Negative electrode active material

Abstract

To provide a negative electrode active material particle with less deterioration. A novel negative electrode active material particle is provided. A power storage device with little deterioration is provided. A power storage device with high safety is provided. A novel power storage device is provided.SOLUTION: An electrode includes an active material and a conductive agent, in which the active material includes a metal or a compound including one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium, the conductive agent includes a graphene compound, and the graphene compound includes fluorine.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery using a negative electrode active material and a method for manufacturing the same, or to a mobile information terminal, a vehicle, etc. that has a secondary battery.

[0002] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[0003] 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.

[0004] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, power storage devices such as lithium ion secondary batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors. [Background technology]

[0005] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, thanks to their high output and high energy density, and are used in a variety of applications, including mobile phones, smartphones, and laptop computers, as well as portable music players, digital cameras, medical devices, and next-generation clean-energy vehicles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0006] In order to improve the cycle characteristics and capacity of lithium ion secondary batteries, improvements to negative electrodes having a coating have been investigated (Patent Document 1).

[0007] Fluorine has a high electronegativity, and various studies have been conducted on its reactivity. Non-Patent Document 1 describes the reactions of compounds containing fluorine.

[0008] Silicon-based materials have high capacity and are used as active materials in secondary batteries. Silicon materials can be characterized by chemical shift values ​​obtained from NMR spectra (Patent Document 2).

[0009] X-ray diffraction (XRD) is one of the techniques used to analyze the crystal structure of negative electrode active materials. XRD data can be analyzed using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 2. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-88482 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-156355 [Non-patent literature]

[0011] [Non-Patent Document 1] JM Sangster and AD Pelton, “Critical Coupled Evaluation of Phase Diagrams and Thermodynamic Properties of Binary and Ternary Alkali Salt Systems”, American Ceramic Society; Westerville, Ohio; pp. 4-231 (1987). [Non-patent document 2] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., (2002) B58 364-369. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of one embodiment of the present invention is to provide a method for manufacturing a negative electrode active material that is less susceptible to deterioration, or a novel method for manufacturing a negative electrode active material.

[0013] An object of one embodiment of the present invention is to provide negative electrode active material particles that are less susceptible to deterioration.An object of one embodiment of the present invention is to provide novel negative electrode active material particles.An object of one embodiment of the present invention is to provide a power storage device that is less susceptible to deterioration.An object of one embodiment of the present invention is to provide a highly safe power storage device.An object of one embodiment of the present invention is to provide a novel power storage device.

[0014] Another object of one embodiment of the present invention is to provide a novel substance, active material particles, a power storage device, or a manufacturing method thereof.

[0015] 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. [Means for solving the problem]

[0016] One embodiment of the present invention is an electrode including an active material and a conductive agent. The active material includes a metal or a compound including one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium. The conductive agent includes a graphene compound, and the graphene compound includes fluorine.

[0017] In the above structure, the graphene compound preferably has a two-dimensional structure formed of six-membered carbon rings.

[0018] Alternatively, one embodiment of the present invention is a method for producing a negative electrode active material, including: a first step of mixing a first material, a second material having a halogen, and a third material having oxygen and carbon to prepare a first mixture; and a second step of heating the first mixture, wherein the first material is one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene, and the heating is performed in a reducing atmosphere.

[0019] In the above configuration, the second material is preferably a fluoride or chloride containing one or more elements selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, titanium, vanadium, and niobium.

[0020] In the above-mentioned configuration, the third material is preferably a carbonate containing one or more elements selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel.

[0021] In the above-described configuration, the reducing atmosphere is preferably a nitrogen atmosphere or a rare gas atmosphere.

[0022] Alternatively, one embodiment of the present invention is a method for manufacturing a negative electrode active material, the method including: a first step of mixing a first material, lithium fluoride, and lithium carbonate to prepare a first mixture; and a second step of heating the first mixture, in which the heating is performed at a temperature of 350° C. to 900° C. for 1 hour to 60 hours inclusive, in a nitrogen atmosphere or a rare gas atmosphere.

[0023] In the above-described configuration, the first material is preferably one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene.

[0024] In the above structure, the first material preferably includes a metal or a compound having one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium.

[0025] In the above structure, the first material preferably has an oxide containing one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0026] Alternatively, one embodiment of the present invention is a negative electrode active material including a first region and a second region, the first region including at least one of fluorine and oxygen, lithium, and carbon; the first region including a first material; the second region being located outside the first region and in contact with at least a part of a surface of the first region; the second region having a higher fluorine concentration than the first region and a higher oxygen concentration than the first region; and the first material being one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene.

[0027] In the above structure, at least a part of the first region preferably includes a surface of the negative electrode active material.

[0028] In the above structure, the lithium concentration in the second region is preferably higher than the lithium concentration in the first region.

[0029] Alternatively, one embodiment of the present invention provides a negative electrode active material including a first region and a second region, the first region including a first material, the second region including at least one of lithium fluoride and lithium carbonate, and the second region being located outside the first region and in contact with at least a part of the first region.

[0030] In the above structure, at least a part of the first region preferably includes a surface of the negative electrode active material.

[0031] In the above configuration, when the negative electrode active material is measured by energy dispersive X-ray analysis using a scanning electron microscope, the fluorine concentration is preferably 10 atomic % or more and 70 atomic % or less, with the concentration being measured in atomic %.

[0032] In the above-described structure, the first material is a negative electrode active material that is one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene.

[0033] In the above-described configuration, when the negative electrode active material is measured by X-ray photoelectron spectroscopy, the fluorine concentration is preferably 1 atomic % or more.

[0034] In the above-described configuration, the first material is one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene, and when the negative electrode active material is measured by X-ray photoelectron spectroscopy, the fluorine concentration is preferably 1 atomic % or more with respect to the total concentration of fluorine, oxygen, lithium, and carbon.

[0035] Another embodiment of the present invention is a secondary battery including a negative electrode having any of the above negative electrode active materials, a positive electrode, and an electrolyte.

[0036] Another embodiment of the present invention is a vehicle including the above-described secondary battery, an electric motor, and a circuit unit, in which the circuit unit has a function of controlling the secondary battery.

[0037] Another embodiment of the present invention is an electronic device including the above secondary battery, a display portion, and a circuit portion, in which the circuit portion has a function of controlling the secondary battery. [Effects of the Invention]

[0038] According to one embodiment of the present invention, a method for manufacturing a negative electrode active material that is less susceptible to deterioration can be provided.Furthermore, according to one embodiment of the present invention, a novel method for manufacturing a negative electrode active material can be provided.

[0039] According to one embodiment of the present invention, negative electrode active material particles that are less likely to deteriorate can be provided. According to another embodiment of the present invention, a method for manufacturing a negative electrode active material can be provided. According to another embodiment of the present invention, novel negative electrode active material particles can be provided. According to another embodiment of the present invention, a novel power storage device can be provided.

[0040] According to one embodiment of the present invention, a novel substance, active material particles, a power storage device, or a manufacturing method thereof can be provided.

[0041] 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. [Brief explanation of the drawings]

[0042] [Figure 1] FIG. 1A is a diagram showing an example of a cross section of a negative electrode, FIG. 1B is a diagram showing an example of a graphene compound, and FIG. 1C is a schematic diagram illustrating the graphene compound and an active material. [Figure 2] Figure 2 is a phase diagram showing the relationship between the ratio of LiF to Li2CO3 and temperature. [Figure 3] FIG. 3 shows a method for preparing the material. [Figure 4] 4A, 4B, 4C, and 4D are diagrams showing examples of cross sections of negative electrode active materials. [Figure 5] FIG. 5 shows the calculation results of the stabilization energy. [Figure 6] FIG. 6 is a diagram showing the structure of graphite. [Figure 7] FIG. 7 is a diagram showing the structure of graphite. [Figure 8] FIG. 8 is a diagram showing the structure of graphite. [Figure 9] FIG. 9 shows the calculation results of the stabilization energy. [Figure 10] FIG. 10 shows a method for preparing the material. [Figure 11] FIG. 11 is an example of a cross-sectional view showing a process of one embodiment of the present invention. [Figure 12] FIG. 12 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 13] FIG. 13 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 14] FIG. 14 is a diagram illustrating a method for producing a positive electrode active material. [Figure 15] 15A and 15B are diagrams illustrating an example of a secondary battery. [Figure 16] 16A, 16B, and 16C are diagrams illustrating examples of secondary batteries. [Figure 17] 17A and 17B are diagrams illustrating an example of a secondary battery. [Figure 18] 18A, 18B, and 18C are diagrams illustrating a coin-type secondary battery. [Figure 19] 19A, 19B, 19C, and 19D are diagrams illustrating a cylindrical secondary battery. [Figure 20] 20A and 20B are diagrams illustrating an example of a secondary battery. [Figure 21]21A, 21B, 21C, and 21D are diagrams illustrating examples of secondary batteries. [Figure 22] 22A, 22B, and 22C are diagrams illustrating examples of secondary batteries. [Figure 23] 23A, 23B, and 23C are diagrams illustrating examples of secondary batteries. [Figure 24] 24A, 24B, and 24C are diagrams illustrating a laminated secondary battery. [Figure 25] 25A and 25B are diagrams illustrating a laminated secondary battery. [Figure 26] FIG. 26 is a diagram showing the appearance of a secondary battery. [Figure 27] FIG. 27 is a diagram showing the appearance of a secondary battery. [Figure 28] 28A, 28B, and 28C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 29] 29A, 29B, 29C, 29D, and 29E are diagrams illustrating a bendable secondary battery. [Figure 30] 30A and 30B are diagrams illustrating a bendable secondary battery. [Figure 31] 31A, 31B, 31C, 31D, 31E, 31F, 31G, and 31H are diagrams illustrating an example of an electronic device. [Figure 32] 32A, 32B, and 32C are diagrams illustrating an example of an electronic device. [Figure 33] FIG. 33 is a diagram illustrating an example of an electronic device. [Figure 34] 34A, 34B, and 34C are diagrams illustrating an example of an electronic device. [Figure 35] 35A, 35B, and 35C are diagrams showing examples of electronic devices. [Figure 36] FIG. 36A is a perspective view showing a battery pack, FIG. 36B is a block diagram of the battery pack, and FIG. 36C is a block diagram of a vehicle having a motor. [Figure 37]37A, 37B, and 37C are diagrams illustrating an example of a vehicle. [Figure 38] Figures 38A and 38B are SEM images. [Figure 39] FIG. 39A shows the EDX observation points, and FIG. 39B shows the EDX spectrum. [Figure 40] FIG. 40A shows the EDX observation points, and FIG. 40B shows the EDX spectrum. [Figure 41] 41A, 41B, 41C, and 41D are diagrams showing XPS. [Figure 42] 42A, 42B, 42C, and 42D are diagrams showing XPS. [Figure 43] 43A, 43B, 43C, and 43D are diagrams showing XPS. [Figure 44] 44A, 44B, 44C, and 44D are diagrams showing XPS. [Figure 45] FIG. 45 is a diagram showing XPS. [Figure 46] 46A and 46B are diagrams showing XPS. [Figure 47] 47A and 47B are diagrams showing XPS. [Figure 48] FIG. 48A is a graph showing rate characteristics, and FIG. 48B is a graph showing cycle characteristics. [Figure 49] 49A and 49B are graphs showing cycle characteristics. [Figure 50] FIG. 50 shows the results of XRD measurement. DETAILED DESCRIPTION OF THE INVENTION

[0043] 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.

[0044] Furthermore, in this specification and the like, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar after the number, but in this specification and the like, due to restrictions on application notation, numbers may be expressed by a minus sign (-) before them instead of a bar above them. Furthermore, individual directions indicating directions within a crystal are expressed with [ ], collective directions indicating all equivalent directions are expressed with < >, individual planes indicating crystal planes are expressed with ( ), and collective planes with equivalent symmetry are expressed with {}.

[0045] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of multiple elements (for example, A, B, and C).

[0046] In this specification, the surface layer of particles of active material or the like is preferably, for example, a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. Surfaces formed by cracks and fissures may also be referred to as the surface. The region deeper than the surface layer is referred to as the interior.

[0047] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0048] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0049] In this specification and the like, the O3'-type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure of space group R-3m, which is not a spinel-type crystal structure, but in which ions of cobalt, magnesium, etc. occupy hexacoordinated oxygen positions and the arrangement of cations has a symmetry similar to that of the spinel type. Note that in the O3'-type crystal structure, a light element such as lithium may occupy tetracoordinated oxygen positions, and in this case, the arrangement of ions also has a symmetry similar to that of the spinel type.

[0050] It can also be said that the O3' type crystal structure is similar to the CdCl2 type crystal structure, although it has random Li between the layers. This CdCl2 type-like crystal structure was observed when lithium nickel oxide was charged to a charge depth of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobalt oxide (NiO2), but it is known that simply pure lithium cobalt oxide or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0051] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in the O3'-type crystal structure also have a cubic close-packed structure. When these contact, there is a crystal plane where the cubic close-packed structure formed by the anions is oriented in the same direction. However, since the space group of the layered rock salt crystals and O3'-type crystal structures is R-3m, which is different from the space group of the rock salt crystal, Fm-3m (the space group of general rock salt crystals), the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystals and O3'-type crystal structures and the rock salt crystals. In this specification, when the cubic close-packed structure formed by the anions is oriented in the same direction in the layered rock salt crystals, O3'-type crystal structures, and rock salt crystals, it may be said that the crystal orientation is approximately the same.

[0052] The general alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope), STEM (scanning transmission electron microscope), HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope), and ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, and neutron diffraction can also be used. In TEM images, the arrangement of cations and anions can be observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure of the layered rock salt crystal and the rock salt crystal is aligned, the angle between the repeated bright and dark lines between the crystals can be observed to be less than 5 degrees, preferably less than 2.5 degrees. Light elements such as oxygen and fluorine may not be clearly visible in TEM images, but in such cases, the alignment of the orientations can be determined from the arrangement of metal elements.

[0053] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0054] In this specification and the like, the depth of charge when all intercalable and deintercalable lithium is intercalated is defined as 0, and the depth of charge when all intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated is defined as 1.

[0055] In this specification, charging refers to the transfer of lithium ions from the positive electrode to the negative electrode within a battery and the transfer of electrons from the positive electrode to the negative electrode in an external circuit. Regarding a positive electrode active material, charging refers to the removal of lithium ions. A positive electrode active material with a charge depth of 0.7 to 0.9 is sometimes referred to as a positive electrode active material charged at a high voltage.

[0056] Similarly, discharging refers to the transfer of lithium ions from the negative electrode to the positive electrode within the battery and the transfer of electrons from the negative electrode to the positive electrode in an external circuit. For positive electrode active materials, discharging refers to the insertion of lithium ions. A fully discharged positive electrode active material is defined as a positive electrode active material with a charge depth of 0.06 or less, or a positive electrode active material that has been discharged to 90% or more of its charge capacity from a high-voltage charged state.

[0057] In this specification, a non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity. For example, a non-equilibrium phase change occurs around the peak in the dQ / dV curve obtained by differentiating capacitance (Q) with voltage (V), and it is believed that the crystal structure changes significantly.

[0058] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may partially contain a substance that does not contribute to the charge / discharge capacity.

[0059] In this specification and the like, the positive electrode active material of one embodiment of the present invention may be referred to as a positive electrode material, a positive electrode material for a secondary battery, or the like. Also, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a compound. Also, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composition. Also, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composite.

[0060] Discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging at a current of 2X (A), it is said to have been discharged at 2C, and when discharging at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same is true for charge rate; when charging at a current of 2X (A), it is said to have been charged at 2C, and when charging at a current of X / 5 (A), it is said to have been charged at 0.2C.

[0061] Constant current charging, for example, refers to a method of charging at a constant charge rate. Constant voltage charging, for example, refers to a method of charging at a constant voltage once the upper voltage limit is reached. Constant current discharging, for example, refers to a method of discharging at a constant discharge rate.

[0062] (Embodiment 1) In this embodiment, a negative electrode, a negative electrode active material, and a manufacturing method of the negative electrode active material according to one embodiment of the present invention will be described.

[0063] <Negative electrode> 1A illustrates an example of a cross section of a negative electrode according to one embodiment of the present invention. In the negative electrode according to one embodiment of the present invention, a negative electrode active material layer including a negative electrode active material 561, graphene 554, and acetylene black 553 is formed over a current collector 550.

[0064] The active material of one embodiment of the present invention preferably has fluorine in the surface layer portion.

[0065] In secondary batteries, irreversible reactions, such as reactions between electrodes and electrolytes, can cause a decrease in charge / discharge efficiency, particularly during the first charge / discharge.

[0066] The negative electrode active material of one embodiment of the present invention has a halogen in the surface layer portion, which can suppress a decrease in charge / discharge efficiency. It is believed that the halogen in the surface layer portion of the negative electrode active material of one embodiment of the present invention suppresses a reaction with an electrolyte on the active material surface. Furthermore, the negative electrode active material of one embodiment of the present invention may have at least a portion of its surface covered with a region containing a halogen. The region may be, for example, in the form of a film.

[0067] The surface layer is preferably a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. The region deeper than the surface layer is referred to as the interior.

[0068] By including a halogen in the surface layer of the negative electrode active material of one embodiment of the present invention, a secondary battery can achieve excellent characteristics even at high charge / discharge rates. Therefore, the charge / discharge rate can be increased. When the negative electrode active material has graphite inside and a halogen in the surface layer, the halogen or a halogen compound may be intercalated between the graphite layers. The intercalation of the halogen or a halogen compound between the layers increases the interlayer distance on or near the surface of the graphite, facilitating the interlayer insertion and desorption of carrier ions. This may enable the secondary battery to achieve excellent characteristics at high charge / discharge rates. The interlayer distance of graphite can be analyzed using XRD, transmission electron microscopy, EDX (energy dispersive X-ray spectroscopy), or the like.

[0069] Furthermore, since the negative electrode active material of one embodiment of the present invention has a halogen in the surface layer portion, a solvent solvated with carrier ions in an electrolyte solution may be easily desorbed from the surface of the negative electrode active material. The ease of desorption of the solvent solvated with carrier ions may enable a secondary battery to achieve excellent characteristics at high charge / discharge rates.

