Method for producing positive electrode active material

Abstract

Provided is a positive electrode active material that is not susceptible to deterioration. Also provided are positive electrode active material particles that is not susceptible to deterioration. Also provided is a power storage device that is not susceptible to deterioration. Also provided is a safe power storage device. Also provided is a novel power storage device. Specifically provided is a secondary battery comprising a positive electrode and a negative electrode, wherein: the positive electrode has a positive electrode active material; the positive electrode active material has crystals exhibiting a layered rock salt crystal structure; the crystals belong to the space group R-3m; the positive electrode active material is composed of particles that contain lithium, cobalt, titanium, magnesium, and oxygen; the magnesium concentration in a surface layer part of the particles is higher than the magnesium concentration in the interiors of the particles; and in the positive electrode active material, the titanium concentration in the surface layer part of the particles is higher than the titanium concentration in the interiors of the particles.

Description

[Technical field]

[0001] The present invention relates to a secondary battery using a positive electrode active material and a method for producing the same, or to a portable information terminal, a vehicle, etc. having 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 an electro-optical device having a power storage device, an information terminal device having a power storage device, and the like are all classified as electronic devices.

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

[0006] Therefore, in order to improve the cycle characteristics and capacity of lithium ion secondary batteries, improvements in the positive electrode active material have been investigated (Patent Document 1).

[0007] Furthermore, characteristics required of power storage devices include safety in various operating environments and improved long-term reliability.

[0008] On the other hand, fluorides such as fluorite (calcium fluoride) have long been used as fluxes in steelmaking and other processes, and their physical properties have been studied (Non-Patent Document 1).

[0009] Furthermore, titanium-containing compounds are used in a variety of applications, and their physical properties have been studied (Non-Patent Document 2). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2019-21456 A [Non-patent literature]

[0011] [Non-Patent Document 1] WECounts, R. Roy, and EFOsborn, "Fluoride Model Systems: II, The Binary Systems CaF▲2▼-BeF▲2▼, MgF▲2▼-BeF▲2▼, and LiF-MgF▲2▼", Journal of the American Ceramic Society, 36[1]12-17 (1953). [Non-Patent Document 2] C. Gicquel, M. Mayer, and R. Bouaziz, “Sue quelues composes oxygenes du titane et des alcalins(Li,Na); etude des binaries M▲2▼O-TiO▲2▼ alcalin”, Acad.Sci., Ser.C, 275

[23] 1427-1430(1972). 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 positive electrode active material that is less deteriorated, or to provide a novel method for manufacturing a positive electrode active material.

[0013] An object of one embodiment of the present invention is to provide positive electrode active material particles that deteriorate little.Another object of one embodiment of the present invention is to provide novel positive electrode active material particles.Another object of one embodiment of the present invention is to provide a power storage device that deteriorates little.Another object of one embodiment of the present invention is to provide a highly safe power storage device.Another 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 it is possible to extract problems other than these from the description of the specification, drawings, and claims. [Means for solving the problem]

[0016] One embodiment of the present invention is a secondary battery having a positive electrode and a negative electrode, the positive electrode having a positive electrode active material, the positive electrode active material having a crystal expressed by a layered rock salt crystal structure, the crystal having a space group expressed by R-3m, the positive electrode active material being particles having lithium, cobalt, titanium, magnesium and oxygen, the magnesium concentration in the surface portion of the particles being higher than the magnesium concentration in the interior of the particles, and the titanium concentration in the surface portion of the particles in the positive electrode active material being higher than the titanium concentration in the interior of the particles.

[0017] In the above structure, the positive electrode active material preferably contains fluorine.

[0018] Another aspect of the present invention is a vehicle including the secondary battery described above, an electric motor, and a control device, the control device having a function of supplying electric power from the secondary battery to the electric motor.

[0019] Alternatively, one embodiment of the present invention is a portable information terminal that has the secondary battery described above, a sensor, and an antenna, and has a function of wireless communication using the antenna, where the sensor has a function of measuring 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 rays.

[0020] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, comprising: a first step of mixing a titanium compound, a lithium compound, and a cobalt-containing material to produce a first mixture; and a second step of heating the first mixture, wherein the cobalt-containing material contains magnesium and oxygen, and the heating temperature in the second step is 780° C. or higher and 1150° C. or lower.

[0021] In the above structure, the cobalt-containing material preferably contains fluorine.

[0022] In the above structure, it is preferable that the titanium compound contains oxygen, and the lithium compound contains oxygen.

[0023] In the above-mentioned structure, the titanium compound and the lithium compound preferably have a eutectic point of 780° C. or higher and 1150° C. or lower.

[0024] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, the method including: a first step of mixing lithium cobalt oxide, a magnesium compound, and a fluoride to produce a first mixture; a second step of heating the first mixture to produce a cobalt-containing material; a third step of mixing the cobalt-containing material, a titanium compound, and a lithium compound to produce a second mixture; and a fourth step of heating the second mixture, wherein the heating temperature in the fourth step is 780° C. or higher and 1150° C. or lower.

[0025] In the above structure, it is preferable that the titanium compound contains oxygen, and the lithium compound contains oxygen.

[0026] In the above structure, it is preferable that the magnesium compound is magnesium fluoride, and the fluoride is lithium fluoride.

[0027] In the above-mentioned structure, the titanium compound and the lithium compound preferably have a eutectic point of 780° C. or higher and 1150° C. or lower.

[0028] Alternatively, one embodiment of the present invention is a method for producing a positive electrode active material, the method including: a first step of mixing a composite oxide, a magnesium compound, and a fluoride to produce a first mixture; a second step of heating the first mixture to produce a cobalt-containing material; a third step of mixing the cobalt-containing material, a titanium compound, and a lithium compound to produce a second mixture; and a fourth step of heating the second mixture, wherein the composite oxide has a layered rock-salt crystal structure, the composite oxide contains cobalt, and the composite oxide contains one or more elements selected from nickel, manganese, and aluminum; and the heating temperature in the fourth step is 780° C. or higher and 1150° C. or lower.

[0029] In the above structure, it is preferable that the titanium compound contains oxygen, and the lithium compound contains oxygen.

[0030] In the above structure, it is preferable that the magnesium compound is magnesium fluoride, and the fluoride is lithium fluoride.

[0031] In the above-mentioned structure, the titanium compound and the lithium compound preferably have a eutectic point of 780° C. or higher and 1150° C. or lower. Effect of the Invention

[0032] According to one embodiment of the present invention, a method for manufacturing a positive electrode active material that is less deteriorated can be provided. In addition, according to one embodiment of the present invention, a novel method for manufacturing a positive electrode active material can be provided.

[0033] According to one embodiment of the present invention, a positive electrode active material particle that is less deteriorated can be provided. According to one embodiment of the present invention, a method for manufacturing a positive electrode active material can be provided. According to one embodiment of the present invention, a novel positive electrode active material particle can be provided. According to one embodiment of the present invention, a novel power storage device can be provided.

[0034] 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.

[0035] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract effects other than these from the description in the specification, drawings, claims, etc. [Brief description of the drawings]

[0036] FIG. 1 is a phase diagram showing the relationship between the composition of Li2O and TiO2 and temperature. FIG. 2 shows the results of DSC. FIG. 3 is a diagram showing a method for producing a positive electrode active material. FIG. 4 is a diagram showing a method for producing a positive electrode active material. FIG. 5 is a diagram showing a method for preparing the material. FIG. 6 is a diagram showing a method for producing a positive electrode active material. FIG. 7 is an example of a process cross-sectional view showing one embodiment of the present invention. FIG. 8 is a diagram illustrating the crystal structure of the positive electrode active material. FIG. 9 is a diagram illustrating the crystal structure of the positive electrode active material. 10A and 10B are diagrams illustrating an example of a secondary battery. 11A, 11B, and 11C are diagrams illustrating an example of a secondary battery. 12A and 12B are diagrams illustrating an example of a secondary battery. 13A, 13B, and 13C are diagrams illustrating a coin-type secondary battery. 14A, 14B, 14C, and 14D are diagrams illustrating a cylindrical secondary battery. 15A and 15B are diagrams illustrating an example of a secondary battery. 16A, 16B, 16C, and 16D are diagrams illustrating examples of secondary batteries. 17A, 17B, and 17C are diagrams illustrating an example of a secondary battery. 18A, 18B, and 18C are diagrams illustrating an example of a secondary battery. 19A, 19B, and 19C are diagrams illustrating a laminated type secondary battery. 20A and 20B are diagrams illustrating a laminated type secondary battery. FIG. 21 is a diagram showing the external appearance of a secondary battery. FIG. 22 is a diagram showing the appearance of a secondary battery. 23A, 23B, and 23C are diagrams illustrating a method for producing a secondary battery. 24A, 24B, 24C, 24D, and 24E are diagrams illustrating a bendable secondary battery. 25A and 25B are diagrams illustrating a bendable secondary battery. 26A, 26B, 26C, 26D, 26E, 26F, 26G, and 26H are diagrams for explaining an example of an electronic device. 27A, 27B, and 27C are diagrams illustrating an example of an electronic device. FIG. 28 is a diagram illustrating an example of an electronic device. 29A, 29B, and 29C are diagrams illustrating an example of an electronic device. 30A, 30B, and 30C are diagrams showing an example of an electronic device. 31A, 31B, and 31C are diagrams illustrating an example of a vehicle. 32A and 32B are SEM photographs. 33A and 33B are SEM photographs. 34A, 34B, 34C, 34D, 34E, and 34F are diagrams showing the results of SEM-EDX. FIG. 35 is a graph showing cycle characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the description of the embodiments shown below.

[0038] In addition, in this specification and the like, crystal planes and directions are indicated using Miller indices. In crystallography, crystal planes and directions are indicated by placing a superscript bar on the numbers, but in this specification and the like, due to restrictions on notation in applications, numbers may be indicated by placing a - (minus sign) before them instead of placing a bar above them. Individual directions indicating directions within a crystal are indicated with [ ], collective directions indicating all equivalent directions with < >, individual planes indicating crystal planes with ( ), and collective planes with equivalent symmetry with {}.

[0039] In this specification and the like, segregation refers to a phenomenon in which a certain element (eg, B) is spatially non-uniformly distributed in a solid composed of a plurality of elements (eg, A, B, C).

[0040] In this specification, the surface layer of a particle of an 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 caused by cracks or fissures may also be called the surface. A region deeper than the surface layer is called the interior.

[0041] 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 deficiencies of cations or anions may be present. Strictly speaking, the layered rock-salt type crystal structure may have a structure in which the lattice of the rock-salt type crystal is distorted.

[0042] 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 acceptable for there to be a deficiency of cations or anions.

[0043] In the present specification and the like, the O3' type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure that has a space group of R-3m, is not a spinel type crystal structure, but has ions of cobalt, magnesium, etc. occupying 6-coordination oxygen positions, and has a symmetry of the arrangement of cations similar to that of the spinel type. In the O3' type crystal structure, light elements such as lithium may occupy 4-coordination oxygen positions, and in this case, the arrangement of ions also has a symmetry similar to that of the spinel type.

[0044] It can also be said that the O3' type crystal structure is 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 close to that of lithium cobalt oxide (NiO2), but it is known that simple pure lithium cobalt oxide or layered rock salt type positive electrode active materials that contain a lot of cobalt do not usually have this crystal structure.

[0045] The layered rock salt type crystal and the anions of the rock salt type crystal have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3' type crystal also have a cubic close-packed structure. When they contact, there is a crystal plane where the orientation of the cubic close-packed structure formed by the anions is aligned. However, the space group of the layered rock salt type crystal and the O3' type crystal is R-3m, which is different from the space group Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of a rock salt type crystal with the simplest symmetry) of the rock salt type crystal, so the Miller indices of the crystal plane that satisfies the above conditions are different between the layered rock salt type crystal and the O3' type crystal and the rock salt type crystal. In this specification, when the orientation of the cubic close-packed structure formed by the anions is aligned in the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal, it may be said that the crystal orientation is approximately the same.

[0046] The crystal orientation of the two regions roughly coincides with each other, which can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc. can also be used for the determination. In TEM images, etc., the arrangement of cations and anions can be observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure in the layered rock salt type crystal and the rock salt type crystal is aligned, it can be observed that the angle between the repeated bright and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. In TEM images, etc., light elements such as oxygen and fluorine may not be clearly observed, but in such cases, the agreement of the orientation can be determined from the arrangement of metal elements.

[0047] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and removed from the positive electrode active material is removed. 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.

[0048] 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.

[0049] In this specification, charging refers to moving lithium ions from the positive electrode to the negative electrode in the battery and moving electrons from the positive electrode to the negative electrode in an external circuit. For a positive electrode active material, charging refers to removing lithium ions. A positive electrode active material with a charge depth of 0.7 to 0.9 is sometimes called a positive electrode active material charged at a high voltage.

[0050] Similarly, discharging refers to the movement of lithium ions from the negative electrode to the positive electrode within the battery and the movement 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 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 state charged at a high voltage, is called a fully discharged positive electrode active material.

