Method for producing secondary battery

Abstract

To provide a high-capacity lithium ion secondary battery and a method for producing the same.SOLUTION: A spherical resin is subjected to first heat treatment at a temperature higher than or equal to 500°C in an inert atmosphere to perform surface modification. By the heating, the contraction of a particle, the void formation due to a gas release from an inside of the particle, the crack on a particle surface, and the like are caused so as to form a support for sulfur that is to be mixed later. After obtained spherical particles and sulfur powder are mixed, the mixture is stored in a container and subjected to second heat treatment at a temperature higher than or equal to 120°C without being exposed to outside air.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One aspect of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect 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.

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

[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, an electricity storage device of a lithium ion secondary battery (also called a secondary battery), a lithium ion capacitor, and an electric double layer capacitor. [Background technology]

[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 carried out. In particular, the demand for high-output, high-energy-density lithium ion secondary batteries has rapidly expanded along with the development of portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical equipment, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and the semiconductor industry, and they have become indispensable in the modern information society as a repeatedly rechargeable energy source.

[0005] In addition, there is a demand for lightweight, high-capacity secondary batteries, and secondary batteries that use materials containing elemental sulfur 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 as well.

[0006] Furthermore, materials containing elemental sulfur are abundant resources, and therefore have the advantage of being cheaper than rare metals such as cobalt.

[0007] For example, research is being conducted on the use of sulfur and graphene sponge (3DGS) as a secondary battery using sulfur (also called a lithium-sulfur battery, Li-S battery) (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Chao Lin et al., “A facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles for flexible Li-S cathodes”, Phys. Chem. Chem. Phys., 2016, 18, 22146-22153 Summary of the Invention [Problem to be solved by the invention]

[0009] In secondary batteries that use a material containing elemental sulfur as the positive electrode active material, lithium metal is used as an example of the negative electrode active material. During discharge, lithium metal dissolves in the electrolyte at the negative electrode and becomes ions, which react with sulfur at the positive electrode and are oxidized to form the intermediate reaction product, lithium polysulfide (Li2S n (2≦n≦8) to form lithium sulfide (Li2S).

[0010] An object of one embodiment of the present invention is to provide a high-capacity lithium-ion secondary battery and a manufacturing method thereof. Another object of one embodiment of the present invention is to provide a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof.

[0011] 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 a long cycle life and high safety or reliability and a manufacturing method thereof.

[0012] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that it is possible to extract problems other than these from the description of the specification, drawings, and claims. [Means for solving the problem]

[0013] The spherical resin is subjected to a first heat treatment at 500°C or higher in an inert atmosphere to modify the surface. Heating causes the particles to shrink, gas inside the particles is released to form voids, and the particle surface cracks, making the particles a carrier for the sulfur that will be mixed in later.

[0014] The first heat treatment changes the particle size distribution or resistance component of the spherical resin. Therefore, it is preferable to set the heating conditions so that the particle size distribution is narrow and the resistance is low. Specifically, the conditions of the first heat treatment are in an inert atmosphere, 500°C to 1000°C, 2 hours to 10 hours, preferably 650°C, 4 hours.

[0015] Spherical particles are obtained by heating the spherical resin. At least a part of the spherical particles is carbonized and becomes porous. The whole particle may be carbonized. The spherical particles obtained by heating under the above heating conditions have a small average particle size, but a significantly large BET (Brunauer Emmett Teller) specific surface area. Since the BET specific surface area increases after the first heat treatment, it is presumed that the surface of the spherical particles is modified to form multiple recesses or pores on the surface. The spherical particles after heating can also be called at least a part of carbonized phenolic resin.

[0016] The BET specific surface area is measured using an automatic specific surface area measuring device, Tristar 2 3020. The BET method is an analytical method that extends the Langmuir theory to multilayer adsorption of adsorbed gas molecules, and is the most common method for calculating the specific surface area.

[0017] The resulting spherical particles are mixed with sulfur powder, and then the mixture is placed in a container and subjected to a second heat treatment at 120° C. or higher without being exposed to the outside air.

[0018] If the temperature of the second heat treatment is 120°C or higher, it is above the temperature at which sulfur volatilizes or sublimes, so it is important to store it in a container with a lid to prevent the gasified sulfur from leaking out of the container. In addition, the container may or may not be completely sealed with a lid. If the second heat treatment is performed in an incompletely sealed state, the amount of sulfur after the second heat treatment is reduced compared to before the second heat treatment. The amount of sulfur powder to be mixed is adjusted taking this reduction into consideration.

