Manufacturing method for positive electrode active material

Abstract

To provide a positive electrode active material with less deterioration, a positive electrode active material particle with less deterioration, a power storage device with less deterioration, a power storage device with high safety, or a novel power storage device.SOLUTION: A secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material. The positive electrode active material includes a crystal represented by a layered rock salt type crystal structure. The spatial group of the crystal is represented by R-3m. The positive electrode active material is a particle containing lithium, cobalt, titanium, magnesium, and oxygen. The concentration of magnesium in a surface layer part of the particle is higher than that inside the particle. The titanium concentration in the surface layer part of the particle in the positive electrode active material is higher than that inside the particle.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a secondary battery using a positive electrode active material and a method for manufacturing the same. Alternatively, the present invention relates to a portable information terminal, a vehicle, etc. having a secondary battery.

[0002] One aspect of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect 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 the present specification, the electronic device refers to all devices having a power storage device, and all electro-optical devices having a power storage device, information terminal devices having a power storage device, etc. are electronic devices.

[0004] In the present specification, the power storage device refers to all elements and devices having a power storage function. For example, it includes power storage devices (also referred to as secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double layer capacitors.

Background Art

[0005] In recent years, the development of various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries has been actively carried out. In particular, lithium-ion secondary batteries with high output and high energy density are rapidly expanding in demand along with the development of the semiconductor industry, for portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV), and have become indispensable in modern information society as a source of repeatedly rechargeable energy.

[0006] Therefore, in order to improve the cycle characteristics and increase the capacity of lithium-ion secondary batteries, the improvement of positive electrode active materials has been studied (Patent Document 1).

[0007] In addition, the characteristics required of the power storage device include safety in various operating environments and improvement of long-term reliability.

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

[0009] In addition, compounds containing titanium are used in various applications, and their physical properties have been studied (Non-Patent Document 2).

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

[23] 1427-1430(1972).

Summary of the Invention

Problems to be Solved by the Invention

[0012] One aspect of the present invention is to provide a method for producing a cathode active material with less deterioration. Or, one aspect of the present invention is to provide a novel method for producing a cathode active material.

[0013] One aspect of the present invention is to provide cathode active material particles with less deterioration. Or, one aspect of the present invention is to provide novel cathode active material particles. Or, one aspect of the present invention is to provide a power storage device with less deterioration. Or, one aspect of the present invention is to provide a highly safe power storage device. Or, one aspect of the present invention is to provide a novel power storage device.

[0014] Another aspect of the present invention is to provide a novel substance, active material particles, power storage device, or a method for producing them as one of the problems.

[0015] Note that the description of these problems does not prevent the existence of other problems. Note that one aspect of the present invention does not necessarily need to solve all of these problems. Note that it is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0016] One aspect 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 represented by a layered rock salt type crystal structure, the crystal having a space group represented by R-3m, the positive electrode active material being particles having lithium, cobalt, titanium, magnesium, and oxygen, the concentration of magnesium in the surface layer portion of the particles being higher than the concentration of magnesium in the interior of the particles, and in the positive electrode active material, the concentration of titanium in the surface layer portion of the particles being higher than the concentration of titanium in the interior of the particles.

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

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

[0019] Or one aspect of the present invention is a portable information terminal having the secondary battery described above, a sensor, and an antenna, having a function of performing wireless communication using the antenna, and the sensor having a function of measuring displacement, position, speed, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, inclination, vibration, odor, or infrared rays.

[0020] Or one aspect 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 configuration, the cobalt-containing material preferably contains fluorine.

[0022] In the above configuration, the titanium compound preferably contains oxygen, and the lithium compound preferably contains oxygen.

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

[0024] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material, comprising: a first step of mixing lithium cobaltate, 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 configuration, it is preferable that the titanium compound contains oxygen and the lithium compound contains oxygen.

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

[0027] In the above configuration, it is preferable that the titanium compound and the lithium compound have a eutectic point at 780°C or higher and 1150°C or lower.

[0028] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material, comprising: 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, the composite oxide contains one or more 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 configuration, it is preferable that the titanium compound contains oxygen and the lithium compound contains oxygen.

[0030] In the above configuration, the magnesium compound is preferably magnesium fluoride, and the fluoride is preferably lithium fluoride.

[0031] In the above configuration, it is preferable that the titanium compound and the lithium compound have a eutectic point at 780°C or higher and 1150°C or lower.

Advantages of the Invention

[0032] According to one aspect of the present invention, a method for producing a cathode active material with less deterioration can be provided. Further, according to one aspect of the present invention, a novel method for producing a cathode active material can be provided.