[0051] 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 a dQ / dV curve obtained by differentiating capacitance (Q) with respect to voltage (V), and it is believed that the crystal structure changes significantly.

[0052] 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 material that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may contain a material that does not contribute to the charge / discharge capacity.

[0053] In this specification, etc., the positive electrode active material of one embodiment of the present invention may be expressed as a positive electrode material, a positive electrode material for a secondary battery, or the like. In this specification, etc., the positive electrode active material of one embodiment of the present invention preferably includes a compound. In this specification, etc., the positive electrode active material of one embodiment of the present invention preferably includes a composition. In this specification, etc., the positive electrode active material of one embodiment of the present invention preferably includes a composite.

[0054] 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 a battery is discharged at a current of 2X (A), it is said to have been discharged at 2C, and when a battery is discharged at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same goes for charge rate; when a battery is charged at a current of 2X (A), it is said to have been charged at 2C, and when a battery is charged at a current of X / 5 (A), it is said to have been charged at 0.2C.

[0055] 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 when the upper voltage limit is reached. Constant current discharging, for example, refers to a method of discharging at a constant discharge rate.

[0056] (Embodiment 1) An example of a positive electrode active material and a manufacturing method thereof according to one embodiment of the present invention will be described below.

[0057] The positive electrode active material of one embodiment of the present invention contains lithium, metal Me1, metal X, titanium, and oxygen.

[0058] The metal Me1 is one or more metals including cobalt.

[0059] The metal X is a metal other than cobalt, and examples of metals that can be used as the metal X include magnesium, calcium, zirconium, lanthanum, barium, copper, potassium, sodium, zinc, etc. It is particularly preferable to use magnesium as the metal X.

[0060] Moreover, the positive electrode active material of one embodiment of the present invention preferably contains fluorine.

[0061] Moreover, the positive electrode active material of one embodiment of the present invention may contain, in addition to cobalt as metal Me1, one or more metals selected from nickel, manganese, aluminum, iron, vanadium, chromium, and niobium (hereinafter referred to as metal Me1_2).

[0062] By having metal Me1_2 in addition to cobalt as metal Me1, the bond distance between metal Me1 and oxygen can be controlled in the crystal structure of the positive electrode active material. By controlling the bond distance between metal Me1 and oxygen, for example, when the positive electrode active material of one embodiment of the present invention is used in a secondary battery, excellent characteristics can be realized. Here, it is particularly preferable to use nickel in addition to cobalt as metal Me1.

[0063] For example, in the positive electrode active material of one embodiment of the present invention, the molar ratio of lithium, cobalt, and metal Me1_2 is represented by lithium:cobalt:Me1_2 = 1.03:1 - x:x, where x preferably satisfies 0 < x < 1, more preferably satisfies 0.3 < x < 0.75, and even more preferably satisfies 0.4 ≤ x ≤ 0.6.

[0064] For example, in the positive electrode active material of one embodiment of the present invention, metal Me1 is cobalt and nickel, and the molar ratio of lithium, cobalt, and nickel is represented by lithium:cobalt:nickel = 1.03:1 - x:x, where x preferably satisfies 0 < x < 1, more preferably satisfies 0.3 < x < 0.75, and even more preferably satisfies 0.4 ≤ x ≤ 0.6.

[0065] <Example of method for producing positive electrode active material> An example of the method for producing the positive electrode active material of one embodiment of the present invention will be described using the flowchart shown in FIG. 3.

[0066] First, in step S21, a titanium compound 806 is prepared. The titanium compound 806 preferably has a eutectic point with a lithium compound 807 described later.

[0067] As the titanium compound 806, a compound containing titanium and oxygen can be used. For example, an oxide containing titanium is used. More specifically, titanium oxide (TiO x , where x preferably satisfies 0 < x < 3, more preferably satisfies 1.5 < x < 2.5, and even more preferably x satisfies 2 and values in the vicinity thereof) and the like can be used.

[0068] When the sol-gel method is used, titanium oxide, titanium hydroxide, titanium alkoxide, etc. can be used as the titanium compound 806. By performing the sol-gel method using these compounds, for example, titanium oxide can be produced. As the titanium alkoxide, for example, titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, etc. can be used.

[0069] Also, in step S22, a lithium compound 807 is prepared. The lithium compound 807 preferably has a eutectic point with the titanium compound 806.

[0070] As the lithium compound 807, a compound containing oxygen can be used. As the lithium compound, lithium oxide (Li x O, where x preferably satisfies 0 < x < 3, more preferably satisfies 1.5 < x < 2.5, and even more preferably x satisfies 2 and values in the vicinity thereof), lithium carbonate (Li2Co3), lithium hydroxide (LiOH), etc. can be used.

[0071] Consider the case where titanium compound 806 is titanium oxide or a precursor of titanium oxide. In such a case, lithium oxide is preferable as lithium compound 807 because it has a eutectic point with titanium oxide. When lithium carbonate is used as lithium compound 807, it can decompose during the heating process in the later step S51 to generate lithium oxide. When lithium hydroxide is used as lithium compound 807, lithium oxide may be generated during the heating process in the later step S51. For this reason, it is preferable to use lithium carbonate or lithium hydroxide as lithium compound 807.

[0072] Lithium carbonate has the advantage that it is stable at room temperature and in the air and is easy to handle.

[0073] In addition, when lithium oxide is used as the lithium compound 807, at least a part of it may be converted to a compound such as lithium carbonate or lithium hydroxide by a reaction with a solvent or a gas such as water vapor or carbon dioxide in the atmosphere during the manufacturing method of the positive electrode active material of one embodiment of the present invention.

[0074] Here, as an example, titanium oxide is used as the titanium compound 806 and lithium oxide is used as the lithium compound 807 .

[0075] Next, in step S23, the materials prepared in steps S21 and S22 are mixed together. In step S23, it is preferable to perform pulverization.

[0076] Mixing can be done in a dry or wet manner, but the wet method is preferred because it allows for finer grinding. Fine grinding can sometimes accelerate the reaction of the materials being mixed. When mixing in a wet manner, 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 does not react easily with lithium.

[0077] As an example, acetone is prepared as a solvent, and pulverization is performed using a ball mill.

[0078] For mixing and pulverization, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, for example, it is preferable to use zirconia balls as media. It is preferable to thoroughly carry out this mixing and pulverization process to finely pulverize the mixture 809.

[0079] When the sol-gel method is used, for example, alcohol may be used as the solvent, and the mixture may be stirred using a magnetic stirrer, etc. By stirring, the sol-gel reaction can be promoted.

[0080] Here, the number of moles of titanium contained in the titanium compound 806 is, for example, 0.05% or more and 5% or less, or 0.1% or more and 2% or less, for example, 0.5% (0.005 times), relative to the sum of the number of moles of cobalt, nickel, manganese, and aluminum among the metals contained in the cobalt-containing material prepared in S26 described later.

[0081] The number of moles of lithium contained in the lithium compound 807 is, for example, 1.0 to 10 times, or 1.5 to 5 times, such as 3.4 times, the number of moles of the titanium compound 806.

[0082] The mixture 809 preferably has, for example, an average particle size (D50) smaller than that of the cobalt-containing material 808 described below. The D50 of the mixture 809 is, for example, 0.005 μm or more and 20 μm or less, or 0.005 μm or more and 5 μm or less.

[0083] In step S24, the mixed and pulverized material is recovered, and in step S25, a mixture 809 is obtained. When recovering the material in the solvent, filtration, centrifugation, evaporation to dryness, etc. may be applied for separation from the solvent. Also, separation from the solvent may not be performed in this step, but may be performed in step S28 described later.

[0084] Next, in step S26, a composite oxide having lithium, metal Me1, metal X, and oxygen is used as the cobalt-containing material 808. A material prepared in advance may be used as the cobalt-containing material 808, or the cobalt-containing material 808 may be prepared. The cobalt-containing material 808 may be prepared by one or more methods selected from various methods such as a solid-phase method and a liquid-phase method. For example, a coprecipitation method may be used as the liquid-phase method. By using the coprecipitation method, when the cobalt-containing material has multiple transition metals, the multiple transition metals may be easily distributed uniformly. By uniformly distributing the multiple transition metals, for example, a cobalt-containing material with few grain boundaries may be obtained. Alternatively, one or more methods selected from a spray pyrolysis method, a double decomposition method, a method by a thermal decomposition reaction of a precursor, a reverse micelle method, a method combining these methods with high-temperature baking, and a liquid-phase method such as a freeze-drying method may be used. An example of a method for preparing the cobalt-containing material 808 will be described later.

[0085] Next, in step S27, the mixture 809 obtained in step S25 and the cobalt-containing material 808 prepared in step S26 are mixed and pulverized. At this time, by performing pulverization weaker than that in step S23, it is possible to suppress cleavage, crack generation, crystal defect generation, and the like of the cobalt-containing material 808. For example, wet pulverization is performed in step S23, and dry pulverization is performed in step S27. Here, for example, dry pulverization is performed using a ball mill.

[0086] Next, in step S28, the mixed and crushed materials are collected, and in step S29, a mixture 810 is obtained.

[0087] Next, in step S51, mixture 810 is heated. This step may be called annealing. By performing annealing, a positive electrode active material of one embodiment of the present invention is produced. In this specification, annealing also means heating mixture 810, or at least heating a heating furnace in which mixture 810 is placed. The heating furnace may be equipped with a pump having at least one of the functions of reducing pressure and pressurizing the inside of the heating furnace. For example, pressure may be applied during the annealing in step S51.

[0088] The annealing temperature in S51 is preferably equal to or higher than the temperature at which the reaction between the titanium compound 806 and the lithium compound 807 proceeds. Here, the temperature at which the reaction proceeds may be any temperature at which mutual diffusion of elements contained in the titanium compound 806 and the lithium compound 807 occurs. Therefore, the temperature at which the reaction proceeds may refer to a temperature lower than the melting temperatures of these materials. For example, in the case of oxides, the melting temperature T m 0.757 times (Tammann temperature T d ) solid-state diffusion occurs.

[0089] However, it is preferable that the annealing temperature is equal to or higher than the temperature at which at least a part of the mixture 810 melts, since this makes it easier for the reaction to proceed. Therefore, it is preferable that the annealing temperature is equal to or higher than the eutectic point of the titanium compound 806 and the lithium compound 807. When the titanium compound 806 contains TiO2 and the lithium compound 807 contains Li2O, the eutectic point P of TiO2 and Li2O is around 1030°C, as shown in Figure 1 (quoted from Non-Patent Document 2, Figure 1 with additions). It is preferable that the annealing temperature of S51 is 780°C or higher.

[0090] Also, from FIG. 1, at the eutectic point P, the weight of TiO2 is 44% of the sum of the weights of TiO2 and Li2O, which corresponds to a molar ratio of TiO2:Li2O=1:3.4.

[0091] The eutectic mixture of TiO2 and Li2O, or a melt of either of them, may cover a part of the surface of the cobalt-containing material 808, thereby smoothing the surface of the positive electrode active material 811. Alternatively, the eutectic mixture of TiO2 and Li2O, or a melt of either of them may react with the cobalt-containing material 808, thereby smoothing the surface of the positive electrode active material 811.

[0092] When the surface of the positive electrode active material is smooth, the concentration of stress is alleviated, and the positive electrode active material is less likely to crack during pressure application and charge / discharge. Here, for example, the positive electrode active material has a particulate form.

[0093] The smoothness of the surface can be quantified, for example, by image analysis of a microscopic image of the particles of the positive electrode active material. For example, a surface SEM, a cross-sectional SEM, a cross-sectional TEM, etc. can be used as the microscope. The particle contour line can be extracted, and the smoothness can be judged based on the ratio of the convex area to the concave area on the contour line.

[0094] Furthermore, by mixing the titanium compound 806 and the cobalt-containing material 808 and heating them, at least a part of the metal X may migrate to the surface of the cobalt-containing material due to an interaction or reaction between the metal X and titanium contained in the cobalt-containing material, forming a compound containing the metal X and titanium, or a mixture containing the metal X and titanium, on the surface of the particulate positive electrode active material. In such cases, convex portions may be formed on the surface of the positive electrode active material.

[0095] When a material that forms a eutectic mixture with the titanium compound 806 is used as the lithium compound 807, the interaction or reaction between the titanium compound 806 and the cobalt-containing material 808 is weakened by mixing and heating the titanium compound 806 and the cobalt-containing material 808 in addition to the lithium compound 807. This makes it possible to suppress the migration of the metal X to the surface of the cobalt-containing material.

[0096] When it is difficult to form a eutectic mixture of TiO2 and Li2O, for example, when the ratio of TiO2 and Li2O is significantly different from the condition for forming the eutectic point, TiO2 cannot spread over a wide area on the surface of the cobalt-containing material 808, and many irregularities may be formed on the surface of the positive electrode active material. If there are many irregularities on the surface of the positive electrode active material, there is a risk that the positive electrode active material may be easily broken or cracked due to the occurrence of points where stress is concentrated. If the positive electrode active material is broken or cracked, the elution of transition metals, excessive side reactions, etc. are likely to occur. Such a phenomenon is undesirable in terms of cycle characteristics, reliability, safety, etc.