[0070] The negative electrode active material according to one embodiment of the present invention preferably contains fluorine as the halogen.

[0071] Fluorine has a large electronegativity, and when the negative electrode active material has fluorine in the surface layer portion, it may have the effect of facilitating the elimination of the solvent solvated with the carrier ions on the surface of the negative electrode active material.

[0072] <Conductive agent> 1A, graphene 554 and acetylene black 553 preferably function as a conductive agent. Alternatively, a conductive agent such as graphene 554 or acetylene black 553 may function as an active material. Here, graphene and a graphene compound can be used as graphene 554. Details of the graphene compound will be described later.

[0073] 1A shows an example in which the negative electrode has graphene 554 and acetylene black 553, but the negative electrode may have only one of them. In addition, various materials can be used as a conductive agent for the negative electrode.

[0074] The conductive agent may be a carbon material, a metal material, a conductive ceramic material, or the like. Alternatively, a fibrous material may be used as the conductive agent. The content of the conductive agent relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, more preferably 1 wt% to 5 wt%.

[0075] The conductive agent can form an electrically conductive network in the active material layer. The conductive agent can maintain an electrical conduction path between the negative electrode active materials. By adding the conductive agent to the active material layer, an active material layer with high electrical conductivity can be realized.

[0076] The conductive agent may be a graphene compound, natural graphite, artificial graphite such as mesocarbon microbeads, or carbon fiber.

[0077] Examples of usable carbon fibers include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Furthermore, the carbon fibers can be one or more selected from carbon nanofibers and carbon nanotubes. Carbon nanotubes can be produced, for example, by vapor phase growth. Furthermore, the conductive agent can be one or more selected from carbon materials such as carbon black (e.g., acetylene black (AB)), graphite particles, graphene, and fullerene. Furthermore, the conductive agent can be one or more selected from metal powders, metal fibers, and conductive ceramic materials, for example, copper, nickel, aluminum, silver, and gold.

[0078] [Graphene compounds] In this specification and the like, graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Furthermore, graphene compounds refer to compounds that contain carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may also be referred to as a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a curved shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0079] As the conductive agent, the above-mentioned materials can be used in combination.

[0080] In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0081] In this specification, reduced graphene oxide refers to a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. It may also be called a carbon sheet. Although a single sheet of reduced graphene oxide can function, multiple sheets may also be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is between 2 atomic % and 15 atomic %. By adjusting the carbon and oxygen concentrations in this range, it can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D between the G band and the D band in a Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0082] In a longitudinal cross section of the active material layer, the sheet-like graphene compound is dispersed substantially uniformly in an internal region of the active material layer. The plurality of graphene compounds are formed so as to partially cover the plurality of granular negative electrode active material particles or to be attached to the surfaces of the plurality of granular negative electrode active material particles, and therefore the plurality of graphene compounds are in surface contact with each other.

[0083] Here, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphene compounds together. When an active material is covered with a graphene net, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or can be eliminated, thereby improving the ratio of the active material to the electrode volume and electrode weight. In other words, the charge / discharge capacity of the secondary battery can be increased.

[0084] Here, it is preferable to use graphene oxide as the graphene compound, mix it with an active material to form a layer that will become an active material layer, and then reduce it. That is, the completed active material layer preferably contains reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in polar solvents, to form the graphene compound, the graphene compound can be dispersed approximately uniformly in the internal region of the active material layer. Since the solvent is volatilized and removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compound remaining in the active material layer partially overlaps and is dispersed to such an extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or using a reducing agent.

[0085] Figure 1C shows a schematic diagram of the active material and graphene compound. Unlike granular conductive agents such as acetylene black, which form point contact with the active material, graphene compounds enable surface contact with low contact resistance. Therefore, a smaller amount of graphene compound than a conventional conductive agent can improve the electrical conductivity between the granular negative electrode active material and the graphene compound. This allows for a larger ratio of the negative electrode active material in the active material layer, thereby increasing the discharge capacity of the secondary battery.

[0086] Furthermore, by using a spray dryer in advance, a graphene compound, which is a conductive agent, can be formed as a coating that covers the entire surface of the active material, and further a conductive path can be formed between the active material particles by the graphene compound.

[0087] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO2, SiO x (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a D50 (also called median diameter) of 1 μm or less, more preferably 100 nm or less.

[0088] [Fluorine-modified conductive agent] In the negative electrode of one embodiment of the present invention, the conductive agent is preferably modified with fluorine. For example, the conductive agent may be any of the above-described conductive agents modified with fluorine.

[0089] The conductive agent can be modified with fluorine by, for example, treatment with a fluorine-containing gas, heat treatment, plasma treatment in a fluorine-containing gas atmosphere, etc. Examples of the fluorine-containing gas that can be used include fluorine gas and lower fluorine hydrocarbon gases such as fluoromethane (CF4).

[0090] Alternatively, the conductive agent may be immersed in a solution containing hydrofluoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, or the like, or a solution containing a fluorine-containing ether compound, for example, to modify the conductive agent with fluorine.

[0091] Fluorine modification of the conductive agent is expected to stabilize the structure of the conductive agent and suppress side reactions during the charge and discharge process of the secondary battery. Suppression of side reactions can improve charge and discharge efficiency. Furthermore, capacity reduction due to repeated charge and discharge can be suppressed. Therefore, by using a fluorine-modified conductive agent in the negative electrode of one embodiment of the present invention, an excellent secondary battery can be realized.

[0092] By stabilizing the structure of the conductive agent, the conductive properties are stabilized, and high output characteristics may be achieved.

[0093] <Components of secondary batteries> Furthermore, a fluorine-containing material is preferably used as a component of a secondary battery according to one embodiment of the present invention. For example, a positive electrode according to one embodiment of the present invention preferably includes a fluorine-containing positive electrode active material. As will be described in detail later, the positive electrode active material according to one embodiment of the present invention includes fluorine. The fluorine-containing positive electrode active material has a stable structure during charging and can be repeatedly charged at a high charging voltage. Increasing the charging voltage can increase the energy density of the secondary battery.

[0094] In the positive electrode of one embodiment of the present invention, by using the positive electrode active material containing fluorine in combination with the fluorine-modified conductive agent described above, a synergistic effect can be obtained in the secondary battery, such as realizing high energy density, high output characteristics, and long life.

[0095] Fluorine-containing materials are stable, and their use as components of secondary batteries can stabilize the characteristics and extend the battery life. Therefore, they are preferably used in the separator, electrolyte, or exterior. The separator, electrolyte, and exterior will be described in detail below.

[0096] <Example of negative electrode configuration> For the negative electrode of one embodiment of the present invention, a high-capacity material is used as an active material in combination with graphene or a graphene compound as a conductive agent, whereby a synergistic effect can be obtained, such that a secondary battery having high capacity and high output characteristics can be realized.

[0097] As a high-capacity material, various negative electrode active materials, which will be described later, can be used. Here, as an example, a metal, material, or compound containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium is used as the negative electrode active material. The use of these materials can increase the capacity of secondary batteries. For example, silicon has a dramatically high theoretical capacity of 4200 mAh / g, making it possible to realize high-capacity secondary batteries.

[0098] Examples of silicon-containing materials include SiO x (x is preferably smaller than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0099] As a silicon-containing material, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or multiple silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide around the silicon crystal grain. Furthermore, the silicon oxide may be amorphous.

[0100] Furthermore, examples of compounds that can be used include Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may each be crystalline or amorphous.

[0101] Graphene terminated with fluorine is used as the conductive agent. Figure 1B shows a schematic diagram of graphene terminated with fluorine. While an example in which graphene is terminated with fluorine is shown here, graphene may also be terminated with a functional group containing fluorine. Furthermore, in addition to fluorine and functional groups containing fluorine, graphene may also contain functional groups such as carbonyl groups, carboxyl groups, hydroxyl groups, and ether groups.

[0102] Fluorine-modified conductive agents have excellent conductivity. Electrodes using high-capacity materials are charged and discharged at higher current densities. By using conductive agents with excellent conductivity, high output characteristics can be achieved even in electrodes using high-capacity materials.

[0103] <Example of manufacturing method> The negative electrode active material of one embodiment of the present invention can be manufactured, for example, by mixing a first material that can contribute to a reaction in a secondary battery and a compound having a halogen as a second material, and performing heat treatment on the mixture.

[0104] In addition to the second material, a third material that undergoes a eutectic reaction with the second material may be mixed. The eutectic point resulting from the eutectic reaction is preferably lower than at least one of the melting points of the second material and the third material. The lowering of the melting point due to the eutectic reaction may facilitate the second and third materials to cover the surface of the first material during heat treatment, thereby improving the coating properties.

[0105] Furthermore, by using, as the second material and the third material, materials having a metal whose ions function as carrier ions in the reaction of the secondary battery, when the metal is contained in the negative electrode active material, the metal may contribute to charging and discharging as a carrier ion.

[0106] The third material may be, for example, a material containing oxygen and carbon, such as a carbonate, or an organic compound.

[0107] Alternatively, a hydroxide may be used as the third material.

[0108] Carbonates, hydroxides, etc. are preferred because they are inexpensive and highly safe materials, and carbonates, hydroxides, etc. are also preferred because they may have a eutectic point with a material containing a halogen.

[0109] The negative electrode active material described below may have the effect of increasing the electrical conductivity of the electrode. In addition, when the negative electrode active material has the effect of increasing the electrical conductivity, it may not be a problem if the amount of reaction between carrier ions and the negative electrode active material in the battery reaction is small.

[0110] The method for manufacturing a negative electrode active material described below may be applied to a method for manufacturing a conductive agent. For example, in order to modify graphene as a conductive agent with fluorine, the first material 801 in the flow shown in FIG. 3 described below is graphene, and steps S31 to S53 are performed to obtain fluorine-modified graphene as a conductive material.

[0111] A more specific example of the second material and the third material will be described. When lithium fluoride is used as the second material, when it is mixed with the first material and heated, the lithium fluoride may not cover the surface of the first material and may aggregate on its own. In such cases, the coverage of the surface of the first material may be improved by using a material that undergoes a eutectic reaction with lithium fluoride as the third material.

[0112] As an example of the third material that undergoes a eutectic reaction with lithium fluoride, lithium carbonate will be described.

[0113] Figure 2 is a phase diagram showing the relationship between the ratio of LiF to Li2CO3 and temperature. Figure 2 is based on data from FACT Salt Phase Diagrams. As shown in Figure 2, the melting point of LiF is approximately 850°C, but by mixing Li2CO3, the melting point can be lowered. Therefore, for example, at the same heating temperature, a mixture of LiF and Li2CO3 is more easily melted than when using LiF alone, improving the coating properties on the surface of the first material. It also allows for a lower heating temperature.

[0114] Furthermore, by using a eutectic reaction, the affinity with the surface of the first material can be increased. For example, when graphite is used as the first material, the region of the graphite surface formed by C-H bonds may have low affinity with fluorine. The eutectic reaction between LiF and Li2CO3 improves the affinity between the graphite surface and the fluorine-containing material, thereby improving surface coverage.

[0115] Also, from Figure 2, at point P shown in Figure 2, the molar amount of LiF relative to the total molar amount of LiF and Li2CO3 [LiF / (Li2CO3 + LiF)] is approximately 0.48, and the melting point is lowest. In other words, if the molar ratio of LiF to Li2CO3 is LiF:Li2CO3 = a1:(1-a1), the melting point can be lowest by setting a1 to around 0.48. The temperature T at point P is approximately 615°C.

[0116] By setting a1 to a value greater than 0.48, the surface of the first material can be coated with a material having a higher fluorine content. Therefore, a1 is preferably greater than 0.2, and more preferably 0.3 or greater. However, if the fluorine content is too high, the melting point may increase, resulting in poor coating properties. a1 is preferably less than 0.9, and more preferably 0.8 or less.

[0117] An example of a method for manufacturing a negative electrode active material of one embodiment of the present invention will be described with reference to a flow chart shown in FIG.

[0118] In step S21, a first material 801 is prepared.

[0119] As the first material 801, it is preferable to use a material capable of reacting with carrier ions of the secondary battery, a material capable of inserting and desorbing carrier ions, a material capable of alloying with a metal that becomes a carrier ion, a material capable of dissolving and precipitating a metal that becomes a carrier ion, or the like.

[0120] Examples of carrier ions that can be used in secondary batteries include alkali metal ions such as lithium ions, sodium ions, and potassium ions, and alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions.

[0121] As the first material 801, for example, a carbon material such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene can be used.

[0122] The first material 801 may be, for example, a metal, material, or compound containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium.

[0123] Furthermore, impurity elements such as phosphorus, arsenic, boron, aluminum, or gallium may be added to silicon to lower its resistance.

[0124] Examples of silicon-containing materials include SiO x (x is preferably smaller than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0125] As a silicon-containing material, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or multiple silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide around the silicon crystal grain. Furthermore, the silicon oxide may be amorphous.

[0126] Furthermore, examples of compounds that can be used include Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may each be crystalline or amorphous.

[0127] The silicon-containing compound can be analyzed using NMR, XRD, Raman spectroscopy, or the like.

[0128] The first material 801 may be, for example, an oxide containing one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0129] As the first material 801, a combination of the above-listed metals, materials, compounds, etc. can be used.

[0130] When first material 801 is heated, a reaction with oxygen in the atmosphere may occur during the heating, forming an oxide film on the surface. In the preparation of the negative electrode active material of one embodiment of the present invention, a eutectic reaction between halogen-containing material 802 and oxygen- and carbon-containing material 803 occurs in step S51 described later, which allows heating to be performed at a low temperature, thereby suppressing oxidation reactions and the like on the surface.

[0131] Furthermore, when a carbon material is used as the first material 801, a reaction between the carbon material and oxygen in the atmosphere during heating generates carbon dioxide, which may cause a weight loss of the first material 801 and damage to the surface of the first material 801. Since heating can be performed at a low temperature in the preparation of the negative electrode active material of one embodiment of the present invention, weight loss, surface damage, and the like can be suppressed even when a carbon material is used as the first material.

[0132] Here, graphite is prepared as the first material 801. As the graphite, flake graphite, spherical natural graphite, MCMB, etc. may be used. In addition, the surface of the graphite may be coated with a low-crystalline carbon material.

[0133] In step S22, a halogen-containing material 802 is prepared as a second material. A halogen compound containing a metal A1 can be used as the halogen-containing material 802. For example, the metal A1 can be one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, titanium, vanadium, and niobium. For example, a fluoride or a chloride can be used as the halogen compound. The halogen contained in the halogen-containing material 802 is represented by element Z.

[0134] Here, lithium fluoride is prepared as an example.

[0135] In step S23, a material 803 containing oxygen and carbon is prepared as a third material. For example, a carbonate containing metal A2 can be used as the material 803 containing oxygen and carbon. For example, one or more elements selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel can be used as the metal A2.

[0136] Here, lithium carbonate is prepared as an example.

[0137] Next, in step S31, a first material 801, a material 802 containing halogen, and a material 803 containing oxygen and carbon are mixed, the mixture is recovered in step S32, and a mixture 804 is obtained in step S33.

[0138] The halogen-containing material 802 and the oxygen and carbon-containing material 803 are preferably mixed in a ratio of (halogen-containing material 802):(oxygen and carbon-containing material 803)=a1:(1-a1) [unit: mol], where a1 is preferably greater than 0.2 and less than 0.9, and more preferably greater than 0.3 and less than 0.8.

[0139] Furthermore, it is preferable that the first material 801 and the halogen-containing material 802 are mixed in a ratio of (first material 801):(halogen-containing material 802)=1:b1 [unit: mol], and b1 is preferably 0.001 or more and 0.2 or less.

[0140] Next, in step S51, the mixture 804 is heated.

[0141] Heating in a reducing atmosphere is preferable because it can suppress oxidation of the surface of the first material 801 and reaction between the first material 801 and oxygen. The reducing atmosphere may be, for example, a nitrogen atmosphere or a rare gas atmosphere. A mixture of two or more types of nitrogen and rare gas may also be used. Heating may also be performed under reduced pressure.

[0142] When the melting point of the halogen-containing material 802 is expressed as M2 [°C], the heating temperature is preferably higher than (M2-550) [K] and lower than (M2+50) [K], and more preferably higher than (M2-400) [°C] and lower than (M2) [°C].

[0143] Furthermore, solid-state diffusion of compounds is likely to occur at temperatures equal to or higher than the Tammann temperature. For example, the Tammann temperature is 0.757 times the melting point of an oxide. Therefore, for example, the heating temperature is preferably 0.757 times the eutectic point or higher, or a temperature close to that temperature.

[0144] Furthermore, in the case of lithium fluoride, a representative example of a material containing a halogen, the amount of evaporation increases rapidly above the melting point, so for example, the heating temperature is preferably below the melting point of the material containing a halogen.

[0145] The eutectic point of the halogen-containing material 802 and the oxygen and carbon-containing material 803 is M 23 When expressed as [K], the heating temperature is, for example, (M 23 × 0.7) [K] and lower than (M2 + 50) [K], and 23 × 0.75) [K] or more and (M2 + 20) [K] or less, and (M 23 × 0.75) [K] or more and (M2 + 20) [K] or less, and M 23 It is preferable that the temperature is higher than (M2+10)[K] and lower than (M 23 ×0.8) [K] or more and M2 [K] or less is more preferable, and (M 23 ) [K] or more and M2 [K] or less is more preferable.

[0146] When lithium fluoride is used as the halogen-containing material 802 and lithium carbonate is used as the oxygen- and carbon-containing material 803, the heating temperature is, for example, preferably greater than 350°C and less than 900°C, more preferably 390°C or higher and 850°C or lower, even more preferably 520°C or higher and 910°C or lower, even more preferably 570°C or higher and 860°C or lower, and even more preferably 610°C or higher and 860°C or lower.

[0147] The heating time is, for example, preferably 1 hour or more and 60 hours or less, and more preferably 3 hours or more and 20 hours or less.