[0019] Thereafter, the mixture is crushed to obtain a positive electrode active material having a plurality of spherical particles inside and on the surface of the obtained sulfur compound.

[0020] Fig. 3(A) shows an SEM image of the mixture, and Fig. 3(B) is a schematic diagram thereof, showing a state in which a plurality of spherical particles 302 are embedded in one lump 309 of sulfur compound, and a plurality of spherical particles are fixed to the surface of one lump of sulfur compound.

[0021] The present invention also provides a secondary battery using the mixture obtained by the above-mentioned method as one of the materials for the positive electrode active material layer, and the positive electrode active material layer is a secondary battery having a conductive assistant and a binder. To form the positive electrode active material layer, the mixture, a solvent, a conductive material, and a binder are mixed to prepare a slurry, which is then applied to a positive electrode current collector.

[0022] The heat treatment conditions under reduced pressure for drying the applied positive electrode active material layer are preferably those that make it difficult for sulfur in the positive electrode active material layer to volatilize, such as 40° C. or higher and lower than 80° C., and 1 hour or higher and lower than 24 hours.

[0023] The lithium-sulfur secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector.

[0024] In the above structure, the negative electrode is made of lithium metal. Effect of the Invention

[0025] A secondary battery using sulfur in the positive electrode and lithium metal in the negative electrode can realize a lightweight and high-capacity secondary battery. The secondary battery obtained by this manufacturing process can maintain stability for a long period of time and is less likely to short circuit or generate heat, resulting in a highly safe secondary battery. In addition, the secondary battery obtained by this manufacturing process has high charge / discharge efficiency and an improved lifespan.

[0026] According to one embodiment of the present invention, a high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided. Alternatively, according to one embodiment of the present invention, a lightweight and high-capacity lithium-ion secondary battery and a manufacturing method thereof can be provided.

[0027] According to one embodiment of the present invention, a lithium ion secondary battery having excellent charge / discharge cycle characteristics and a manufacturing method thereof can be provided. Alternatively, according to one embodiment of the present invention, a secondary battery having a long cycle life and high safety or reliability and a manufacturing method thereof can be provided.

[0028] 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 effects other than these from the description in the specification, drawings, claims, etc. [Brief description of the drawings]

[0029] [Figure 1]FIG. 1 is an example of a flow diagram illustrating a manufacturing process according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an example of a flow diagram illustrating a manufacturing process according to one embodiment of the present invention. [Diagram 3] FIG. 3(A) is an SEM image showing one embodiment of the present invention, and FIG. 3(B) is a schematic diagram of FIG. 3(A). [Figure 4] FIG. 4(A) is an exploded perspective view of a coin-type secondary battery, FIG. 4(B) is a perspective view of the coin-type secondary battery, and FIG. 4(C) is a cross-sectional perspective view thereof. [Diagram 5] 5A to 5D are diagrams illustrating examples of electronic devices. [Figure 6] 6A to 6C are diagrams illustrating examples of electronic devices. [Figure 7] 7(A) to 7(C) are diagrams illustrating an example of a vehicle. [Figure 8] 8(A) and 8(B) are diagrams illustrating an example of an electric bicycle. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. 11A is an example of a schematic cross-sectional view of a spherical resin particle, and FIGS. 11B to 11D are examples of schematic cross-sectional views of spherical particles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, the 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 those skilled in the art will easily understand that the form and details of the present invention can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the description of the embodiments shown below.

[0031] In this specification, the words "first" and "second" are used for the convenience of understanding the technical content or to identify each component. Therefore, the words "first" and "second" do not limit the number of each component. Furthermore, the words "first" and "second" do not limit the order of each component. Furthermore, the words "first" and "second" or identifying symbols used in this specification may not match the words or identifying symbols in the claims.

[0032] (Embodiment 1) In this embodiment, a manufacturing process up to forming a positive electrode active material layer on a positive electrode current collector will be described below.

[0033] FIG. 1 shows an example of a flow of a process for producing a positive electrode active material.

[0034] First, spherical resin particles 301 are prepared and subjected to a first heating step for surface modification. The "spherical" shape of the spherical resin particles 301 refers to one or more shapes selected from a perfect sphere, an oval sphere, and a sphere having a plurality of recesses. The spherical resin particles 301 may have protrusions or recesses on a portion of their surface. The shape of the spherical resin particles 301 can be observed using an electron microscope.

[0035] Although there is no particular limitation, a phenolic resin is used as the spherical resin particles 301. The spherical resin particles 301 are obtained by synthesizing a condensation reaction between a phenol including a polyhydric phenol and an aldehyde, and then separating and recovering the phenolic resin.