[0097] Here, the differential scanning calorimetry (DSC) of the mixture 809 will be described with reference to FIG. 2. The result indicated by "809" in FIG. 2 is the measurement result of the mixture 809, in which TiO2 was used as the titanium compound and Li2O was used as the lithium compound. They were mixed so that TiO2:Li2O=1:3.4 (molar ratio). The result indicated by "806" in FIG. 2 is the measurement result of the titanium compound 806, in which TiO2 was used as the titanium compound.

[0098] 2, endothermic peaks are observed in the vicinity of 427° C., 689° C., and 1139° C. in the mixture 809. No significant peaks are observed in the titanium compound 806.

[0099] The endothermic peaks at 427°C and 689°C may be due to the decomposition products of lithium or titanium compounds. Considering the melting points of the decomposition products, for example, the endothermic peak near 427°C may be due to the peak of LiOH (melting point is about 450°C), and the endothermic peak near 689°C may be due to the peak of Li2CO3 (melting point is about 700°C).

[0100] The eutectic point of the mixture 809 is estimated to be an endothermic peak near 1139° C., suggesting that the mixture 809 has a lower melting point than the titanium compound 806.

[0101] The annealing temperature in step S51 is preferably 780° C. or higher and 1150° C. or lower, more preferably 860° C. or higher and 1140° C. or lower, and further preferably 950° C. or higher and 1100° C. or lower, and for example, 1050° C. or lower.

[0102] Next, in step S52, the annealed material is recovered, and in step S53, positive electrode active material 811 is obtained.

[0103] <Example 2 of a method for producing a positive electrode active material> As shown in FIG. 4, in step S31, a titanium compound 806, a lithium compound 807 and a cobalt-containing material 808 may be mixed, and steps S23, S24 and S25 in FIG. 3 may be omitted.

[0104] 4, the materials prepared in steps S21, S22, and S26 are mixed and pulverized. The mixing can be performed in a dry or wet manner.

[0105] In step S32, the mixed materials are collected, and in step S33, a mixture 810 is obtained.

[0106] In FIG. 4, steps S51 and thereafter can be carried out with reference to FIG.

[0107] <Examples of how to prepare cobalt-containing materials> Next, an example of a method for producing LiMO2, which is one embodiment of a material applicable as the cobalt-containing material 808, will be described with reference to FIG. 5. The metal M includes the metal Me1 listed above. The metal M can further include the metal X listed above in addition to the metal Me1 listed above. In the following, a cobalt-containing material in which the metal M includes the metal X and the metal X is Mg will be described as an example. Note that the positive electrode active material of one embodiment of the present invention has a crystal structure of a lithium composite oxide represented by LiMO2, but the composition is not limited to Li:M:O=1:1:2.

[0108] First, in step S11, a composite oxide containing lithium, a transition metal, and oxygen is used as the composite oxide 801. Here, it is preferable to use one or more transition metals including cobalt.

[0109] A composite oxide having lithium, a transition metal, and oxygen can be synthesized by heating a lithium source and a transition metal source in an oxygen atmosphere. As the transition metal source, it is preferable to use a metal that can form a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. As the transition metal, for example, at least one of manganese, cobalt, and nickel can be used. In addition to these transition metals, aluminum can be used. That is, as the transition metal source, only a cobalt source may be used, only a nickel source may be used, two types of a cobalt source and a manganese source, two types of a cobalt source and a nickel source may be used, or three types of a cobalt source, a manganese source, and a nickel source may be used. Furthermore, in addition to these metal sources, an aluminum source may be used. The heating temperature at this time is preferably higher than that of step S17 described later. For example, it can be performed at 1000°C. This heating step may be called firing.

[0110] When using a composite oxide having lithium, transition metals, and oxygen that has been synthesized in advance, it is preferable to use one with few impurities. In this specification, the main components of the composite oxide having 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 impurities. For example, when analyzed by glow discharge mass spectrometry, the total impurity concentration is preferably 10,000 ppmw (parts per million weight) or less, and more preferably 5000 ppmw or less. For example, the total impurity concentration of transition metals and arsenic is 3000 ppmw or less, or 1500 ppmw or less. For example, the total impurity concentration of transition metals such as titanium and arsenic is 3000 ppmw or less, or 1500 ppmw or less.

[0111] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as the pre-synthesized lithium cobalt oxide. This is lithium cobalt oxide with an average particle diameter (D50) of about 12 μm, and in impurity analysis by glow discharge mass spectrometry (GD-MS), the magnesium concentration and fluorine concentration are 50 ppmw or less, the calcium concentration, aluminum concentration and silicon concentration 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.

[0112] The composite oxide 801 in step S11 preferably has a layered rock-salt type crystal structure with few defects and distortion. 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 highly likely to have a crystal structure with many defects or distortion.

[0113] In step S12, fluoride 802 is prepared. As the fluoride, 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, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), sodium aluminum hexafluoride (Na3AlF6), etc. can be used. The fluoride 802 may be any material that functions as a fluorine source. Therefore, instead of or as a part of the fluoride 802, for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. may be used and mixed into the atmosphere.

[0114] When a compound having a metal X is used as the fluoride 802, the compound 803 (a compound having a metal X) described later can also serve as the fluoride 802.

[0115] In this embodiment, lithium fluoride (LiF) is prepared as the fluoride 802. LiF is preferable because it has a common cation with LiCoO2. LiF is also preferable because it has a relatively low melting point of 848°C and is easily melted in the annealing process described below.

[0116] Furthermore, when LiF is used as the fluoride 802, it is preferable to prepare a compound 803 (a compound having a metal X) in addition to the fluoride 802 in step S13. The compound 803 is a compound having a metal X.

[0117] In step S13, a compound 803 is prepared. As the compound 803, a fluoride, oxide, hydroxide, or the like of a metal X can be used, and it is particularly preferable to use a fluoride.

[0118] When magnesium is used as the metal X, a magnesium compound can be used as the compound 803. For example, MgF2 or the like can be used as the compound 803. Magnesium can be arranged in high concentration near the surface of the cobalt-containing material.

[0119] In addition to the fluoride 802 and the compound 803, a material having a metal other than cobalt and other than the metal X may be mixed. Examples of the material having a metal other than cobalt and other than the metal X include 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. For example, it is preferable to pulverize and mix the hydroxide, fluoride, oxide, etc. of each metal. The pulverization can be performed, for example, by a wet method.

[0120] Furthermore, the order of steps S11, S12 and S13 may be freely combined.

[0121] Next, in step S14, the materials prepared in steps S11, S12, and S13 are mixed and pulverized. Mixing can be performed in a dry or wet manner, but the wet method is preferable because it allows for finer pulverization. When performing the wet method, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used.

[0122] For example, a ball mill, a bead mill, etc. 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 carry out this mixing and grinding process to finely pulverize the mixture 804.

[0123] Next, in step S15, the mixed and crushed materials are collected, and in step S16, a mixture 804 is obtained.

[0124] The mixture 804 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.

[0125] Next, in step S17, heating is performed. This step is sometimes called annealing. The heating temperature is preferably equal to or higher than the temperature at which the mixture 804 melts. In addition, the annealing temperature is preferably equal to or lower than the decomposition temperature (1130° C.) of LiCoO2.

[0126] By using LiF as the fluoride 802 and performing annealing in step S17 with a lid on, it is possible to produce a cobalt-containing material 808 with good cycle characteristics, etc. In addition, when LiF and MgF2 are used as the fluoride 802, since the eutectic point of LiF and MgF2 is around 742°C, it is considered that the reaction with LiCoO2 is promoted and LiMO2 is generated by setting the annealing temperature in step S17 to 742°C or higher.

[0127] In addition, LiF, MgF2 and LiCoO2 show endothermic peaks in differential scanning calorimetry (DSC) at around 820° C. Therefore, the annealing temperature is preferably 742° C. or higher, and more preferably 820° C. or higher.

[0128] Therefore, the annealing temperature in step S17 is preferably 742° C. or higher and 1130° C. or lower, more preferably 742° C. or higher and 1000° C. or lower, preferably 820° C. or higher and 1130° C. or lower, and more preferably 820° C. or higher and 1000° C. or lower.

[0129] In addition, in this embodiment, it is considered 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 804 will decrease, suppressing the generation of LiMO2. Therefore, it is necessary to heat while suppressing the volatilization of LiF.

[0130] Therefore, the mixture 804 is heated in an atmosphere containing LiF, that is, the mixture 804 is heated in a state where the partial pressure of LiF in the heating furnace is high, thereby suppressing the volatilization of LiF in the mixture 804. By annealing with a lid using a fluoride (LiF or MgF) that forms a eutectic mixture, the annealing temperature can be lowered to the decomposition temperature of LiCoO2 (1130°C) or lower, specifically, to 742°C to 1000°C, and the generation of LiMO2 can be efficiently promoted. Therefore, a cobalt-containing material with good characteristics can be produced, and the annealing time can also be shortened.

[0131] An example of the annealing method in S17 is shown in FIG.

[0132] The heating furnace 120 shown in FIG. 7 has a heating furnace space 102, a hot plate 104, a heater unit 106, and a heat insulating material 108. It is more preferable to place a lid 118 on the container 116 and perform annealing. With this configuration, the space 119 formed by the container 116 and the lid 118 can be made into an atmosphere containing fluoride. During annealing, if the state is maintained by closing the lid so that the concentration of gasified fluoride in the space 119 is constant or does not decrease, fluorine and magnesium can be contained in the vicinity of the particle surface. Since the space 119 has a smaller volume than the heating furnace space 102, a small amount of fluoride volatilizes, and the atmosphere containing fluoride can be made. That is, the reaction system can be made into an atmosphere containing fluoride without significantly impairing the amount of fluoride contained in the mixture 804. Therefore, LiMO2 can be efficiently generated. In addition, by using the lid 118, the mixture 804 can be annealed in an atmosphere containing fluoride easily and inexpensively.

[0133] Here, the valence of Co (cobalt) in LiMO2 produced by one embodiment of the present invention is preferably approximately trivalent. Cobalt can be divalent or trivalent. Therefore, in order to suppress the reduction of cobalt, it is preferable that the atmosphere in the heating furnace space 102 contains oxygen, and it is more preferable that the ratio of oxygen to nitrogen in the atmosphere in the heating furnace space 102 is equal to or higher than the air atmosphere, and it is even more preferable that the oxygen concentration in the atmosphere in the heating furnace space 102 is equal to or higher than the air atmosphere. Therefore, it is necessary to introduce an atmosphere containing oxygen into the heating furnace space. However, since there is a possibility that divalent cobalt atoms are more stable for cobalt atoms with magnesium atoms present nearby, all cobalt atoms do not have to be trivalent.

[0134] Therefore, in one embodiment of the present invention, before heating, a step of making the space 102 inside the heating furnace an atmosphere containing oxygen and a step of placing the container 116 containing the mixture 804 in the space 102 inside the heating furnace are performed. By performing the steps in this order, the mixture 804 can be annealed in an atmosphere containing oxygen and fluoride. It is also preferable to seal the space 102 inside the heating furnace during annealing so that gas is not transported to the outside. For example, it is preferable to perform annealing without flowing gas.

[0135] There is no particular limitation on the method for making the space 102 inside the heating furnace an atmosphere containing oxygen, but one example is a method of evacuating the space 102 inside the heating furnace and then introducing an oxygen-containing gas such as oxygen gas or dry air, or a method of flowing in 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 space 102 inside the heating furnace and then introduce oxygen gas (oxygen replacement). The air in the space 102 inside the heating furnace may be considered to be an atmosphere containing oxygen.

[0136] When lid 118 is placed on container 116 and an oxygen-containing atmosphere is created and then heated, a moderate amount of oxygen enters container 116 through the gap in lid 118 placed on container 116, and a moderate amount of fluoride can be retained inside container 116.

[0137] In addition, 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 804 .

[0138] The annealing in step S17 is preferably performed at an appropriate temperature and time. The appropriate temperature and time vary depending on conditions such as the size and composition of the particles of the complex oxide 801 in step S11. If the particles are small, a lower temperature or a shorter time may be more preferable than if the particles are large. After the annealing in S17, a step of removing the lid is included.

[0139] For example, when the average particle size (D50) of the particles in step S11 is about 12 μm, the annealing time is preferably, for example, 3 hours or more, and more preferably 10 hours or more.

[0140] On the other hand, when the average particle size (D50) of the particles in step S11 is about 5 μm, the annealing time is preferably, for example, from 1 hour to 10 hours, and more preferably about 2 hours.

[0141] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0142] Next, in step S18, the annealed material is recovered, and in step S19, a cobalt-containing material 808 is obtained.