[0148] By heating, one or more of element Z, oxygen, carbon, metal A1, and metal A2 may be diffused into the surface layer of first material 801. When first material 801 contains these elements, insertion and desorption of carrier ions may be facilitated in first material 801. Also, desolvation of carrier ions may be facilitated. Alternatively, it may be possible to suppress the collapse of the crystal structure of first material 801 due to repeated insertion and desorption of carrier ions.

[0149] Next, in step S52, the heated mixture is recovered, and in step S53, negative electrode active material 805 is obtained.

[0150] Through the above steps, the negative electrode active material of one embodiment of the present invention can be obtained.

[0151] Next, a negative electrode and a negative electrode active material according to one embodiment of the present invention will be described.

[0152] A negative electrode according to one embodiment of the present invention includes a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may also include a conductive agent, a binder, or the like. The negative electrode active material layer may also include an electrolyte. The presence of the electrolyte in the negative electrode active material layer can facilitate the diffusion of carrier ions in the negative electrode active material layer. The electrolyte can be incorporated into the negative electrode active material layer by mixing the electrolyte into a slurry for forming the negative electrode active material layer and applying the slurry to a negative electrode current collector. Alternatively, the electrolyte can be incorporated into the negative electrode active material layer by applying the slurry to a negative electrode current collector, drying the slurry, and then immersing the negative electrode in a solution containing the electrolyte.

[0153] The negative electrode of one embodiment of the present invention preferably includes a negative electrode current collector, and a negative electrode active material layer is preferably provided over the negative electrode current collector.

[0154] <Negative electrode active material> 4A, 4B, 4C, and 4D show examples of cross sections of negative electrode active material 400. FIG.

[0155] By exposing a cross section of the negative electrode active material 400 by processing, the cross section can be observed and analyzed.

[0156] 4A has a region 401 and a region 402. The region 402 is located outside the region 401. The region 402 is preferably in contact with the surface of the region 401.

[0157] At least a portion of the region 402 preferably includes the surface of the negative electrode active material 400 .

[0158] Region 401 is, for example, a region including the inside of negative electrode active material 400 .

[0159] Region 401 includes the first material 801 described above. Region 402 is a region formed using the halogen-containing material 802 and the oxygen and carbon-containing material 803 described above. Region 402 includes, for example, element Z, oxygen, carbon, metal A1, and metal A2. Element Z is, for example, fluorine or chlorine. Note that region 402 may not include some of element Z, oxygen, carbon, metal A1, and metal A2. Alternatively, the concentration of some of element Z, oxygen, carbon, metal A1, and metal A2 in region 402 may be so low that they cannot be detected by analysis.

[0160] The region 402 may be referred to as a surface layer portion of the negative electrode active material 400 or the like.

[0161] The negative electrode active material 400 can have various forms, such as a single particle, an aggregate of multiple particles, or a thin film.

[0162] The region 401 may be a particle of the first material 801. Alternatively, the region 401 may be an aggregate of a plurality of particles of the first material 801. Alternatively, the region 401 may be a thin film of the first material 801.

[0163] Region 402 may be a part of a particle. For example, region 402 may be the surface layer of a particle. Alternatively, region 402 may be a part of a thin film. For example, region 402 may be the upper layer of a thin film.

[0164] Region 402 may be a coating layer formed on the surface of a particle.

[0165] Furthermore, region 402 may be a region having a bond between an element constituting first material 801 and element Z. For example, the surface of first material 801 may be modified with element Z or a functional group having element Z at region 402 or the interface between region 401 and region 402. Therefore, in the negative electrode active material of one embodiment of the present invention, a bond between an element constituting first material 801 and element Z may be observed. For example, when first material 801 is graphite and element Z is fluorine, a C—F bond may be observed. For example, when first material 801 contains silicon and element Z is fluorine, a Si—F bond may be observed.

[0166] For example, when graphite is used as the first material 801, the region 401 is a graphite particle, and the region 402 is a coating layer of the graphite particle. Alternatively, when graphite is used as the first material 801, the region 401 is a region including the inside of the graphite particle, and the region 402 is a surface layer of the graphite particle.

[0167] The region 402 has, for example, a bond between the element Z and carbon. The region 402 also has, for example, a bond between the element Z and a metal A1. The region 402 also has, for example, a carbonate group.

[0168] When analyzing the negative electrode active material 400 by X-ray photoelectron spectroscopy (XPS), it is preferable to detect element Z, and element Z is preferably detected at a concentration of 1 atomic % or more. In this case, the concentration of element Z can be calculated, for example, by setting the sum of the concentrations of carbon, oxygen, metal A1, metal A2, and element Z to 100%. Alternatively, the concentration of these elements plus the concentration of nitrogen may be calculated to be 100%. Furthermore, the concentration of element Z is, for example, 60 atomic % or less, or, for example, 30 atomic % or less.

[0169] When analyzing negative electrode active material 400 by XPS, it is preferable to detect a peak resulting from a bond between element Z and carbon. Alternatively, a peak resulting from a bond between element Z and metal A1 may be detected.

[0170] When element Z is fluorine and metal A1 is lithium, in the XPS F1s spectrum, a peak suggesting a carbon-fluorine bond (hereinafter, peak F2) is observed at a position near 688 eV, for example, in the energy range higher than 686.5 eV and lower than 689.5 eV, and a peak suggesting a lithium-fluorine bond (hereinafter, peak F1) is observed at a position near 685 eV, for example, in the energy range higher than 683.5 eV and lower than 686.5 eV. The intensity of peak F2 is preferably greater than 0.1 times but less than 10 times the intensity of peak F1, for example, 0.3 times or more but 3 times or less.

[0171] When analyzing the negative electrode active material 400 by XPS, it is preferable that a peak corresponding to carbonate or a carbonate group is observed. In the XPS C1s spectrum, the peak corresponding to carbonate or a carbonate group is observed at a peak position in the vicinity of 290 eV, for example, in an energy range higher than 288.5 eV and lower than 291.5 eV.

[0172] In the example shown in Fig. 4B, region 401 has an area that is not covered by region 402. In the example shown in Fig. 4C, region 402 that covers the recessed area on the surface of region 401 has a large thickness.

[0173] 4D, region 401 includes regions 401a and 401b. Region 401a includes the interior of region 401, and region 401b is located outside region 401a. Region 401b preferably contacts region 402.

[0174] Region 401b is the surface layer of region 401.

[0175] Region 401b contains one or more of element Z, oxygen, carbon, metal A1, and metal A2 contained in region 402. Furthermore, in region 401b, the elements contained in region 402, such as element Z, oxygen, carbon, metal A1, and metal A2, may have a concentration gradient in which the concentration gradually decreases from the surface or near the surface toward the interior.

[0176] The concentration of element Z in region 401b is higher than the concentration of element Z in region 401a. In addition, the concentration of element Z in region 401b is preferably lower than the concentration of element Z in region 402.

[0177] The concentration of oxygen in the region 401b may be higher than the concentration of oxygen in the region 401a, and the concentration of oxygen in the region 401b may be lower than the concentration of oxygen in the region 402.

[0178] When the negative electrode active material of one embodiment of the present invention is measured by energy dispersive X-ray analysis using a scanning electron microscope, it is preferable to detect element Z. Furthermore, the concentration of element Z is preferably 10 atomic % or more and 70 atomic % or less, where the total concentration of element Z and oxygen is 100 atomic %.

[0179] The region 402 has a thickness of, for example, 50 nm or less, more preferably 1 nm or more and 35 nm or less, and even more preferably 5 nm or more and 20 nm or less.

[0180] The region 401b has a thickness of, for example, 50 nm or less, more preferably 1 nm or more and 35 nm or less, and even more preferably 5 nm or more and 20 nm or less.

[0181] When fluorine is used as element Z and lithium is used as metal A1 and metal A2, region 402 may have a region covered with a region containing lithium fluoride and a region covered with a region containing lithium carbonate relative to region 401. Furthermore, region 402 does not inhibit the insertion and extraction of lithium, and therefore an excellent secondary battery can be realized without deteriorating the output characteristics, etc., of the secondary battery.

[0182] <Fluorine-modified graphite> The stabilization energy of the fluorine-modified graphite structure was calculated using first-principles calculations.

[0183] Atomic relaxation calculations were performed using the first-principles electronic structure calculation package VASP (Vienna ab initio Simulation Package). The functional used was GGA+U (DFT-D2), and the pseudopotential was PAW. The cutoff energy was set to 600 eV. The total number of atoms was 144 C (carbon) atoms, 32 H (hydrogen) atoms, 32 F (fluorine) atoms, and 24 Li (lithium) atoms. The k-points were set to 1 × 1 × 1. The lattice and atomic positions were optimized under constant volume conditions for the calculations.

[0184] The stabilization energy ΔE was calculated using the following formula:

[0185]

number

[0186] where E total (C 144H 32-x F x Li y ) is the energy of a model in which F atoms are substituted and Li atoms are introduced into graphite, and E total (H) is the energy of one H atom, E total (F) is the energy of one F atom, and E total (Li) is the energy of one Li atom, and E total (C 144 H 32 ) is the energy of graphite, x is the number of H atoms in graphite replaced by F atoms, and y is the number of Li atoms introduced into the graphite.

[0187] Figure 5 shows the interplanar spacing d of graphite when the number of substituted F atoms is changed. Note that no Li atoms are introduced.

[0188] The horizontal axis in Figure 5 represents the F concentration. When the concentration is 50%, 16 H atoms are replaced with F atoms, and when the concentration is 100%, 32 H atoms, i.e., all H atoms, are replaced with F atoms.

[0189] Even when the F concentration increased up to 50%, the d spacing tended to remain stable. However, when the F concentration exceeded 50%, the d spacing increased, suggesting that the crystal structure became unstable. This is thought to be due to the high density of introduced F atoms and the repulsion between the F atoms, which causes instability.

[0190] Figure 6 shows the calculated graphite structure for an F concentration of 0%, Figure 7 for an F concentration of 50%, and Figure 8 for an F concentration of 100%. F atoms are replaced by H atoms at the edge faces of the graphite. As the F concentration increases, the graphene layers of the graphite appear to become distorted, and the F atoms appear to repel each other.

[0191] FIG. 9 shows the change in stabilization energy ΔE when Li atoms are introduced at F concentrations of 0%, 50% and 100%.

[0192] With increasing Li concentration, the stabilization energy ΔE decreased significantly, suggesting stabilization.

[0193] When fluorine modification is performed on graphite, it was suggested that appropriate addition of fluorine has little effect on the crystal structure and the crystallinity is well maintained.

[0194] This embodiment can be used in appropriate combination with other embodiments.

[0195] (Embodiment 2) In this embodiment, a positive electrode active material of one aspect of the present invention will be described.

[0196] Examples of the positive electrode active material include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, and a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0197] In addition, it is preferable to mix a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as the positive electrode active material with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0198] In addition, as the positive electrode active material, the composition formula Li a Mn b M c O dA lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among elements other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire lithium-manganese composite oxide particle, <a / (b+c)<2、かつc>it is preferable that the composition be 0 0 during discharge and satisfy the relationship 0.26≦(b+c) / d<0.5. The composition of metal, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured using, for example, an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen ratio in the entire lithium-manganese composite oxide particle can be measured using, for example, EDX. In addition, the composition can be determined by using fusion gas analysis and valence evaluation by XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.

[0199] <Example of how to make cobalt-containing materials> Next, an example of a method for producing LiMO2, which is one embodiment of a material that can be used as a positive electrode active material, will be described with reference to FIG. 10. For example, at least one of manganese, cobalt, and nickel can be used as the metal M. Furthermore, the metal M can further contain a metal X in addition to the metals listed above. Furthermore, there are no particular limitations on the substitution position of the metal M. Below, a cobalt-containing material in which the metal X is Mg will be used as an example. Note that the positive electrode active material of one embodiment of the present invention has a crystalline structure of a lithium composite oxide represented by LiMO2, but its composition is not limited to Li:M:O=1:1:2.

[0200] First, in step S11, a composite oxide containing lithium, a transition metal, and oxygen is used as the composite oxide 811. Here, it is preferable to use one or more transition metals containing cobalt.​

[0201] A composite oxide containing lithium, a transition metal, and oxygen can be synthesized by heating a lithium source and a transition metal source in an oxygen atmosphere. The transition metal source is preferably a metal capable of forming a layered rock-salt composite oxide belonging to the space group R-3m with lithium. For example, at least one of manganese, cobalt, and nickel can be used. Aluminum may also be used in addition to these transition metals. That is, the transition metal source may be a cobalt source alone, a nickel source alone, a combination of a cobalt source and a manganese source, a combination of a cobalt source and a nickel source, or a combination of a cobalt source, a manganese source, and a nickel source. Furthermore, an aluminum source may also be used in addition to these metal sources. The heating temperature in this step is preferably higher than that in step S17, which will be described later. For example, the heating step may be performed at 1000°C. This heating step is sometimes referred to as calcination.

[0202] When using a pre-synthesized composite oxide containing lithium, transition metals, and oxygen, it is preferable to use one with few impurities. In this specification, the main components of the composite oxide containing lithium, transition metals, and oxygen, the cobalt-containing material, and the positive electrode active material are lithium, cobalt, nickel, manganese, aluminum, and oxygen, and elements other than the main components are considered impurities. For example, when analyzed by glow discharge mass spectrometry (GD-MS), the total impurity concentration is preferably 10,000 ppmw (parts per million weight) or less, more preferably 5000 ppmw or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppmw or less, more preferably 1500 ppmw or less.

[0203] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as pre-synthesized lithium cobalt oxide. This lithium cobalt oxide has an average particle diameter (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry reveals that the magnesium and fluorine concentrations are 50 ppmw or less, the calcium, aluminum, and silicon concentrations are 100 ppmw or less, the nickel concentration is 150 ppmw or less, the sulfur concentration is 500 ppmw or less, the arsenic concentration is 1100 ppmw or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppmw or less.

[0204] The composite oxide 811 in step S11 preferably has a layered rock-salt crystal structure with few defects and strain. Therefore, it is preferable that the composite oxide has few impurities. If a composite oxide containing lithium, a transition metal, and oxygen contains a large amount of impurities, it is likely to have a crystal structure with many defects or strains.

[0205] In step S12, a fluoride 812 is prepared. Examples of the fluoride 812 that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride (MnF2), iron fluoride (FeF3), chromium fluoride (CrF3), niobium fluoride (NbF5), zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). The fluoride 812 may be any compound that functions as a fluorine source. Therefore, instead of or as part of the fluoride 812, for example, fluorine (F), fluorocarbon (CF), sulfur fluoride (SF, SF, SF, S, F) may be used. 10), oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. may be used and mixed in the atmosphere.

[0206] When the fluoride 812 is a compound having a metal X, it can also serve as the compound 813 (a compound having a metal X) described later.

[0207] In this embodiment, lithium fluoride (LiF) is prepared as the fluoride 812. LiF is preferable because it has a cation in common with LiCoO2. LiF is also preferable because it has a relatively low melting point of 848°C and is easily melted in the heating process described below.

[0208] Furthermore, when LiF is used as fluoride 812, it is preferable to prepare compound 813 (a compound having metal X) in addition to fluoride 812 in step S13. Compound 813 is a compound having metal X. In step S13, compound 813 is prepared. As compound 813, a fluoride, oxide, hydroxide, or the like of metal X can be used, and it is particularly preferable to use a fluoride.

[0209] When magnesium is used as the metal X, MgF2 or the like can be used as the compound 813. Magnesium can be distributed in high concentration near the surface of the cobalt-containing material.

[0210] In addition to the fluoride 812 and the compound 813, a material containing a metal other than cobalt and other than the metal X may be mixed. As the material containing a metal other than cobalt and other than the metal X, for example, at least one of a nickel source, a manganese source, an aluminum source, an iron source, a vanadium source, a chromium source, a niobium source, and a titanium source may be mixed. For example, it is preferable to finely pulverize the hydroxide, fluoride, or oxide of each metal and mix it. The fine pulverization can be performed, for example, by a wet method.

[0211] Furthermore, the order of steps S11, S12 and S13 may be freely combined.

[0212] Next, in step S14, the materials prepared in steps S11, S12, and S13 are mixed and pulverized. Mixing can be performed dry or wet, but wet mixing is preferred because it allows for finer pulverization. If wet mixing is used, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used.

[0213] For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media. It is preferable to thoroughly perform this mixing and grinding process to finely pulverize the powder that will become mixture 814.

[0214] Next, in step S15, the mixed and crushed materials are collected, and in step S16, a mixture 814 is obtained.

[0215] The mixture 814 preferably has a D50 of, for example, 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

[0216] It is more preferable that the temperature is equal to or higher than the melting temperature of the mixture 814. Also, the heating temperature is preferably equal to or lower than the decomposition temperature of LiCoO2 (1130°C).

[0217] By using LiF as the fluoride 812 and heating S17 with a lid on, it is possible to produce a cobalt-containing material 808 with good cycle characteristics, etc. Furthermore, when LiF and MgF2 are used as the fluoride 812, the eutectic point of LiF and MgF2 is around 742°C, so if the heating temperature of S17 is set to 742°C or higher, the reaction with LiCoO2 is promoted, and LiMO2 is produced.

[0218] Furthermore, LiF, MgF2 and LiCoO2 exhibit an endothermic peak in differential scanning calorimetry (DSC) at around 820° C. Therefore, the heating temperature is preferably 742° C. or higher, and more preferably 820° C. or higher.

[0219] Therefore, the heating temperature is preferably 742° C. or higher and 1130° C. or lower, and more preferably 742° C. or higher and 1000° C. or lower. Also, the heating temperature is preferably 820° C. or higher and 1130° C. or lower, and more preferably 820° C. or higher and 1000° C. or lower.

[0220] In addition, in this embodiment, it is believed that LiF, which is a fluoride, functions as a flux. Therefore, since the volume inside the heating furnace is larger than the volume of the container and is lighter than oxygen, it is expected that LiF will volatilize and the amount of LiF in the mixture 814 will decrease, suppressing the generation of LiMO2. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF.