[0036] The D50 of the spherical resin particles 301 is preferably 5 μm or more and 10 μm or less. If it is within this range, it is preferable because it has high mechanical strength and is easy to maintain a spherical shape. In addition, if it is within this range, it is difficult for aggregated lumps to form during the formation of the slurry, making it easy to apply. Breakage of the particles is suppressed in the pressing process performed during the subsequent formation of the positive electrode active material layer. Note that D50 refers to the particle diameter at 50% of the calculated cumulative distribution of the particles. The measurement of the particle size is not limited to laser diffraction particle size distribution measurement, and the major axis of the particle cross section may be measured by analysis such as SEM or TEM (Transmission Electron Microscope). Note that, as a method for measuring D50 from analysis such as SEM or TEM, for example, 20 or more particles are measured, an accumulated particle amount curve is created, and the particle diameter when the accumulated amount accounts for 50% can be taken as D50.

[0037] The spherical resin particles 301 are subjected to a first heating for surface modification at a temperature in the range of 500°C to 1000°C for 2 hours to 10 hours; in this embodiment, the particles are heat-treated at 650°C for 4 hours in a nitrogen atmosphere. The particles are black after this heat treatment, which indicates that at least a portion of the surface of the spherical resin particles 301 is carbonized. The first heating causes atoms such as oxygen or hydrogen contained in the spherical resin particles 301 to be released, resulting in carbonization or the formation of pores. The resulting powder is called spherical particles 302.

[0038] A schematic cross-sectional view of the spherical resin particle 301 is shown in FIG. 11(A). Variations of the spherical particle 302 after the first heating process are shown in FIG. 11(B), FIG. 11(C), and FIG. 11(D). The spherical resin particle 301 is an organic compound, and the carbonization process is very complicated and the composition is different. When an organic compound is heated, atoms other than carbon such as oxygen, hydrogen, and nitrogen are released and carbonized. Depending on the material of the spherical resin particle 301 or the processing conditions of the first heating, one or more of FIG. 11(B), FIG. 11(C), and FIG. 11(D) will be obtained. FIG. 11(B) shows a state in which only the surface layer of the spherical resin particle 301 is carbonized, and less than half of the radius r of the spherical resin particle 301 is carbonized. FIG. 11(C) shows a state in which the spherical resin particle 301 is carbonized except for the center portion, and more than half of the radius r of the spherical resin particle 301 is carbonized. Also, FIG. 11(D) shows an example in which most of the particles are carbonized. FIG. 11(D) shows a case in which most of the particles are porous carbon. In the state shown in FIG. 11(D), if the particles have a structure in which many regular six-membered rings of carbon atoms are connected on a plane, they can be called graphite. Of course, in this case, the graphite is not natural graphite but artificial graphite. The degree of graphitization can be known by high-resolution electron microscope images, X-ray diffraction method, etc. In the present invention, it is sufficient that at least a part of the surface of the spherical resin particles 301 is carbonized by the first heating so that the particles can be easily fixed to the sulfur to be mixed later.

[0039] Sulfur 300 is prepared in order to mix the spherical particles 302 and sulfur powder 303. Commercially available sulfur 300 is crushed under an argon atmosphere and then sieved (with mesh size of 53 μm) to prepare sulfur powder 303. Sulfur 300 with high purity is preferable, with a purity of 99.999% or higher. Mixing is performed using an agate mortar so that the ratio of the weight of sulfur 300 to the weight of spherical particles 302 is 30% or more and 50% or less.

[0040] Next, the spherical particles 302 and the sulfur powder 303 are mixed. After that, a second heat treatment is performed. In the second heat treatment, the powder is placed in an alumina boat, which is a container, and covered with aluminum foil. The powder is placed in a tubular furnace with the lid on, and heated at 150°C to 160°C for 3 hours to 20 hours while flowing argon gas. In this embodiment, the heat treatment is performed at 155°C for 6 hours. Since sulfur evaporates easily, it is preferable to heat the powder in a container with the lid on. The container is not limited to an alumina boat, and the powder may be wrapped in aluminum foil in an argon atmosphere and placed in a sealable cylindrical metal container for heating.

[0041] The second heating causes the sulfur powder 303 and the spherical particles 302 to adhere to each other, forming a mass 309. This mass is then crushed and sieved (with a mesh size of 53 μm) to obtain a mixed powder 305. The mixed powder 305 has a plurality of spherical particles 302 on the surface or inside of the sulfur mass 309.

[0042] The obtained mixed powder 305 was attached to an indium foil for SEM observation. In addition, energy dispersive X-ray spectroscopy (EDX) analysis was performed at several points. As a result, sulfur was detected in the surface layer of the spherical particles, and it was confirmed that sulfur was held in the pores of the surface layer.