[0143] <Example 3 of a method for producing a positive electrode active material> In the flow diagram shown in FIG. 6, the manufacturing method can be simplified as compared with the steps shown in FIGS.

[0144] 6, the materials in steps S11, S12, S13, S21 and S22 are prepared and mixed. It is also preferable to perform pulverization in step S33.

[0145] Next, in step S34, the material that has undergone step S33 is collected, and in step S35, mixture 810 is obtained.

[0146] For steps S51 and onwards, refer to FIG.

[0147] By using the flow shown in FIG. 6, the process can be simplified.

[0148] This embodiment mode can be used in appropriate combination with other embodiment modes.

[0149] (Embodiment 2) In this embodiment, an example of a structure of a positive electrode active material manufactured by a manufacturing method of one embodiment of the present invention will be described.

[0150] [Positive electrode active material structure] Materials having a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have a high discharge capacity and to be excellent as positive electrode active materials for secondary batteries. An example of a material having a layered rock-salt crystal structure is a composite oxide represented by LiMO2. The metal M includes the metal Me1 listed above. In addition to the metal Me1 listed above, the metal M can further include the metal X listed above.

[0151] 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.

[0152] In compounds containing nickel, distortion may occur easily due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltage, there is a concern that the crystal structure may collapse due to distortion. It is suggested that the influence of the Jahn-Teller effect is small in LiCoO2, and it may have better resistance to charging and discharging at high voltage, which is preferable.

[0153] The positive electrode active material will be described with reference to FIG. 8 and FIG.

[0154] The positive electrode active material produced in one embodiment of the present invention can reduce the displacement of the CoO2 layer during repeated charging and discharging at high voltage. Furthermore, the change in volume can be reduced. Therefore, the compound can achieve excellent cycle characteristics. In addition, the compound can have a stable crystal structure in a high-voltage charged state. Therefore, the compound may be less likely to short when a high-voltage charged state is maintained. In such a case, safety is further improved, which is preferable.

[0155] 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.

[0156] The positive electrode active material 811 contains lithium, metal M, oxygen, and titanium. The positive electrode active material 811 contains the metal Me1 listed above as the metal M. The metal M preferably contains the metal X listed above in addition to the metal Me1 listed above. It also preferably contains a halogen such as fluorine or chlorine.

[0157] The positive electrode active material 811 preferably has a particulate form. When the positive electrode active material 811 has a particulate form, the titanium concentration in the surface layer of the particle is higher than the titanium concentration in the interior. The magnesium concentration in the surface layer is higher than the magnesium concentration in the interior. The surface layer of the positive electrode active material 811 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 (Mg / Ti) in the first region may be higher than the ratio of magnesium concentration to titanium (Mg / Ti) in a region of the surface layer located more inward than the first region.

[0158] In addition, in each region such as the surface layer, the inside, and the first region in the surface layer, the concentration of elements such as metal M, titanium, etc., has, for example, a gradient. 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, nickel, etc. can be used as metal M. In such a case, aluminum and nickel each have, for example, a concentration gradient in each region such as the surface layer, the inside, and the first region in the surface layer.

[0159] The positive electrode active material 811 has a first region. When the positive electrode active material 811 has a particulate form, the first region preferably includes a region inside the surface layer portion. At least a part of the surface layer portion may be included in the first region. The first region is preferably represented by a layered rock salt type crystal structure, and the region is represented by a space R-3m. The first region is a region having lithium, metal Me1, oxygen, and metal X. An example of the crystal structure of the first region before and after charging and discharging is shown in FIG. 8. In addition, the surface layer portion of the positive electrode active material 811 may have a crystal represented by a structure different from the layered rock salt type crystal structure, which has titanium, magnesium, and oxygen, in addition to or instead of the region represented by the layered rock salt type crystal structure described in FIG. 8 and the like below. For example, the surface layer portion may have a crystal represented by a spinel structure, which has titanium, magnesium, and oxygen.

[0160] The crystal structure at a charge depth of 0 (discharged state) in FIG. 8 is the same as that in FIG. 9, R-3m (O3). On the other hand, the first region has a crystal structure different from the H1-3 type crystal structure when the charge depth is fully charged. This structure is in the space group R-3m, and although it is not a spinel type crystal structure, ions of cobalt, magnesium, etc. occupy the oxygen 6 coordination positions, and the arrangement of cations has a symmetry similar to that of the spinel type. In addition, the symmetry of the CoO2 layer of this structure is the same as that of the O3 type. This structure is referred to as an O3' type crystal structure or a pseudo-spinel type crystal structure in this specification. In addition, in the diagram of the O3' type crystal structure shown in FIG. 8, lithium can be present at any lithium site with a probability of about 20%, but this is not limited to this. It may be present only at a specific part of the lithium sites. In addition, in both the O3 type crystal structure and the O3' type crystal structure, it is preferable that magnesium is present in a dilute amount between the CoO2 layers, that is, at the lithium sites. It is also preferable that halogen such as fluorine is present randomly and dilutely at the oxygen sites.

[0161] In the O3' type crystal structure, a light element 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.

[0162] It can also be said that the O3' type crystal structure is 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 close to that of lithium cobalt oxide (NiO2), but it is known that pure lithium cobalt oxide or layered rock salt type positive electrode active materials that contain a large amount of cobalt do not usually have this crystal structure.

[0163] The layered rock salt type crystal and the anions of the rock salt type crystal have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3' type crystal also have a cubic close-packed structure. When they contact, there is a crystal plane where the orientation of the cubic close-packed structure formed by the anions is aligned. However, the space group of the layered rock salt type crystal and the O3' type crystal is R-3m, which is different from the space group Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of a rock salt type crystal with the simplest symmetry) of the rock salt type crystal, so the Miller indices of the crystal plane that satisfies the above conditions are different between the layered rock salt type crystal and the O3' type crystal and the rock salt type crystal. In this specification, when the orientation of the cubic close-packed structure formed by the anions is aligned in the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal, it may be said that the crystal orientation is approximately the same.

[0164] In the first region, the change in the crystal structure when a large amount of lithium is released during charging at a high voltage is suppressed more than in the comparative example described later. For example, as shown by the dotted line in Figure 8, there is almost no displacement of the CoO2 layer in these crystal structures.

[0165] More specifically, the first region has a high structural stability even when the charging voltage is high. For example, in the comparative example, the H1-3 crystal structure is formed at a voltage of about 4.6 V based on the potential of lithium metal, but the positive electrode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure even at the charging voltage of 4.6 V. Even at a higher charging voltage, for example, a voltage of about 4.65 V to 4.7 V based on the potential of lithium metal, the positive electrode active material of one embodiment of the present invention can have the O3' crystal structure. When the charging voltage is further increased to more than 4.7 V, the H1-3 crystal may finally be observed in the positive electrode active material of one embodiment of the present invention. In addition, when the charging voltage is lower (for example, even when the charging voltage is 4.5 V or more and less than 4.6 V based on the potential of lithium metal), the positive electrode active material of one embodiment of the present invention may have the O3' crystal structure. Note that, when graphite is used as the negative electrode active material in the secondary battery, the voltage of the secondary battery is lowered by the amount of the potential of the graphite. The potential of graphite is about 0.05 V to 0.2 V based on the potential of lithium metal. Therefore, for example, even when the voltage of a secondary battery using graphite as a negative electrode active material is 4.3 V to 4.5 V, the positive electrode active material of one embodiment of the present invention can maintain the R-3m(O3) crystal structure, and there is a region in which the O3'-type crystal structure can be formed even in a region where the charging voltage is further increased, for example, when the voltage of the secondary battery is more than 4.5 V and is 4.6 V to 4.55 V. Furthermore, when the charging voltage is lower, for example, when the voltage of the secondary battery is 4.2 V to 4.3 V, the positive electrode active material of one embodiment of the present invention may be able to form the O3' structure.

[0166] Therefore, in the first region, the crystal structure is not easily destroyed even when charging and discharging are repeated at a high voltage.

[0167] In the positive electrode active material 904, 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. Note that the O3' type crystal structure can have the coordinates of cobalt and oxygen in the unit cell expressed as Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25.

[0168] 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 voltages. Therefore, when magnesium exists between the CoO2 layers, the O3' type crystal structure is easily formed.

[0169] 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 it may have adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0170] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment for distributing magnesium throughout the particles. The addition of 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 a fluorine compound is expected to improve corrosion resistance against hydrofluoric acid produced by decomposition of the electrolyte.

[0171] If the magnesium concentration is increased above a desired value, the effect of stabilizing the crystal structure may be reduced. This is believed to be because magnesium enters the cobalt site in addition to the lithium site. The number of magnesium atoms in the positive electrode active material produced according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less than the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably about 0.02. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particle of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition in the process of producing the positive electrode active material.

[0172] The number of nickel atoms in the positive electrode active material 811 is preferably 7.5% or less of the number of cobalt atoms, more 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.

[0173] <Particle size> If the particle size of the positive electrode active material 811 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. For this reason, the average particle size (D50: also called the median diameter) 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.

[0174] <Analysis method> Whether or not a certain positive electrode active material exhibits an 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 beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable in that 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 degree 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 the secondary battery.

[0175] As described above, the positive electrode active material 811 is characterized by a small change in crystal structure between a state charged at a high voltage and a discharged state. A material in which a crystal structure that changes greatly from a discharged state when charged at a high voltage accounts for 50 wt% or more is not preferable because it cannot withstand high-voltage charging and discharging. It is also important to note that the desired crystal structure may not be obtained by simply adding an impurity element. For example, even if lithium cobalt oxide containing magnesium and fluorine is common in that it is charged at a high voltage, there are cases in which the O3' type crystal structure accounts for 60 wt% or more and cases in which the H1-3 type crystal structure accounts for 50 wt% or more. In addition, at a certain voltage, the O3' type crystal structure is almost 100 wt%, and when the certain voltage is further increased, the H1-3 type crystal structure may occur. Therefore, it is preferable to analyze the crystal structure of the positive electrode active material 811 by XRD or the like. By using it in combination with measurements such as XRD, a more detailed analysis can be performed.

[0176] However, when the positive electrode active material is charged or discharged at a high voltage, its crystal structure may change when it comes into contact with the air. For example, it may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere, such as an atmosphere containing argon.

[0177] <Comparative Example> The positive electrode active material shown in Fig. 9 is lithium cobalt oxide (LiCoO2) to which no metal X is added. The crystal structure of the lithium cobalt oxide shown in Fig. 9 changes depending on the depth of charge.

[0178] As shown in Figure 9, lithium cobalt oxide at a charge depth of 0 (discharged state) has a region with a crystal structure of space group R-3m, and there are three CoO2 layers in the unit cell. Therefore, this crystal structure is sometimes called an O3 type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and the octahedral structure is continuous on a plane with edge sharing.

[0179] At a charge depth of 1, the crystal structure has the space group P-3m1, and there is one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called the O1 type crystal structure.

[0180] Lithium cobalt oxide at a charge depth of about 0.8 has a crystal structure of space group R-3m. This structure can be said to be 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 called an H1-3 type crystal structure. In reality, the number of cobalt atoms per unit cell in the H1-3 type crystal structure is twice that of other structures. However, in FIG. 9 and other parts of this specification, the c-axis of the H1-3 type crystal structure is shown as half the unit cell in order to make it easier to compare with other structures.

[0181] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type 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 oxygen atoms. Thus, the H1-3 type crystal structure is expressed by a unit cell using one cobalt and two oxygens. On the other hand, the O3' type crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen is different in the O3' type crystal structure and the H1-3 type structure, and the O3' type crystal structure has a smaller change from the structure of O3 than the H1-3 type 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 good of fitness (GOF) value is smaller in Rietveld analysis of XRD.

[0182] When lithium cobalt oxide is repeatedly charged at a high voltage of 4.6 V or higher based on the redox potential of lithium metal, or when it is repeatedly charged to a deep depth of charge of 0.8 or higher, and then discharged, it undergoes repeated changes in crystal structure (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0183] However, these two crystal structures have a large deviation in the CoO2 layer. As shown by the dotted line and arrow in Figure 9, in the H1-3 type crystal structure, the CoO2 layer is significantly deviated from R-3m(O3). Such a dynamic structural change can have a negative effect on the stability of the crystal structure.

[0184] 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%.

[0185] In addition, the H1-3 crystal structure, which has continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0186] As a result, the crystal structure of lithium cobalt oxide breaks down when it is repeatedly charged and discharged at high voltages. This break in the crystal structure causes a deterioration in cycle characteristics. This is thought to be because the break in the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult to insert and remove lithium.

[0187] This embodiment mode can be used in appropriate combination with other embodiment modes.

[0188] (Embodiment 3) In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS.

[0189] <Secondary battery configuration example 1> 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.

[0190]

Positive Electrode

[0191] Also, the positive electrode active material described in the previous embodiment and another positive electrode active material may be mixed and used.

[0192] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0193] Also, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed 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.