[0221] Therefore, by heating the mixture 814 in an atmosphere containing LiF, that is, by heating the mixture 814 in a state where the partial pressure of LiF is high in the heating furnace, the volatilization of LiF in the mixture 814 is suppressed. By heating with a lid using a fluoride (LiF or MgF) that forms a eutectic mixture, the heating temperature can be lowered to below the decomposition temperature of LiCoO2 (1130°C), specifically to between 742°C and 1000°C, allowing the formation of LiMO2 to proceed efficiently. As a result, a cobalt-containing material with good properties can be produced, and the annealing time can also be shortened.

[0222] An example of the heating method in S17 is shown in FIG.

[0223] The heating furnace 120 shown in FIG. 11 includes a furnace space 102, a hot plate 104, a heater 106, and an insulating material 108. Annealing is preferably performed with a lid 118 attached to the container 116. This configuration allows the space 119 defined by the container 116 and lid 118 to be filled with a fluoride-containing atmosphere. By maintaining the lid during heating to maintain a constant or stable concentration of gasified fluoride in the space 119, fluorine and magnesium can be incorporated near the particle surfaces. Because the space 119 has a smaller volume than the furnace space 102, a small amount of fluoride volatilizes, creating a fluoride-containing atmosphere. In other words, the reaction system can be filled with a fluoride-containing atmosphere without significantly reducing the amount of fluoride contained in the mixture 814. This allows for efficient production of LiMO2. Furthermore, the use of the lid 118 allows the mixture 814 to be heated in a fluoride-containing atmosphere conveniently and inexpensively.

[0224] Here, the valence of Co (cobalt) in LiMO2 produced according to one embodiment of the present invention is preferably approximately trivalent. Cobalt can be divalent or trivalent. Therefore, to suppress the reduction of cobalt, the atmosphere in the heating furnace space 102 preferably contains oxygen, and more preferably the ratio of oxygen to nitrogen in the atmosphere in the heating furnace space 102 is equal to or greater than that of the air atmosphere, and even more preferably the oxygen concentration in the atmosphere in the heating furnace space 102 is equal to or greater than that of the air atmosphere. Therefore, it is necessary to introduce an oxygen-containing atmosphere into the heating furnace space. However, since cobalt atoms with nearby magnesium atoms may be more stable in a divalent state, not all cobalt atoms need to be trivalent.

[0225] Therefore, in one embodiment of the present invention, before heating, a step of creating an oxygen-containing atmosphere in the heating furnace space 102 and a step of placing the container 116 containing the mixture 814 in the heating furnace space 102 are performed. By performing these steps in this order, the mixture 814 can be heated in an atmosphere containing oxygen and fluoride. Furthermore, it is preferable to seal the heating furnace space 102 during heating to prevent gas from being transported to the outside. For example, it is preferable to perform heating without flowing gas.

[0226] There are no particular limitations on the method for creating an oxygen-containing atmosphere in the heating furnace space 102, but examples include a method of evacuating the heating furnace space 102 and then introducing an oxygen-containing gas such as oxygen gas or dry air, and a method of infusing an oxygen-containing gas such as oxygen gas or dry air for a certain period of time. Among these, it is preferable to evacuate the heating furnace space 102 and then introduce oxygen gas (oxygen substitution). Note that the air in the heating furnace space 102 may be considered to be an oxygen-containing atmosphere.

[0227] When the lid 118 is placed on the container 116, an oxygen-containing atmosphere is created, and the container 116 is heated, an appropriate amount of oxygen enters the container 116 through the gap in the lid 118 placed on the container 116, and an appropriate amount of fluoride can be retained in the container 116.

[0228] Furthermore, there is a possibility that fluoride and the like adhering to the inner walls of the container 116 and the lid 118 may fly again due to heating and adhere to the mixture 814 .

[0229] The heating in step S17 is preferably carried out at an appropriate temperature for an appropriate time. The appropriate temperature and time vary depending on conditions such as the size and composition of the particles of the composite oxide 811 in step S11. When the particles are small, a lower temperature or a shorter time may be more preferable than when the particles are large. After the heating in step S17, a step of removing the lid is included.

[0230] For example, when the average particle size (D50) of the particles in step S11 is about 12 μm, the heating time is preferably, for example, 3 hours or more, and more preferably 10 hours or more.

[0231] On the other hand, when the average particle size (D50) of the particles in step S11 is about 5 μm, the heating time is preferably, for example, from 1 hour to 10 hours, and more preferably about 2 hours.

[0232] The temperature-lowering time after heating is preferably, for example, 10 hours or more and 50 hours or less.

[0233] Next, in step S18, the heated material is recovered, and in step S19, a cobalt-containing material 808 is obtained.

[0234] [Positive electrode active material structure] Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock-salt crystal structure is a composite oxide represented by LiMO2. Metal M includes the metals listed above. Furthermore, metal M can include metal X listed above in addition to the metals listed above.

[0235] It is known that the strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal.

[0236] In compounds containing nickel, distortion may occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the influence of the Jahn-Teller effect is suggested to be small, and LiCoO2 may have better durability against charge and discharge at high voltages, which is preferable.

[0237] The positive electrode active material will be described with reference to FIGS.

[0238] The positive electrode active material prepared according to one embodiment of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charge and discharge. Furthermore, the volume change can be reduced. Therefore, the compound can achieve excellent cycle characteristics. Furthermore, the compound can have a stable crystal structure in a high-voltage charged state. Therefore, the compound may be less likely to cause a short circuit when maintained in a high-voltage charged state. In such cases, safety is further improved, which is preferable.

[0239] In this compound, the change in crystal structure and the difference in volume between a fully discharged state and a high-voltage charged state are small when compared per the same number of transition metal atoms.

[0240] The positive electrode active material of one embodiment of the present invention contains lithium, the metal M described above, oxygen, and titanium. The positive electrode active material of one embodiment of the present invention preferably contains a halogen such as fluorine or chlorine.

[0241] The cathode active material of one embodiment of the present invention preferably has a particulate form. When the cathode active material of one embodiment of the present invention has a particulate form, the titanium concentration in the surface layer portion of the particle is higher than the titanium concentration in the interior. The magnesium concentration in the surface layer portion is higher than the magnesium concentration in the interior. The surface layer portion of the cathode active material of one embodiment of the present invention may further have a first region within 10 nm, 5 nm, or 3 nm from the surface toward the interior, in which the magnesium concentration is particularly high. For example, the ratio of magnesium concentration to titanium concentration (Mg / Ti) in the first region may be higher than the ratio of magnesium concentration to titanium concentration (Mg / Ti) in a region of the surface layer located more inward than the first region.

[0242] In addition, in each region such as the surface layer portion, the interior, and the first region in the surface layer portion, the concentration of elements such as metal M, titanium, etc., has a gradient, for example. That is, for example, at the boundary between each region, the concentration of each element does not change abruptly, but changes with a gradient. Here, in addition to cobalt and magnesium, for example, aluminum and nickel can be used as metal M. In such a case, aluminum and nickel each have a concentration gradient, for example, in each region such as the surface layer portion, the interior, and the first region in the surface layer portion.

[0243] A cathode active material according to one embodiment of the present invention has a first region. When the cathode active material according to one embodiment of the present invention has a particulate form, the first region preferably includes a region inside the surface layer portion. At least a portion of the surface layer portion may be included in the first region. The first region preferably has a layered rock-salt structure and is represented by the space group R-3m. The first region is a region containing lithium and a metal M. FIG. 12 shows an example of the crystal structure of the first region before and after charge and discharge. Furthermore, the surface layer portion of the cathode active material according to one embodiment of the present invention may have a crystal containing titanium, magnesium, and oxygen and having a structure different from the layered rock-salt structure, in addition to or instead of the region having a layered rock-salt structure described below in FIG. 12 and the like. For example, the surface layer portion may have a crystal containing titanium, magnesium, and oxygen and having a spinel structure.

[0244] The crystal structure at a charge depth of 0 (discharged state) in Figure 12 is the same as that in Figure 13, R-3m(O3). On the other hand, the first region has a crystal structure different from the H1-3 crystal structure when the charge depth is fully charged. This structure is in the space group R-3m and is not a spinel crystal structure. However, ions such as cobalt and magnesium occupy the oxygen hexacoordination sites, and the cation arrangement has a symmetry similar to that of the spinel structure. Furthermore, the symmetry of the CoO2 layers in this structure is the same as that of the O3 type. Therefore, this structure is referred to herein as an O3' type crystal structure or a pseudospinel type crystal structure. Note that in the diagram of the O3' type crystal structure shown in Figure 12, lithium can be present at any lithium site with a probability of approximately 20%, but this is not limited to this. Lithium may be present only at a specific portion of the lithium sites. In both the O3 type crystal structure and the O3' type crystal structure, it is preferable for magnesium to be present in a dilute amount between the CoO2 layers, i.e., at the lithium sites. Furthermore, halogens such as fluorine may be present randomly and dilutely at the oxygen sites.

[0245] In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen tetracoordination site, and in this case too, the arrangement of ions has a symmetry similar to that of the spinel type.

[0246] The O3'-type crystal structure can also be said to be a crystal structure similar to the CdCl2-type crystal structure, although it has random Li between the layers. This CdCl2-type-like crystal structure was observed when lithium nickel oxide was charged to a charge depth of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0247] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in the O3'-type crystal structure also have a cubic close-packed structure. When these contact, there is a crystal plane where the cubic close-packed structure formed by the anions is aligned. However, the space group of the layered rock salt crystals and the O3'-type crystal structure is R-3m, which is different from the space groups Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry) of rock salt crystals. Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt crystals and the O3'-type crystal structure and the rock salt crystal. In this specification, when the cubic close-packed structure formed by the anions is aligned in the layered rock salt crystals, the O3'-type crystal structure, and the rock salt crystal, the crystal orientation may be said to be approximately aligned.

[0248] In the first region, the change in the crystal structure when a large amount of lithium is released during high-voltage charging is suppressed more than in the comparative example described below. For example, as shown by the dotted line in Figure 12, there is almost no displacement of the CoO2 layers in these crystal structures.

[0249] More specifically, the first region exhibits high structural stability even at high charge voltages. For example, in FIG. 13, the H1-3 crystal structure is formed at a voltage of approximately 4.6 V relative to the potential of lithium metal. However, the cathode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure even at a charge voltage of approximately 4.6 V. Even at higher charge voltages, for example, at voltages of approximately 4.65 V to 4.7 V relative to the potential of lithium metal, the cathode active material of one embodiment of the present invention can also adopt the O3' crystal structure. When the charge voltage is further increased above 4.7 V, the H1-3 crystal structure may finally be observed in the cathode active material of one embodiment of the present invention. Furthermore, at lower charge voltages (for example, even when the charge voltage is 4.5 V or higher but less than 4.6 V relative to the potential of lithium metal), the cathode active material of one embodiment of the present invention may also adopt the O3' crystal structure.

[0250] Note that when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above-mentioned value by the potential of the graphite. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, even when the voltage of a secondary battery using graphite as the negative electrode active material is 4.3 V or higher and 4.5 V or lower, the positive electrode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure. Furthermore, even when the charge voltage is higher, for example, when the voltage of the secondary battery is higher than 4.5 V and lower than 4.6 V, there is a region in which the O3'-type crystal structure can be formed. Furthermore, even when the charge voltage is lower, for example, when the voltage of the secondary battery is 4.2 V or higher but lower than 4.3 V, the positive electrode active material of one embodiment of the present invention can sometimes form the O3'-type crystal structure.

[0251] Therefore, in the first region, the crystal structure is less likely to collapse even when charging and discharging are repeated at a high voltage.

[0252] In addition, in a positive electrode active material according to one embodiment of the present invention, the difference in volume per unit cell between the O3-type crystal structure at a charge depth of 0 and the O3'-type crystal structure at a charge depth of 0.8 is 2.5% or less, more specifically 2.2% or less.

[0253] In addition, the O3' type crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25.

[0254] Magnesium, which exists randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers when charged at high voltage. Therefore, when magnesium exists between the CoO2 layers, the O3'-type crystal structure is easily formed.

[0255] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. Magnesium present in the cobalt site may not be effective in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns that adverse effects such as cobalt being reduced to a divalent state and lithium evaporating may occur.

[0256] Therefore, it is preferable to add a halogen compound such as fluoride to the lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. Adding the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of fluoride is expected to improve corrosion resistance against hydrofluoric acid produced by decomposition of the electrolyte.

[0257] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the positive electrode active material prepared according to one embodiment of the present invention is preferably 0.001 to 0.1 times the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably approximately 0.02. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the preparation of the positive electrode active material.

[0258] The number of nickel atoms in the positive electrode active material of one embodiment of the present invention is preferably 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, and more preferably 0.1% to 2%. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0259] <Particle size> If the particle size of the positive electrode active material of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte occur. Therefore, the average particle size (D50) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0260] <Analysis method> Whether a certain positive electrode active material exhibits the O3'-type crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can provide sufficient accuracy even when measuring the positive electrode obtained by disassembling a secondary battery.

[0261] As described above, the positive electrode active material of one embodiment of the present invention is characterized by minimal change in crystal structure between the high-voltage charged state and the discharged state. Materials in which 50 wt% or more of a crystal structure exhibiting a significant change from the discharged state during high-voltage charging are undesirable because they cannot withstand high-voltage charging and discharging. It should be noted that the desired crystal structure may not be achieved simply by adding impurity elements. For example, even if both materials share the common feature of being lithium cobalt oxide containing magnesium and fluorine, there are cases in which the O3'-type crystal structure accounts for 60 wt% or more during high-voltage charging, and cases in which the H1-3-type crystal structure accounts for 50 wt% or more. Furthermore, at a certain voltage, the O3'-type crystal structure may be nearly 100 wt%, and further increasing the voltage may result in the H1-3-type crystal structure. Therefore, it is preferable to analyze the crystal structure of the positive electrode active material of one embodiment of the present invention using XRD or other methods. By combining these methods with measurements such as XRD, more detailed analysis can be performed.

[0262] However, when positive electrode active materials are charged or discharged at high voltage, their crystal structure may change when exposed to air. For example, they may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is recommended that all samples be handled in an inert atmosphere, such as an argon-containing atmosphere.

[0263] The positive electrode active material shown in Fig. 13 is lithium cobalt oxide (LiCoO2) to which no metal X is added. The crystal structure of the lithium cobalt oxide shown in Fig. 13 changes depending on the depth of charge.

[0264] As shown in Figure 13, lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0265] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0266] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.8 has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as an H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 13 and other parts of this specification, for ease of comparison with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0267] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 crystal structure can be expressed as Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, the O3' crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' crystal structure and the H1-3 structure, and that the O3' crystal structure exhibits smaller changes from the O3 structure than the H1-3 structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (good of fitness) value is smaller in Rietveld analysis of XRD.

[0268] When lithium cobalt oxide is repeatedly charged and discharged at a high voltage of 4.6 V or higher, based on the redox potential of lithium metal, or at a deep charge depth of 0.8 or higher, the crystal structure of the lithium cobalt oxide changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0269] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 13, in the H1-3 type crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0270] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0271] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0272] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is thought to be because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0273] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0274] (Embodiment 3) In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0275] <Step S61> In step S61 of FIG. 14, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen.

[0276] As the lithium source, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, etc. can be used.

[0277] The transition metal M is preferably a metal that can form a layered rock-salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, as the source of the transition metal M, only cobalt may be used, only nickel may be used, or two types of cobalt and manganese, or two types of cobalt and nickel, or three types of cobalt, manganese, and nickel may be used.

[0278] When using metals capable of forming a layered rock-salt complex oxide, it is preferable to mix cobalt, manganese, and nickel in a ratio that allows a layered rock-salt crystal structure to be formed. Aluminum may also be added to these transition metals in a ratio that allows a layered rock-salt crystal structure to be formed.

[0279] As the transition metal M source, oxides, hydroxides, etc. of the metals exemplified above as the transition metal M can be used. As the cobalt source, for example, cobalt oxide and cobalt hydroxide can be used. As the manganese source, manganese oxide and manganese hydroxide can be used. As the nickel source, nickel oxide and nickel hydroxide can be used. As the aluminum source, aluminum oxide and aluminum hydroxide can be used.

[0280] <Step S62> Next, in step S62, the lithium source and the transition metal M source are mixed. Mixing can be performed by a dry method or a wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding medium.

[0281] <Step S63> Next, in step S63, the mixed materials are heated. This step is sometimes referred to as calcination or first heating to distinguish it from subsequent heating steps. Heating is preferably performed at a temperature of 800°C or higher but lower than 1100°C, more preferably 900°C or higher but lower than 1000°C, and even more preferably around 950°C. Alternatively, 800°C or higher but lower than 1000°C is preferred. Alternatively, 900°C or higher but lower than 1100°C is preferred. If the temperature is too low, the decomposition and melting of the lithium source and transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal used as the transition metal M, which is responsible for the redox reaction, or lithium evaporation. For example, if cobalt is used as the transition metal M, defects may occur due to the cobalt becoming divalent.

[0282] The heating time can be, for example, from 1 hour to 100 hours, preferably from 2 hours to 20 hours. Alternatively, from 1 hour to 20 hours is preferred. Alternatively, from 2 hours to 100 hours is preferred. Firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or less, more preferably -100°C or less). For example, heating is preferably carried out at 1000°C for 10 hours, with a temperature increase rate of 200°C / h and a flow rate of the dry atmosphere of 10 L / min. The heated material can then be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably from 10 hours to 50 hours.

[0283] However, cooling to room temperature in step S63 is not essential, and cooling to a temperature higher than room temperature may be performed if there is no problem in carrying out the subsequent steps S81 to S83.

[0284] <Step S64> Next, in step S64, the calcined material is recovered to obtain a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen. Specifically, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is substituted with manganese, lithium cobalt oxide in which some of the cobalt is substituted with nickel, or lithium nickel-manganese-cobalt oxide is obtained.

[0285] Alternatively, a composite oxide containing lithium, a transition metal M, and oxygen that has been synthesized in advance may be used in step S64, in which case steps S61 to S63 can be omitted.

[0286] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as a pre-synthesized composite oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0287] Alternatively, lithium cobalt oxide particles (product name: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This is lithium cobalt oxide with an average particle size (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0288] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0289] <Step S71> Next, in step S71, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. It is also preferable to prepare a lithium source.

