during charging, significantly reducing the charge-discharge efficiency. Furthermore, many organic solvents react with lithium polysulfides.

[0111] As the organic solvent that is liquid at room temperature, an aprotic organic solvent is preferred, and 1,3-dioxolane (DOL) or 1,2-dimethoxyethane (DME) can be used as an ether-based electrolyte. Furthermore, 1,1,2,2-tetrafluoroethyl (TTE) or bis(2,2,2-trifluoromethyl)ethyl (BTFE) can be used as a fluorine-based ether-based electrolyte. Furthermore, sulfolane (SL) can be used as an electrolyte. Furthermore, glymes (methyl monoglyme, ethyl monoglyme, butyl diglyme, triglyme, tetraglyme, etc.) can be used as an electrolyte.

[0112] The lithium salt to be dissolved in the organic solvent is not particularly limited, and any known lithium salt that can be used in lithium-sulfur batteries can be used. For example, LiCl, LiPF ６ , LiSCN, lithium bis(trifluoromethane)sulfonimide (LiTFSI), etc. can be used.

[0113] <Additives> The organic solvent may contain additives such as lithium nitrate, imide salts, sulfonated compounds, aromatic compounds, and halogen-substituted products thereof.

[0114] [Separator] The secondary battery preferably has a separator. Examples of separators that can be used include those made of paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0115] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0116] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0117] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0118] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the discharge capacity per volume of the secondary battery can be increased.

[0119] It is preferable to use glass fiber or the like as the separator, which has a high porosity and high wettability with the electrolyte, since it is less likely to inhibit the movement of lithium ions and provides good charge / discharge characteristics.

[0120] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector.

[0121] [Negative Electrode Active Material] As the negative electrode active material, for example, metallic lithium or an alloy material (alloy with copper, tin, or cobalt) can be used.

[0122] [Negative Electrode Current Collector] For the negative electrode current collector, in addition to copper, the same materials as those for the positive electrode current collector can be used.

[0123] [Coin-type secondary battery] Fig. 4A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 4B is an external view, and Fig. 4C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0124] 4A is a schematic diagram showing the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 4A and 4B are not completely corresponding views.

[0125] In Fig. 4A, a positive electrode 201, a separator 210, a negative electrode 207, a spacer 222, and a washer 212 are stacked. These are sealed with a negative electrode can 202, a positive electrode can 204, and a gasket. Note that the gasket for sealing is not shown in Fig. 4A. The spacer 222 and the washer 212 are used to protect the inside or to fix the position inside the can when the positive electrode can 204 and the negative electrode can 202 are crimped together. The spacer 222 and the washer 212 are made of stainless steel or an insulating material.

[0126] The positive electrode 201 has a laminated structure in which a positive electrode active material layer 206 is formed on a positive electrode current collector 205 .

[0127] FIG. 4B is a perspective view of the completed coin-type secondary battery.

[0128] In the coin-type secondary battery 200, a positive electrode can 204, which also serves as a positive electrode terminal, and a negative electrode can 202, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 203 made of polypropylene or the like. The positive electrode 201 is formed of a positive electrode current collector 205 and a positive electrode active material layer 206 provided in contact with the positive electrode current collector. The negative electrode 207 is formed of a negative electrode current collector 208 and a negative electrode active material layer 209 provided in contact with the negative electrode current collector. The negative electrode 207 is not limited to a laminated structure, and may be made of metallic lithium foil or a lithium-aluminum alloy foil.

[0129] It is to be noted that it is sufficient for each of the positive electrode 201 and the negative electrode 207 used in the coin-type secondary battery 200 to have an active material layer formed on only one surface.

[0130] The positive electrode can 204 and the negative electrode can 202 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, or the like. The positive electrode can 204 is electrically connected to the positive electrode 201, and the negative electrode can 202 is electrically connected to the negative electrode 207.

[0131] These negative electrode 207, positive electrode 201, and separator 210 are immersed in an electrolyte solution, and as shown in FIG. 4C , the positive electrode 201, separator 210, negative electrode 207, and negative electrode can 202 are stacked in this order with the positive electrode can 204 facing downward, and the positive electrode can 204 and the negative electrode can 202 are crimped together via a gasket 203, thereby producing a coin-shaped secondary battery 200.

[0132] By using the above positive electrode 201 as a positive electrode active material of one embodiment of the present invention, the coin-type secondary battery 200 can be lightweight, have high capacity, and have excellent cycle characteristics.

[0133] Embodiment 4 In this embodiment, an example of a lithium ion battery will be described.

[0134] [Laminated Lithium-ion Battery] An example of a laminated lithium-ion battery 500 is shown in Figures 5A and 5B. Figures 5A and 5B are external views, and the lithium-ion battery 500 includes the electrolyte and separator (not shown in Figure 5) described in the above embodiment, a negative electrode 506, and a positive electrode 507. In the lithium-ion battery 500, the negative electrode 506 preferably has a larger area than the positive electrode 507. The lithium-ion battery 500 further includes a negative electrode lead electrode 510 electrically connected to the negative electrode 506 and a positive electrode lead electrode 511 electrically connected to the positive electrode 507. The electrolyte layer, the negative electrode 506, and the positive electrode 507 are housed in an outer casing 509, and a portion of the negative electrode lead electrode 510 and a portion of the positive electrode lead electrode 511 protrude from the outer casing 509. An adhesive region 508 is provided on a portion of the outer periphery of the outer casing 509. Fig. 5A shows an example in which the negative electrode lead electrode 510 and the positive electrode lead electrode 511 protrude from the same side of the exterior body 509, and the adhesive region 508 is located at least on the side from which each lead electrode protrudes and two sides adjacent to that side. Fig. 5B shows an example in which the side from which the negative electrode lead electrode 510 protrudes from the exterior body 509 and the side from which the positive electrode lead electrode 511 protrudes from the exterior body 509 face each other, and the adhesive region 508 is located at least on the two sides from which each lead electrode protrudes and one side sandwiched between those two sides. In Figs. 5A and 5B, the sides on which the adhesive region 508 is not located preferably correspond to the sides along which the exterior body 509 is folded.

[0135] By using the positive electrode active material of one embodiment of the present invention in the laminated lithium-ion battery 500, the secondary battery can be lightweight, have a large capacity, and exhibit excellent cycle characteristics.