[0033] Also, according to one aspect of the present invention, cathode active material particles with less deterioration can be provided. Further, one aspect of the present invention can provide a method for producing a cathode active material. Also, according to one aspect of the present invention, novel cathode active material particles can be provided. Further, according to one aspect of the present invention, a novel power storage device can be provided.

[0034] Also, according to one aspect of the present invention, a novel substance, active material particles, power storage device, or a method for producing them can be provided.

[0035] Note that the description of these effects does not prevent the existence of other effects. Note that one aspect of the present invention does not necessarily have all of these effects. Note that other effects will be obvious from the description in the specification, drawings, claims, etc., and it is possible to extract these other effects from the description in the specification, drawings, claims, etc.

Brief Description of the Drawings

[0036]

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Embodiments for Carrying Out the Invention

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that its form and details can be variously changed. Also, the present invention is not to be construed as limited to the description of the embodiments shown below.

[0038] In addition, in this specification and the like, crystal planes and directions are indicated by Miller indices. In crystallography, the notation for crystal planes and directions has a bar above the number, but in this specification and the like, due to the constraints of the application notation, instead of putting a bar above the number, a -(minus sign) may be attached before the number for expression. In addition, individual orientations indicating directions within a crystal are represented by [], collective orientations indicating all equivalent directions are represented by <>, individual planes indicating crystal planes are represented by (), and collective planes having equivalent symmetries are represented by {}.

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

[0040] In this specification and the like, the surface layer part of particles such as active materials is preferably, for example, a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. The surface formed by cracks or fissures may also be referred to as the surface. Also, a region deeper than the surface layer part is referred to as the interior.

[0041] In this specification and the like, 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 the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as deficiencies of cations or anions. Also, strictly speaking, the layered rock salt-type crystal structure may be a structure in which the lattice of the rock salt-type crystal is distorted.

[0042] In addition, in this specification and the like, the rock salt-type crystal structure refers to a structure in which cations and anions are alternately arranged. Note that there may be deficiencies of cations or anions.

[0043] In this specification and the like, the O3' type crystal structure of the composite oxide containing lithium and transition metals is a crystal structure with the space group R-3m, which is not a spinel type crystal structure. However, ions such as cobalt and magnesium occupy the oxygen six-coordination positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Note that in the O3' type crystal structure, light elements such as lithium may occupy the oxygen four-coordination positions. In this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0044] Also, it can be said that the O3' type crystal structure is a crystal structure similar to the CdCl2 type crystal structure although it has Li randomly between the layers. This crystal structure similar to the CdCl2 type is close to the crystal structure of lithium nickelate when charged to a charge depth of 0.94 (Li 0.06 NiO2), but it is known that simple pure lithium cobaltate or layered rock salt type cathode active materials containing a large amount of cobalt usually do not take this crystal structure.

[0045] The anions of the layered rock salt type crystal and the rock salt type crystal take a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3' type crystal also take a cubic close-packed structure. When these are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned. However, since the space groups of the layered rock salt type crystal and the O3' type crystal are R-3m, which is different from the space groups of the rock salt type crystal, Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of the rock salt type crystal with the simplest symmetry), the Miller indices of the crystal planes satisfying 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, in the case of the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are generally in agreement.

[0046] The approximate alignment of the crystal orientations of the two regions 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 as materials for determination. In TEM images, etc., the arrangement of cations and anions can be observed as a repetition of bright and dark lines. When the orientations of the cubic close-packed structures are aligned in layered rock salt-type crystals and rock salt-type crystals, it can be observed that the angle formed by the repetition of bright and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that in TEM images, etc., light elements such as oxygen and fluorine may not be clearly observable, but in such cases, the alignment can be determined by the arrangement of metal elements.

[0047] Also, in this specification, etc., the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been 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] Also, in this specification, etc., the state of charge when all the insertable and removable lithium has been inserted is defined as 0, and the state of charge when all the insertable and removable lithium in the positive electrode active material has been removed is defined as 1.

[0049] Also, in this specification, etc., charging refers to moving lithium ions from the positive electrode to the negative electrode inside the battery and moving electrons from the positive electrode to the negative electrode in the external circuit. For the positive electrode active material, removing lithium ions is called charging. Also, a positive electrode active material with a state of charge of 0.7 or more and 0.9 or less may be called a positively charged positive electrode active material at a high voltage.

[0050] Similarly, discharging refers to moving lithium ions from the negative electrode to the positive electrode within the battery and moving electrons from the negative electrode to the positive electrode in the external circuit. Regarding the positive electrode active material, inserting lithium ions is referred to as discharging. Also, a positive electrode active material with a state of charge (SOC) of 0.06 or less, or a positive electrode active material that has discharged 90% or more of its capacity from a state of being charged at a high voltage, shall be referred to as a fully discharged positive electrode active material.