[0290] Examples of fluorine sources include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4, TiF3), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride (MnF2, MnF3), iron fluoride (FeF2, Fe Examples of fluorine sources that can be used include fluorine fluoride (CrF2, CrF3), chromium fluoride (CrF2, CrF3), niobium fluoride (NbF5), zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). A mixture of multiple fluorine sources may also be used. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the heating process described below.

[0291] As the chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used.

[0292] As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used.

[0293] Examples of lithium sources include lithium fluoride and lithium carbonate. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0294] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The melting point is most effectively lowered when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, excessive lithium fluoride can lead to excessive lithium, which can degrade cycle characteristics. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0≦x≦1.9), more preferably LiF:MgF2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF2 = x:1 (near x = 0.33). In this specification, "near" refers to a value greater than 0.9 times but less than 1.1 times the value.

[0295] If the subsequent mixing and grinding steps are performed wet, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used.

[0296] <Step S72> Next, in step S72, the materials for the mixture 902 are pulverized and mixed. Mixing can be performed by either a dry or wet method, but a wet method is preferred because it allows for finer pulverization. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the pulverizing medium. It is preferable to thoroughly perform this mixing and pulverization process to finely pulverize the mixture 902.

[0297] <Step S73> Next, in step S73, the mixed and crushed materials are collected to obtain a mixture 902.

[0298] The D50 (median diameter) of the mixture 902 is preferably, for example, 600 nm to 20 μm, more preferably 1 μm to 10 μm, or more preferably 600 nm to 10 μm, or more preferably 1 μm to 20 μm. If the mixture 902 is finely powdered in this manner, when it is mixed with a composite oxide containing lithium, a transition metal M, and oxygen in a later step, the mixture 902 can be easily distributed uniformly on the surfaces of the composite oxide particles.

[0299] <Step S81> Next, in step S81, the LiMO obtained in step S64 is mixed with mixture 902. The ratio of the number of transition metal atoms M in the composite oxide containing lithium, transition metal, and oxygen to the number of magnesium atoms Mg in mixture 902 is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0300] The mixing in step S81 is preferably performed under milder conditions than those in step S62 so as not to destroy the composite oxide particles. For example, it is preferable to perform the mixing under conditions with a lower rotation speed or shorter time than those in step S62. It can also be said that a dry method is less likely to destroy particles than a wet method. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0301] <Step S82> Next, in step S82, the mixed materials are collected to obtain a mixture 903.

[0302] Although this embodiment describes a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities, one embodiment of the present invention is not limited to this. Instead of the mixture 903 in step S82, a lithium cobalt oxide starting material to which a magnesium source, a fluorine source, and the like are added and then fired may be used. In this case, there is no need to separate steps S61 to S64 from steps S71 to S73, which simplifies the process and increases productivity.

[0303] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used. If lithium cobalt oxide to which magnesium and fluorine have been added is used, the steps up to step S82 can be omitted, which is simpler.

[0304] Alternatively, a magnesium source and a fluorine source may be further added to lithium cobalt oxide to which magnesium and fluorine have been added in advance.

[0305] <Step S83> Next, in step S83, the mixture 903 is heated in an atmosphere containing oxygen. This step is sometimes referred to as the first heating (first temperature conditions) to distinguish it from other heating steps. It is more preferable that this heating be performed under conditions that have an adhesion suppression effect so that the particles of the mixture 903 do not adhere to each other.

[0306] Examples of heating that has the effect of suppressing adhesion include heating while stirring the mixture 903, heating while vibrating the container containing the mixture 903, and the like.

[0307] The heating temperature in step S83 must be equal to or higher than the temperature at which the reaction between LiMO2 and mixture 902 proceeds. The temperature at which the reaction proceeds here means any temperature at which mutual diffusion of elements contained in LiMO2 and mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in salts and oxides, solid-state diffusion begins at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td).

[0308] However, the reaction proceeds more easily if the temperature is equal to or higher than the temperature at which at least a portion of mixture 903 melts. Therefore, the heating temperature is preferably equal to or higher than the eutectic point of mixture 902. When mixture 902 contains LiF and MgF2, the temperature in step S83 is preferably equal to or higher than the eutectic point of 742°C.

[0309] Furthermore, in the mixture 903, which is mixed so that the molar ratio of LiCoO2:LiF:MgF2 is 100:0.33:1, an endothermic peak is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, a heating temperature of 830°C or higher is more preferable. The mixture 903 contains at least fluorine, lithium, cobalt, and magnesium. The mixture 903 also has an O3'-type crystal structure.

[0310] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is increased.

[0311] However, the heating temperature must be below the decomposition temperature of LiMO2 (1130°C in the case of LiCoO2). At temperatures close to the decomposition temperature, there is a concern that LiMO2 may decompose, albeit in a small amount. Therefore, the heating temperature is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0312] Therefore, the heating temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, the heating temperature is preferably 742°C to 1130°C, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, the heating temperature is preferably 830°C to 1130°C, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0313] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range.

[0314] In the fabrication method described in this embodiment, some materials, such as LiF, a fluorine source, function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of LiMO2, for example, between 742°C and 950°C, and allows additives such as magnesium to be distributed more highly in the surface layer than in the center, resulting in the fabrication of a positive electrode active material with excellent characteristics.

[0315] However, because LiF is lighter than oxygen molecules, it can volatilize and dissipate when heated. In this case, the amount of LiF in the mixture 903 decreases, weakening its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li and F on the LiMO2 surface may react to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0316] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, the volatilization of LiF in the mixture 903 can be suppressed.

[0317] Heating is preferably performed for an appropriate time. The appropriate heating time varies depending on conditions such as the heating temperature, the size and composition of the LiMO particles in step S64, etc. If the particles are small, a lower temperature or shorter heating time may be more preferable than if the particles are large.

[0318] For example, when the average particle size (D50) of the particles in step S64 is about 12 μm, the heating temperature is preferably, for example, 600° C. or more and 950° C. or less. The heating time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0319] On the other hand, when the average particle size (D50) of the particles in step S73 is about 5 μm, the heating temperature is preferably, for example, 600° C. to 950° C. The heating time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0320] The temperature-lowering time after heating is preferably, for example, 10 hours or more and 50 hours or less.

[0321] <Step S84> In step S84, the mixture is crushed and mixed if necessary. After mixing, the powder is preferably recovered and sieved.

[0322] <Step S91> Next, in step S91, an additive source is prepared. The additive may be, for example, one or more selected from nickel, aluminum, manganese, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. In step S91, an example in which an aluminum source is used as the additive source will be described.

[0323] The additives can be mixed by, for example, a solid phase method, a sol-gel method, a sputtering method, a mechanochemical method, a CVD method, etc. A combination of these methods may also be used.

[0324] <Step S92> Next, in step S92, an additive source is prepared. The additive may be, for example, one or more selected from nickel, aluminum, manganese, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. In step S92, an example in which a nickel source is used as the additive source will be described.

[0325] The additives can be mixed by, for example, a solid phase method, a sol-gel method, a sputtering method, a mechanochemical method, a CVD method, etc. A combination of these methods may also be used.

[0326] <Step S101> Next, in step S101, the heated mixture 903 is mixed with an additive source. It can be said that the additive is contained in the surface of the heated mixture 903.

[0327] Examples of the mixing method that can be used include a solid phase method, a sol-gel method, a sputtering method, a mechanochemical method, a CVD method, a spray-drying method, etc. The solid phase method and the sol-gel method are preferable because they allow the additive to be easily incorporated into the surface of the mixture 903 after heating at atmospheric pressure and room temperature.

[0328] The precipitate is recovered from the mixed solution after the above treatment. The recovery method can be filtration, centrifugation, evaporation to dryness, spray drying, or the like. In this embodiment, the precipitate is recovered by evaporation to dryness. In this embodiment, the precipitate is dried by ventilation at 95°C.

[0329] <Step S102> Next, in step S102, the dried material is collected to obtain a mixture 904.

[0330] <Step S103> Next, the mixture 904 synthesized in step S102 is heated. (If S83 is referred to as the first heating, the heating in S103 may be referred to as the second heating (second temperature conditions).) The heating time is preferably maintained at the specified temperature for 50 hours or less, more preferably 2 to 10 hours, and even more preferably 1 to 3 hours.

[0331] The temperature range of the specified temperature is preferably 500°C or higher and 1200°C or lower, and more preferably 800°C or higher and 1000°C or lower.

[0332] It is also preferable to heat in an atmosphere containing oxygen.

[0333] In this embodiment, the specified temperature is set to 800° C. and is maintained for two hours, the temperature is increased at a rate of 200° C. / h, and the flow rate of the dry atmosphere is set to 10 L / min.

[0334] <Step S104> In step S104, crushing is carried out, and mixing is carried out if necessary.

[0335] <Step S106> Next, in step S106, the crushed material is recovered to produce the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. By sieving, if the positive electrode active material particles are stuck together, this can be resolved.

[0336] (Fourth embodiment) In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS.

[0337] <Configuration example 1 of secondary battery> The following description will be given taking as an example a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.

[0338] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive agent and a binder.

[0339] [Negative electrode active material] The negative electrode active material may be any of the negative electrode active materials described in the above embodiment. Alternatively, a combination of the negative electrode active materials described in the above embodiment may be used as the negative electrode active material.

[0340] As the conductive agent, the conductive agent described in the previous embodiment can be used.

[0341] [Binder] 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. Also, fluororubber can be used as the binder.

[0342] 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 selected from 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 aforementioned rubber material.

[0343] Alternatively, 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, and nitrocellulose as the binder.

[0344] The binder may be used in combination with two or more of the above.

[0345] For example, a material with particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjusting effect. Furthermore, as a water-soluble polymer with particularly excellent viscosity adjusting effect, one or more selected from the aforementioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch may be used.

[0346] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with the active material and other components when preparing electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0347] Water-soluble polymers stabilize viscosity by dissolving in water and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl or carboxyl groups, and the functional groups are expected to allow interactions between polymers, resulting in widespread coverage of the active material surface.

[0348] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and suppress decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable for the passive film to suppress electrical conductivity and also to conduct lithium ions.

[0349] [Current collector] Positive and negative electrode current collectors can be made of highly conductive materials that do not alloy with carrier ions such as lithium, such as metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, and titanium, as well as alloys thereof. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. They can also be made of metal elements that react with silicon to form silicides. Metal elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collectors can be in various shapes, such as sheet, mesh, punched metal, and expanded metal. The current collectors should preferably have a thickness of 10 μm to 30 μm.

[0350] The negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium.

[0351] A titanium compound may be provided as a current collector by being laminated on the metal element shown above. Examples of titanium compounds include titanium nitride, titanium oxide, titanium nitride in which part of the nitrogen is substituted with oxygen, titanium oxide in which part of the oxygen is substituted with nitrogen, and titanium oxynitride (TiO x N yOne selected from (0 < x < 2, 0 < y < 1), or two or more can be mixed or laminated and used. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxidation. By providing a titanium compound on the surface of the current collector, for example, the reaction between the material and the metal in the active material layer formed on the current collector can be suppressed. When the active material layer contains a compound having oxygen, the oxidation reaction between the metal element and oxygen can be suppressed. For example, when aluminum is used as the current collector and the active material layer is formed using graphene oxide described later, there may be a concern about the oxidation reaction between the oxygen in graphene oxide and aluminum. In such a case, by providing a titanium compound on aluminum, the oxidation reaction between the current collector and graphene oxide can be suppressed.

[0352] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material and may have a conductive agent and a binder. As the positive electrode active material, the positive electrode active material produced by the production method described in the previous embodiment is used.

[0353] As the conductive agent and the binder that the positive electrode active material layer can have, the same materials as the conductive agent and the binder that the negative electrode active material layer can have can be used.

[0354] [Electrolyte] As the electrolyte, an electrolytic solution containing a solvent and a salt having carrier ions can be used. Also, a solid electrolyte can be used as the electrolyte.

[0355] The electrolyte, which includes a solvent and a salt having a carrier ion, is described below. The solvent for the electrolyte is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone, or any combination and ratio of two or more of these.

[0356] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the electrolyte solvent, it is possible to prevent the secondary battery from short-circuiting its internal region and from exploding or catching fire when the internal region temperature rises due to overcharging or other reasons. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0357] Furthermore, a fluorine-containing organic solvent can be used as the solvent for the electrolyte. Examples of the fluorine-containing organic solvent include fluorinated carbonate, fluorinated carboxylic acid ester, and fluorine-containing ether compound.

[0358] For example, tetrafluoroethylene carbonate (F4EC) represented by the following chemical formula (1) can be used.

[0359] [ka]

[0360] Fluorinated cyclic carbonates can improve non-flammability and enhance the safety of lithium ion secondary batteries.

[0361] Also, difluoroethylene carbonate (DFEC, F2EC) represented by the following chemical formula (2) can be used.

[0362] [ka]

[0363] Furthermore, monofluoroethylene carbonate (FEC, F1EC) represented by the following chemical formula (3) can be used.

[0364] [ka]

[0365] In addition, examples of salts that can be dissolved in the above solvents include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2 can be used alone or in any combination and ratio of two or more of these.

[0366] The electrolyte used in the secondary battery is preferably a highly purified electrolyte with a low content of granular waste and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0367] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the added material may be, for example, 0.1 wt% to 5 wt% of the total solvent.

[0368] Alternatively, a polymer gel electrolyte in which a polymer is swollen with an electrolyte may be used.

[0369] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0370] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0371] Examples of polymers that can be used include polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0372] An example of a solid electrolyte is described below. It is possible to use a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymeric materials such as polyethylene oxide (PEO). When a solid electrolyte is used, the installation of a separator and / or spacer is unnecessary. Furthermore, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.

[0373] [Separator] A separator is placed between the positive electrode and the negative electrode. The separator can be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0374] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0375] Coating with a ceramic material improves oxidation resistance, thereby suppressing separator deterioration during high-voltage charge / discharge and improving the reliability of the secondary battery. Coating with a fluorine-based material also facilitates adhesion between the separator and electrodes, improving output characteristics. Coating with a polyamide material, especially aramid, improves heat resistance, improving the safety of the secondary battery. Coating the surface of the separator or electrode layer with a ceramic material can prevent the separator from coming into direct contact with the active material.

[0376] 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.

[0377] 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 capacity per volume of the secondary battery can be increased.

[0378] [Exterior body] The exterior of a secondary battery can be made of one or more materials selected from metal materials such as aluminum and resin materials. Film-like exteriors can also be used. Examples of films include a three-layer structure consisting of a membrane made of polyethylene, polypropylene, polycarbonate, ionomer, polyamide, or other material, a thin, flexible metal film made of aluminum, stainless steel, copper, nickel, or other material, and a further insulating synthetic resin film made of polyamide resin or polyester resin, which serves as the exterior of the exterior. Fluororesin films are also preferred. Fluororesin films are highly stable against acids, alkalis, organic solvents, and other factors, and can suppress side reactions and corrosion associated with secondary battery reactions, thereby achieving superior secondary batteries. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylene propene copolymer: a copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylene tetrafluoroethylene copolymer: a copolymer of tetrafluoroethylene and ethylene).

[0379] <Configuration example 2 of secondary battery> As an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte layer will be described below.

[0380] As shown in FIG. 15A, a secondary battery 440 according to one embodiment of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0381] The positive electrode 410 includes a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 includes a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is formed using the positive electrode active material formed by the method described in the above embodiment. The positive electrode active material layer 414 may include a conductive agent and a binder.

[0382] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0383] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive agent and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 15B. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 440.

[0384] As the solid electrolyte 421 of the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0385] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0386] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON-type crystal structure (Li 1-X Al X Ti 2-X(PO4)3, etc.), materials with garnet-type crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON-type crystal structure (Li 14 ZnGeO 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide glass-ceramics (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0387] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0388] Also, different solid electrolytes may be mixed and used.

[0389] Among them, Li with NASICON type crystal structure 1+x Al x Ti 2-x Since (PO4)3(0[x[1]) (hereinafter referred to as LATP) contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 440 of one embodiment of the present invention, a synergistic effect in improving cycle characteristics can be expected, which is preferable. Furthermore, improved productivity can be expected due to a reduction in the number of steps. In this specification and elsewhere, the NASICON-type crystal structure refers to a compound represented by M2(AO4)3 (M: transition metal, A: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and AO4 tetrahedra are arranged three-dimensionally with vertices shared.

[0390] [Shapes of exterior body and secondary battery] The exterior of the secondary battery 440 of one embodiment of the present invention can be made of various materials and in various shapes, and preferably has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0391] For example, Figure 16 shows an example of a cell for evaluating materials for all-solid-state batteries.

[0392] 16A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and one or both of a fixing screw and a wing nut 764 that secure them together, and electrode plate 753 is pressed to fix the evaluation material by rotating a holding screw 763. An insulator 766 is provided between lower member 761 and upper member 762, both of which are made of stainless steel. An O-ring 765 is also provided between upper member 762 and holding screw 763 to provide a tight seal.

[0393] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 16B.

[0394] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Figure 16C. Note that the same reference numerals are used for the same parts in Figures 16A, 16B, and 16C.

[0395] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0396] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0397] Fig. 17A shows a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 16. The secondary battery in Fig. 17A has external electrodes 771 and 772 and is sealed in an exterior body having multiple package members.

[0398] An example of a cross section taken along the dashed line in Figure 17A is shown in Figure 17B. A laminate including positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is enclosed and sealed within package member 770a, which is a flat plate with electrode layer 773a provided thereon, frame-shaped package member 770b, and package member 770c, which is a flat plate with electrode layer 773b provided thereon. Package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[0399] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0400] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0401] (Embodiment 5) In this embodiment, an example of the shape of a secondary battery having the positive electrode described in the previous embodiment will be described. The description in the previous embodiment can be referred to for materials used in the secondary battery described in this embodiment.

[0402] <Coin-type secondary battery> First, an example of a coin-type secondary battery will be described. Fig. 18A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 18B is a cross-sectional view thereof.