[0136] [Cylindrical Lithium-ion Battery] An example of a cylindrical lithium-ion battery will be described with reference to Fig. 6A. As shown in Fig. 6A, a cylindrical lithium-ion battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0137] 6B is a schematic diagram showing a cross section of a cylindrical lithium-ion battery. The cylindrical lithium-ion battery shown in FIG. 6B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0138] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with an electrolyte layer 605 sandwiched therebetween. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. Inside the battery can 602, the wound battery element, in which the positive electrode, the negative electrode, and the separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. An electrolyte (not shown) of one embodiment of the present invention is injected into the battery can 602 in which the battery element is provided.

[0139] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector. While the lithium-ion battery 616 shown in Figures 6A to 6D has a cylinder whose height is greater than its diameter, this is not limiting. A lithium-ion battery whose diameter is greater than its height may also be used. This configuration, for example, can reduce the size of the lithium-ion battery.

[0140] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. The positive electrode terminal 603 can be made of aluminum, and the negative electrode terminal 607 can be made of a metal material such as copper. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and this increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO ３ )-based ceramic materials, etc. can be used.

[0141] 6C shows an example of a power storage system 615. The power storage system 615 has multiple lithium-ion batteries 616 and is sometimes called a battery pack. The positive electrodes of each lithium-ion battery are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of each lithium-ion battery are electrically connected to the control circuit 620 via wiring 626. A protection circuit or the like that prevents overcharging or overdischarging can be used as the control circuit 620.

[0142] 6D shows an example of a power storage system 615. The power storage system 615 has multiple lithium ion batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The multiple lithium ion batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The multiple lithium ion batteries 616 may be connected in parallel, in series, or in parallel and then in series. By configuring the power storage system 615 to include multiple lithium ion batteries 616, a large amount of power can be extracted.

[0143] A plurality of lithium ion batteries 616 may be connected in parallel and then further connected in series.

[0144] A temperature control device may be provided between the plurality of lithium ion batteries 616. When the lithium ion batteries 616 are overheated, they can be cooled by the temperature control device, and when the lithium ion batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the influence of the outside air temperature.

[0145] 6D , the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of lithium ion batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of lithium ion batteries 616 via a conductive plate 614.

[0146] By using the positive electrode active material of one embodiment of the present invention for the cylindrical lithium-ion battery 616, the secondary battery can be lightweight, have high capacity, and have excellent cycle characteristics.

[0147] [Another Example of the Structure of the Lithium-Ion Battery] An example of the structure of the lithium-ion battery will be described with reference to FIGS. 7 and 8. FIG.

[0148] The lithium ion battery 913 shown in FIG. 7A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is impregnated with an electrolyte according to one embodiment of the present invention inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 7A , the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum), a composite material of metal and resin, or the like.

[0149] 7B, the housing 930 shown in Fig. 7A may be formed using a plurality of materials. For example, the lithium-ion battery 913 shown in Fig. 7B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0150] The housing 930a can be made of an insulating material. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the lithium ion battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0151] 7C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the electrolyte layer 933 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the electrolyte layer 933 may be stacked.

[0152] 8A to 8C may be used as a lithium ion battery 913 having a wound body 950a. The wound body 950a shown in Fig. 8A includes a negative electrode 931, a positive electrode 932, and an electrolyte layer 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0153] The electrolyte layer 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0154] 8B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0155] 8C , wound body 950 a is covered with housing 930 to form lithium ion battery 913. Housing 930 is preferably provided with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0156] As shown in Fig. 8B, the lithium ion battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a lithium ion battery 913 with a larger charge / discharge capacity. For other elements of the lithium ion battery 913 shown in Figs. 8A and 8B, the descriptions of the lithium ion battery 913 shown in Figs. 7A to 7C can be referenced.

[0157] By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery 913 having a wound body, the secondary battery can be lightweight, have high capacity, and have excellent cycle characteristics.

[0158] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0159] Fifth Embodiment In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIG.

[0160] 9A , the electric vehicle is equipped with first batteries 1301a and 1301b as main driving lithium-ion batteries and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. By using the positive electrode active material of one embodiment of the present invention for the first batteries 1301a and 1301b, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0161] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0162] The internal structure of the first battery 1301a may be a wound type or a stacked type. The first battery 1301a may be an all-solid-state battery including the positive electrode active material of one embodiment of the present invention. By using an all-solid-state battery for the first battery 1301a, a high capacity, improved safety, and reduced size and weight can be achieved.

[0163] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple lithium ion batteries, it is possible to extract large amounts of power. The multiple lithium ion batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of lithium ion batteries is also called a battery pack.

[0164] In addition, in an in-vehicle lithium-ion battery, in order to cut off power from multiple lithium-ion batteries, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0165] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0166] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0167] The first battery 1301a will be described with reference to FIG. 9B.

[0168] FIG. 9B shows an example in which nine prismatic lithium-ion batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic lithium-ion batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also referred to as a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (e.g., from the road surface), it is preferable to fix multiple lithium-ion batteries using the fixing portions 1413 and 1414 and the battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0169] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0170] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In—Ga oxide or an In—Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface where the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region is also a region with a uniform lattice arrangement. Furthermore, a CAAC-OS has a region where multiple crystalline regions are connected in the a-b plane direction, and the region may have distortion. Note that distortion refers to a portion where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with another uniform lattice arrangement in a region where multiple crystalline regions are connected. In other words, a CAAC-OS is an oxide semiconductor with a c-axis aligned and no clear orientation in the a-b plane direction.

[0171] Furthermore, since the control circuit unit 1320 can be used in low-temperature environments, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has a wider operating ambient temperature range than single-crystal Si, from −40° C. to 150° C., and its characteristics change less when the lithium-ion battery is heated than single-crystal Si. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150° C., whereas the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150° C., the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety.

[0172] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for lithium-ion batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for lithium-ion batteries can be miniaturized.

[0173] Micro-short circuits are tiny short circuits that occur inside lithium-ion batteries. One of the causes of micro-short circuits is said to be local current concentration in parts of the positive electrode and negative electrode due to uneven distribution of the positive electrode active material caused by multiple charge and discharge cycles, or the generation of by-products due to side reactions, which causes micro-short circuits.