[0051] Also, in this specification and the like, non-equilibrium phase change shall refer to a phenomenon that causes a non-linear change in physical quantities. For example, non-equilibrium phase changes occur before and after the peak in the dQ / dV curve obtained by differentiating the capacitance (Q) with respect to the voltage (V) (dQ / dV), and it is considered that the crystal structure changes significantly.

[0052] A secondary battery has, for example, a positive electrode and a negative electrode. As a material constituting the positive electrode, there is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction contributing to the charge and discharge capacity. Note that the positive electrode active material may contain, in part, a substance that does not contribute to the charge and discharge capacity.

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

[0054] The discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. In a battery with a rated capacity of X (Ah), a current equivalent to 1C is X (A). When discharging with a current of 2X (A), it is said to be discharging at 2C, and when discharging with a current of X / 5 (A), it is said to be discharging at 0.2C. Also, the charge rate is the same. When charging with a current of 2X (A), it is said to be charging at 2C, and when charging with a current of X / 5 (A), it is said to be charging at 0.2C.

[0055] Constant current charging refers to a method of charging with a constant charging rate, for example. Constant voltage charging refers to a method of charging with a constant voltage when the charging reaches the upper limit voltage, for example. Constant current discharging refers to a method of discharging with a constant discharging rate, for example.

[0056] (Embodiment 1) Hereinafter, an example of a positive electrode active material and a method for producing the same according to one aspect of the present invention will be described.

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

[0058] Metal Me1 is one or more metals containing cobalt.

[0059] Metal X is a metal other than cobalt, and metals such as magnesium, calcium, zirconium, lanthanum, barium, copper, potassium, sodium, and zinc can be used as metal X. In particular, it is preferable to use magnesium as metal X.

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

[0061] In addition, the positive electrode active material according to one aspect 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 in the crystal structure of the positive electrode active material can be controlled. By controlling the bond distance between metal Me1 and oxygen, for example, when the positive electrode active material according to one aspect 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 cathode 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 cathode 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 the method for producing the cathode active material> An example of the method for producing the cathode 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) etc. 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 the titanium compound 806 is titanium oxide or a precursor of titanium oxide. In such a case, since lithium oxide has a eutectic point with titanium oxide, it is preferable as the lithium compound 807. Also, when lithium carbonate is used as the lithium compound 807, it can decompose during the heating process in the subsequent step S51 to generate lithium oxide. When lithium hydroxide is used as the lithium compound 807, lithium oxide may be generated during the heating process in the subsequent step S51. Therefore, it is preferable to use lithium carbonate or lithium hydroxide as the lithium compound 807.

[0072] Lithium carbonate is stable at room temperature in an air atmosphere and has the advantage of being easy to handle.

[0073] Also, when lithium oxide is used as the lithium compound 807, in the process of the method for producing the positive electrode active material according to one aspect of the present invention, at least a part may change into compounds such as lithium carbonate and lithium hydroxide due to reaction with a solvent or reaction with gases such as water vapor or carbon dioxide in the atmosphere.

[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. Also, in step S23, it is preferable to perform pulverization.

[0076] The mixing can be carried out either dry or wet, but wet mixing is preferred because it can achieve finer pulverization. Finer pulverization may promote the reaction of the materials to be mixed. When performing wet mixing, 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 hardly reacts with lithium.

[0077] Here, as an example, acetone is prepared as the solvent and pulverization is carried out 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, it is preferable to use zirconia balls as the media, for example. It is preferable to perform this mixing and pulverization step sufficiently to pulverize the mixture 809 into fine powder.

[0079] When using the sol-gel method, for example, alcohol can be used as the solvent, and for mixing, stirring using a magnetic stirrer or the like can be performed. By performing stirring, the sol-gel reaction can be advanced.

[0080] Here, the number of moles of titanium 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 in the cobalt-containing material prepared in S26 described later.

[0081] Also, the number of moles of lithium in the lithium compound 807 is, for example, 1.0 times or more and 10 times or less, or 1.5 times or more and 5 times or less, for example 3.4 times, the number of moles of the titanium compound 806.

[0082] 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 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 materials mixed and pulverized above are recovered, and in step 25, mixture 809 is obtained. When recovering the materials in a 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, and separation from the solvent may be performed in step S28 described below.