[0043] Next, a slurry for forming a positive electrode active material layer on the positive electrode current collector is prepared. Figure 2 shows a part of the flow of the positive electrode active material layer preparation process.

[0044] The slurry refers to a mixture containing at least a positive electrode active material and a solvent 908, and further containing one or more of a binder 907 and a conductive material 906. The slurry is also called an electrode slurry or an active material slurry, and is also called a positive electrode slurry when a positive electrode active material layer is formed, and is also called a negative electrode slurry when a negative electrode active material layer is formed.

[0045] The binder 907 is also called a binding material. The binder 907 is a resin, and if a large amount of the binder 907 is included, the ratio of the active material in the positive electrode decreases, and the discharge capacity of the secondary battery decreases. Therefore, the amount of the binder 907 is kept to a minimum.

[0046] Moreover, one or more materials selected from carbon, copper, tin, zinc, silver, and nickel can be used as the conductive material 906. A representative carbon material used for the conductive material 906 is 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 906.

[0047] As the binder 907, it is preferable to use a material such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, or the like.

[0048] In addition, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer as the binder 907. In addition, fluororubber can be used as the binder 907.

[0049] NMP (N-methylpyrrolidone) or acetone is used as the solvent 908. The viscosity of the slurry material can be adjusted appropriately by the amount of the solvent, the reaction temperature, or the reaction time.

[0050] Binder 907 is dissolved in solvent 908, and mixed with mixed powder 305 and conductive material 906 to prepare a slurry. The viscosity of the slurry material is adjusted as appropriate depending on the amount of solvent 908 or solvent 909, the reaction temperature, or the reaction time. For example, solvent 909, NMP in this embodiment, is added in a thick kneaded state, and kneading is performed. If necessary, degassing is performed.

[0051] The obtained slurry is applied onto a positive electrode current collector, which is made of carbon-coated aluminum foil.

[0052] Next, drying is performed under reduced pressure. Drying for volatilizing the solvent can be performed by a method such as ventilation drying or reduced pressure (vacuum) drying. Drying is performed at 50° C. or higher and lower than 120° C. Pressing may be performed if necessary.

[0053] Through the above steps, the positive electrode 201 can be obtained.

[0054] (Embodiment 2) An example of manufacturing a secondary battery using the positive electrode 201 obtained in the first embodiment will be described below.

[0055] The secondary battery has at least a positive electrode 201, an electrolyte, a separator, and a negative electrode.

[0056] [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 includes a solid electrolyte, and also includes an electrolyte (semi-solid electrolyte) that contains both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature. Note that an electrolyte in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature is sometimes called an electrolyte solution.

[0057] One of the issues with secondary batteries using sulfur is that the battery performance is greatly affected by the formation and dissolution of lithium polysulfides. X, x = 2 to 8) is generated, which reduces the capacity. In addition, lithium polysulfides undergo shuttle reactions during charging, significantly reducing the charge / discharge efficiency. In addition, many organic solvents react with lithium polysulfides.

[0058] The organic solvent that is liquid at room temperature is preferably an aprotic organic solvent, and 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), or sulfolane (SL) can be used as an ether-based electrolyte. In addition, 1,1,2,2-tetrafluoroethyl (TTE) or bis(2,2,2-trifluoromethyl)ethyl (BTFE) can be used as a fluorine-based ether-based electrolyte. In addition, glymes (methyl monoglyme, ethyl monoglyme, butyl diglyme, triglyme, tetraglyme, etc.) can be used as an electrolyte.

[0059] The lithium salt to be dissolved in the organic solvent is not particularly limited as long as it can be used in known lithium-sulfur batteries, and examples of the lithium salt include LiCl, LiPF6, LiSCN, and lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0060] <Additives> The organic solvent may contain an additive such as lithium nitrate, imide salts, sulfonated compounds, aromatic compounds, or halogen-substituted compounds thereof.

[0061] [Separator] The secondary battery preferably has a separator. The separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0062] The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these. As the ceramic material, for example, aluminum oxide particles or silicon oxide particles may be used. As the fluorine material, for example, PVDF or polytetrafluoroethylene may be used. As the polyamide material, for example, nylon or aramid (meta-aramid or para-aramid) may be used.

[0063] Coating with ceramic materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and discharging, and improving the reliability of the secondary battery. 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 the secondary battery.

[0064] For example, both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.Alternatively, the surface of the polypropylene film that contacts the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0065] By using a separator with a multi-layer structure, 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.

[0066] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector.