[0174] In addition to detecting micro-short circuits, the control circuit 1320 can also be said to detect the terminal voltage of the lithium-ion battery and manage the charge / discharge state of the lithium-ion battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0175] FIG. 9C shows an example of a block diagram of the battery pack 1415 shown in FIG. 9B.

[0176] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the lithium-ion battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits for the lithium-ion battery is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0177] The switch unit 1324 can be configured by combining an n-channel transistor and a p-channel transistor. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO ｘThe switch portion 1324 may be formed using a power transistor having gallium oxide (x is a real number greater than 0). Furthermore, a memory element using an OS transistor can be freely arranged by stacking it on a circuit using a Si transistor, and thus integration can be easily achieved. By stacking the control circuit portion 1320 using an OS transistor on the switch portion 1324 and integrating them, it is possible to form it into a single chip, thereby enabling miniaturization.

[0178] The first batteries 1301a and 1301b mainly supply power to on-board equipment in the 42V system (high voltage system), while the second battery 1311 supplies power to on-board equipment in the 14V system (low voltage system). Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Using a lithium-ion battery as the second battery 1311 offers the advantage of being maintenance-free, but over long periods of use, such as three years or more, there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, even if the first batteries 1301a and 1301b have remaining capacity, the second battery 1311 is charged to maintain a full charge state by supplying power from the first battery to the second battery.

[0179] In this embodiment, an example in which lithium ion batteries are used for both the first battery 1301 a and the second battery 1311 is shown, but a lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. By using the positive electrode active material of the present invention in the above-mentioned lithium ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0180] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0181] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the lithium ion batteries used, and can perform rapid charging.

[0182] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The control circuit unit 1320 may also be provided in the connection cable or the charger's connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0183] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0184] Next, an example in which the lithium ion battery according to one embodiment of the present invention is mounted on a vehicle or the like will be described.

[0185] Furthermore, installing lithium-ion batteries in vehicles will enable next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), etc. Lithium-ion batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0186] 10A and 10D illustrate examples of a transportation vehicle or the like using one embodiment of the present invention. The automobile 2001 shown in FIG. 10A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor and an engine as a power source for traveling. When a lithium-ion battery is installed in a vehicle, an example of the lithium-ion battery described in the above embodiment is installed in one or more locations. By using the positive electrode active material of one embodiment of the present invention in a lithium-ion battery installed in a vehicle, a secondary battery that is lightweight, has a high capacity, and has excellent cycle characteristics can be obtained.

[0187] 10A includes a battery pack 2200, which includes a battery module to which a plurality of lithium-ion batteries are connected. The battery pack 2200 preferably further includes a charge control device electrically connected to the battery module.

[0188] Furthermore, the automobile 2001 can charge its lithium-ion battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. The charging method and connector standards may be appropriately determined using a predetermined system such as CHAdeMO (registered trademark) or Combo. The external charging facility may be a charging station installed in a commercial facility, a household power source, or the like. For example, plug-in technology can be used to charge the power storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0189] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the lithium-ion battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0190] 10B shows, as an example, a large transport vehicle 2002 having an electrically controlled motor. The battery module of the transport vehicle 2002 has, for example, one hundred or more lithium-ion batteries with a nominal voltage of 3.0 V to 5.0 V connected in series to achieve a maximum voltage of 600 V. Furthermore, except for the number of lithium-ion batteries constituting the battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 9A , and therefore a description thereof will be omitted. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion batteries included in the module, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0191] 10C illustrates, as an example, a ship 2003 having an electrically controlled motor, lighting, or communication device. The ship 2003 includes a battery module 2202 from which power can be supplied to the motor, lighting, communication device, and the like. The ship 2003 may further include a solar panel 2203. The solar panel 2203 enables the battery module 2202 to be charged even in an environment in which an onshore power grid cannot be accessed. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery included in the module, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0192] Fig. 10D shows, as an example, an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Fig. 10D has wheels for takeoff and landing, and can therefore be considered part of a transport vehicle, and has a battery pack 2204 that includes a battery module formed by connecting multiple lithium-ion batteries and a charge control device.

[0193] The battery module of the aircraft 2004 is, for example, eight 4 V lithium ion batteries connected in series, with a maximum voltage of 32 V. Other than the number of lithium ion batteries constituting the battery module of the battery pack 2204, the battery module has the same functions as those shown in FIG. 9B, and therefore a description thereof will be omitted.

[0194] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0195] Embodiment 6 In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a vehicle such as a motorcycle or a bicycle will be described.

[0196] 11A illustrates an example of an electric bicycle using the lithium-ion battery of one embodiment of the present invention. The lithium-ion battery of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 11A. The lithium-ion battery of one embodiment of the present invention may include a protection circuit.

[0197] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 11B . The power storage device 8702 includes a plurality of lithium-ion batteries 8701 of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery 8701, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0198] The power storage device 8702 also includes a control circuit 8704 capable of controlling charging or detecting an abnormality of the lithium ion battery, an example of which is shown in Embodiment 8. The control circuit 8704 is electrically connected to the positive electrode and the negative electrode of the lithium ion battery 8701. This can greatly contribute to eliminating accidents such as fires caused by lithium ion batteries.

[0199] 11C illustrates an example of a two-wheeled vehicle using the lithium-ion battery of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 11C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. By using the positive electrode active material of one embodiment of the present invention in a lithium-ion battery, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0200] 11C can store a power storage device 8602 in an under-seat storage space 8604. The power storage device 8602 can be stored in the under-seat storage space 8604 even if the under-seat storage space 8604 is small.

[0201] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0202] Embodiment 7 In this embodiment, an example of mounting a lithium-ion battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a lithium-ion battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, mobile phones, and wearable devices.

[0203] 12A illustrates an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, an operation button 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a lithium-ion battery 2107. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery, the secondary battery can be lightweight, have a large capacity, and exhibit excellent cycle characteristics.

[0204] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0205] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0206] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0207] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0208] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0209] 12B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a lithium-ion battery 2301 of one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0210] Fig. 12C shows an example of a robot. A robot 6400 shown in Fig. 12C includes a lithium ion battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0211] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0212] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0213] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of 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 the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0214] The robot 6400 includes a lithium-ion battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery, the secondary battery can be lightweight, have a large capacity, and exhibit excellent cycle characteristics.