[0084] Next, in step S26, as the cobalt-containing material 808, a composite oxide having lithium, metal Me1, metal X, and oxygen is used. A material prepared in advance may be used as the cobalt-containing material 808, or the cobalt-containing material 808 may be prepared. For the preparation of the cobalt-containing material 808, one or more selected from various methods such as solid-phase methods and liquid-phase methods can be used. As the liquid-phase method, for example, the coprecipitation method can be used. By using the coprecipitation method, when the cobalt-containing material has a plurality of transition metals, the plurality of transition metals may be likely to be uniformly distributed. By the uniform distribution of the plurality of transition metals, for example, a cobalt-containing material with few grain boundaries may be obtained. Alternatively, one or more selected from liquid-phase methods such as spray pyrolysis method, metathesis method, method by thermal decomposition reaction of a precursor, reverse micelle method, methods combining these methods with high-temperature firing, and freeze-drying method can also be used. An example of the preparation method of 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, splitting, generation of cracks, generation of crystal defects, etc. of the cobalt-containing material 808 can be suppressed. For example, pulverization is performed wet in step S23 and dry in step S27. Here, for example, dry pulverization is performed using a ball mill.

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

[0087] Next, in step S51, the mixture 810 is heated. This step may be referred to as annealing. By performing annealing, the positive electrode active material of one aspect of the present invention is produced. In this specification, annealing includes the case of heating the mixture 810, or heating at least the heating furnace in which the mixture 810 is disposed. The heating furnace may be provided with a pump having at least one of the functions of reducing pressure and increasing pressure inside the heating furnace. For example, pressure may be increased 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 the elements possessed by each of 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 temperature of these materials. For example, in the case of an oxide, solid-phase diffusion occurs from 0.757 times the melting temperature T m (Tammann temperature T d ).

[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, as the reaction will proceed more readily. Therefore, the annealing temperature is preferably 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, as shown in FIG. 1 (cited from Non-Patent Document 2, FIG. 1 and modified), the eutectic point P of TiO2 and Li2O is around 1030°C. It is preferable that the annealing temperature in 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, and the molar ratio of TiO2 to Li2O corresponds to approximately TiO2:Li2O = 1:3.4.

[0091] The surface of the cathode active material 811 may be smoothed when the eutectic mixture of TiO2 and Li2O, or the melt of one of them, covers a part of the surface of the cobalt-containing material 808. Alternatively, the surface of the cathode active material 811 may be smoothed when the eutectic mixture of TiO2 and Li2O, or the melt of one of them, reacts with the cobalt-containing material 808.

[0092] Since the surface of the cathode active material is smooth, the concentration of stress is alleviated, and the cathode active material is less likely to crack during the processes of pressurization and charge-discharge. Here, for example, the cathode active material has a particulate form.

[0093] The smoothness of the surface can be quantified, for example, by image analysis of the microscopic image of the particles of the cathode active material. As the microscope, for example, surface SEM, cross-sectional SEM, cross-sectional TEM, etc. can be used. The contour line of the particle can be extracted, and the smoothness can be determined by the ratio of the convex region to the concave region on the contour line.

[0094] Further, by mixing the titanium compound 806 and the cobalt-containing material 808 and heating them, due to the interaction or reaction between metal X contained in the cobalt-containing material and titanium, at least a part of metal X moves to the surface of the cobalt-containing material, and a compound containing metal X and titanium, or a mixture containing metal X and titanium may be formed on the surface of the particulate positive electrode active material. In such a case, protrusions 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, by further mixing and heating the lithium compound 807 in addition to the titanium compound 806 and the cobalt-containing material 808, the interaction or reaction between the titanium compound 806 and the cobalt-containing material 808 is weakened. Therefore, the movement of metal X to the surface of the cobalt-containing material can be suppressed.

[0096] When it is difficult to form a eutectic mixture of TiO2 and Li2O, for example, when the ratio of TiO2 and Li2O significantly deviates from the conditions for forming the eutectic point, TiO2 cannot spread over a large 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. When there are many irregularities on the surface of the positive electrode active material, there is a risk that stress concentration points will occur and the positive electrode active material will be easily cracked or cracks will be easily generated. When the positive electrode active material cracks or cracks occur, elution of transition metals, excessive side reactions, etc. are likely to occur. Such a phenomenon is not preferable in terms of cycle characteristics, reliability, safety, etc.

[0097] Here, the differential scanning calorimetry (DSC measurement) 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, with TiO2 used as the titanium compound and Li2O used as the lithium compound. The mixture was prepared 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, with TiO2 used as the titanium compound.

[0098] As shown in FIG. 2, endothermic peaks are observed in the mixture 809 at around 427°C, around 689°C, and around 1139°C, respectively. No significant peak is seen in the titanium compound 806.

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

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

[0101] As the annealing temperature in step S51, 780°C or higher and 1150°C or lower is preferable, 860°C or higher and 1140°C or lower is more preferable, 950°C or higher and 1100°C or lower is even more preferable, and for example, 1050°C is preferable.

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

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

[0104] In step S31 of FIG. 4, the materials prepared in steps S21, S22, and S26 are mixed and pulverized. The mixing can be performed dry or wet.