[0403] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0404] In addition, in the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layer may be formed on only one surface of each.

[0405] Positive electrode can 301 and negative electrode can 302 can be made of metals such as nickel, aluminum, titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, to prevent corrosion by the electrolyte, it is preferable to coat them with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0406] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 18B, the positive electrode can 301 is placed downward, and the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, to produce a coin-type secondary battery 300.

[0407] By using the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can have high charge / discharge capacity and excellent cycle characteristics.

[0408] Here, we will explain the current flow during charging of a secondary battery using Figure 18C. When a lithium secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In lithium secondary batteries, the anode (positive electrode) and cathode (negative electrode) are interchanged during charging and discharging, and the oxidation and reduction reactions are alternated. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Therefore, in this specification, whether during charging, discharging, when a reverse pulse current is applied, or when a charging current is applied, the positive electrode will be called the "positive electrode" or "+ electrode," and the negative electrode will be called the "negative electrode" or "- electrode." Using the terms anode (positive electrode) or cathode (negative electrode), which are related to oxidation and reduction reactions, may lead to confusion because they are reversed during charging and discharging. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode (positive electrode) or cathode (negative electrode) are used, it should be clearly stated whether they are used during charging or discharging, and whether they correspond to the positive electrode (plus pole) or negative electrode (minus pole).

[0409] A charger is connected to the two terminals shown in Fig. 18C to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0410] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to Fig. 19. Fig. 19A shows an external view of a cylindrical secondary battery 600. Fig. 19B is a schematic diagram showing a cross section of the cylindrical secondary battery 600. As shown in Fig. 19B, the cylindrical secondary battery 600 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 the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0411] 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 a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 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). To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the interior of the battery can 602, where the battery element is provided. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0412] Because the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active materials on both sides of the current collector. 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. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element can be made of barium titanate (BaTiO3)-based semiconductor ceramics or the like.

[0413] 19C , a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between conductive plates 613 and 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0414] FIG. 19D is a top view of module 615. For clarity, conductive plate 613 is shown with dotted lines. As shown in FIG. 19D, module 615 may have conductors 616 that electrically connect multiple secondary batteries 600. A conductive plate can be superimposed on the conductors 616. Furthermore, a temperature control device 617 may be provided between multiple secondary batteries 600. When a secondary battery 600 overheats, it can be cooled by the temperature control device 617, and when a secondary battery 600 is too cold, it can be heated by the temperature control device 617. This makes the performance of module 615 less susceptible to the influence of the outside air temperature. The heat medium in temperature control device 617 is preferably insulating and non-flammable.

[0415] By using the positive electrode active material described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 can have high charge / discharge capacity and excellent cycle characteristics.

[0416] <Example of secondary battery structure> Another structural example of the secondary battery will be described with reference to FIGS.

[0417] 20A and 20B are diagrams showing the appearance of a battery pack. The battery pack has a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to an antenna 914 via the circuit board 900. A label 910 is attached to the secondary battery 913. Furthermore, as shown in FIG. 20B, the secondary battery 913 is connected to terminals 951 and 952. The circuit board 900 is fixed with a sticker 915.

[0418] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to a terminal 951, a terminal 952, an antenna 914, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0419] The circuit 912 may be provided on the back surface of the circuit board 900. The antenna 914 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Also, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0420] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 913. The layer 916 can be made of, for example, a magnetic material.

[0421] The circuit 912 is preferably a circuit unit having a function of controlling a secondary battery. The circuit 912 may be a memory circuit including a transistor using an oxide semiconductor. 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.

[0422] The oxide semiconductor used in a transistor is preferably a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) may be used. In particular, the In-M-Zn oxide that can be used as the metal 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. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each of which has a 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 on which 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, the CAAC-OS has a region where multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a location where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with a different uniform lattice arrangement in the region where multiple crystalline regions are connected. In other words, the CAAC-OS is an oxide semiconductor that is c-axis oriented but not clearly oriented in the ab-plane direction. A CAC-OS is, for example, a material in which elements constituting a metal oxide are unevenly distributed within a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof. In the following, a state in which one or more metal elements are unevenly distributed in a metal oxide and regions containing the metal elements are mixed in a size of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a size close to this size, is also referred to as a mosaic or patch state.

[0423] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0424] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0425] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0426] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0427] For example, in the case of a CAC-OS made of an In-Ga-Zn oxide, EDX mapping obtained using EDX confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0428] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0429] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0430] Furthermore, since the circuit 912 functioning as a control circuit can be used in a high-temperature environment, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the circuit 912 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 secondary battery is heated than that of a single-crystal Si transistor. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of the 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.

[0431] The circuit 912, which uses a memory circuit including a transistor using an oxide semiconductor, can also function as an automatic control device for a secondary battery 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 a 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 circuit 912 has at least one of these functions. Furthermore, the automatic control device for a secondary battery can be miniaturized.

[0432] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0433] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0434] In addition to detecting micro-shorts, circuit 912 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0435] The structure of the battery pack is not limited to that shown in FIG.

[0436] For example, as shown in Figures 21A and 21B, an antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 20A and 20B. Figure 21A is an external view showing one of the pair of surfaces, and Figure 21B is an external view showing the other of the pair of surfaces. Note that for the same parts as those of the secondary battery shown in Figures 20A and 20B, the description of the secondary battery shown in Figures 20A and 20B can be used as appropriate.

[0437] 21A, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in Fig. 21B, an antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The layer 917 has a function of, for example, being able to shield an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0438] The above structure allows the sizes of both antenna 914 and antenna 918 to be increased. Antenna 918 has a function of, for example, performing data communication with an external device. For example, an antenna having a shape applicable to antenna 914 can be used as antenna 918. As a communication method between the secondary battery and other devices via antenna 918, a response method that can be used between the secondary battery and other devices, such as NFC (near field wireless communication), can be used.

[0439] Alternatively, as shown in Fig. 21C, a display device 920 may be provided on the secondary battery 913 shown in Figs. 20A and 20B. The display device 920 is electrically connected to the terminal 911. Note that the label 910 does not need to be provided on the portion where the display device 920 is provided. Note that the description of the secondary battery shown in Figs. 20A and 20B can be used as appropriate for the same portions as those of the secondary battery shown in Figs. 20A and 20B.

[0440] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored power. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0441] Alternatively, as shown in Fig. 21D, a sensor 921 may be provided in the secondary battery 913 shown in Fig. 20A and 20B. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. Note that the description of the secondary battery shown in Fig. 20A and 20B can be used as appropriate for the same parts as those of the secondary battery shown in Fig. 20A and 20B.

[0442] The sensor 921 may have a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared ray. By providing the sensor 921, for example, data indicating the environment in which the secondary battery is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0443] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0444] 22A has a wound body 950 in which terminals 951 and 952 are provided in the internal region of housing 930. The wound body 950 is impregnated with an electrolyte solution in the internal region of housing 930. Terminal 952 contacts housing 930, and terminal 951 is not in contact with housing 930 by using an insulating material or the like. Note that in FIG. 22A, for convenience, housing 930 is shown separated, but in reality, wound body 950 is covered by housing 930, and terminals 951 and 952 extend outside housing 930. Housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0445] 22B, the housing 930 shown in Fig. 22A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 22B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by housings 930a and 930b.

[0446] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, an antenna such as the antenna 914 may be provided in an internal region of the housing 930a. The housing 930b can be made of, for example, a metal material.

[0447] 22C shows the structure of wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the resulting laminated sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked one on top of the other.

[0448] 20 via one of terminal 951 and terminal 952. The positive electrode 932 is connected to terminal 911 shown in FIG.

[0449] Alternatively, a secondary battery 913 may be provided having a wound body 950a as shown in FIGS. 23A to 23C. The wound body 950a shown in FIG. 23A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a. The separator 933 has a width greater than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable because of its high safety and productivity.

[0450] 23B, negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. Positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0451] 23C, wound body 950a and the electrolyte are covered with casing 930 to form secondary battery 913. It is preferable that casing 930 be provided with a safety valve, an overcurrent protection element, and the like.

[0452] As shown in Fig. 23B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a secondary battery 913 with a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 23A and 23B, the descriptions of the secondary battery 913 shown in Figs. 22A to 22C can be referred to.

[0453] By using the positive electrode active material described in the above embodiment for the positive electrode 932, the secondary battery 913 can have high charge / discharge capacity and excellent cycle characteristics.

[0454] <Laminated secondary battery> Next, examples of laminated secondary batteries will be described with reference to Figures 24 to 36. If a laminated secondary battery has a flexible configuration, or if it is mounted in an electronic device that has at least a flexible portion, the secondary battery can be bent to match the deformation of the electronic device.

[0455] A laminated secondary battery 980 will be described using Fig. 24. The laminated secondary battery 980 has a wound body 993 shown in Fig. 24A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950a described in Fig. 23, the wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 on top of each other with the separator 996 sandwiched therebetween, and winding the laminated sheet.

[0456] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed depending on the required charge / discharge capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0457] 24B, a film 981 serving as an exterior body and a film 982 having a recess are bonded together by thermocompression or the like to form a space, and the above-described wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 24C. The wound body 993 has lead electrodes 997 and 998, and the internal regions of the film 981 and the film 982 having a recess are impregnated with an electrolyte.

[0458] For example, a metal material such as aluminum or a resin material can be used for film 981 and film 982 having recesses. If a resin material is used for film 981 and film 982 having recesses, film 981 and film 982 having recesses can be deformed when an external force is applied, and a flexible storage battery can be produced.

[0459] Although an example using two films is shown in FIGS. 24B and 24C, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0460] By using the positive electrode active material described in the above embodiment for the positive electrode 995, the secondary battery 980 can have high charge / discharge capacity and excellent cycle characteristics.

[0461] Furthermore, although Figure 24 describes an example of a secondary battery 980 having a wound body in a space formed by a film that serves as an outer casing, it may also be a secondary battery having multiple strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing, as shown in Figure 25, for example.

[0462] 25A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte 508, and an exterior body 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. The exterior body 509 is filled with the electrolyte 508. The electrolyte solution described in Embodiment 3 can be used as the electrolyte solution 508.

[0463] 25A , the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged so as to be partially exposed to the outside from the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the exterior body 509, and a lead electrode may be used to ultrasonically bond the positive electrode current collector 501 or the negative electrode current collector 504 to the outside, thereby exposing the lead electrode to the outside.

[0464] In the laminated secondary battery 500, the exterior body 509 can be a three-layer laminate film in which a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film made of polyamide-based resin, polyester-based resin, or the like is further provided on the metal thin film as the outer surface of the exterior body.

[0465] 25B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 25A shows an example configured with two current collectors, but in reality, as shown in Fig. 25B, it is configured with multiple electrode layers.

[0466] In FIG. 25B, the number of electrode layers is 16 as an example. Note that even if the number of electrode layers is 16, the secondary battery 500 remains flexible. FIG. 25B shows a structure with a total of 16 layers, including 8 layers of negative electrode current collectors 504 and 8 layers of positive electrode current collectors 501. Note that FIG. 25B also shows a cross section of the negative electrode lead-out portion, in which 8 layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16 and may be more or less. When the number of electrode layers is large, a secondary battery with a larger charge / discharge capacity can be obtained. Furthermore, when the number of electrode layers is small, a secondary battery can be made thinner and have excellent flexibility.

[0467] 26 and 27 show an example of an external view of a laminated secondary battery 500. The battery 500 includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0468] FIG. 28A shows the appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area and shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 28A.

[0469] <Method for manufacturing laminated secondary batteries> Here, an example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 26 will be described with reference to FIGS. 28B and 28C.

[0470] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 28B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0471] Next, negative electrode 506 , separator 507 and positive electrode 503 are placed on exterior body 509 .

[0472] Next, as shown in Fig. 28C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that electrolyte 508 can be introduced later.

[0473] Next, electrolyte 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolyte 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, laminated secondary battery 500 can be produced.

[0474] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have high charge / discharge capacity and excellent cycle characteristics.

[0475] <Bendable secondary battery> Next, an example of a bendable secondary battery will be described with reference to FIGS. 29 and 30. FIG.

[0476] FIG. 29A shows a schematic top view of a bendable secondary battery 250. FIGS. 29B, 29C, and 29D show schematic cross-sectional views taken along the lines C1-C2, C3-C4, and A1-A2 in FIG. 29A, respectively. The secondary battery 250 includes an exterior housing 251 and an electrode stack 210 housed within the interior of the exterior housing 251. The electrode stack 210 includes at least a positive electrode 211a and a negative electrode 211b. The positive electrode 211a and the negative electrode 211b together constitute the electrode stack 210. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior housing 251. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed within the area enclosed by the exterior housing 251.

[0477] The positive electrode 211a and the negative electrode 211b of the secondary battery 250 will be described with reference to Fig. 30. Fig. 30A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 30B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0478] 30A, secondary battery 250 has a plurality of strip-shaped positive electrodes 211a, a plurality of strip-shaped negative electrodes 211b, and a plurality of separators 214. Positive electrode 211a and negative electrode 211b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of positive electrode 211a in the portion other than the tab, and a negative electrode active material layer is formed on one surface of negative electrode 211b in the portion other than the tab.

[0479] The positive electrode 211a and the negative electrode 211b are stacked so that the surfaces of the positive electrode 211a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

[0480] Furthermore, separator 214 is provided between the surface of positive electrode 211a on which the positive electrode active material is formed and the surface of negative electrode 211b on which the negative electrode active material is formed. Separator 214 is shown by dotted lines in Figures 30A and 30B for ease of viewing.

[0481] 30B, the plurality of positive electrodes 211a and the lead 212a are electrically connected at a joint 215a, and the plurality of negative electrodes 211b and the lead 212b are electrically connected at a joint 215b.

[0482] Next, exterior body 251 will be described with reference to FIGS. 29B, 29C, 29D, and 29E.

[0483] The exterior body 251 has a film-like shape and is folded in two to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b, and can also be called side seals. The sealing portion 263 has a portion that overlaps with the lead 212a and the lead 212b, and can also be called a top seal.

[0484] The exterior body 251 preferably has a wave shape in which ridge lines 271 and valley lines 272 are alternately arranged in the portions overlapping the positive electrode 211a and the negative electrode 211b. Furthermore, the seal portions 262 and 263 of the exterior body 251 are preferably flat.

[0485] Fig. 29B is a cross section taken at a portion overlapping with ridge line 271, and Fig. 29C is a cross section taken at a portion overlapping with valley line 272. Fig. 29B and Fig. 29C both correspond to widthwise cross sections of secondary battery 250 and positive electrode 211a and negative electrode 211b.

[0486] Here, the distance La is defined as the distance between the widthwise ends of the positive electrode 211a and the negative electrode 211b, i.e., the ends of the positive electrode 211a and the negative electrode 211b, and the seal portion 262. When the secondary battery 250 is deformed, such as by bending, the positive electrode 211a and the negative electrode 211b deform so as to be displaced from each other in the longitudinal direction, as described below. In this case, if the distance La is too short, the exterior body 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, resulting in damage to the exterior body 251. In particular, if the metal film of the exterior body 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the secondary battery 250 increases.

[0487] Furthermore, it is preferable that the distance La between the positive electrode 211a and the negative electrode 211b and the seal portion 262 is increased as the total thickness of the stacked positive electrode 211a and the negative electrode 211b increases.

[0488] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is t, the distance La is preferably 0.8 to 3.0 times the thickness t, preferably 0.9 to 2.5 times, and more preferably 1.0 to 2.0 times. Alternatively, 0.8 to 2.5 times is preferred. Alternatively, 0.8 to 2.0 times is preferred. Alternatively, 0.9 to 3.0 times is preferred. Alternatively, 0.9 to 2.0 times is preferred. Alternatively, 1.0 to 3.0 times is preferred. Alternatively, 1.0 to 2.5 times is preferred. By setting the distance La within this range, a compact battery with high reliability against bending can be realized.

[0489] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to make distance Lb sufficiently larger than the width of the positive electrode 211a and the negative electrode 211b (here, width Wb of the negative electrode 211b). This allows parts of the positive electrode 211a and the negative electrode 211b to shift in the width direction even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251 when deformation such as repeated bending is applied to the secondary battery 250, thereby effectively preventing the positive electrode 211a and the negative electrode 211b from rubbing against the exterior body 251.

[0490] For example, the difference between the distance Lb between the pair of seal portions 262 and the width Wb of the negative electrode 211b is preferably 1.6 to 6.0 times, preferably 1.8 to 5.0 times, and more preferably 2.0 to 4.0 times the thickness t of the positive electrode 211a and the negative electrode 211b. Alternatively, 1.6 to 5.0 times is preferred. Alternatively, 1.6 to 4.0 times is preferred. Alternatively, 1.8 to 6.0 times is preferred. Alternatively, 1.8 to 4.0 times is preferred. Alternatively, 2.0 to 6.0 times is preferred. Alternatively, 2.0 to 5.0 times is preferred.

[0491] 29D is a cross section including lead 212a, and corresponds to a cross section in the longitudinal direction of secondary battery 250, positive electrode 211a, and negative electrode 211b. As shown in FIG. 29D, it is preferable that a space 273 be formed between exterior body 251 and the ends of positive electrode 211a and negative electrode 211b in the longitudinal direction at bent portion 261.

[0492] Fig. 29E shows a schematic cross-sectional view of the bent secondary battery 250. Fig. 29E corresponds to the cross section taken along the cutting line B1-B2 in Fig. 29A.

[0493] When the secondary battery 250 is bent, a portion of the exterior body 251 located on the outside of the bend expands, and another portion located on the inside contracts. More specifically, the portion located on the outside of the exterior body 251 deforms so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the portion located on the inside of the exterior body 251 deforms so that the wave amplitude becomes larger and the wave period becomes smaller. In this way, the deformation of the exterior body 251 relieves the stress applied to the exterior body 251 due to bending, so the material that constitutes the exterior body 251 itself does not need to expand or contract. As a result, the exterior body 251 does not break, and the secondary battery 250 can be bent with a small force.