[0215] 12D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a lithium-ion battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0216] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a lithium-ion battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal region. By using the positive electrode active material of one embodiment of the present invention in the lithium-ion battery, a lightweight secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0217] 13A to 13C show an example of a wearable terminal. Fig. 13A is a rear view of electronic device 4400, Fig. 13B is a top view of electronic device 4400, and Fig. 13C is a front view of electronic device 4400. Electronic device 4400 can be worn on the user's head and can be used as an electronic device for XR (Cross Reality) such as AR (Augmented Reality), VR (Virtual Reality), and MR (Mixed Reality).

[0218] The electronic device 4400 has a housing, and the housing includes a cover portion 4150, a frame portion 4420, and a band portion 4430. The frame portion 4420 and the band portion 4430 are composed of multiple members and have a function of fixing the cover portion 4150 to the user's head. The band portion 4430 has a shape that fits the user's back of the head 4000. A secondary battery 5000 including a positive electrode active material of one embodiment of the present invention can be provided inside the band portion 443. By using a secondary battery including a positive electrode active material of one embodiment of the present invention that is lightweight, has a high capacity, and has excellent cycle characteristics, the wearable device 4400 can be lightweight and easy to wear. The secondary battery 5000 may be a secondary battery whose cell itself is flexible, or a secondary battery that is flexible as a module formed by combining multiple inflexible cells.

[0219] The electronic device 4400 preferably includes a speaker 4440. The secondary battery 5000 inside the band portion 4430 preferably includes a monitoring circuit 4500. The monitoring circuit 4500 may be a monitoring circuit for detecting an abnormality in the secondary battery 5000, or may be a monitoring circuit for charging the secondary battery 5000. The monitoring circuit 4500 may be an IC chip with a relatively small area.

[0220] 13C , cameras 4410R and 4410L are preferably provided on the surface of cover unit 4150. Lenses 4120R and 4120L that function as eyepieces for the right eye and left eye are preferably provided on the user's side of cover unit 4150 in portions that are located in front of the user's eyes. Also, display devices 4110R and 4110L that display images for the right eye and left eye are preferably provided inside cover unit 4150.

[0221] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0222] Embodiment 8 In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on space equipment will be described.

[0223] 14A shows an artificial satellite 6800 as an example of space equipment. The artificial satellite 6800 has a body 6801, a solar panel 6802, an antenna 6803, and a lithium-ion battery 6805. The solar panel may be called a solar cell module.

[0224] When sunlight is irradiated onto the solar panel 6802, power required for the operation of the satellite 6800 is generated. However, for example, when sunlight is not irradiated onto the solar panel or when the amount of sunlight irradiating the solar panel is small, the generated power is small. Therefore, the power required for the operation of the satellite 6800 may not be generated. To operate the satellite 6800 even under conditions where the generated power is small, the satellite 6800 may be provided with a lithium-ion battery 6805. By using the positive electrode active material of one embodiment of the present invention for the lithium-ion battery, a lightweight secondary battery with a large capacity and excellent cycle characteristics can be obtained.

[0225] The satellite 6800 can generate a signal. The signal is transmitted via the antenna 6803, and can be received by, for example, a receiver installed on the ground or another satellite. By receiving the signal transmitted by the satellite 6800, the position of the receiver that received the signal can be measured, for example. As described above, the satellite 6800 can constitute, for example, a satellite positioning system.

[0226] Alternatively, the artificial satellite 6800 may be configured to include a sensor. For example, by including a visible light sensor, the artificial satellite 6800 may have the function of detecting sunlight reflected from an object on the ground. Alternatively, by including a thermal infrared sensor, the artificial satellite 6800 may have the function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may function as, for example, an earth observation satellite.

[0227] FIG. 14B shows a probe 6900 with a solar sail (also called a sun sail) as an example of space equipment. The probe 6900 includes a body 6901, a solar sail 6902, and a lithium-ion battery 6905. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained. When photons emitted from the sun strike the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, the surface of the solar sail 6902 preferably has a thin film with high reflectivity, and more preferably faces the sun.

[0228] The solar sail 6902 may also be designed to be folded up small until it leaves the atmosphere, and then deployed into a large sheet shape outside the Earth's atmosphere (outer space) as shown in Figure 14B.

[0229] FIG. 14C shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 has a body 6911, a solar panel 6912, and a lithium-ion battery 6913. By using the positive electrode active material of the present invention in the lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained. The body 6911 can have, for example, a pressurized compartment and a non-pressurized compartment. The pressurized compartment may be designed to accommodate a crew member. Electricity generated by sunlight irradiating the solar panel 6912 can be charged into the lithium-ion battery 6913.

[0230] 14D illustrates a rover 6920 as an example of space equipment. The rover 6920 includes a body 6921 and a lithium-ion battery 6923. By using the positive electrode active material of one embodiment of the present invention in the lithium-ion battery, a lightweight secondary battery with a large capacity and excellent cycle characteristics can be obtained. The rover 6920 may include a solar panel 6922.

[0231] The rover 6920 may be designed to accommodate a crew member. The lithium ion battery 6923 may be charged with electricity generated by sunlight irradiating the solar panel 6912, or the lithium ion battery 6923 may be charged with electricity generated by other power sources, such as a fuel cell, a radioisotope thermoelectric converter, or the like.

[0232] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0233] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0234] In this example, activated spherical porous carbon was produced and its characteristics were analyzed. Furthermore, a positive electrode active material was produced using the activated spherical porous carbon, and a secondary battery was produced using the positive electrode active material, and the characteristics and electrochemical properties of these batteries were evaluated. It should be noted that the present invention is not limited to the following examples.

[0235] <Preparation of Activated Spherical Porous Carbon> A method for preparing activated spherical porous carbon will be described with reference to Fig. 2. First, in step S11, spherical phenolic resin (product name Marilyn HF-008, manufactured by Gun-ei Chemical Industry Co., Ltd.) was prepared.

[0236] Next, in step S12, 5 g of spherical phenolic resin was placed in a 100 ml aluminum oxide crucible, and with the aluminum oxide lid in place, the crucible was placed in a muffle furnace and heated for 4 hours at 650° C. In the heat treatment of step S12, the temperature was increased and decreased at 200° C. per hour, and nitrogen gas was flowed at 5 L / min to create an inert atmosphere.