[0105] In step S32, the material mixed above is recovered, and in step S33, the mixture 810 is obtained.

[0106] In FIG. 4, for steps after step S51, refer to FIG. 3.

[0107] <Example of method for producing cobalt-containing material> Next, with reference to FIG. 5, 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. Metal M includes the metal Me1 listed above. In addition to the metal Me1 listed above, metal M can further include the metal X listed above. Hereinafter, a cobalt-containing material in which metal M includes metal X and 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 its composition is not limited to Li:M:O = 1:1:2.

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

[0109] The 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 also be used. That is, only a cobalt source can be used as the transition metal source, only a nickel source can be used, two types of a cobalt source and a manganese source, or two types of a cobalt source and a nickel source can be used, or three types of a cobalt source, a manganese source, and a nickel source can be used. Further, in addition to these metal sources, an aluminum source can be used. The heating temperature at this time is preferably higher than the temperature in 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 containing lithium, a transition metal, and oxygen that has been synthesized in advance, it is preferable to use one with few impurities. In this specification and the like, for the composite oxide containing lithium, a transition metal, and oxygen, the cobalt-containing material, and the positive electrode active material, the main components are lithium, cobalt, nickel, manganese, aluminum, and oxygen, and elements other than the above main components are regarded as 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 5,000 ppmw or less. For example, the total impurity concentrations of the transition metal and arsenic are 3,000 ppmw or less, or 1,500 ppmw or less. Also, for example, the total impurity concentrations of transition metals such as titanium and arsenic are 3,000 ppmw or less, or 1,500 ppmw or less.

[0111] For example, as the lithium cobaltate synthesized in advance, lithium cobaltate particles (trade name: Celsiode C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used. This is a lithium cobaltate having 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 1,100 ppmw or less, and the concentrations of 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 strains. Therefore, it is preferably a composite oxide with few impurities. When the composite oxide containing lithium, a transition metal, and oxygen contains a large amount of impurities, there is a high possibility of having a crystal structure with many defects or strains.

[0113] Also, 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 hexafluoroaluminate (Na3AlF6), etc. can be used. Fluoride 802 may function as a fluorine source. Therefore, instead of or as a part of fluoride 802, for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. can be used and mixed in the atmosphere.

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

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

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

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

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

[0119] In addition to the fluoride 802 and the compound 803, a material having a metal other than cobalt and other than metal X may be mixed. As a material having a metal other than cobalt and other than metal X, for example, a nickel source, a manganese source, an aluminum source, an iron source, a vanadium source, a chromium source, a niobium source, a titanium source, etc. can be mixed. For example, it is preferable to pulverize and mix hydroxides, fluorides, oxides, etc. of each metal. Pulverization can be performed, for example, wet.

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

[0121] Next, as step S14, the materials prepared in step S11, step S12, and step S13 are mixed and pulverized. The mixing can be performed dry or wet, but wet is preferable because it can be pulverized smaller. When performing wet, 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 hardly reacts with lithium. In this embodiment, acetone will be used.

[0122] For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the media, for example. It is preferable to sufficiently perform this mixing and pulverization step to pulverize the mixture 804.

[0123] Next, in step S15, the materials mixed and pulverized above are recovered, and in step S16, the mixture 804 is obtained.

[0124] The mixture 804 preferably has a D50 of 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less.

[0125] Next, heating is performed in step S17. This step may be referred to as annealing. The heating temperature is more preferably equal to or higher than the temperature at which the mixture 804 melts. Also, the annealing temperature is preferably equal to or lower than the decomposition temperature of LiCoO2 (1130 °C).

[0126] By using LiF as the fluoride 802 and performing the annealing in step S17 with a lid, a cobalt-containing material 808 with good cycle characteristics and the like can be produced. Also, when using LiF and MgF2 as the fluoride 802, since the eutectic point of LiF and MgF2 is around 742 °C, if the annealing temperature in step S17 is set to 742 °C or higher, the reaction with LiCoO2 is promoted and it is considered that LiMO2 is generated.

[0127] Also, for LiF, MgF2, and LiCoO2, an endothermic peak is observed by differential scanning calorimetry (DSC measurement) around 820 °C. Therefore, the annealing temperature is preferably 742 °C or higher, 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, more preferably 820 °C or higher and 1000 °C or lower.

[0129] Also, 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 large compared to the volume of the container and it is lighter than oxygen, LiF volatilizes, and if the LiF in the mixture 804 decreases, the generation of LiMO2 is expected to be suppressed. Therefore, it is necessary to heat while suppressing the volatilization of LiF.