[0194] Also, as another positive electrode active material, a composition formula Li a Mn b M c O dIt is possible to use a lithium manganese composite oxide that can be expressed by the following formula. Here, the element M is preferably a metal element selected from 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 is 0 0 during discharge and 0.26≦(b+c) / d<0.5 is satisfied. The composition of metal, silicon, phosphorus, etc. of the entire lithium manganese composite oxide particle can be measured using, for example, an ICP-MS (inductively coupled plasma mass spectrometer). The composition of oxygen of the entire lithium manganese composite oxide particle can be measured using, for example, an EDX (energy dispersive X-ray spectrometry). It can also be obtained by using valence evaluation of melt gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS 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.

[0195] A graphene compound may be used as the conductive material. In the present specification and the like, the graphene compound includes graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. The graphene compound has carbon, has a shape such as a plate shape or a sheet shape, and has a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by the six-membered carbon rings may be called a carbon sheet. The graphene compound may have a functional group. In addition, the graphene compound preferably has a bent shape. In addition, the graphene compound may be rolled up like a carbon nanofiber.

[0196] ​In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet-like shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0197] In the present specification and the like, reduced graphene oxide refers to a material having carbon and oxygen, a sheet-like shape, and a two-dimensional structure formed of six-membered carbon rings. It may be called a carbon sheet. Although reduced graphene oxide functions as a single sheet, multiple sheets may be stacked. Reduced graphene oxide preferably has a portion in which the carbon concentration is greater than 80 atomic % and the oxygen concentration is 2 atomic % or more and 15 atomic % or less. By setting such carbon concentration and oxygen concentration, it can function as a conductive material with high conductivity even in a small amount. In addition, reduced graphene oxide preferably has an intensity ratio G / D of G band to D band in Raman spectrum of 1 or more. Reduced graphene oxide with such intensity ratio can function as a conductive material with high conductivity even in a small amount.

[0198] In the vertical cross section of the active material layer, the sheet-like graphene compound is dispersed approximately uniformly in the internal region of the active material layer. The graphene compounds are formed so as to cover a part of the positive electrode active material particles or to be attached to the surfaces of the positive electrode active material particles, and are in surface contact with each other.

[0199] 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 no binder can be used, and the ratio of the active material to the electrode volume and electrode weight can be improved. In other words, the charge / discharge capacity of the secondary battery can be increased.

[0200] Here, it is preferable to use graphene oxide as the graphene compound, mix it with the active material to form a layer that becomes the active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced acid graphene. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene compound, the graphene compound can be dispersed approximately uniformly in the inner 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 compounds remaining in the active material layer are partially overlapped and dispersed to such an extent that they are in surface contact with each other, thereby forming a three-dimensional conductive path. The reduction of the graphene oxide may be performed, for example, by heat treatment or by using a reducing agent.

[0201] Therefore, unlike granular conductive materials such as acetylene black, which are in point contact with the active material, the graphene compound allows for surface contact with low contact resistance, and therefore the electrical conductivity between the granular positive electrode active material and the graphene compound can be improved with a smaller amount than that of a normal conductive material. Therefore, the ratio of the positive electrode active material in the active material layer can be increased. This can increase the discharge capacity of the secondary battery.

[0202] Furthermore, by using a spray drying apparatus in advance, a graphene compound, which is a conductive material, can be formed as a coating to cover the entire surface of the active material, and further a conductive path can be formed between adjacent particles of the active material by the graphene compound.

[0203] In addition, 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 of 1 μm or less, more preferably 100 nm or less.

[0204] [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 include a conductive material and a binder.

[0205] [Negative electrode active material] As the negative electrode active material, for example, one or more materials selected from alloy-based materials, carbon-based materials, and the like can be used.

[0206] As the negative electrode active material, an element capable of carrying out a charge / discharge reaction by alloying / dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger charge / discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used. For example, SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, elements capable of carrying out charge / discharge reactions through alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0207] In this specification, SiO refers to, for example, silicon monoxide. Alternatively, SiO x Here, x preferably has a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less, or preferably 0.2 or more and 1.2 or less, or preferably 0.3 or more and 1.5 or less.

[0208] As the carbon-based material, graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, and the like may be used.

[0209] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, as the artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. In addition, it is relatively easy to reduce the surface area of ​​MCMB, which may be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0210] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of lithium metal (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has the advantages of relatively high charge / discharge capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal.

[0211] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0212] In addition, the negative electrode active material is Li3N-type Li, a complex nitride of lithium and transition metals. 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0213] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it is preferable to combine it with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material that contains lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first removing the lithium ions contained in the positive electrode active material.

[0214] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs in sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0215] As the conductive material and binder that can be contained in the negative electrode active material layer, materials similar to the conductive material and binder that can be contained in the positive electrode active material layer can be used.

[0216] [Negative electrode current collector] The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector is made of a material that does not form an alloy with carrier ions such as lithium.

[0217] [Electrolyte] The electrolytic solution has a solvent and an electrolyte. The solvent of the electrolytic solution is preferably an aprotic organic solvent, and for example, one of 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, sultone, etc., or two or more of these can be used in any combination and ratio.

[0218] In addition, by using one or more ionic liquids (room-temperature molten salts) that are flame-retardant and non-volatile as a solvent for the electrolyte, it is possible to prevent short-circuiting of the internal region of the secondary battery, and explosion and ignition of the secondary battery when the internal region temperature rises due to overcharging, etc. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0219] Examples of the electrolyte to be dissolved in the above-mentioned solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10, Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these.

[0220] 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, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0221] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive may be, for example, 0.1 wt% to 5 wt% of the total solvent.

[0222] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0223] The use of a polymer gel electrolyte improves safety against leakage, etc. Also, it is possible to make the secondary battery thinner and lighter.

[0224] Examples of the polymer that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0225] The polymer may be one or more selected from a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), may be used. The polymer formed may have a porous shape.

[0226] In addition, instead of the electrolyte, one or more selected from a solid electrolyte having an inorganic sulfide material, a solid electrolyte having an inorganic oxide material, and a solid electrolyte having a polymer material such as PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator and a spacer becomes unnecessary. In addition, since the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.

[0227] [Separator] The secondary battery preferably has a separator. The separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0228] The separator may have a multi-layer structure. For example, an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these. As the ceramic material, for example, aluminum oxide particles or silicon oxide particles may be used. As the fluorine material, for example, PVDF or polytetrafluoroethylene may be used. As the polyamide material, for example, nylon or aramid (meta-aramid or para-aramid) may be used.

[0229] Coating with ceramic materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and discharging, and improving the reliability of the secondary battery. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of the secondary battery.

[0230] For example, both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.Alternatively, the surface of the polypropylene film that contacts the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0231] By using a separator with a multi-layer structure, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the charge / discharge capacity per volume of the secondary battery can be increased.

[0232] [Exterior body] The exterior body of the secondary battery can be made of at least one material selected from metal materials such as aluminum and resin materials. A film-shaped exterior body can also be used. As the film, a three-layer structure film can be used in which a thin metal film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as polyamide-based resin or polyester-based resin is further provided on the thin metal film as the outer surface of the exterior body.

[0233] <Secondary battery configuration example 2> As an example of the configuration of the secondary battery, the configuration of a secondary battery using a solid electrolyte layer will be described below.

[0234] As shown in FIG. 10A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0235] 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 additive and a binder.

[0236] 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.

[0237] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive assistant and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not have a solid electrolyte 421, as shown in FIG. 10B. When metallic lithium is used for the negative electrode 430, the energy density of the secondary battery 400 can be improved, which is preferable.

[0238] 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.

[0239] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S 30P2S5, 30Li2S 26B2S3 44LiI, 63Li2S 38SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 50Li2S 50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 , Li 3.25 P 0.95Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, making it easy to maintain conductive paths even after charging and discharging.

[0240] 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 (PO4)3, etc. Oxide-based solid electrolytes have the advantage of being stable in the air.

[0241] 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.

[0242] Also, different solid electrolytes may be used in combination.

[0243] Among them, Li with NASICON type crystal structure 1+x Al x Ti 2-x(PO4)3(0 < x < 1) (hereinafter referred to as LATP) contains elements such as aluminum and titanium, which may be included in the positive electrode active material used in the secondary battery 400 of one aspect of the present invention. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. In addition, an improvement in productivity due to the reduction of processes can also be expected. In this specification and the like, the NASICON-type crystal structure is a compound represented by M2(AO4)3 (M: transition metal, A: S, P, As, Mo, W, etc.), and has a structure in which MO6 octahedra and AO4 tetrahedra share vertices and are three-dimensionally arranged.

[0244] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it preferably has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0245] For example, FIG. 11 shows an example of a cell for evaluating the materials of an all-solid-state battery.

[0246] FIG. 11A is a schematic cross-sectional view of the evaluation cell. The evaluation cell has one or more selected from a lower member 761, an upper member 762, and fixing screws and wing nuts 764 for fixing them, and fixes the evaluation material by pressing the electrode plate 753 by rotating the pressing screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762 made of a stainless steel material. Also, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0247] The evaluation material is placed on the electrode plate 751, surrounded by an insulating tube 752 around it, and is in a state of being pressed by the electrode plate 753 from above. A perspective view of the periphery of this evaluation material enlarged is shown in FIG. 11B.

[0248] As an example of the evaluation material, a lamination of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in FIG. 11C. In addition, the same reference numerals are used for the same parts in FIGS. 11A, 11B, and 11C.

[0249] The electrode plate 751 and the lower member 761 electrically connected to the positive electrode 750a can be said to correspond to a positive electrode terminal. The electrode plate 753 and the upper member 762 electrically connected to the negative electrode 750c can be said to correspond to a negative electrode terminal. The electrical resistance and the like can be measured while applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0250] In addition, it is preferable to use a package with excellent airtightness for the exterior body of the secondary battery of one embodiment of the present invention. For example, a ceramic package or a resin package can be used. In addition, it is preferable to seal the exterior body in a sealed atmosphere, for example, in a glove box, while blocking the outside air.

[0251] Fig. 12A shows a perspective view of a secondary battery of one embodiment of the present invention having an exterior body and shape different from those in Fig. 11. The secondary battery in Fig. 12A has external electrodes 771 and 772, and is sealed in an exterior body having a plurality of packaging members.

[0252] An example of a cross section cut along the dashed line in Fig. 12A is shown in Fig. 12B. A laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is surrounded and sealed by a package member 770a having an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c having an electrode layer 773b on a flat plate. An insulating material such as a resin material or ceramic can be used for the package members 770a, 770b, and 770c.

[0253] 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.

[0254] This embodiment mode can be used in appropriate combination with other embodiment modes.

[0255] (Embodiment 4) 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 the material used in the secondary battery described in this embodiment.

[0256] <Coin-type secondary battery> First, an example of a coin-type secondary battery will be described. Fig. 13A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 13B is a cross-sectional view thereof.

[0257] In the 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 with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed of 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 of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0258] In addition, the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each need only have an active material layer formed on one side.

[0259] Metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys of these metals, or alloys of these metals with other metals (e.g., stainless steel, etc.) can be used for the positive electrode can 301 and the negative electrode can 302. To prevent corrosion by the electrolyte, it is preferable to coat them with at least one material selected from nickel, aluminum, etc. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0260] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 13B, positive electrode can 301 is placed at the bottom, and positive electrode can 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order, and positive electrode can 301 and negative electrode can 302 are crimped together via gasket 303, to produce coin-type secondary battery 300.

[0261] 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.

[0262] Here, the flow of current during charging of a secondary battery will be described with reference to FIG. 13C. When a secondary battery using lithium is regarded as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In a secondary battery using lithium, the anode (positive electrode) and the cathode (negative electrode) are interchanged during charging and discharging, and the oxidation reaction and the reduction reaction are interchanged, so the electrode with a high reaction potential is called the positive electrode, and the electrode with a low 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 (plus electrode)" and the negative electrode will be called the "negative electrode" or "- electrode (minus electrode)". If the terms anode (positive electrode) or cathode (negative electrode) related to the oxidation reaction or reduction reaction are used, the terms will be reversed during charging and discharging, which may cause confusion. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode or cathode are used, it should be specified whether they are used during charging or discharging, and also whether they correspond to the positive or negative pole.

[0263] 13C are connected to a charger to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0264] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to Fig. 14. Fig. 14A shows an external view of a cylindrical secondary battery 600. Fig. 14B is a schematic diagram showing a cross section of the cylindrical secondary battery 600. As shown in Fig. 14B, 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.

[0265] Inside a hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched therebetween. 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. For the battery can 602, metals such as nickel, aluminum, and titanium that are resistant to corrosion by the electrolyte, or alloys of these, or alloys of these and other metals (e.g., stainless steel, etc.) can be used. In addition, in order to prevent corrosion by the electrolyte, it is preferable to coat the battery can 602 with one or more selected from nickel, aluminum, etc. Inside the battery can 602, the 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. In addition, a nonaqueous electrolyte (not shown) is injected into the internal region of the battery can 602 in which the battery element is provided. The nonaqueous electrolyte can be the same as that of a coin-type secondary battery.