[0237] The heated material was crushed in an agate mortar for about 5 minutes (step S13), and then passed through a sieve with 53 μm openings (step S14) to obtain spherical porous carbon (step S15). This was designated as sample PC.

[0238] Next, in step S21, 3 g of sodium hydroxide was prepared as the base, and 45 ml of pure water was prepared as the water.

[0239] Sodium hydroxide and water were mixed to prepare an alkaline solution, to which 1 g of the spherical porous carbon obtained in step S15 was added, followed by stirring with a stirrer at 800 rpm for 1 hour (step S22).

[0240] In step S23, the stirred mixture was placed in a 100 ml aluminum oxide crucible, and with an aluminum oxide lid attached, the crucible was placed in a muffle furnace and heated for 1 hour at 800° C. The heating treatment in step S23 was carried out using the same temperature increase and decrease processes and atmosphere as in step S12.

[0241] The heated product was added with pure water, filtered by suction, and washed (step S24). This was repeated until the filtrate became neutral.

[0242] Next, 200 ml of 1 M hydrochloric acid was prepared as an acidic solution in step S25. The hydrochloric acid was mixed with the material washed in step S24, and the mixture was stirred with a stirrer at 600 rpm for 1 hour (step S26).

[0243] Thereafter, the substrate was washed with pure water in the same manner as in step S24 (step S27).

[0244] Next, in step S28, the substrate was dried in vacuum at 60° C. for 10 hours.

[0245] The dried product was crushed in an agate mortar (step S29), and passed through a sieve with 53 μm openings (step S30) to obtain activated spherical porous carbon (step S31), which was designated as sample AC-3.

[0246] Sample AC-5 was prepared in the same manner as sample AC-3, except that 5 g of sodium hydroxide was used as the base in step S21 and hydrochloric acid was not mixed in step S25.

[0247] Sample AC-1 was prepared in the same manner as sample AC-3, except that 1 g of sodium hydroxide was used as the base in step S21 and hydrochloric acid was not mixed in step S25.

[0248] The particle size distribution, BET specific surface area, and differential pore volume distribution of the samples prepared above were measured.

[0249] Figure 15 shows the particle size distributions of Samples PC and AC-3 and the raw material spherical phenolic resin (Resin) measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-2200). All samples showed extremely sharp distributions, indicating that the particle size and particle size distribution of the raw material were maintained. The D10, D50, D90, etc. of Sample AC-3 are shown in Table 1. The (D90 - D10) / D50 of Sample AC-3 was 0.1 or more and 1 or less, more specifically, 0.4446.

[0250]

[0251] The BET specific surface areas of PC, AC-1, AC-3, and AC-5 are shown in Figure 16. The measurement equipment, conditions, and pretreatment were as follows: Pretreatment: Vacuum drying at 300°C for 10 hours or more Measurement equipment: Automatic specific surface area measurement equipment Tristar II 3020 Gas used: Nitrogen Measurement temperature: -195.8°C

[0252] For PC and AC-3, n = 2, and for AC-1 and AC-5, n = 1. No increase in the specific surface area was confirmed for AC-1, which used the same amount of sodium hydroxide as the spherical porous carbon. However, for AC-3, which used three times the amount of sodium hydroxide, and AC-5, which used five times the amount of sodium hydroxide, the specific surface area was shown to be significantly larger. The BET specific surface area of ​​AC-3 was 1500 m ２ / g or more 2500m ２ / g or less, and the BET specific surface area of ​​AC-5 is 3500 m ２ / g or more.

[0253] Figure 17 shows the differential pore volume distributions of PC, AC-1, AC-3, and AC-5, measured by gas adsorption using a TriStar II 3020 automatic specific surface area analyzer. n = 2 for PC and AC-3, and n = 1 for AC-1 and AC-5. As with the specific surface area, AC-1 did not achieve sufficient results, but AC-3 and AC-5 demonstrated that the alkali activation process increased the pore radius. AC-5, which contained a higher amount of sodium hydroxide, tended to have a larger pore radius. The most common pore radius for PC and AC-1 was 0.28 nm. The most common pore radius for AC-3 was between 0.30 nm and 0.40 nm, more specifically, 0.38 nm. AC-5 had a mode at 0.28 nm, but also had a high frequency of pore radii of 0.38 nm or greater.

[0254] <Preparation of Positive Electrode Active Material> A method for preparing a positive electrode active material will be described with reference to FIG. 3A . First, in step S41, sulfur (5N, manufactured by Strem Chem) was crushed in an argon atmosphere glove box and sieved through a 53 μm mesh. The activated spherical porous carbons AC-3 and AC-5 prepared above were also prepared.

[0255] Next, in step S42, sulfur (S) / activated spherical porous carbon (C) were weighed in a glove box under an argon atmosphere so as to give a weight ratio of 5 / 5, 6 / 4 or 7 / 3, and mixed in an agate mortar.

[0256] Next, in step S43, the mixture was wrapped in silicone-coated aluminum foil (Cookpar (registered trademark) frying pan foil, manufactured by Asahi Kasei Corporation) in an argon atmosphere glove box and sealed in a cylindrical container. The cylindrical container was then heated. The heating in step S43 was performed at 155°C for 6 hours in an argon atmosphere. The argon flow rate was 0.2 L / min. The temperature-raising process involved raising the temperature from 25°C to 120°C over 30 minutes, and then raising the temperature to 155°C over 1 hour. By raising the temperature in this stepwise manner, the temperature could be raised without significantly deviating from the set temperature. After heating at 155°C for 6 hours, the mixture was allowed to cool naturally in an argon atmosphere.

[0257] The heated material was sieved through a sieve with 53 μm openings in a dry room (step S44), to obtain a positive electrode active material (step S45). If the material did not pass through the sieve, it was lightly crushed in an agate mortar and then sieved.

[0258] The preparation conditions for the samples prepared above and the BET specific surface area of ​​the activated spherical porous carbon used as the material are shown in Table 2. As a comparative example, sample 5 / 5 PC was prepared in the same manner as above except that PC that had not been alkali activated was used and the sulfur / spherical porous carbon was mixed at a ratio of 5 / 5.