[0067] [Negative electrode active material] As the negative electrode active material, for example, lithium metal or an alloy material (alloy with copper, tin, or cobalt) can be used.

[0068] [Negative electrode current collector] For the negative electrode current collector, in addition to copper, the same material as that for the positive electrode current collector can be used.

[0069] [Coin-type secondary battery] Fig. 4(A) is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 4(B) is an external view, and Fig. 4(C) is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0070] In addition, in order to make it easier to understand, Fig. 4(A) is a schematic diagram showing the overlapping of components (upper and lower relationships and positional relationships). Therefore, Fig. 4(A) and Fig. 4(B) are not completely corresponding views.

[0071] In Fig. 4(A), 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. 4(A). 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.

[0072] A laminated structure in which a positive electrode active material layer 206 is formed on a positive electrode current collector 205 is used as a positive electrode 201 .

[0073] FIG. 4(B) is a perspective view of the completed coin-type secondary battery.

[0074] In the coin-type secondary battery 200, a positive electrode can 204 also serving as a positive electrode terminal and a negative electrode can 202 also serving as a negative electrode terminal are insulated and sealed with 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 a lithium metal foil or a lithium-aluminum alloy foil.

[0075] In addition, the positive electrode 201 and the negative electrode 207 used in the coin-type secondary battery 200 each only need to have an active material layer formed on one side.

[0076] Metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys of these metals or alloys of these metals with other metals (e.g., stainless steel, etc.) can be used for the cathode can 204 and anode can 202. In order to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, etc. The cathode can 204 is electrically connected to the cathode 201, and the anode can 202 is electrically connected to the anode 207.

[0077] These negative electrode 207, positive electrode 201 and separator 210 are immersed in an electrolyte, and as shown in FIG. 4(C), the positive electrode can 204 is placed down, and the positive electrode can 204 and the negative electrode can 202 are laminated in this order, and the positive electrode can 204 and the negative electrode can 202 are crimped together via a gasket 203, to produce a coin-type secondary battery 200.

[0078] With the above-described configuration, the coin-type secondary battery 200 can have a high capacity, a high discharge capacity, and excellent cycle characteristics.

[0079] (Embodiment 3) In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS.

[0080] Figure 5(A) shows an example of a wearable device. Wearable devices use high-capacity and lightweight secondary batteries as a power source. In addition, when a user uses the device in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as by wire with an exposed connector to improve splash-proof, water-resistant, or dust-proof performance.

[0081] For example, the secondary battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 5A. The glasses-type device 4000 includes a frame 4000a and a display unit 4000b. By mounting a secondary battery on the temples of the curved frame 4000a, the glasses-type device 4000 can be lightweight, well-balanced in weight, and has a long continuous use time. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0082] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset type device 4001. The headset type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A high-capacity, lightweight secondary battery can be provided in the flexible pipe 4001b and / or the earphone unit 4001c. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0083] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A high-capacity and lightweight secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0084] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A high-capacity and lightweight secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0085] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the belt type device 4006. The belt type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and a high-capacity, lightweight secondary battery can be mounted inside the belt portion 4006a. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0086] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and a high-capacity, lightweight secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0087] The display unit 4005a can display not only the time, but also various other information such as incoming e-mails and phone calls.

[0088] In addition, since the wristwatch type device 4005 is a wearable device that is directly wrapped around the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's amount of exercise and health can be accumulated to manage the user's health.

[0089] FIG. 5B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0090] 5C shows a side view of the display portion 4005. Fig. 5C shows a state in which a secondary battery 913 is built in. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0091] 5D shows an example of a wireless earphone. Here, the wireless earphone is illustrated having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0092] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0093] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0094] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows the main units 4100a and 4100b to play back audio data sent from other electronic devices. If the main units 4100a and 4100b have a microphone, the audio captured by the microphone can be sent to the other electronic device, and the audio data processed by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the main units 4100a and 4100b to be used as a translator, for example.

[0095] The secondary battery 4103 in the main body 4100a can be charged from the secondary battery 4111 in the case 4110. A coin-type secondary battery, a cylindrical secondary battery, or the like can be used as the secondary battery 4111 and the secondary battery 4103. The secondary battery obtained in the first embodiment is lightweight and has a high energy density. By using the secondary battery 4103 and the secondary battery 4111, it can contribute to space saving and weight reduction associated with miniaturization of the wireless earphone.

[0096] 6A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0097] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine the presence or absence of an obstacle such as a wall, furniture, or a step. When an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the weight of the cleaning robot 6300 can be reduced, and therefore the cleaning robot 6300 can be an electronic device with a long operating time.