[0266] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form an active material 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 element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the rise in the internal pressure of the battery exceeds a predetermined threshold value. The PTC element 611 is a thermosensitive resistor whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO3)-based semiconductor ceramics can be used for the PTC element.

[0267] 14C, a plurality of secondary batteries 600 may be sandwiched between conductive plates 613 and 614 to form a module 615. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then further in series. By forming a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0268] FIG. 14D is a top view of the module 615. To clarify the drawing, the conductive plate 613 is shown by a dotted line. As shown in FIG. 14D, the module 615 may have a conductor 616 that electrically connects the multiple secondary batteries 600. A conductive plate can be provided by overlapping the conductor 616. Also, a temperature control device 617 may be provided between the multiple secondary batteries 600. When the secondary battery 600 is overheated, it can be cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of the module 615 is less susceptible to the influence of the outside air temperature. It is preferable that the heat medium of the temperature control device 617 is insulating and non-flammable.

[0269] 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.

[0270] <Structure example of secondary battery> Another structural example of the secondary battery will be described with reference to FIGS.

[0271] 15A and 15B are diagrams showing the external 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. As shown in FIG. 15B, the secondary battery 913 is connected to a terminal 951 and a terminal 952. The circuit board 900 is fixed with a sticker 915.

[0272] 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 a control signal input terminal, a power supply terminal, or the like.

[0273] 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. In addition, an antenna such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, or 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 the capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

[0274] 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 caused by the secondary battery 913. The layer 916 can be made of, for example, a magnetic material.

[0275] The structure of the battery pack is not limited to that shown in FIG.

[0276] For example, as shown in Figures 16A and 16B, an antenna may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in Figures 15A and 15B. Figure 16A is an external view showing one of the pair of surfaces, and Figure 16B is an external view showing the other of the pair of surfaces. Note that the description of the secondary battery shown in Figures 15A and 15B can be used as appropriate for the same parts as those of the secondary battery shown in Figures 15A and 15B.

[0277] 16A, 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. 16B, 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.

[0278] The above structure allows the sizes of both the antenna 914 and the antenna 918 to be increased. The antenna 918 has a function of performing data communication with, for example, an external device. For example, an antenna having a shape applicable to the antenna 914 can be applied to the antenna 918. As a communication method between the secondary battery and other devices via the 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 applied.

[0279] Alternatively, as shown in Fig. 16C, a display device 920 may be provided on the secondary battery 913 shown in Figs. 15A and 15B. 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. 15A and 15B can be appropriately applied to the same portions as those of the secondary battery shown in Figs. 15A and 15B.

[0280] For example, an image indicating whether charging is in progress, an image indicating the amount of stored power, etc. may be displayed on the display device 920. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, etc. can be used as the display device 920. For example, the use of electronic paper can reduce the power consumption of the display device 920.

[0281] Alternatively, as shown in Fig. 16D, a sensor 921 may be provided in the secondary battery 913 shown in Fig. 15A and 15B. 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. 15A and 15B can be appropriately applied to the same parts as those of the secondary battery shown in Fig. 15A and 15B.

[0282] 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.

[0283] Further, a structural example of the secondary battery 913 will be described with reference to FIGS.

[0284] A secondary battery 913 shown in FIG. 17A has a wound body 950 in which terminals 951 and 952 are provided in an internal region of a housing 930. The wound body 950 is impregnated with an electrolyte in an internal region of the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 does not contact the housing 930 by using an insulating material or the like. Note that in FIG. 17A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0285] As shown in Fig. 17B, the housing 930 shown in Fig. 17A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 17B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0286] 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.

[0287] 17C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the laminated sheet is wound. Note that the stack of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked a plurality of times.

[0288] 15 via one of the terminal 951 and the terminal 952. The positive electrode 932 is connected to the terminal 911 shown in FIG 15 via the other of the terminal 951 and the terminal 952.

[0289] Alternatively, a secondary battery 913 having a wound body 950a as shown in FIG. 18A to FIG. 18C may be used. The wound body 950a shown in FIG. 18A 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 wider 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. In terms of safety, it is preferable that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. In addition, the wound body 950a having such a shape is preferable because of its high safety and productivity.

[0290] 18B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0291] 18C, wound body 950a and the electrolyte are covered with housing 930 to form secondary battery 913. Housing 930 is preferably provided with a safety valve, an overcurrent protection element, and the like.

[0292] As shown in Fig. 18B, the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, the secondary battery 913 can have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 18A and 18B, the description of the secondary battery 913 shown in Figs. 17A to 17C can be referred to.

[0293] 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.

[0294] <Laminated secondary battery> Next, examples of laminated secondary batteries will be described with reference to Fig. 19 to Fig. 31. If the laminated secondary battery has a flexible structure, and is mounted in an electronic device having at least a flexible portion, the secondary battery can be bent in accordance with the deformation of the electronic device.

[0295] A laminated secondary battery 980 will be described with reference to Fig. 19. The laminated secondary battery 980 has a wound body 993 shown in Fig. 19A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. 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, similar to the wound body 950 described in Fig. 18.

[0296] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to 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.

[0297] As shown in Fig. 19B, 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-mentioned wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 19C. 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.

[0298] For example, one or more materials selected from a metal material such as aluminum and a resin material can be used for the film 981 and the film 982 having the recesses. If a resin material is used as the material for the film 981 and the film 982 having the recesses, the film 981 and the film 982 having the recesses can be deformed when an external force is applied, and a flexible storage battery can be produced.

[0299] Although an example in which two films are used is shown in FIG. 19B and FIG. 19C, a space may be formed by folding one film, and the above-mentioned wound body 993 may be housed in the space.

[0300] 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.

[0301] In addition, while Figure 19 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 rectangular positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing, as shown in Figure 20, for example.

[0302] 20A 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 interior of 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.

[0303] 20A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining 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, but may be exposed to the outside by using a lead electrode and ultrasonically bonding the lead electrode to the positive electrode current collector 501 or the negative electrode current collector 504.

[0304] In the laminated secondary battery 500, the exterior body 509 may be a three-layer laminate film having a highly flexible thin metal film such as aluminum, stainless steel, copper, nickel, etc., provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and further having an insulating synthetic resin film such as a polyamide-based resin, polyester-based resin, etc., provided on the thin metal film as the outer surface of the exterior body.

[0305] 20B shows an example of a cross-sectional structure of a laminated secondary battery 500. For simplicity, Fig. 20A shows an example of a battery made up of two current collectors, but in reality, the battery is made up of multiple electrode layers as shown in Fig. 20B.

[0306] In FIG. 20B, the number of electrode layers is 16 as an example. Even if the number of electrode layers is 16, the secondary battery 500 has flexibility. FIG. 20B shows a structure of 16 layers in total, including 8 layers of negative electrode collector 504 and 8 layers of positive electrode collector 501. FIG. 20B shows a cross section of the negative electrode lead-out portion, in which 8 layers of negative electrode collector 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 having a larger charge / discharge capacity can be obtained. When the number of electrode layers is small, a secondary battery can be made thin and excellent in flexibility.

[0307] 21 and 22 show an example of an external view of a laminated secondary battery 500. In FIGS. 21 and 22, a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511 are provided.

[0308] FIG. 23A shows an external view 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 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 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. The areas and shapes of the tab regions of the positive electrode and the negative electrode are not limited to the example shown in FIG. 23A.

[0309] <Method of manufacturing laminated secondary battery> Here, an example of a method for producing the laminate type secondary battery whose external view is shown in FIG. 21 will be described with reference to FIGS. 23B and 23C.

[0310] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 23B shows the laminated negative electrode 506, the separator 507, and the 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 the 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 the joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0311] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0312] Next, as shown in Fig. 23C, exterior body 509 is folded at the portion indicated by the dashed line. After that, 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, a region (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.

[0313] Next, electrolytic solution 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolytic solution 508 is preferably performed under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, laminated secondary battery 500 can be produced.

[0314] 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.

[0315] <Bendable secondary battery> Next, an example of a bendable secondary battery will be described with reference to FIGS. 24 and 25. FIG.

[0316] FIG. 24A shows a schematic top view of a secondary battery 250 that can be bent. FIG. 24B, FIG. 24C, and FIG. 24D are schematic cross-sectional views taken along the lines C1-C2, C3-C4, and A1-A2 in FIG. 24A, respectively. The secondary battery 250 has an exterior body 251 and an electrode laminate 210 housed in the internal region of the exterior body 251. The electrode laminate 210 has at least a positive electrode 211a and a negative electrode 211b. The positive electrode 211a and the negative electrode 211b together constitute the electrode laminate 210. The lead 212a electrically connected to the positive electrode 211a and the lead 212b electrically connected to the negative electrode 211b extend outside the exterior body 251. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed in the region surrounded by the exterior body 251.

[0317] The positive electrode 211a and the negative electrode 211b of the secondary battery 250 will be described with reference to Fig. 25. Fig. 25A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 25B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0318] 25A, secondary battery 250 has a plurality of rectangular positive electrodes 211a, a plurality of rectangular 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.

[0319] 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.

[0320] Furthermore, a separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material is formed and the surface of the negative electrode 211b on which the negative electrode active material is formed. In Figures 25A and 25B, the separator 214 is shown by a dotted line for ease of viewing.

[0321] 25B, the multiple positive electrodes 211a and the lead 212a are electrically connected at a joint 215a, and the multiple negative electrodes 211b and the lead 212b are electrically connected at a joint 215b.

[0322] Next, exterior body 251 will be described with reference to Figs. 24B, 24C, 24D, and 24E.

[0323] 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 overlapping the lead 212a and the lead 212b, and can also be called a top seal.

[0324] It is preferable that exterior body 251 has a corrugated shape in which ridge lines 271 and valley lines 272 are alternately arranged in the portions overlapping with positive electrode 211a and negative electrode 211b. In addition, it is preferable that seal portion 262 and seal portion 263 of exterior body 251 are flat.

[0325] Fig. 24B is a cross section taken at a portion overlapping with ridge line 271, and Fig. 24C is a cross section taken at a portion overlapping with valley line 272. Fig. 24B and Fig. 24C both correspond to cross sections in the width direction of secondary battery 250 and positive electrode 211a and negative electrode 211b.

[0326] Here, the distance between the ends of the positive electrode 211a and the negative electrode 211b in the width direction, i.e., the ends of the positive electrode 211a and the negative electrode 211b, and the seal portion 262 is defined as the distance La. When the secondary battery 250 is deformed, such as by bending, the positive electrode 211a and the negative electrode 211b are deformed so as to be displaced from each other in the length direction, as described below. At that time, if the distance La is too short, the exterior body 251 and the positive electrode 211a and the negative electrode 211b may rub strongly against each other, and the exterior body 251 may be damaged. 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.

[0327] Moreover, 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 negative electrode 211b is increased.

[0328] More specifically, when the total thickness of the laminated positive electrode 211a and 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, more preferably 1.0 to 2.0 times. Or preferably 0.8 to 2.5 times. Or preferably 0.8 to 2.0 times. Or preferably 0.9 to 3.0 times. Or preferably 0.9 to 2.0 times. Or preferably 1.0 to 3.0 times. Or preferably 1.0 to 2.5 times. By setting the distance La in this range, a compact battery with high reliability against bending can be realized.

[0329] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to set distance Lb sufficiently larger than the width of positive electrode 211a and negative electrode 211b (here, width Wb of negative electrode 211b). As a result, even if positive electrode 211a and negative electrode 211b come into contact with exterior body 251 when secondary battery 250 is repeatedly deformed, such as by bending, parts of positive electrode 211a and negative electrode 211b can be displaced in the width direction, so that rubbing between positive electrode 211a and negative electrode 211b and exterior body 251 can be effectively prevented.

[0330] For example, it is preferable that the difference between the distance Lb between the pair of seal portions 262 and the width Wb of the negative electrode 211b is 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. Or, it is preferable that it is 1.6 to 5.0 times. Or, it is preferable that it is 1.6 to 4.0 times. Or, it is preferable that it is 1.8 to 6.0 times. Or, it is preferable that it is 1.8 to 4.0 times. Or, it is preferable that it is 2.0 to 6.0 times. Or, it is preferable that it is 2.0 to 5.0 times.

[0331] Here, a satisfies 0.8 or more and 3.0 or less, preferably 0.9 or more and 2.5 or less, more preferably 1.0 or more and 2.0 or less. Or 0.8 or more and 2.5 or less. Or 0.8 or more and 2.0 or less. Or 0.9 or more and 3.0 or less. Or 0.9 or more and 2.0 or less. Or 1.0 or more and 3.0 or less. Or 1.0 or more and 2.5 or less.

[0332] 24D 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. 24D, it is preferable that a space 273 is provided between exterior body 251 and the ends of positive electrode 211a and negative electrode 211b in the longitudinal direction at bent portion 261.