[0130] Therefore, by heating the mixture 804 in an atmosphere containing LiF, that is, by heating the mixture 804 in a state where the partial pressure of LiF in the heating furnace is high, the volatilization of LiF in the mixture 804 is suppressed. By covering and annealing with a fluoride (LiF or MgF) that forms a eutectic mixture, the annealing temperature can be lowered to below the decomposition temperature of LiCoO2 (1130 °C), specifically, 742 °C or higher and 1000 °C or lower, and the formation of LiMO2 can proceed efficiently. Therefore, a cobalt-containing material with good characteristics can be produced, and the annealing time can be further shortened.

[0131] An example of the annealing method in S17 is shown in FIG. 7.

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

[0133] Here, the valence of Co (cobalt) in LiMO₂ produced according to one embodiment of the present invention is preferably approximately trivalent. Cobalt can take divalent and trivalent states. Therefore, in order to suppress the reduction of cobalt, the atmosphere in the heating furnace space 102 preferably contains oxygen, more preferably the ratio of oxygen to nitrogen in the atmosphere of the heating furnace space 102 is equal to or greater than that of the atmospheric atmosphere, and even more preferably the oxygen concentration in the atmosphere of the heating furnace space 102 is equal to or greater than that of the atmospheric atmosphere. Thus, it is necessary to introduce an atmosphere containing oxygen into the heating furnace space. However, since divalent cobalt atoms may be more stable when magnesium atoms are present nearby, not all cobalt atoms need to be trivalent.

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

[0135] The method of making the heating furnace space 102 into an atmosphere containing oxygen is not particularly limited. For example, after evacuating the heating furnace space 102, a method of introducing a gas containing oxygen such as oxygen gas or dry air, or a method of flowing a gas containing oxygen such as oxygen gas or dry air for a certain period of time can be mentioned. Among them, after evacuating the heating furnace space 102, it is preferable to introduce oxygen gas (oxygen replacement). Note that the atmosphere in the heating furnace space 102 may be regarded as an atmosphere containing oxygen.

[0136] When a lid 118 is arranged on the container 116 and heating is performed after making it into an atmosphere containing oxygen, an appropriate amount of oxygen can enter the container 116 through the gap of the lid 118 arranged on the container 116, and an appropriate amount of fluoride can be retained in the container 116.

[0137] In addition, fluorides and the like adhering to the inner walls of the container 116 and the lid 118 may re-fly due to heating and adhere to the mixture 804.

[0138] The annealing in step S17 is preferably performed at an appropriate temperature and for an appropriate time. The appropriate temperature and time vary depending on conditions such as the particle size and composition of the composite oxide 801 in step S11. When the particles are small, a lower temperature or a shorter time may be more preferable than when they are large. There is a step of removing the lid after the annealing in S17.

[0139] For example, when the average particle diameter (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 diameter (D50) of the particles in step S11 is about 5 μm, the annealing time is preferably, for example, 1 hour or more and 10 hours or less, and more preferably about 2 hours.

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

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

[0143] <Example 3 of the method for producing a positive electrode active material> In the flowchart shown in FIG. 6, the manufacturing method can be simplified as compared with the processes of FIGS. 3 and 4 above.

[0144] In step S33 of FIG. 6, the materials of 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 above is recovered, and in step S35, a mixture 810 is obtained.

[0146] For steps after step S51, refer to FIG. 3.

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

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

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

[0150] [Structure of Positive Electrode Active Material] Materials having a layered rock salt-type crystal structure such as lithium cobaltate (LiCoO2) are known to have a high discharge capacity and be excellent as a positive electrode active material for secondary batteries. Examples of materials having a layered rock salt-type crystal structure include composite oxides 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 Jahn-Teller effect in transition metal compounds varies in strength depending on the number of electrons in the d orbitals of the transition metal.

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

[0153] The positive electrode active material will be described with reference to FIGS. 8 and 9.

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

[0155] In this compound, the change in crystal structure and the volume difference per the same number of transition metal atoms in a fully discharged state and a state charged at high voltage are small.

[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 metal M. In addition, it is preferable that metal M further contains the metal X listed above in addition to the metal Me1. It is also preferable to have halogens such as fluorine and 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 concentration of titanium in the surface layer portion of the particles is higher than the concentration of titanium inside. Also, the concentration of magnesium in the surface layer portion is higher than the concentration of magnesium inside. Further, the surface layer portion of the positive electrode active material 811 may further have a first region within 10 nm, or within 5 nm, or within 3 nm from the surface toward the inside, where the concentration of magnesium 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 the region located deeper inside than the first region in the surface layer portion.

[0158] In each region such as the surface layer portion, the interior, and the first region in the surface layer portion, the concentrations of elements such as metal M and titanium, for example, have a gradient. That is, for example, at the boundary of 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 a concentration gradient, for example, in each region such as the surface layer portion, the interior, and the first region in the surface layer portion.