[0098] Fig. 6(B) shows an example of a robot. The robot 6400 shown in Fig. 6(B) includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a computing device, and the like.

[0099] The microphone 6402 has a function of detecting the user's 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.

[0100] 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 removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.

[0101] The upper camera 6403 and the lower camera 6406 have a function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of an obstacle in the moving direction when the robot 6400 moves forward using the moving 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.

[0102] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component inside the robot 6400. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the weight of the entire robot 6400 can be reduced, and the robot 6400 can be an electronic device with a long operating time.

[0103] Fig. 6C shows an example of an aircraft (also called a drone). The aircraft 6500 shown in Fig. 6C has a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has a function of flying autonomously.

[0104] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of an obstacle when moving. The electronic component 6504 can estimate the remaining battery level from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention therein. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the secondary battery is lightweight and has a high capacity, so that the flying object 6500 can be made lighter overall and has a long operating time.

[0105] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0106] (Embodiment 4) In this embodiment, an example in which a secondary battery of one embodiment of the present invention is mounted on a vehicle will be described.

[0107] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0108] 7A and 7B illustrate a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 7A is an electric automobile using an electric motor as a power source for running. Alternatively, the automobile 8400 is a hybrid automobile that can use an electric motor and an engine as a power source for running. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. The automobile 8400 has a secondary battery 8402. For example, modules of the secondary battery 8402 can be arranged on the floor of the vehicle. The secondary battery 8402 can not only drive an electric motor 8406 but also supply power to a light-emitting device such as a headlight 8401 and a room light (not shown).

[0109] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0110] The automobile 8500 shown in FIG. 7(B) can charge the secondary battery of the automobile 8500 by receiving power supply from an external charging facility by a plug-in method and / or a non-contact power supply method. FIG. 7(B) shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector standards may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or combo. The charging device 8021 may be a charging station installed in a commercial facility or a home power source. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ACDC converter.

[0111] Although not shown, a power receiving device may be mounted on a vehicle, and charging may be performed by supplying power contactlessly from a ground power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device in the road and / or an exterior wall, charging may be performed not only while the vehicle is stopped but also while it is moving. This contactless power supply method may also be used to transmit and receive power between vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle, and a secondary battery may be charged while the vehicle is stopped and / or moving. For such contactless power supply, an electromagnetic induction method and / or a magnetic field resonance method may be used.

[0112] 7C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 7C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0113] 7(C) is capable of storing a secondary battery 8602 in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0114] According to one aspect of the present invention, the secondary battery can be made lighter and the discharge capacity of the secondary battery can be increased. Therefore, the capacity per unit weight can be increased, and the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, this contributes to reducing the weight of the vehicle, and the cruising distance can be improved. In addition, the secondary battery mounted on the vehicle can be used as a power supply source other than for the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions.

[0115] 8A is an example of an electric bicycle using the secondary battery of one embodiment of the present invention. The secondary battery of one embodiment of the present invention can be applied to the electric bicycle 8700 shown in FIG 8A. The power storage device of the electric bicycle 8700 of one embodiment of the present invention includes, for example, a plurality of secondary batteries and a charge / discharge control unit.

[0116] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor (electric unit) that assists the rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 8B, and corresponds to a secondary battery unit. The power storage device 8702 includes a plurality of batteries 8701, and the remaining battery charge can be displayed on a display unit 8703. The power storage device 8702 also includes a charge / discharge control unit 8704 that can control charging or detect an abnormality of the secondary battery. The charge / discharge control unit 8704 is electrically connected to the positive and negative electrodes of the battery 8701. An operation unit 8712 is provided on the handle of the electric vehicle main unit of the electric bicycle 8700. The operation unit 8712 includes a display unit 8713, a power switch 8714, and a power storage device 8711.

[0117] Since the secondary battery of one embodiment of the present invention is made of inexpensive materials, the cost of the electric bicycle 8700 can be significantly reduced.

[0118] This embodiment mode can be implemented in appropriate combination with other embodiment modes. EXAMPLES

[0119] In this example, a coin cell was fabricated and a charge / discharge test was performed, and the results are shown. Note that the present invention is not limited to the following example.

[0120] The procedure for producing a battery cell using the mixed powder 305 obtained in the first embodiment as a positive electrode active material will be described below. The procedure will be described with reference to FIGS.