[0333] Fig. 24E shows a schematic cross-sectional view of the bent secondary battery 250. Fig. 24E corresponds to the cross section taken along the cutting line B1-B2 in Fig. 24A.

[0334] When the secondary battery 250 is bent, a part of the exterior body 251 located on the outside of the bend is stretched, and another part located on the inside is deformed so as to contract. More specifically, the part located on the outside of the exterior body 251 is deformed so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the part located on the inside of the exterior body 251 is deformed 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 that the material constituting the exterior body 251 itself does not need to expand or contract. As a result, the exterior body 251 is not damaged, and the secondary battery 250 can be bent with a small force.

[0335] 24E, when the secondary battery 250 is bent, the positive electrode 211a and the negative electrode 211b are displaced relative to each other. At this time, since one end of the multiple stacked positive electrodes 211a and negative electrodes 211b on the seal portion 263 side is fixed by the fixing member 217, the positive electrodes 211a and negative electrodes 211b are displaced such that the amount of displacement increases toward the bent portion 261. This relieves the stress applied to 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.

[0336] 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 inside when bent can be relatively displaced without coming into contact with exterior body 251.

[0337] 24 and 25 is a battery that is unlikely to suffer damage to the exterior body, the positive electrode 211a and the negative electrode 211b, etc., even if repeatedly bent and stretched, and the battery characteristics are also unlikely to deteriorate. 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 further excellent cycle characteristics.

[0338] In an all-solid-state battery, the positive electrode and the negative electrode are stacked, and a predetermined pressure is applied in the stacking direction 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, expansion in the stacking direction due to charging and discharging of the all-solid-state battery can be suppressed, and the reliability of the all-solid-state battery can be improved.

[0339] This embodiment mode can be used in appropriate combination with other embodiment modes.

[0340] (Embodiment 5) In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described.

[0341] First, examples of electronic devices incorporating the bendable secondary battery described in the previous embodiment are shown in Figures 26A to 26G. Examples of electronic devices to which the bendable secondary battery is applied 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.

[0342] Furthermore, a secondary battery having a flexible shape can be incorporated along the inner wall of a house, the inner wall of a building, the outer wall of a house, the outer wall of a building, the curved surface of an automobile interior, or the curved surface of an automobile exterior.

[0343] 26A illustrates an example of a mobile phone. A 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.

[0344] FIG. 26B shows a state in which the mobile phone 7400 is bent. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided in the internal region is also bent. FIG. 26C 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 a copper foil, and a part of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, so that the secondary battery 7407 has a high reliability when bent.

[0345] FIG. 26D illustrates an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, an operation button 7103, and a secondary battery 7104. FIG. 26E illustrates a bent state of the secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing is deformed, and the curvature of the secondary battery 7104 changes in part or in whole. Note that the degree of bending at any point of the curve expressed by the value of 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, the housing or the main surface of the secondary battery 7104 changes in part or in whole within a range of the radius of curvature of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature of the main surface of the secondary battery 7104 is within a range of 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight portable display device with a long life can be provided.

[0346] 26F shows an example of a wristwatch-type portable information terminal 7200. A 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.

[0347] The portable information terminal 7200 can execute various applications such as mobile telephone, e-mail, document browsing and creation, music playback, Internet communication, and computer games.

[0348] The display surface of the display portion 7202 is curved, and 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, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0349] The operation button 7205 can have various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / cancellation, power saving mode activation / cancellation, etc. For example, the function of the operation button 7205 can be freely set by an operating system built into the mobile information terminal 7200.

[0350] The mobile information terminal 7200 can also perform short-distance wireless communication according to a communication standard. For example, hands-free conversation can be performed by communicating with a headset capable of wireless communication. The mobile information terminal 7200 may have an antenna. The antenna may also be used for wireless communication.

[0351] 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.

[0352] 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. 26E can be incorporated in the inner region of the housing 7201 in a curved state or in the inner region of the band 7203 in a bendable state.

[0353] The portable 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, as well as a touch sensor, a pressure sensor, an acceleration sensor, and the like.

[0354] 26G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and a secondary battery of one embodiment of the present invention. The display device 7300 can also include a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0355] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. In addition, the display device 7300 can change the display state by short-range wireless communication according to a communication standard.

[0356] The display device 7300 also includes an input / output terminal, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed by wireless power supply without using the input / output terminal.

[0357] By using the secondary battery of one embodiment of the present invention as a secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0358] An example in which the secondary battery described in the above embodiment is mounted on an electronic device will be described with reference to FIGS. 26H, 27, and 28. FIG.

[0359] By using the 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 the secondary battery of these products, a stick-shaped secondary battery that is small, lightweight, and has a large charge and discharge capacity is desired in consideration of ease of holding by users.

[0360] FIG. 26H is a perspective view of a device also called a tobacco-receiving smoking device (electronic cigarette). In FIG. 26H, the electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including one or more selected from a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents either or both of overcharging and overdischarging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 26H has an external terminal so that it can be connected to a charging device. Since the secondary battery 7504 is the tip part when held, it is desirable that the total length is short and the weight is light. Since the secondary battery of one embodiment of the present invention has a high charge / discharge capacity and good cycle characteristics, a small and lightweight electronic cigarette 7500 that can be used for a long period of time can be provided.

[0361] Next, an example of a tablet terminal that can be folded in two is shown in Fig. 27A and Fig. 27B. The tablet terminal 9600 shown in Fig. 27A and Fig. 27B has a housing 9630a, a housing 9630b, a movable part 9640 that connects the housings 9630a and 9630b, a display part 9631 having a display part 9631a and a display part 9631b, a switch 9625, a switch 9626 and a switch 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display part 9631, a tablet terminal having a wider display part can be obtained. Fig. 27A shows the tablet terminal 9600 in an open state, and Fig. 27B shows the tablet terminal 9600 in a closed state.

[0362] The tablet terminal 9600 also includes a power storage unit 9635 in an internal region of the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housings 9630a and 9630b.

[0363] 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.

[0364] A keyboard may be displayed on the display portion 9631b of the housing 9630b, and information such as characters 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 a keyboard may be displayed on the display portion 9631 by touching the button with a finger or a stylus.

[0365] In addition, a touch input can be simultaneously made to 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.

[0366] 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 switching on and off the power of the tablet terminal 9600. 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 black and white 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 according to the amount of external light during use detected by an optical sensor built into the tablet terminal 9600. Note that the tablet terminal may have built-in not only an optical sensor but also other detection devices such as a gyro, an acceleration sensor, or the like for detecting tilt.

[0367] 27A 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 substantially the same, but the display areas of the display portions 9631a and 9631b are not particularly limited, and one may have a different size from the other, and the display quality may also be different. For example, one may be a display panel that can display with higher resolution than the other.

[0368] 27B 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.

[0369] As described above, the tablet terminal 9600 can be folded in half, and therefore the housing 9630a and the housing 9630b can be folded so as to overlap each other when not in use. By folding, the display portion 9631 can be protected, and therefore durability of the tablet terminal 9600 can be improved. 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, and therefore the tablet terminal 9600 that can be used for a long period of time can be provided.

[0370] In addition, the tablet terminal 9600 shown in Figures 27A and 27B can have a function to display various information (still images, videos, text images, etc.), a function to display a calendar, date or time on the display unit, a touch input function to perform touch input operations or edit information displayed on the display unit, and a function to control processing using various software (programs), etc.

[0371] 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. The use of a lithium ion battery as the power storage unit 9635 has the advantage of enabling miniaturization.

[0372] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 27B are described with reference to a block diagram in Fig. 27C. Fig. 27C shows a solar cell 9633, a power storage unit 9635, a DCDC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 27B.

[0373] First, an example of operation in the case where power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is stepped up or stepped 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 for the operation of the display unit 9631, a switch SW1 is turned on, and the 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, SW1 is turned off and SW2 is turned on to charge the power storage unit 9635.

[0374] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and may be configured to charge the power storage unit 9635 using other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a configuration having a non-contact power transmission module that transmits and receives power wirelessly (non-contact) for charging, or a configuration in which power generation by the solar cell is combined with other charging means may be used.

[0375] FIG. 28 illustrates an example of another electronic device. In FIG. 28, 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 a TV broadcast and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one embodiment of the present invention is provided in an internal region of the housing 8001. The display device 8000 can receive power from a commercial power source, and can also use power stored in the secondary battery 8004. Thus, even when power cannot be supplied from a 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.

[0376] 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).

[0377] The display device includes all display devices for displaying information, such as display devices for receiving TV broadcasts, display devices for personal computers, display devices for advertisements, and the like.

[0378] 28, 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. FIG. 28 illustrates an example in which the secondary battery 8103 is provided in an internal area of ​​a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, but the secondary battery 8103 may be provided in an internal area of ​​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. Thus, even when power cannot be supplied from a 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 source.

[0379] Note that although Figure 28 illustrates an example of a stationary lighting device 8100 provided on a ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided on a surface 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.

[0380] 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 a discharge lamp such as an incandescent light bulb or a fluorescent lamp, and a light-emitting element such as an LED or an organic EL element.

[0381] 28, 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 according to 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. FIG. 28 illustrates an example in which the secondary battery 8203 is provided in the indoor unit 8200, but 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 a secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power cannot be supplied from a commercial power source due to a power outage or the like, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power source.

[0382] Note that although FIG. 28 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 air conditioner that has the functions of an indoor unit and an outdoor unit in a single housing.

[0383] 28, an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to 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. 28, the secondary battery 8304 is provided in an internal area 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. Thus, 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 according to one embodiment of the present invention as an uninterruptible power source.

[0384] Among the electronic devices described above, electronic devices such as high-frequency heating devices such as microwave ovens 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.

[0385] Also, by storing power in the secondary battery during time periods when electronic devices are not used, 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 source (called the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of the above time periods. For example, in the case of an electric refrigerator-freezer 8300, power is stored in the secondary battery 8304 during the night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed. Then, during the daytime when the temperature is high and the refrigerator door 8302 and the freezer door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0386] According to one embodiment of the present invention, the cycle characteristics of the secondary battery are improved, and the reliability can be improved. According to another embodiment of the present invention, the secondary battery has a high charge / discharge capacity, and therefore the characteristics of the secondary battery can be improved, and therefore 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.

[0387] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0388] (Embodiment 6) In this embodiment mode, examples of electronic devices using the secondary battery described in the above embodiment mode will be described with reference to FIGS.

[0389] FIG. 29A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. In addition, when a user uses the device in daily life or outdoors, in order to improve splash-proof performance, water resistance, or dust resistance, a wearable device that can be charged wirelessly as well as by wire with an exposed connector is desired.

[0390] For example, the secondary battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 29A. The glasses-type device 4000 has a frame 4000a and a display unit 4000b. By mounting a secondary battery on the temples of the curved frame 4000a, the glasses-type device 4000 can be made lightweight, well-balanced in weight, and capable of long continuous use. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0391] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset type device 4001. The headset type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A secondary battery can be provided in one or more of the flexible pipe 4001b and the earphone unit 4001c. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0392] 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 configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0393] 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 configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0394] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the belt type device 4006. The belt type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an internal region of the belt portion 4006a. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0395] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0396] The display unit 4005a can display not only the time, but also various other information such as incoming e-mails and phone calls.

[0397] In addition, since the wristwatch type device 4005 is a wearable device that is directly wrapped around the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's amount of exercise and health can be accumulated to manage the user's health.

[0398] FIG. 29B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0399] 29C shows a side view of the display portion 4005a. FIG. 29C shows a state in which 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.

[0400] 30A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port provided on the bottom surface.

[0401] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine the presence or absence of an obstacle such as a wall, furniture, or a step. When an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in an internal region thereof. 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 an electronic device with long operating time and high reliability.

[0402] Fig. 30B shows an example of a robot. The robot 6400 shown in Fig. 30B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a computing device, and the like.

[0403] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0404] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.

[0405] The upper camera 6403 and the lower camera 6406 have a function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of an obstacle in the moving direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0406] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or 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.

[0407] Fig. 30C shows an example of an aircraft. An aircraft 6500 shown in Fig. 30C has a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has a function of flying autonomously.

[0408] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of an obstacle when moving. The electronic component 6504 can estimate the remaining battery 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.

[0409] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0410] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0411] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0412] FIG. 31 illustrates a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 31A 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 and 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. The automobile 8400 includes a secondary battery. The secondary battery may be used by arranging modules of the secondary batteries illustrated in FIG. 14C and FIG. 14D on the floor of the vehicle. A battery pack in which a plurality of secondary batteries illustrated in FIG. 17 are combined may be installed on the floor of the vehicle. The secondary battery can not only drive the electric motor 8406, but also supply power to a light-emitting device such as a headlight 8401 and a room light (not shown). The vehicle according to one embodiment of the present invention preferably includes the secondary battery according to one embodiment of the present invention, an electric motor, and a control device. The control device preferably has a function of supplying power from the secondary battery to the electric motor.

[0413] 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.