[0494] 29E, when the secondary battery 250 is bent, the positive electrodes 211a and the negative electrodes 211b are displaced relative to each other. At this time, because one end of each of the stacked positive electrodes 211a and negative electrodes 211b on the sealing portion 263 side is fixed by the fixing member 217, the amount of displacement increases toward the bending portion 261. This relieves stress on the positive electrodes 211a and negative electrodes 211b, and the positive electrodes 211a and negative electrodes 211b themselves do not need to expand or contract. As a result, the secondary battery 250 can be bent without damaging the positive electrodes 211a and negative electrodes 211b.

[0495] Furthermore, by providing space 273 between positive electrode 211a and negative electrode 211b and exterior body 251, positive electrode 211a and negative electrode 211b located on the inner side when bent can be relatively displaced without coming into contact with exterior body 251.

[0496] 29 and 30 is a battery that is resistant to damage to the exterior body, the positive electrode 211a, and the negative electrode 211b, etc., even when repeatedly bent and stretched, and the battery characteristics are also resistant to deterioration. By using the positive electrode active material described in the previous embodiment for the positive electrode 211a of the secondary battery 250, it is possible to obtain a battery with even better cycle characteristics.

[0497] In an all-solid-state battery, by stacking the positive electrode and the negative electrode and applying a predetermined pressure in the stacking direction, it is possible to maintain good contact at the interface in the internal region. By applying a predetermined pressure in the stacking direction of the positive electrode and the negative electrode, it is possible to suppress expansion in the stacking direction due to charging and discharging of the all-solid-state battery, and it is possible to improve the reliability of the all-solid-state battery.

[0498] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0499] (Sixth embodiment) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on an electronic device will be described.

[0500] 31A to 31G show examples of electronic devices incorporating the bendable secondary battery described in the previous embodiment. Examples of electronic devices that use the bendable secondary battery include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.

[0501] Furthermore, a secondary battery having a flexible shape can be incorporated along the curved surfaces of the interior or exterior walls of houses and buildings, and the interior or exterior surfaces of automobiles.

[0502] 31A illustrates an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.

[0503] FIG. 31B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 disposed in its internal region is also bent. FIG. 31C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration in which the secondary battery 7407 has high reliability even when bent.

[0504] FIG. 31D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. FIG. 31E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing deforms, causing a change in the curvature of part or the entire secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or the entire main surface of the housing or the secondary battery 7104 changes when the radius of curvature is in the range of 40 mm to 150 mm. High reliability can be maintained when the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm. By using a secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0505] 31F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0506] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0507] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with a touch sensor, and can be operated by touching the screen with a finger or a stylus. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0508] The operation button 7205 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 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0509] The mobile information terminal 7200 can also perform short-range wireless communication according to a communication standard. For example, hands-free communication is possible by communicating with a wireless headset. The mobile information terminal 7200 may have an antenna. The antenna may also be used for wireless communication.

[0510] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0511] The display portion 7202 of the mobile information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight mobile information terminal with a long life can be provided. For example, the secondary battery 7104 shown in FIG. 31E can be incorporated in a curved state into the interior region of the housing 7201 or in a bendable state into the interior region of the band 7203.

[0512] The mobile information terminal 7200 preferably has a sensor. For example, the sensor is preferably one or more selected from a human body sensor such as a fingerprint sensor, a pulse sensor, and a body temperature sensor, a touch sensor, a pressure sensor, and an acceleration sensor.

[0513] 31G illustrates an example of a wristband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0514] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0515] The display device 7300 also includes an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may also be performed by wireless power supply without using the input / output terminal.

[0516] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0517] An example in which the secondary battery shown in the above embodiment is mounted in an electronic device will be described with reference to FIGS. 31H, 32, and 33. FIG.

[0518] By using a secondary battery of one embodiment of the present invention as a secondary battery in daily electronic devices, products that are lightweight and have a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For secondary batteries in these products, a stick-shaped secondary battery that is easy for users to hold, small, lightweight, and has a large charge / discharge capacity is desired.

[0519] FIG. 31H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 31H, electronic cigarette 7500 includes atomizer 7501 including a heating element, secondary battery 7504 that supplies power to the atomizer, and cartridge 7502 including one or more components selected from a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and / or overdischarging of secondary battery 7504 may be electrically connected to secondary battery 7504. Secondary battery 7504 shown in FIG. 31H has external terminals that allow connection to a charging device. Because secondary battery 7504 is the tip portion when held, it is desirable that its total length be short and its weight be light. The secondary battery of one embodiment of the present invention has a high charge / discharge capacity and favorable cycle characteristics, making it possible to provide a compact and lightweight electronic cigarette 7500 that can be used for a long period of time.

[0520] Next, an example of a foldable tablet terminal is shown in FIGS. 32A and 32B. The tablet terminal 9600 shown in FIGS. 32A and 32B includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display portion 9631 having display portions 9631a and 9631b, a switch 9625, a switch 9626, and a switch 9627, a fastener 9629, and an operation switch 9628. Using a flexible panel for the display portion 9631 allows the tablet terminal to have a larger display area. FIG. 32A shows the tablet terminal 9600 in an open state, and FIG. 32B shows the tablet terminal 9600 in a closed state.

[0521] The tablet terminal 9600 also includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housing 9630a and the housing 9630b.

[0522] The entire or part of the display portion 9631 can be a touch panel area, and data can be input by touching an image including an icon, text, an input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display portion 9631a on the housing 9630a side, and information such as text and images may be displayed on the display portion 9631b on the housing 9630b side.

[0523] A keyboard may be displayed on the display portion 9631b of the housing 9630b, and information such as text and images may be displayed on the display portion 9631a of the housing 9630a. A keyboard display switch button of a touch panel may be displayed on the display portion 9631, and the keyboard may be displayed on the display portion 9631 by touching the button with a finger or a stylus.

[0524] In addition, touch input can be simultaneously performed on the touch panel area of ​​the display portion 9631a on the housing 9630a side and the touch panel area of ​​the display portion 9631b on the housing 9630b side.

[0525] The switches 9625 to 9627 may be interfaces capable of switching various functions in addition to interfaces for operating the tablet terminal 9600. For example, at least one of the switches 9625 to 9627 may function as a switch for turning the tablet terminal 9600 on and off. For example, at least one of the switches 9625 to 9627 may have a function for switching the display orientation, such as portrait or landscape, or a function for switching between monochrome and color display. For example, at least one of the switches 9625 to 9627 may have a function for adjusting the brightness of the display unit 9631. The brightness of the display unit 9631 can be optimized depending on the amount of external light detected by an optical sensor built into the tablet terminal 9600 during use. The tablet terminal may also have built-in not only an optical sensor but also other detection devices, such as a gyroscope, an acceleration sensor, or other sensors for detecting tilt.

[0526] 32A shows an example in which the display area of ​​the display portion 9631a on the housing 9630a side and the display portion 9631b on the housing 9630b side are approximately the same, the display areas of the display portion 9631a and the display portion 9631b are not particularly limited, and one size and the other size may be different, and the display quality may also be different. For example, one may be a display panel that can display at a higher resolution than the other.

[0527] 32B shows a tablet terminal 9600 folded in half, and the tablet terminal 9600 includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. In addition, a power storage unit according to one embodiment of the present invention is used as a power storage unit 9635.

[0528] As described above, the tablet terminal 9600 can be folded in half, and therefore, the housing 9630a and the housing 9630b can be folded together when not in use. By folding, the display portion 9631 can be protected, thereby improving durability of the tablet terminal 9600. Furthermore, the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high charge / discharge capacity and favorable cycle characteristics; therefore, the tablet terminal 9600 can be used for a long period of time.

[0529] In addition, the tablet terminal 9600 shown in Figures 32A and 32B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch inputting or editing information displayed on the display unit, and controlling processing using various software (programs).

[0530] A solar cell 9633 attached to the surface of the tablet terminal 9600 can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 9633 can be provided on one or both sides of the housing 9630, and can be configured to efficiently charge the power storage unit 9635. Use of a lithium-ion battery as the power storage unit 9635 has the advantage of enabling miniaturization.

[0531] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 32B will be described with reference to a block diagram in Fig. 32C. Fig. 32C shows a solar cell 9633, a power storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 32B.

[0532] First, an example of operation when power is generated by a solar cell 9633 that uses external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 9636 to a voltage for charging a power storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, a switch SW1 is turned on, and a converter 9637 steps up or steps down the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, the switch SW1 is turned off and the switch SW2 is turned on to charge the power storage unit 9635.

[0533] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and the power storage unit 9635 may be configured to be charged by one or more other power generating means selected from a piezoelectric element (piezo element), a thermoelectric conversion element (Peltier element), etc. For example, a configuration may be used in which a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging is combined with one or more other charging means.

[0534] FIG. 33 illustrates an example of another electronic device. In FIG. 33, a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one embodiment of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power source.

[0535] The display unit 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0536] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0537] 33 , a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. Although FIG. 33 illustrates the case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0538] Note that although Figure 33 illustrates an example of a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided in places other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device or the like.

[0539] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include discharge lamps such as incandescent lamps and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0540] 33, an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although FIG. 33 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or can use power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0541] Note that although FIG. 33 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, a secondary battery according to one embodiment of the present invention can also be used in an integrated-type air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing.

[0542] 33 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 33 , the secondary battery 8304 is provided in an internal region of the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 of one embodiment of the present invention as an uninterruptible power source.

[0543] Among the electronic devices described above, electronic devices such as microwave ovens and other high-frequency heating devices and electric rice cookers require a large amount of power for a short period of time. Therefore, by using a secondary battery according to one embodiment of the present invention as an auxiliary power source for supplementing the power that cannot be supplied by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0544] Furthermore, by storing power in the secondary battery during time periods when electronic devices are not in use, particularly during time periods when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these time periods. For example, in the case of electric refrigerator-freezer 8300, power is stored in secondary battery 8304 during the night when the temperature is low and refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature rises and refrigerator door 8302 and freezer door 8303 are opened and closed, secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0545] According to one embodiment of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be improved. Furthermore, according to one embodiment of the present invention, a secondary battery with high charge / discharge capacity can be obtained, thereby improving the characteristics of the secondary battery, and thus the secondary battery itself can be made smaller and lighter. Therefore, by incorporating the secondary battery according to one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and be lighter.

[0546] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0547] (Embodiment 7) In this embodiment, examples of electronic devices using the secondary battery described in the above embodiment will be described with reference to FIGS.

[0548] Figure 34A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0549] For example, a secondary battery according to one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 34A . The eyeglasses-type device 4000 includes a frame 4000a and a display unit 4000b. Mounting a secondary battery on temples of the curved frame 4000a makes it possible to provide an eyeglasses-type device 4000 that is lightweight, has a good weight balance, and can be used for a long time. The inclusion of a secondary battery according to one embodiment of the present invention makes it possible to realize a configuration that can accommodate space savings associated with a smaller housing.

[0550] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b and the earphone unit 4001c. By including the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0551] 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 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 space-saving configuration can be realized that accompanies a miniaturized housing.

[0552] 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 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 space-saving configuration can be realized that accompanies a miniaturized housing.

[0553] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an internal region of the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0554] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0555] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0556] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0557] FIG. 34B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0558] 34C shows a side view of the display portion 4005a. FIG. 34C shows that a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0559] 35A 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 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 the dust from a suction port arranged on the bottom surface.

[0560] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal area. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be a highly reliable electronic device with a long operating time.

[0561] Fig. 35B shows an example of a robot. A robot 6400 shown in Fig. 35B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0562] 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.

[0563] 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.

[0564] 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.

[0565] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in an internal region thereof. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be a highly reliable electronic device with a long operating time.

[0566] Fig. 35C shows an example of an aircraft. Aircraft 6500 shown in Fig. 35C has propeller 6501, camera 6502, secondary battery 6503, etc., and has the function of flying autonomously.

[0567] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of obstacles when moving. Furthermore, the electronic component 6504 can estimate the remaining battery charge from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention in its internal area. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the flying object 6500 can be an electronic device with a long operating time and high reliability.

[0568] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0569] (Embodiment 8) In this embodiment, an example in which the secondary battery is applied to an electric vehicle (EV) will be shown.

[0570] As shown in Fig. 36C, an electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (starter battery). The second battery 1311 only needs to have high output, and does not necessarily 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.

[0571] As the first batteries 1301a and 1301b, secondary batteries manufactured using the manufacturing method of a secondary battery described in the above embodiment can be used.

[0572] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0573] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0574] 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 DC-DC 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.

[0575] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0576] The first battery 1301a will be described with reference to FIG. 36A.

[0577] FIG. 36A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries by fixing portions 1413 and 1414 or a battery housing box. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0578] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having 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.

[0579] The control circuit 1320 detects the terminal voltage of the secondary battery and manages the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0580] FIG. 36B shows an example of a block diagram of the battery pack 1415 shown in FIG. 36A.

[0581] The control circuit unit 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 unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range between the lower and upper voltage limits of the secondary 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 unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging or 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. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0582] The switch unit 1324 can be configured by combining n-channel transistors or p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be configured using, 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 unit 1324 may be formed using a power transistor having gallium oxide (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, which facilitates integration. Furthermore, OS transistors can be manufactured using the same manufacturing equipment as Si transistors, which allows for low-cost manufacturing. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The volume occupied by the control circuit unit 1320 can be reduced, enabling miniaturization.

[0583] The first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and the second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. A lead-acid battery is often used as the second battery 1311 because of its cost advantage.

[0584] In this embodiment, an example is shown in which lithium ion secondary batteries are used as both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0585] Furthermore, regenerated 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 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. 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 regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0586] 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 secondary battery used, and can perform rapid charging.

[0587] 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. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also 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.

[0588] Next, an example in which the secondary battery according to one embodiment of the present invention is mounted on a mobile object such as a vehicle will be described.

[0589] Furthermore, when the secondary battery of one embodiment of the present invention is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0590] FIG. 37 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 37A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery. The secondary battery may be arranged in the form of secondary battery modules shown in FIGS. 19C and 19D on the floor of the vehicle. Alternatively, a battery pack including a combination of a plurality of secondary batteries as shown in FIG. 22 may be installed on the floor of the vehicle. The secondary battery not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0591] 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.

[0592] The automobile 8500 shown in FIG. 37B can charge its secondary battery by receiving power from an external charging facility using a plug-in method, a contactless power supply method, or the like. FIG. 37B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged via a cable 8022 from a ground-mounted charging device 8021. The charging method and connector specifications may be determined as appropriate using a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0593] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, one or both of the electromagnetic induction method and the magnetic field resonance method can be used.

[0594] 37C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 37C 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.

[0595] 37C, the secondary battery 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0596] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the charge / discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. Reducing the size and weight of the secondary battery itself contributes to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery installed in the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand periods. Avoiding the use of a commercial power source during peak power demand periods can contribute to energy conservation and the reduction of carbon dioxide emissions. Furthermore, good cycle characteristics allow the secondary battery to be used for a long period of time, thereby reducing the amount of rare metals used, such as cobalt. [Example]

[0597] In this example, a negative electrode active material according to one embodiment of the present invention is fabricated and its characteristics are evaluated.

[0598] <Preparation of negative electrode active material> A negative electrode active material was prepared according to the flow shown in Figure 3. A first material 801 was prepared using a material having a specific surface area of ​​1.5 m 2 / g MCMB graphite was used. Lithium fluoride was used as the halogen-containing material 802. Lithium carbonate was used as the oxygen- and carbon-containing material 803.

[0599] As negative electrode active materials, active materials AG1, AG2, AG3, and AG4 were prepared.

[0600] [AG1] Graphite, lithium fluoride, and lithium carbonate were prepared as materials for the active material AG1 (see steps S21, S22, and S23 in FIG. 3). The materials were mixed in a ratio of graphite:lithium fluoride:lithium carbonate=100:5:5 (weight%) and dry mixed (see steps S31 to S33 in FIG. 3).

[0601] [AG2] Graphite and lithium carbonate were prepared as materials for the active material AG2. The graphite and lithium carbonate were mixed at a ratio of 100:10 (weight %) and dry mixed.

[0602] [AG3] Graphite and lithium fluoride were prepared as materials for the active material AG3. The graphite and lithium fluoride were mixed at a ratio of 100:10 (weight %) and dry mixed.

[0603] The mixture of materials for each active material was fired at 850° C. for 10 hours in a nitrogen atmosphere to obtain each active material (see steps S51 to S53 in FIG. 3).

[0604] [AG4] Graphite was prepared as the active material AG4. It was not fired.

[0605] <SEMおよびEDX> The prepared active materials AG1 and AG3 were observed under a scanning electron microscope (SEM) and analyzed by EDX using an SU8030 manufactured by Hitachi High-Technologies Corp. The observed image of active material AG1 is shown in Figure 38A, and the observed image of active material AG3 is shown in Figure 38B.

[0606] Active material AG1 was subjected to EDX analysis at point Q1 shown in Figure 39A, and the resulting spectrum is shown in Figure 39B.

[0607] The concentrations of each element obtained by EDX are shown in Table 1. In active material AG1, oxygen and fluorine were detected as the main elements, suggesting that regions containing oxygen and fluorine were formed on the particle surfaces.

[0608] [Table 1]

[0609] Active material AG3 was subjected to EDX analysis at point Q2 shown in Figure 40A, and the resulting spectrum is shown in Figure 40B.

[0610] The concentrations of each element obtained by EDX are shown in Table 2. In active material AG3, fluorine and copper were detected as the main elements, suggesting that regions containing fluorine and copper were formed on the particle surface.

[0611] [Table 2]

[0612] <xps> XPS measurements were performed on each of the prepared active materials. The detection area was approximately 100 μmφ, and the take-off angle was 45°. The narrow spectra obtained are shown in Figures 41 to 47. In each figure, the vertical axis represents the spectral intensity, and the horizontal axis represents the binding energy.

[0613] 41A, 41B, 41C, and 41D are the C1s spectra of active materials AG1, AG2, AG3, and AG4, respectively.

[0614] 42A, 42B, 42C, and 42D are F1s spectra of active materials AG1, AG2, AG3, and AG4, respectively.

[0615] 43A, 43B, 43C, and 43D are O1s spectra of active materials AG1, AG2, AG3, and AG4, respectively.