[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. Also, 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 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 charge and discharge is shown in FIG. 8. In addition to or instead of the region represented by the layered rock salt type crystal structure described in FIG. 8 and the like, the surface layer portion of the positive electrode active material 811 may have crystals having titanium, magnesium, and oxygen and represented by a structure different from the layered rock salt type crystal structure. For example, it may have crystals having titanium, magnesium, and oxygen and represented by a spinel structure.

[0160] The crystal structure of the 0% depth of charge (discharge state) in Fig. 8 is the same R-3m (O3) as in Fig. 9. On the other hand, in the case of the first region, when fully charged, it has crystals with a structure different from the H1-3 type crystal structure. This structure is of the space group R-3m and is not a spinel-type crystal structure, but ions such as cobalt and magnesium occupy the oxygen six-coordination positions, and the cation arrangement has symmetry similar to that of the spinel type. Also, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. This structure is referred to as the O3'-type crystal structure or a pseudo-spinel-type crystal structure in this specification, etc. Note that in the diagram of the O3'-type crystal structure shown in Fig. 8, lithium may exist in any lithium site with a probability of about 20%, but it is not limited to this. It may exist only in specific partial lithium sites. Also, in both the cases of the O3-type crystal structure and the O3'-type crystal structure, it is preferable that magnesium exists thinly between the CoO2 layers, that is, in the lithium sites. Also, it is preferable that a halogen such as fluorine exists randomly and thinly in the oxygen sites.

[0161] Note that in the O3'-type crystal structure, light elements such as lithium may occupy the oxygen four-coordination positions, and in this case as well, the ion arrangement has symmetry similar to that of the spinel type.

[0162] Also, it can be said that the O3'-type crystal structure has a crystal structure similar to the CdCl2 type although it has Li randomly between the layers. This crystal structure similar to the CdCl2 type is close to the crystal structure when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 NiO2), but it is known that pure lithium cobaltate or a layered rock salt-type cathode active material containing a large amount of cobalt usually does not take this crystal structure.

[0163] The anions of the layered rock salt-type crystal and the rock salt-type crystal adopt a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3'-type crystal also adopt a cubic close-packed structure. When these are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned. However, since the space groups of the layered rock salt-type crystal and the O3'-type crystal are R-3m, which are different from the space group Fm-3m (the space group of a general rock salt-type crystal) and Fd-3m (the space group of the rock salt-type crystal having the simplest symmetry) of the rock salt-type crystal, the Miller indices of the crystal planes satisfying 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, in the layered rock salt-type crystal, the O3'-type crystal, and the rock salt-type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are substantially the same.

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

[0165] More specifically, in the first region, the structural stability is high even when the charging voltage is high. For example, in the comparative example, when the voltage is about 4.6V based on the potential of lithium metal, the H1-3 type crystal structure is formed, but the cathode active material of one embodiment of the present invention can maintain the crystal structure of R-3m(O3) even at the charging voltage of 4.6V. Even at a higher charging voltage, for example, at a voltage of about 4.65V to 4.7V based on the potential of lithium metal, the cathode active material of one embodiment of the present invention can adopt the O3' type crystal structure. When the charging voltage is further increased beyond 4.7V, the H1-3 type crystal may be observed for the cathode active material of one embodiment of the present invention. Also, when the charging voltage is lower (for example, even when the charging voltage is 4.5V or more and less than 4.6V based on the potential of lithium metal), the cathode active material of one embodiment of the present invention may adopt the O3' type crystal structure. In a secondary battery, when using graphite as the anode active material, for example, the voltage of the secondary battery decreases by the potential difference of graphite compared to the above. The potential of graphite is about 0.05V to 0.2V based on the potential of lithium metal. Therefore, for example, even when the voltage of the secondary battery using graphite as the anode active material is 4.3V or more and 4.5V or less, the cathode active material of one embodiment of the present invention can maintain the crystal structure of R-3m(O3), and there is a region where the O3' type crystal structure can be adopted even in a region where the charging voltage is further increased, for example, when the voltage of the secondary battery exceeds 4.5V and is 4.6V or more and 4.55V or less. Furthermore, when the charging voltage is lower, for example, even when the voltage of the secondary battery is 4.2V or more and less than 4.3V, the cathode active material of one embodiment of the present invention may adopt the O3' structure.

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

[0167] Also, in the cathode active material 904, the volume difference 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. The O3' type crystal structure can be represented by the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), and 0.20 ≤ x ≤ 0.25.

[0168] Magnesium randomly and thinly present in the CoO₂ interlayer, i.e., the lithium site, has the effect of suppressing the shift of the CoO₂ layer when charged at a high voltage. Therefore, when magnesium is present in the CoO₂ interlayer, it is likely to have an O3'-type crystal structure.