[0259]

[0260] XRD measurements were performed on the positive electrode active materials 5 / 5 PC, 5 / 5 AC-3(2), 6 / 4 AC-3, 7 / 3 AC-3, 5 / 5 AC-5, 6 / 4 AC-5, and 7 / 3 AC-5 shown in Table 2. The equipment and conditions were as follows: XRD equipment: D8 ADVANCE manufactured by Bruker AXS X-ray source: Cu Output: 40 kV, 40 mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scan Measurement range (2θ): 10° to 60° Step width (2θ): 0.01° setting Counting time: 0.5 s / step Sample stage rotation: 5 rpm

[0261] The obtained XRD pattern is shown in Figure 21. An enlarged pattern of the range of 2θ from 20° to 30° in Figure 21 is shown in Figure 22. The XRD patterns shown in Figures 21 and 22 are relative intensities normalized by the maximum value in the range of 2θ from 10° to 60°, and the background and CuKa ２ The wires were not removed. For comparison, the sulfur (S ８ ) and Al ２ O ３ The diffraction pattern for Cu-Kα1 calculated from the literature value (ICSD Coll Code 9770) is also shown.

[0262] As shown in FIGS. 21 and 22, peaks derived from sulfur crystals were observed in 5 / 5 PC, which had not been subjected to alkali activation.

[0263] On the other hand, in the positive electrode active material that had undergone alkali activation, Al was ２ O ３ A peak due to Al was observed. This was thought to be due to contamination from the aluminum oxide crucible used as a container during alkali activation. The sample using AC-5, which used a larger amount of sodium hydroxide for activation, had a higher Al ２ O ３ The peaks of origin tended to be stronger.

[0264] Furthermore, peaks derived from sulfur crystals were observed in both AC-3 and AC-5 samples with an S / C ratio of 7 / 3, but not in AC-3 or AC-5 samples with an S / C ratio of 6 / 4 or 5 / 5. Therefore, in the 6 / 4 and 5 / 5 positive electrode active materials, AC-3 and AC-5, sulfur penetrated into the carbon pores and existed in an amorphous state, suggesting that sulfur and carbon were sufficiently composited.

[0265] In this specification, "a peak is observed in XRD" means that a signal having a width three times or more the average noise width is detected. Similarly, "no peak is observed" means that a signal having a width less than three times the average noise width.

[0266] In addition, in samples in which no peak derived from sulfur crystals was observed, the presence of a broad peak derived from activated spherical porous carbon was confirmed in the 2θ range of 20° to 30°. The maximum value of the broad peak varied depending on the S / C ratio, being 21° to 23° for 5 / 5 and 22.5° to 24.5° for 6 / 4.

[0267] <Preparation of Positive Electrode> A method for preparing a positive electrode will be described with reference to FIG. 3B . First, in step S51, the positive electrode active material prepared above, acetylene black (Denka Black manufactured by Denka) as a conductive material, and a 5% PVDF solution (Solef 5130 manufactured by Solvay) using NMP as a solvent as a binder solution were prepared. In step S52, these were mixed while adjusting the amount of the 5% PVDF solution to achieve a desired viscosity, and the mixture was kneaded using a planetary mixer (Awatori Rentaro manufactured by THINKY Corporation). Next, in step S53, the 5% PVDF solution and solvent were added to prepare a slurry with a final ratio of positive electrode active material:acetylene black:PVDF of 8:1:1 (by weight).

[0268] Next, in step S54, the slurry was applied to a positive electrode current collector. The positive electrode current collector was a carbon-coated aluminum foil (SDX-PM, manufactured by Showa Denko Packaging Co., Ltd.). The amount of positive electrode active material carried and the electrode density are shown in Table 2. This was dried (step S55), and a positive electrode was obtained (step S56).

[0269] The positive electrode prepared above was subjected to cross-sectional SEM-EDX analysis.

[0270] Figure 23A shows a cross-sectional SEM image of a positive electrode fabricated using the positive electrode active material 5 / 5 AC-3(1). The spherical positive electrode active material was observed to have a circular cross section. At least a portion of the cross section of the positive electrode active material had a diameter of 5 μm or more. No sulfur lumps or the like were observed.

[0271] The map sum spectrum of characteristic X-rays in the field of view shown in Figure 23A is shown in Figure 23B. Carbon, oxygen, fluorine, aluminum, and sulfur were detected, but nitrogen was not detected.

[0272] Figure 24 shows an SEM-EDX mapping image of the same field of view as Figure 23A. The electron beam acceleration voltage was 5 kV. Figure 24A shows a mapping image of carbon, Figure 24B shows oxygen, Figure 24C shows fluorine, Figure 24D shows aluminum, and Figure 24E shows sulfur. Sulfur and carbon were detected in the cross section of the positive electrode active material, i.e., inside the positive electrode active material. Fluorine was mainly detected on the surface of the positive electrode active material and was thought to originate from the PVDF binder. Aluminum was thought to originate from the current collector and was caused by cross-section processing.

[0273] Figure 25A shows the locations of SEM-EDX point analysis on the same SEM image as Figure 23A. Table 3 shows the results of the EDX point analysis of the locations marked with crosses 1 to 4. Figures 25B to 26C show the characteristic X-ray spectra obtained by these point analyses. Figure 25B shows the characteristic X-ray spectrum of the location marked with 1, Figure 26A shows the location marked with 2, Figure 26B shows the location marked with 3, and Figure 26C shows the location marked with 4. As is clear from Figure 25A, locations 1 to 4 are all located inside the positive electrode active material.

[0274]

[0275] 25B to 26C , sulfur and carbon were detected in the cross section of the positive electrode active material, i.e., inside the positive electrode active material, but no nitrogen was detected. The sulfur / carbon (mass ratio) detected inside the positive electrode active material is preferably 0.01 or more and 2.5 or less, and more preferably 0.02 or more and 2 or less. These results demonstrate that spherical positive electrode active materials containing carbon and sulfur all the way to the inside were successfully produced.

[0276] In this specification, the detection of a certain element in EDX point analysis means that a K-line or L-line peak of the element is detected in the characteristic X-ray spectrum. Similarly, the non-detection of a certain element means that a K-line or L-line peak of the element is not observed in the characteristic X-ray spectrum.