[0414] The automobile 8500 shown in FIG. 31B can charge the secondary battery of the automobile 8500 by receiving power supply from an external charging facility by one or more methods selected from a plug-in method, a non-contact power supply method, and the like. FIG. 31B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector standards may be appropriately performed by a predetermined method such as CHAdeMO (registered trademark) or combo. The charging device 8021 may be a charging station installed in a commercial facility, or may be a home power source. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ACDC converter.

[0415] Also, although not shown, a power receiving device can be mounted on a vehicle, and charging can be performed by supplying power contactlessly from a ground power transmitting device. In the case of this contactless power supply method, by incorporating a power transmitting device in one or both of the road and the exterior wall, charging can be performed not only while the vehicle is stopped but also while it is moving. Furthermore, this contactless power supply method can be used to transmit and receive power between vehicles. Furthermore, a solar cell can be provided on the exterior of the vehicle, and a secondary battery can be charged while the vehicle is stopped or moving. For such contactless power supply, one or more of an electromagnetic induction method and a magnetic field resonance method can be used.

[0416] 31C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG 31C 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.

[0417] 31C, 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.

[0418] 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 small and lightweight. If the secondary battery itself can be made small and lightweight, it contributes to reducing the weight of the vehicle, and the cruising distance can be improved. In addition, the secondary battery mounted on the vehicle can be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it is possible to contribute to energy conservation and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, including cobalt, can be reduced.

[0419] This embodiment mode can be implemented in appropriate combination with other embodiment modes. EXAMPLES

[0420] In this example, a positive electrode active material of one embodiment of the present invention was prepared and its characteristics were evaluated.

[0421] <Preparation of cobalt-containing materials> First, according to the flow shown in FIG. 5, the cobalt-containing material prepared in step S26 in FIG. 3 was produced.

[0422] Lithium cobalt oxide (C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) was prepared as the composite oxide 801 in step S11. Magnesium fluoride was prepared as the fluoride 802 in step S12. Lithium fluoride was prepared as the compound 803. Although not shown in FIG. 5, aluminum hydroxide was prepared as the aluminum source, and nickel hydroxide was prepared as the nickel source. When the number of cobalt atoms contained in the composite oxide 801 was 100, each material was prepared so that the number of molecules of lithium fluoride was 0.33, the number of molecules of magnesium fluoride was 1, the number of molecules of aluminum hydroxide was 0.5, and the number of molecules of nickel hydroxide was 0.5.

[0423] In step S14, magnesium fluoride, lithium fluoride, aluminum hydroxide, and nickel hydroxide were mixed together to prepare a mixture. Lithium cobalt oxide was mixed into the mixture and collected (step S15), and a mixture 804 was obtained (step S16).

[0424] Next, in step S17, the mixture 804 was placed in an alumina container, which was then covered and placed in a muffle furnace. The mixture 804 was then heated and collected (step S18), and the cobalt-containing material 808 was obtained (step S19). Specifically, the mixture was heated at 900°C for 10 hours in an oxygen atmosphere three times. After each heating, the mixture was crushed in a mortar.

[0425] <Preparation of positive electrode active material 1> Next, a positive electrode active material was produced according to the flow shown in FIG.

[0426] Titanium oxide (TiO2) was prepared as titanium compound 806 in step S21, and lithium oxide (Li2O) was prepared as lithium compound 807 in step S22. When the sum of the numbers of cobalt, nickel, and aluminum atoms contained in cobalt-containing material 808 prepared in step S26 described below was taken as 100, the number of titanium oxide molecules was 0.5 and the number of lithium oxide molecules was 1.7, respectively.

[0427] Next, in step S23, titanium oxide and lithium oxide were mixed. A ball mill was used for mixing, and wet mixing was performed for 12 hours at a rotation speed of 400 rpm. Acetone was used as a solvent. Zirconia balls with a diameter of 1 mm were used.

[0428] Next, in step S24, the mixture was collected, and the solvent was evaporated to obtain a mixture 809 (step S25).

[0429] Next, in step S26, a cobalt-containing material 808 was prepared.

[0430] Next, in step S27, the mixture 809 and the cobalt-containing material 808 were mixed. A ball mill was used for mixing, and dry mixing was performed for 0.5 hours at a rotation speed of 150 rpm. Zirconia balls with a diameter of 1 mm were used.

[0431] Next, in step S28, the mixed mixture was collected to obtain a mixture 810 (step S29).

[0432] Next, in step S51, mixture 810 was heated. The heating conditions were varied. After heating, the mixture was collected (step S52), and sample Sa1 and sample Sa2 were obtained as two positive electrode active materials with different heating conditions.

[0433] Sample Sa1 is a positive electrode active material that was treated in step S51 at 850° C. for 2 hours in an oxygen atmosphere.

[0434] Sample Sa2 is a positive electrode active material that was heated in an oxygen atmosphere at 1050° C. for 2 hours in step S51.

[0435] <Preparation of positive electrode active material 2> Next, a positive electrode active material was prepared without using the lithium compound 807.

[0436] First, a titanium compound 806 and a cobalt-containing material 808 were mixed to prepare a mixture. The prepared mixture was heated. The heating conditions were adjusted. After heating, the mixture was recovered, and samples Sa3 and Sa4 were obtained as two cathode active materials with different heating conditions.

[0437] Sample Sa3 is a cathode active material prepared without using a lithium compound 807, and the heating was carried out at 850 °C for 2 hours in an oxygen atmosphere.

[0438] Sample Sa4 is a cathode active material prepared without using a lithium compound 807, and the heating was carried out at 1050 °C for 2 hours in an oxygen atmosphere.

[0439] <SEM image> Observation of the scanning electron microscope (SEM) images of the prepared samples and EDX analysis were performed using SU8030 manufactured by Hitachi High-Technologies.

[0440] The SEM images of the prepared samples Sa1, Sa2, Sa3, and Sa4 were observed. The acceleration voltage was 5 keV. The SEM images of sample Sa1 are shown in Fig. 32A, those of sample Sa2 are shown in Fig. 32B, those of sample Sa3 are shown in Fig. 33A, and those of sample Sa4 are shown in Fig. 33B.

[0441] In sample Sa2, the surface of the particulate cathode active material was smooth. In sample Sa1 with a lower heating temperature, compared with sample Sa2, irregularities were observed on the surface, and a plurality of convex portions were observed as shown in Fig. 32A. Also, in samples Sa3 and Sa4, which are cathode active materials prepared without using a lithium compound 807, surface irregularities were显著 observed, and in sample Sa3 with a lower heating temperature, a plurality of convex portions were observed as shown in Fig. 33A.

[0442] <edx> An EDX analysis was carried out on sample Sa3, which had a large surface irregularity and multiple protrusions. The acceleration voltage was 15 keV. Figure 34A shows an SEM image. Figure 34B shows the EDX area analysis results for cobalt, Figure 34C shows oxygen, Figure 34D shows aluminum, Figure 34E shows titanium, and Figure 34F shows magnesium. The analysis results suggest that the multiple protrusions seen on the particle surface contain a large amount of titanium and magnesium. This suggests that a reaction or interaction between titanium and magnesium occurred during the heating in step S51.

[0443] <Preparation of secondary battery> A secondary battery was produced using the produced positive electrode active material.

[0444] First, the positive electrodes were prepared using the samples Sa1, Sa2 and Sa4 as the positive electrode active material. The positive electrode active material, AB and PVDF were mixed in a ratio of positive electrode active material:AB:PVDF=95:3:2 (weight ratio) to prepare a slurry, which was then applied to an aluminum current collector. NMP was used as the solvent for the slurry.

[0445] After the slurry was applied to the current collector, the solvent was evaporated. Then, pressure was applied at 210 kN / m, and then further pressure was applied at 1467 kN / m. A positive electrode was obtained by the above process. The amount of support on the prepared positive electrode was approximately 7 mg / cm. 2 In addition, the density of the positive electrode active material layer was higher than 3.8 g / cc.

[0446] Next, the prepared positive electrode was used to prepare a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm).

[0447] Lithium metal was used as the counter electrode.

[0448] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, to which 2 wt% vinylene carbonate (VC) was added.

[0449] The separator was made of polypropylene having a thickness of 25 μm.

[0450] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0451] <Cycle characteristics> Next, the cycle characteristics of the secondary battery were evaluated. The battery was charged at a constant current of 0.5C to an upper limit of 4.6V, and then at 4.6V, it was charged at a constant voltage of 0.05C. The battery was discharged at a constant current of 0.5C to a lower limit of 2.5V. 200mA / g was converted to a 1C rate. The measurements were performed at 45°C.

[0452] The cycle characteristics are shown in Figure 35. The secondary battery using sample Sa2 as the positive electrode active material showed the most excellent characteristics.

[0453] From the cycle characteristics shown in FIG. 35 and the results of the SEM images described above, it is considered that in the process of preparing a positive electrode active material by mixing and heating mixture 809 obtained by mixing titanium compound 806 and lithium compound 807 with cobalt-containing material 808, a eutectic mixture of titanium compound 806 and lithium compound 807 is generated during heating, and the eutectic mixture can be uniformly distributed on the surface of cobalt-containing material 808 and reaction with magnesium, etc. can be suppressed, thereby making it possible to prepare a good positive electrode active material. [Explanation of symbols]

[0454] 102: space inside the heating furnace, 104: hot plate, 106: heater section, 108: heat insulating material, 116: container, 118: lid, 119: space, 120: heating furnace, 210: electrode laminate, 211a: positive electrode, 211b: negative electrode, 212a: lead, 212b: lead, 214: separator, 215a: joint section, 215b: joint section, 217: fixing member, 250: secondary battery, 251: exterior body, 261: folded section, 262: seal section, 263: seal section, 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: secondary battery, 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, 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 liquid, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 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: conductor, 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 part Component, 762: upper component, 764: wing nut, 765: O-ring, 766: insulator, 770a: packaging component, 770b: packaging component, 770c: packaging component, 771: external electrode, 772: external electrode, 773a: electrode layer, 773b: electrode layer, 801: composite oxide, 802: fluoride, 803: compound, 804: mixture, 806: titanium compound, 807: lithium compound, 808: cobalt-containing material, 809: mixture, 810: mixture, 811: positive electrode active material, 900: circuit board, 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: wound body, 950a: wound body, 951: terminal, 952: terminal, 980: secondary battery, 981: film, 982: film, 993: wound body, 994: negative electrode, 995: positive electrode, 996: separator, 997: lead electrode , 998: lead electrode, 4000: glasses-type device, 4000a: frame, 4000b: display unit, 4001: headset-type device, 4001a: microphone unit, 4001b: flexible pipe, 4001c: earphone unit, 4002: device, 4002a: housing, 4002b: secondary battery, 4003: device, 4003a: housing, 4003b: secondary battery, 4005: wristwatch-type device, 4005a: display unit, 4005b: belt unit, 4006: belt-type device, 4006a: belt unit, 4006b: wireless power supply receiving unit, 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 display unit, 7103: operation button, 7104: secondary battery, 7200: mobile 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, 8030: SU, 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 door, 8303: freezer door, 8304: secondary battery, 8400: automobile, 8401: head light, 8406: electric motor, 8500: automobile, 8600: 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,< / edx>

Claims

1. A first step of mixing lithium cobalt oxide, a magnesium compound, and a fluoride to form a first mixture; a second step of heating the first mixture to produce a cobalt-containing material; and a third step of mixing the cobalt-containing material, a titanium compound, and a lithium compound to form a second mixture; and a fourth step of heating the second mixture, The method for producing a positive electrode active material, wherein the heating temperature in the fourth step is 780° C. or higher and 1150° C. or lower.

2. In claim 1, The titanium compound has oxygen, The method for producing a positive electrode active material, wherein the lithium compound contains oxygen.

3. In claim 1 or 2, The magnesium compound is magnesium fluoride, The method for producing a positive electrode active material, wherein the fluoride is lithium fluoride.

4. In any one of claims 1 to 3, The titanium compound and the lithium compound have a eutectic point of 780° C. or higher and 1150° C. or lower.

5. A first step of mixing a composite oxide, a magnesium compound, and a fluoride to prepare a first mixture; a second step of heating the first mixture to produce a cobalt-containing material; and a third step of mixing the cobalt-containing material, a titanium compound, and a lithium compound to form a second mixture; and a fourth step of heating the second mixture, The composite oxide has a layered rock salt type crystal structure, The composite oxide contains cobalt, The composite oxide contains at least one selected from nickel, manganese, and aluminum, The method for producing a positive electrode active material, wherein the heating temperature in the fourth step is 780° C. or higher and 1150° C. or lower.

6. In claim 5, The titanium compound has oxygen, The method for producing a positive electrode active material, wherein the lithium compound contains oxygen.

7. In claim 5 or claim 6, The magnesium compound is magnesium fluoride, The method for producing a positive electrode active material, wherein the fluoride is lithium fluoride.

8. In any one of claims 5 to 7, The titanium compound and the lithium compound have a eutectic point of 780° C. or higher and 1150° C. or lower.

Images