[0121] First, the spherical phenolic resin (ochre powder) was subjected to the first heating to obtain blackened spherical particles. In this example, about 3.5 g of spherical phenolic resin (manufactured by Gun-ei Chemical Industry Co., Ltd.: product name Marilyn HF-008) was used, placed in a 100 ml alumina crucible, and placed in a muffle furnace with an alumina lid on. The first heat treatment was performed in a muffle furnace, and the temperature increase and decrease steps were performed at 200°C per hour. The first heat treatment was performed at 650°C for 4 hours in an inert atmosphere while flowing nitrogen gas. A comparison of the BET specific surface area before and after the first heat treatment showed that the BET specific surface area before heating was 0.332 m 2 / g, but after heating it was 525m 2 / g, which is about 1500 times higher. In addition, the median diameter was almost the same before and after the first heat treatment (median diameter before heating: 7.92 μm, median diameter after heating: 6.67 μm). This suggests that at least the surface was carbonized and pores were formed. The median diameter is the median diameter measured by laser diffraction particle size distribution measurement.

[0122] Sulfur (5N, manufactured by Strem Chem) was ground in a glove box and sieved through a sieve with 53 μm openings.

[0123] The blackened spherical particles and sulfur were weighed out so that the weight ratio was 2:1, and mixed in an agate mortar.

[0124] The mixed powder was transferred to an alumina boat, wrapped in aluminum foil, and subjected to a second heating in a tubular furnace. The second heating was performed at 155°C for 6 hours in an argon atmosphere. The argon flow rate was 0.2 L / min. The temperature increase step was performed by increasing the temperature from 25°C to 120°C in 30 minutes, and then increasing the temperature to 155°C in 1 hour. By increasing the temperature stepwise in this manner, the temperature can be increased without significantly deviating from the set temperature. After heating at 155°C for 6 hours, the mixture was naturally cooled in an argon atmosphere. Although the mixed powder was wrapped in aluminum foil, it was not sealed, so some of the sulfur was volatilized and reduced by heating.

[0125] In a dry room, the mixture was again crushed in an agate mortar and sieved through a sieve with 53 μm openings to obtain an active material.

[0126] A slurry was prepared with the active material, acetylene black, and PVDF in a ratio of 8:1:1. The slurry was applied onto a positive electrode current collector. The positive electrode current collector was a carbon-coated aluminum foil (SDX-PM, Showa Denko Packaging Co., Ltd.). The amount of the active material carried was approximately 2 mg / cm. 2 It was decided.

[0127] Using the sulfur-containing cathode thus obtained, a coin cell (with an aluminum clad cathode can) was produced. Aluminum clad is a cathode can with an aluminum coating on the inside. Aluminum clad is used when there is a risk that the material of the case, such as the cathode can, may chemically react with the electrolyte, and prevents corrosion by the electrolyte.

[0128] The negative electrode was made of lithium metal foil, the separator was made of glass fiber filter paper (GF / C), the lithium salt was LiTFSI, the electrolyte was DOL / DME, and 0.1M LiNO3 was added as an additive to the electrolyte adjusted to 1.0M LiTFSI.

[0129] A cycle test was carried out using the obtained coin cell to obtain charge / discharge characteristics and cycle characteristics.

[0130] Before conducting the cycle test, the battery cell was discharged at a constant current (CC mode) at room temperature (25°C) with a discharge rate of 10 mA / g to 1.4 V, and then charged at a constant current (CC mode) at a charge rate of 10 mA / g to 2.8 V.

[0131] The discharge rate and the charge rate are values ​​calculated by using the weight of the active material (including the weight of the blackened spherical particles) as the active material. In this specification, it is sulfur or a sulfur compound that functions as the active material, and the blackened spherical particles are a conductive material for providing conductivity, but are considered to be included in the category of the positive electrode active material. In addition, the positive electrode active material may be only elemental sulfur or only a sulfur compound, in which case the total weight of the elemental sulfur or the sulfur compound may be measured and the capacity per weight may be calculated. The positive electrode active material has fine particles of sulfurized active material attached to at least a part of the blackened spherical particles that are conductive materials, and the fine particles of the active material are elemental sulfur, lithium disulfide, or lithium polysulfide.

[0132] After charging at a constant current (CC mode) up to the above-mentioned 2.8 V, a 10-minute rest period was provided, followed by discharging at a constant current at a discharge rate of 10 mA / g up to 1.4 V (also called the cutoff voltage), and then charging at a constant current at a charge rate of 10 mA / g up to 2.8 V. A 10-minute rest period was provided.

[0133] Then, as the first discharge of the cycle test, the battery was discharged at a constant current of 10 mA / g at room temperature (25°C) to 1.4 V, and then, as the first charge, the battery was charged at a constant current of 10 mA / g to 2.8 V. This constitutes one cycle, and 50 cycles were performed. A 10-minute rest period was provided between each cycle.