[0277] <Preparation of Secondary Battery> A coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) was prepared using the above-described positive electrode. An aluminum clad positive electrode can was used. Note that an aluminum clad positive electrode can has an aluminum coating on the inside. An aluminum clad positive electrode can is used when there is a risk that the material of the housing, such as the positive electrode can, may chemically react with the electrolyte, and can prevent corrosion by the electrolyte.

[0278] The negative electrode was made of metallic lithium foil. The separator was made of glass fiber filter paper (GF / C). The electrolyte used LiTFSI as the lithium salt, a 1:1 (volume ratio) mixture of DOL and DME as the organic solvent, and 0.1 M LiNO as the additive. ３ were mixed.

[0279] A charge-discharge cycle test was performed on the coin cells prepared as described above. The conditions for the charge-discharge cycle test were discharge: CC (current: 10 mA / g, 20 mA / g, or 100 mA / g, end voltage: 1.4 V), charge: CC (current: 10 mA / g, 20 mA / g, or 100 mA / g, end voltage: 2.8 V), and an ambient temperature of 25°C. The cells were placed in the charge-discharge cycle tester and allowed to stand for 6 hours before the cycle test. A 10-minute pause was provided between each charge and discharge. The above values ​​are current values ​​per weight of positive electrode active material.

[0280] The second charge / discharge curves of coin cells containing 5 / 5 PC, 5 / 5 AC-3(2), 6 / 4 AC-3, or 7 / 3 AC-3 are shown in Figures 27A to 29B. Figure 27A shows the charge / discharge curve per weight of the positive electrode active material at a charge / discharge current of 10 mA / g. Figure 27B shows the charge / discharge curve converted from Figure 27A to a sulfur weight. Similarly, Figure 28A shows the charge / discharge curve per weight of the positive electrode active material at a charge / discharge current of 20 mA / g, and Figure 28B shows the charge / discharge curve converted from Figure 28A to a sulfur weight. Figure 29A shows the charge / discharge curve per weight of the positive electrode active material at a charge / discharge current of 100 mA / g, and Figure 29B shows the charge / discharge curve converted from Figure 29A to a sulfur weight. When converting to a sulfur weight, it was assumed that the S / C ratio did not change due to heating of the sulfur and carbon mixture.

[0281] At any charge / discharge current, 5 / 5 AC-3(2), 6 / 4 AC-3, and 7 / 3 AC-3, which used alkali-activated spherical porous carbon, showed higher charge / discharge capacities than 5 / 5 PC, which did not undergo alkali activation.

[0282] Figure 30A shows the charge-discharge cycle characteristics of the coin cells containing 5 / 5 PC, with respect to the discharge capacity at a charge-discharge current of 100 mA / g. Similarly, Figure 30B shows the characteristics of the coin cells containing 5 / 5 AC-3(2), 6 / 4 AC-3, or 7 / 3 AC-3. Figure 30C shows the characteristics of the coin cells containing 5 / 5 AC-5, 6 / 4 AC-5, or 7 / 3 AC-5.

[0283] Fig. 31A is a graph obtained by converting Fig. 30A into a graph per sulfur weight. Similarly, Fig. 31B is a graph obtained by converting Fig. 30B, and Fig. 31C is a graph obtained by converting Fig. 30C into a graph per sulfur weight.

[0284] Fig. 32A is a graph showing the charge-discharge efficiency of the same test as Fig. 30A. Similarly, Fig. 32B is a graph showing the charge-discharge efficiency of the same test as Fig. 30B, and Fig. 32C is a graph showing the charge-discharge efficiency of the same test as Fig. 30C.

[0285] As shown in 6 / 4 AC-3 and 7 / 3 AC-3 in Fig. 30B and 5 / 5 AC-5, 6 / 4 AC-5, and 7 / 3 AC-5 in Fig. 30C, many of the cells having positive electrode active materials that had undergone alkali activation had higher discharge capacities than 5 / 5 PC shown in Fig. 30A. This is thought to be because alkali activation enlarges the pore diameter of the spherical porous carbon, allowing it to support more sulfur and increasing the amount of sulfur that can chemically react with lithium ions during charge and discharge.

[0286] 32A to 32C, 5 / 5 AC-3(2) and 6 / 4 AC-3, which were activated with three times the amount of sodium hydroxide, had better charge-discharge efficiency than those activated with five times the amount of sodium hydroxide. The cell with the best charge-discharge efficiency was one of the cells with the positive electrode active material of 6 / 4 AC-3, shown in FIG. 32B. This is thought to be because using too much base for activation enlarges the pore size too much, causing some of the sulfur to separate from the spherical porous carbon during charge and discharge, resulting in the sulfur being used for purposes other than the battery reaction.

[0287] In this example, activated spherical porous carbon was prepared, and then a positive electrode active material was prepared. Furthermore, a slurry was prepared using the positive electrode active material, and the presence or absence of a heat press treatment after application was compared or evaluated.

[0288] For the half-cell, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) was fabricated using a lithium foil as the negative electrode. As a comparative example, spherical porous carbon that had not been alkali-activated was used, and a positive electrode active material prepared by mixing sulfur / spherical porous carbon at a ratio of 5:5 was used. After mixing, the mixture was fired at 155°C in the same manner as in step S43 of Example 1. A slurry was then prepared in a ratio of 8:1:1 (weight ratio) of positive electrode active material, acetylene black, and PVDF. The slurry was then coated on a positive electrode current collector and dried to produce a positive electrode. For samples that were heat-pressed after drying, calendering was performed at a roll temperature of 120°C and a linear pressure of 210 kNpm.

[0289] The separator was a glass fiber filter (GF / C). The electrolyte used was a 1M LiTFSI lithium salt, a 1:1 (volume ratio) mixture of DOL and DME organic solvent, and 0.1M LiNO as an additive. ３ The LiTFSI was adjusted to 1M with respect to the DOL:DME = 1:1 (volume ratio), and LiNO ３ was adjusted to 0.1 M relative to 1 M LiTFSI (DOL:DME = 1:1 (volume ratio)).

[0290] A charge-discharge cycle test was performed on the coin cell prepared as described above. The conditions for the charge-discharge cycle test were discharge: CC (current: 100 mA / g, end voltage: 1.4 V), charge: CC (current: 100 mA / g, end voltage: 2.8 V), and an ambient temperature of 25°C. The cell was placed in the charge-discharge cycle tester and allowed to stand for 6 hours before the cycle test. A 10-minute pause was provided between each charge and discharge. The current values ​​shown above are per weight of the positive electrode active material. Note that the weight of the positive electrode active material here refers to the total weight of the mixture of sulfur and carbon.