[0616] 44A, 44B, 44C, and 44D are the Li1s spectra of active materials AG1, AG2, AG3, and AG4, respectively.

[0617] FIG. 45 shows the N1s spectrum of the active material AG1.

[0618] Figure 46A is a graph showing the C1s spectra of each active material superimposed. Figure 46B is a graph showing the Li1s spectra of each active material superimposed. Figure 47A is a graph showing the F1s spectra of each active material superimposed. Figure 47B shows the results of fitting the F1s spectrum of active material AG1 to the peaks associated with the metal-F bonding state and the peaks associated with the C—F bonding state.

[0619] Table 3 shows the concentration of each element calculated from the XPS results for each active material.

[0620] [Table 3]

[0621] As shown in Table 3, fluorine was detected at 1 atomic % or more in active materials AG1 and AG3, which were made using lithium fluoride. Carbon, oxygen, and lithium were detected prominently in active materials AG1 and AG2, which were made using lithium carbonate, with the carbon concentration being more than 1 times the oxygen concentration and the lithium concentration being approximately 0.6 times the oxygen concentration.

[0622] In the active materials AG1 and AG2, a significant peak was observed in the vicinity of 531 eV in the O1s spectrum of XPS, and a significant peak was observed in the vicinity of 290 eV in the C1s spectrum, suggesting the presence of carbonate groups.

[0623] The fitting of active material AG1 suggested the presence of a peak near 688 eV in the XPS F1s spectrum, suggesting that active material AG1 has C—F bonds on its surface, etc. This suggests that the fluorine in lithium fluoride formed bonds with at least one of the carbon in graphite and the carbon in lithium carbonate. [Example]

[0624] In this example, an electrode was produced using the negative electrode active material produced in Example 1, and a secondary battery was produced using the electrode and evaluated.

[0625] <Preparation of electrodes> Next, each of the prepared negative electrode active materials, vapor-grown carbon fiber, and PVDF were mixed in a weight ratio of negative electrode active material:vapor-grown carbon fiber:PVDF=96:1:3, and a slurry was prepared using NMP as a solvent.

[0626] Vapor grown carbon fiber was VGCF (registered trademark)-H (manufactured by Showa Denko K.K., fiber diameter 150 nm, specific surface area 13 m 2 / g) was used.

[0627] The prepared slurry was applied to a current collector and dried to prepare an active material layer. Copper foil with a thickness of 18 μm was used as the current collector. The active material layer was provided on one side of the current collector. The amount of active material carried in the active material layer was approximately 6 mg / cm. 2 to 8 mg / cm 2 The range was.

[0628] <Preparation of secondary battery> Next, for evaluation purposes, a coin-type secondary battery of the CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated.

[0629] The prepared electrode and lithium metal were used as a counter electrode.

[0630] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), which was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7.

[0631] The separator was made of polypropylene with a thickness of 25 μm.

[0632] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0633] <Rate characteristics> The rate dependence of discharge capacity was evaluated using the fabricated secondary batteries. Here, during discharge, lithium is inserted into the negative electrode active material in the electrode having the negative electrode active material fabricated in Example 1. Figure 48A shows the discharge capacity at 0°C for secondary batteries using each negative electrode active material.

[0634] Active material AG1 had a high discharge capacity at all rates, suggesting that the properties were improved by the regions containing oxygen and fluorine formed on the particle surface.

[0635] <Cycle characteristics> The cycle characteristics were evaluated using the fabricated secondary battery. In Fig. 48B, the vertical axis shows the charge capacity in each charge / discharge cycle, and the horizontal axis shows the number of cycles. Here, during charging, lithium is released from the negative electrode active material in the electrode having the negative electrode active material fabricated in Example 1.

[0636] Active material AG1 had a high initial charge capacity, suggesting that the regions containing oxygen and fluorine formed on the particle surface improved the charge-discharge efficiency. [Example]

[0637] In this example, a laminate type secondary battery was produced using the negative electrode active material produced in Example 1, and was evaluated.

[0638] <Preparation of negative electrode> AG1 was mixed with conductive agent, CMC-Na (sodium carboxymethylcellulose) and SBR (styrene butadiene rubber) in a weight ratio of AG1:conductive agent:CMC-Na:SBR = 96:1:1:2, and a slurry was prepared using water as the solvent.

[0639] The degree of polymerization of the CMC-Na used was 600 to 800, and the viscosity of the aqueous solution when used as a 1 wt% solution was in the range of 300 mPa·s to 500 mPa·s. The conductive agent was vapor-grown carbon fiber VGCF (registered trademark)-H (Showa Denko K.K., fiber diameter 150 nm, specific surface area 13 m). 2 / g) was used.

[0640] The prepared slurry was applied to a current collector and dried to form a negative electrode active material layer on the current collector. The current collector was made of copper foil with a thickness of 18 μm. The negative electrode active material layer was formed on one side of the current collector.

[0641] In addition, AG4 was mixed with conductive agent, CMC-Na (sodium carboxymethylcellulose) and SBR (styrene butadiene rubber) in a weight ratio of AG4:conductive agent:CMC-Na:SBR = 96:1:1:2, and a slurry was prepared using water as the solvent.

[0642] The degree of polymerization of the CMC-Na used was 600 to 800, and the viscosity of the aqueous solution when used as a 1 wt% solution was in the range of 300 mPa·s to 500 mPa·s. The conductive agent was vapor-grown carbon fiber VGCF (registered trademark)-H (Showa Denko K.K., fiber diameter 150 nm, specific surface area 13 m). 2 / g) was used.

[0643] The prepared slurry was applied to a current collector and dried to form a negative electrode active material layer on the current collector. The current collector was made of copper foil with a thickness of 18 μm. The negative electrode active material layer was formed on one side of the current collector.

[0644] <Preparation of positive electrode> Next, a positive electrode was fabricated. The sample fabricated in this example will be described with reference to the fabrication method shown in FIG.

[0645] In step S64, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M and no particular additives was prepared as LiMO2. Lithium fluoride and magnesium fluoride were mixed with this by a solid-phase method, as in steps S71 to S73, S81, and S82. The number of lithium fluoride molecules was 0.33, and the number of magnesium fluoride molecules was 1, assuming that the number of cobalt atoms was 100. This was designated mixture 903.

[0646] Next, heating was performed in the same manner as in step S83. 30 g of mixture 903 was placed in a square alumina container, a lid was placed, and the mixture was heated in a muffle furnace. The inside of the furnace was purged, and oxygen gas was introduced, but no gas flow was observed during heating. The heating temperature was 900°C for 20 hours.

[0647] In step S101, nickel hydroxide and aluminum hydroxide were added to the heated composite oxide and dry mixed. The number of nickel atoms was 0.5 and the number of aluminum atoms was 0.5, assuming that the number of cobalt atoms was 100.

[0648] Next, heating was performed in the same manner as in step S103. 30 g of mixture 903 was placed in a square alumina container, a lid was placed, and the mixture was heated in a muffle furnace. The inside of the furnace was purged, oxygen gas was introduced, and flow during heating was performed. The heating temperature was 850°C for 10 hours.

[0649] Thereafter, the powder was collected by sieving through a sieve with an opening diameter of 53 μmφ, and a positive electrode active material was obtained.

[0650] Next, a positive electrode was fabricated using the prepared positive electrode active material. Acetylene black was used as a conductive agent and mixed with the prepared positive electrode active material to prepare a slurry, which was then applied to an aluminum current collector.

[0651] After the slurry was applied to the current collector, the solvent was evaporated. After that, a pressure of 210 kN / m was applied, and then a pressure of 1467 kN / m was applied. A positive electrode was obtained through these steps. The loading amount of the positive electrode was approximately 7 mg / cm. 2 It was decided.

[0652] <Preparation of secondary battery> Using the positive electrode and negative electrode prepared above, a secondary battery was prepared using a film as an exterior body.

[0653] The separator was made of polypropylene with a thickness of 25 μm.

[0654] The positive electrode, separator, and negative electrode were stacked in this order. The positive electrode active material provided on one side of the current collector was arranged to face the negative electrode active material with the separator sandwiched therebetween.

[0655] Leads were attached to the positive and negative electrodes, respectively.

[0656] The laminate, which was made by stacking the positive electrode, the negative electrode, and the separator, was sandwiched between an exterior body folded in half, and the laminate was positioned so that one end of the lead was exposed to the outside of the exterior body. Next, one side of the exterior body was left open, and the other sides were sealed.

[0657] The film used for the exterior body was a film in which a polypropylene layer, an acid-modified polypropylene layer, an aluminum layer, and a nylon layer were laminated in this order. The film had a thickness of approximately 110 μm. The film for the exterior body was folded so that the nylon layer was on the surface that would be placed on the outside of the exterior body, and the polypropylene layer was on the surface that would be placed on the inside. The thickness of the aluminum layer was approximately 40 μm, the thickness of the nylon layer was approximately 25 μm, and the total thickness of the polypropylene layer and the acid-modified polypropylene layer was approximately 45 μm.

[0658] Next, under an argon gas atmosphere, an electrolyte was injected from the side that was left as an open portion.

[0659] The electrolyte used was 1 mol / L lithium hexafluorophosphate (LiPF6), a mixture of fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of FEC:EMC:DMC = 3:3.5:3.5.

[0660] Next, one side of the exterior body that had been left as an open portion was sealed in a reduced pressure atmosphere.

[0661] Through the above steps, two secondary batteries (hereinafter referred to as cell AG1-C1 and cell AG4-C2) using reduced graphene oxide as a conductive agent were fabricated.

[0662] <Cycle characteristics> The cycle characteristics of the fabricated secondary battery were evaluated. The measurement temperature was -40°C. Charging was performed by CC charging at 0.05C with a cut-off voltage of 4.5V, followed by CV charging at 0.02C. Discharging was performed by CC discharging at 0.05C with a cut-off voltage of 3.0V.

[0663] FIG. 49A shows the measurement results for AG1-C1, and FIG. 49B shows the measurement results for AG4-C2.

[0664] AG4-C2 was not able to charge and discharge even when combined with an electrolyte containing FEC, but AG1-C1 was able to charge and discharge when combined with an electrolyte containing FEC, although the capacity was low. [Example]

[0665] <XRD> Next, X-ray diffraction (XRD) measurements were performed on AG1, AG2, and AG3 prepared in Example 1. Figure 50 shows ideal XRD spectra calculated from the crystal structure model of AG1, AG2, and AG3 using CuKα1 radiation. The vertical axis of the figure represents the spectral intensity, and the horizontal axis represents the diffraction angle (2θ). For comparison, ideal XRD patterns calculated from the crystal structures of graphite, LiF, LiCoO2(O3), and Li2O are also shown. The space group of Li2O was Fm-3m(225), and the lattice constant was 4.610 Å (0.4610 nm). The patterns for graphite, LiF, LiCoO2(O3), and Li2O were generated using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the Inorganic Crystal Structure Database (ICSD) (see Non-Patent Document 2). The 2θ range is from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562 × 10 -10 The space group of Li2O was Fm-3m and the lattice constant was 0.4610 nm.

[0666] As shown in Figure 50, the X-ray peaks of AG1 and AG2 are at approximately the same positions as the ideal peak positions of graphite, LiF, and Li2O, and therefore AG1 and AG2 are considered to contain graphite, LiF, and Li2O. On the other hand, the X-ray peaks of AG3 are at approximately the same positions as the ideal peak positions of graphite and LiF, but do not coincide with the ideal peak position of Li2O. From this, it is considered that AG3 does not contain Li2O, and it is thought that the oxygen detected in AG1 and AG2 by XPS etc. may be due to Li2O. [Explanation of symbols]

[0667] 100: positive electrode active material, 102: space inside heating furnace, 104: hot plate, 106: heater part, 108: heat insulating material, 116: container, 118: lid, 119: space, 120: heating furnace, 144: carbon atoms, 210: electrode laminate, 211a: positive electrode, 211b: negative electrode, 212a: lead, 212b: lead, 214: separator, 215a: joint part, 215b: joint part, 217: fixing member, 250: secondary battery, 251: exterior body, 261: folded part, 262: seal part, 263: seal part, 271: ridge line, 272: valley line, 273: space, 300: secondary battery, 301: positive electrode can, 302: Negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 400: negative electrode active material, 401: region, 401a: region, 401b: region, 402: region, 410: positive electrode, 411: positive electrode active material, 413: positive electrode current collector, 414: positive electrode active material layer, 420: solid electrolyte layer, 421: solid electrolyte, 430: negative electrode, 431: negative electrode active material, 433: negative electrode current collector, 434: negative electrode active material layer, 440: secondary battery, 500: secondary battery, 501: positive electrode current collector, 502: positive Electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 550: current collector, 553: acetylene black, 554: graphene, 561: negative electrode active material, 600: secondary battery, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 612: safety valve mechanism, 613: conductive plate, 614 : Conductive plate, 615: Module, 616: Conductive wire, 617: Temperature control device, 750a: Positive electrode, 750b: Solid electrolyte layer, 750c: Negative electrode, 751: Electrode plate, 752: Insulating tube, 753: Electrode plate, 761: Lower member, 762: Upper member, 764: Wing nut, 765: O-ring, 766: Insulator, 770a: Package member, 770b: Package member, 770c: Package member, 771: External electrode, 772: External electrode, 773a: Electrode layer, 773b: Electrode layer, 801: Material, 802: Material, 803: Material, 804: Mixture, 805: Negative electrode active material,808: Cobalt-containing material, 811: Composite oxide, 812: Fluoride, 813: Compound, 814: Mixture, 900: Circuit board, 902: Mixture, 903: Mixture, 904: Mixture, 910: Label, 911: Terminal, 911a: Terminal, 911b: Terminal, 912: Circuit, 913: Secondary battery, 914: Antenna, 915: Seal, 916: Layer, 917: Layer, 918: Antenna, 920: Display device, 921: Sensor, 922: Terminal, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer , 933: separator, 950: winding body, 950a: winding body, 951: terminal, 952: terminal, 980: secondary battery, 981: film, 982: film, 993: winding body, 994: negative electrode, 995: positive electrode, 996: separator, 997: lead electrode, 998: lead electrode, 1300: prismatic secondary battery, 1301a: battery, 1301b: battery, 1302: battery controller, 1303: motor controller, 1304: motor, 1305: gear, 1306: DCDC circuit, 1307: electric power steering, 1308: heater, 1309: defogger, 1310: DCDC circuit, 1311: battery, 1312: inverter, 1313: audio, 1314: power window, 1315: lamps, 1316: tire, 1317: rear motor, 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 1324: switch section, 1325: external terminal, 1326: external terminal, 1413: fixing section, 1414: fixing section, 1415: battery pack, 1421: wiring, 1422: wiring, 4000: eyeglass-type device, 4000a: frame, 4000b: display section, 4001: headset-type device, 40 01a: microphone unit, 4001b: flexible pipe, 4001c: earphone unit, 4002: device, 4002a: housing, 4002b: secondary battery, 4003: device, 4003a: housing, 4003b: secondary battery, 4005: watch-type device, 4005a: display unit, 4005b: belt unit, 4006: belt-type device, 4006a: belt unit, 4006b: wireless power supply receiving unit, 6300: cleaning robot, 6301: housing, 6302: display unit, 6303: camera, 6304: brush, 6305: operation button, 6306: secondary battery, 6310: dust,6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: Speaker, 6405: Display unit, 6406: Lower camera, 6407: Obstacle sensor, 6408: Moving mechanism, 6409: Secondary battery, 6500: Flying object, 6501: Propeller, 6502: Camera, 6503: Secondary battery, 6504: Electronic component, 7100: Portable display device, 7101: Housing, 7102: Display unit, 7103: Operation button, 7104: Secondary battery, 7200: Portable information terminal, 7201: Housing, 7202: Display unit, 7203 : Band, 7204: Buckle, 7205: Operation button, 7206: Input / output terminal, 7207: Icon, 7300: Display device, 7304: Display unit, 7400: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation button, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Secondary battery, 7500: Electronic cigarette, 7501: Atomizer, 7502: Cartridge, 7504: Secondary battery, 8000: Display device, 8001: Housing, 8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8021: charging device, 8022: cable, 8024: secondary battery, 8100: lighting device, 8101: housing, 8102: light source, 8103: secondary battery, 8104: ceiling, 8105: side wall, 8106: floor, 8107: window, 8200: indoor unit, 8201: housing, 8202: air outlet, 8203: secondary battery, 8204: outdoor unit, 8300: electric refrigerator-freezer, 8301: housing, 8302: refrigerator compartment door, 8303: freezer compartment door, 8304: secondary battery, 8400: automobile, 8401: headlight, 8406: electric motor, 8500: automobile, 86 00: Scooter, 8601: Side mirror, 8602: Secondary battery, 8603: Turn signal light, 8604: Under-seat storage, 9600: Tablet terminal, 9625: Switch, 9626: Switch, 9627: Switch, 9628: Operation switch, 9629: Fastener, 9630: Housing, 9630a: Housing, 9630b: Housing, 9631: Display unit, 9631a: Display unit, 9631b: Display unit, 9633: Solar cell, 9634: Charge / discharge control circuit, 9635: Power storage unit, 9636: DCDC converter, 9637: Converter, 9640: Moving part,< / xps>

Claims

1. A first region and a second region, comprising at least one of fluorine and oxygen, lithium, and carbon; the first region comprises a first material; the second region is located outside the first region, the second region is in contact with at least a portion of the surface of the first region; the concentration of the fluorine in the second region is higher than the concentration of the fluorine in the first region; the concentration of the oxygen in the second region is higher than the concentration of the oxygen in the first region; The first material is a negative electrode active material that is at least one selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene.

2. In claim 1, At least a portion of the first region includes a surface of the negative electrode active material.

3. In claim 1 or claim 2, The negative electrode active material, wherein the concentration of the lithium in the second region is higher than the concentration of the lithium in the first region.

4. In any one of claims 1 to 3, When the negative electrode active material is measured by energy dispersive X-ray analysis using a scanning electron microscope, the concentration of fluorine is 10 atomic % or more and 70 atomic % or less, with the concentration unit being atomic %.

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