[0134] The obtained charge / discharge characteristics are shown in Fig. 9, and the cycle characteristics are shown in Fig. 10. In Fig. 9, the vertical axis indicates voltage [V] and the horizontal axis indicates capacity [mAh / g]. In Fig. 10, the vertical axis indicates capacity [mAh / g] and the horizontal axis indicates cycle characteristics [times].

[0135] The maximum charge capacity of the coin cell of this embodiment is about 306 [mAh / g], the discharge capacity is about 307 [mAh / g], and the charge / discharge characteristics are excellent as shown in Fig. 9. In addition, the capacity retention rate is 74.3%, and the cycle characteristics are excellent as shown in Fig. 10.

[0136] In this specification, the term "cycle characteristic" refers to the characteristic of maintaining the charge / discharge capacity of a secondary battery even when the battery is repeatedly charged and discharged under certain conditions. Therefore, a secondary battery that exhibits a small rate of decrease in charge / discharge capacity according to the number of repeated charge / discharge cycles (also called the number of cycles) can be said to have a high capacity retention rate and excellent cycle characteristics. [Explanation of symbols]

[0137] 200 Secondary battery 201 Positive electrode 202 Anode can 203 Gasket 204 Positive electrode can 205 Positive electrode current collector 206 Cathode active material layer 207 Negative electrode 208 Negative electrode current collector 209 Negative electrode active material layer 210 Separator 212 Washer 222 Spacer 300 Sulfur 301 Spherical resin particles 302 Spherical particles 303 Sulfur Powder 305 Mixed powder 309 lump 906 Conductive materials 907 Binder 908 Solvent 909 Solvent 913 Secondary battery 4000a Frame 4000b Display section 4000 Glasses-type device 4001a Microphone section 4001b Flexible Pipe 4001c Earphones 4001 Headset type device 4002a Case 4002b secondary battery 4002 Devices 4003a Case 4003b secondary battery 4003 Device 4005a Display section 4005b Belt section 4005 Wristwatch-type device 4006a Belt section 4006b Wireless power receiving unit 4006 Belt-type device 4100a main unit 4100b main unit 4101 Driver unit 4102 Antenna 4103 Secondary battery 4104 Display section 4110 Case 4111 Secondary battery 6300 Cleaning robot 6301 Case 6302 Display section 6303 Camera 6304 Brush 6305 Operation button 6306 Secondary battery 6310 Garbage 6400 Robot 6401 Illuminance Sensor 6402 Microphone 6403 Upper Camera 6404 Speaker 6405 Display section 6406 Lower Camera 6407 Obstacle Sensor 6408 Moving mechanism 6409 Secondary battery 6500 Flying Objects 6501 Propeller 6502 Camera 6503 Secondary battery 6504 Electronic Components 8021 Charging device 8022 Cable 8024 Secondary battery 8400 Automobiles 8401 Headlight 8402 Secondary battery 8406 Electric Motor 8500 Automobiles 8600 Scooter 8601 Side mirror 8602 Secondary battery 8603 Turn signal light 8604 Under-seat storage 8700 Electric Bike 8701 Battery 8702 Energy storage devices 8703 Display section 8704 Charge / discharge control unit 8711 Energy storage devices 8712 Control unit 8713 Display section 8714 Power Switch

Claims

1. A method for producing a secondary battery, comprising the steps of: subjecting spherical resin to a first heat treatment at 500°C or higher in an inert atmosphere to perform surface modification; mixing the spherical resin with at least a portion of its surface carbonized and sulfur powder; storing the mixture in a container and subjecting it to a second heat treatment at 120°C or higher without exposure to outside air to produce a positive electrode active material.

2. 2. The method for producing a secondary battery according to claim 1, wherein the container has a lid, and the second heat treatment is performed with the lid in place.

3. 2. The method for manufacturing a secondary battery according to claim 1, wherein the second heat treatment is performed in an inert atmosphere.

4. 2. The method for producing a secondary battery according to claim 1, wherein the spherical particles are made of a phenolic resin having at least a portion of a surface that is carbonized.

5. 2. The method for producing a secondary battery according to claim 1, wherein the BET specific surface area is made larger after the first heat treatment than before the first heat treatment.

6. 2. The method for producing a secondary battery according to claim 1, wherein the weight ratio of the sulfur powder is greater than that of the spherical particles before the second heat treatment.

7. 2. The method for producing a secondary battery according to claim 1, wherein the container has a lid, and the second heat treatment is performed by placing the battery in the container, sealing the container with the lid, and heating the battery in an inert atmosphere.

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