[0291] 33A shows the second charge-discharge curves of a half cell using sulfur-loaded spherical porous carbon. The second charge-discharge curves are for a sample with heat pressing and a sample without heat pressing. The discharge capacity per active material weight of the sample with heat pressing was reduced by about 75 mAh / g compared to the sample without heat pressing.

[0292] FIG. 33B shows the second charge-discharge curve of a half-cell using activated spherical porous carbon loaded with sulfur. The half-cell was fabricated under the same conditions as the above sample, except that activated spherical porous carbon was used as the carbon. Activation was performed using three times the amount of sodium hydroxide as the activated spherical porous carbon, followed by washing with hydrochloric acid. In FIG. 33B, the discharge capacity per active material weight of the sample with heat pressing was reduced by approximately 34 mAh / g compared to the sample without heat pressing.

[0293] The energy density (mWh / cm) per electrode layer volume of a half cell using activated spherical porous carbon as the carbon, with heat pressing. ３ The change in the energy density per volume with heat pressing is shown in Figure 34. Compared to the energy density per volume without heat pressing, the energy density per volume with heat pressing is about 200 mWh / cm ３ increased.

[0294] Although the discharge capacity per unit weight of active material decreases due to heat pressing, when activated spherical porous carbon is used, the sulfur is located inside the carbon, making it less susceptible to the effects of heat, and the degree of decrease in discharge capacity is small. In addition, it can be confirmed that the energy density per unit volume is improved due to the improved electrode density.

[0295] 100: Positive electrode active material, 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

Claims

A secondary battery having a positive electrode and a negative electrode, The positive electrode has a positive electrode active material including sulfur and carbon, In a cross-sectional SEM image of the positive electrode, at least a portion of the positive electrode active material has a cross-sectional diameter of 5 μm or more and 50 μm or less, A secondary battery, wherein, when a cross-sectional SEM-EDX point analysis is performed on the positive electrode, sulfur and carbon are detected, but no nitrogen is detected, inside the positive electrode active material. 　 In claim 1, When a cross-sectional SEM-EDX point analysis of the positive electrode was performed, A secondary battery, wherein a sulfur / carbon (mass ratio) detected inside the positive electrode active material is 0.01 or more and 2.5 or less. 　 In claim 2, When the positive electrode active material was analyzed by powder X-ray diffraction using CuKα radiation, the XRD pattern was at least A broad peak having a full width at half maximum of 3° or more in the 2θ range of 15° or more and 35° or less, A secondary battery having no signal that is three times the average noise width in the 2θ ranges of 23.02° to 23.22° and 27.64° to 27.84°. 　 In claim 3, The negative electrode is metallic lithium.

5. The secondary battery according to claim 4, wherein the secondary battery comprises an electrolyte and a separator, the electrolyte comprises lithium bis(trifluoromethane)sulfonimide, 1,3-dioxolane, 1,2-dimethoxyethane, and lithium nitrate; The separator comprises glass fibers. 　 An electronic device comprising the secondary battery according to claim 5. 　 A vehicle comprising the secondary battery according to claim 5. 　 A ship comprising the secondary battery according to claim 5. 　 A step of preparing spherical porous carbon by subjecting spherical resin having a D50 of 3 μm or more and 12 μm or less and a (D90-D10) / D50 of 0.1 or more and 1.5 or less to a first heat treatment at 500° C. or more and 800° C. or less for 1 hour or more and 10 hours or less in an inert atmosphere; a step of mixing the spherical porous carbon with an alkaline solution, and then carrying out a second heat treatment at 600°C or higher and 900°C or lower for 20 minutes or longer and 3 hours or shorter in an inert atmosphere to produce activated spherical porous carbon.

10. The method for producing activated porous carbon spheres according to claim 9, wherein the spherical resin is a phenolic resin. 　 In claim 10, The alkaline solution is an aqueous sodium hydroxide solution, The method for producing activated spherical porous carbon, wherein the aqueous sodium hydroxide solution is prepared by dissolving sodium hydroxide in water in an amount of from 2 to 4 times (by weight) the amount of the spherical porous carbon. 　 A method for producing a positive electrode active material, comprising the steps of: a step of mixing the activated spherical porous carbon with sulfur, sealing the mixture in a container, and performing a third heat treatment at 120° C. or higher and 160° C. or lower for 1 hour or longer and 10 hours or shorter in an inert atmosphere to prepare a positive electrode active material; The activated spherical porous carbon is D50 is 3 μm or more and 12 μm or less, (D90-D10) / D50 is 0.1 or more and 1.5 or less, A method for producing a positive electrode active material, wherein in a differential pore volume distribution obtained by a gas adsorption method, the most frequent value of the pore radius is 0.30 nm or more and 0.40 nm or less. 　 A step of producing spherical porous carbon by subjecting spherical resin having a D50 of 3 μm or more and 12 μm or less and a (D90-D10) / D50 of 0.1 or more and 1.5 or less to a first heat treatment at 500° C. or more and 800° C. or less for 1 hour or more and 10 hours or less in an inert atmosphere; a step of mixing the spherical porous carbon with an alkaline solution, and then performing a second heat treatment in an inert atmosphere at a temperature of 600° C. to 900° C. for 20 minutes to 3 hours to prepare an activated spherical porous carbon; A step of mixing the activated spherical porous carbon with sulfur to prepare a positive electrode active material carrying the sulfur; mixing the sulfur-loaded positive electrode active material with a binder solution to prepare a slurry; a step of applying the slurry onto a surface of a current collector and drying the slurry to prepare a positive electrode; a step of performing a press process on the positive electrode to prepare an electrode for a secondary battery; The method for producing a secondary battery comprising the steps of: The method for producing a secondary battery according to claim 13, wherein the pressing is performed while heating. 　 The method for producing a secondary battery according to claim 13, wherein the spherical resin is a phenolic resin. 　 In claim 13, the alkaline solution is a sodium hydroxide aqueous solution, The sodium hydroxide aqueous solution is prepared by dissolving sodium hydroxide in water in an amount of from 2 to 4 times (by weight) the amount of the spherical porous carbon.