[0169] However, if the heat treatment temperature is too high, cation mixing occurs and magnesium is more likely to enter the cobalt site. Magnesium present in the cobalt site may have a small effect of maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are also concerns about 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 lithium cobaltate before the heat treatment for distributing magnesium throughout the particles. Adding the halogen compound causes a melting point drop of lithium cobaltate. By lowering the melting point, it becomes easier to distribute magnesium throughout the particles at a temperature where cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected to improve the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolyte.

[0171] Note that if the magnesium concentration is increased to a value above the desired level, the effect on stabilizing the crystal structure may become small. This is presumably because magnesium also 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 aspect of the present invention is preferably 0.001 times or more and 0.1 times or less 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 particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material formulation in the process of producing the positive electrode active material.

[0172] The number of nickel atoms in the cathode active material 811 is preferably 7.5% or less, more preferably 0.05% or more and 4% or less, and even more preferably 0.1% or more and 2% or less of the number of cobalt atoms. The nickel concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the cathode active material using ICP-MS or the like, or may be based on the value of the raw material formulation in the process of producing the cathode active material.

[0173] <Particle size> If the particle size of the cathode active material 811 is too large, there are problems such as difficulty in lithium diffusion and the surface of the active material layer becoming too rough when coated on the current collector. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer during coating on the current collector and excessive progress of the reaction with the electrolyte occur. Therefore, the average particle diameter (D50, also referred to as 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 a certain cathode active material exhibits an O3'-type crystal structure when charged at a high voltage can be determined by analyzing the cathode charged at a high voltage using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt in the cathode active material with high resolution, can compare the crystallinity and crystal orientation, can analyze the lattice periodic strain and crystallite size, and sufficient accuracy can be obtained by measuring the cathode obtained by disassembling the secondary battery as it is.

[0175] As described above, the cathode active material 811 is characterized by having little change in crystal structure between the charged state at high voltage and the discharged state. Materials in which the crystal structure with a large change from the discharged state occupies 50 wt% or more in the charged state at high voltage are not preferable because they cannot withstand charge and discharge at high voltage. It should be noted that simply adding impurity elements may not result in the desired crystal structure. For example, even though lithium cobaltate containing magnesium and fluorine is common in this regard, there are cases where the O3' type crystal structure becomes 60 wt% or more and cases where the H1-3 type crystal structure occupies 50 wt% or more in the charged state at high voltage. Also, at a predetermined voltage, the O3' type crystal structure may become almost 100 wt%, and when the predetermined voltage is further increased, the H1-3 type crystal structure may occur. Therefore, it is preferable that the crystal structure of the cathode active material 811 is analyzed by XRD or the like. By using it in combination with measurements such as XRD, more detailed analysis can be performed.

[0176] However, the cathode active material in the charged state or the discharged state at high voltage may change its crystal structure when exposed to the atmosphere. For example, it may change from the O3' type crystal structure to the 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 cathode active material shown in FIG. 9 is lithium cobaltate (LiCoO2) to which metal X is not added. The crystal structure of the lithium cobaltate shown in FIG. 9 changes depending on the depth of charge.

[0178] As shown in FIG. 9, lithium cobaltate at a charge depth of 0 (discharged state) has a region with a crystal structure of space group R-3m and three CoO2 layers in the unit cell. Therefore, this crystal structure may be referred to as the O3 type crystal structure. Note that the CoO2 layer refers to a structure in which octahedral structures in which oxygen is six-coordinated to cobalt are continuously arranged in a plane in a state of sharing edges.

[0179] When the depth of charge is 1, it has a crystal structure of 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] Also, lithium cobaltate when the depth of charge is about 0.8 has a crystal structure of space group R-3m. This structure can also be said to be a structure in which the structure of CoO2 such as P-3m1 (O1) and the structure of LiCoO2 such as R-3m (O3) are alternately stacked. Therefore, this crystal structure is sometimes called the H1-3 type crystal structure. In fact, in the H1-3 type crystal structure, the number of cobalt atoms per unit cell is twice that of other structures. However, in this specification including FIG. 9, for the sake of easy comparison with other structures, it is shown in a figure in which the c-axis of the H1-3 type crystal structure is made 1 / 2 of the unit cell.

[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), O2(0, 0, 0.11535±0.00045). O1 and O2 are oxygen atoms respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, the O3’-type crystal structure of one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen is different between the O3’-type crystal structure and the H1-3 type structure, and the change from the O3 structure in the O3’-type crystal structure is smaller than that in the H1-3 type structure. The choice of which unit cell is more preferable for representing the crystal structure of the positive electrode active material may be made, for example, so that the value of GOF (good of fitness) is smaller in the Rietveld analysis of XRD.

[0182] When high-voltage charging is performed such that the charging voltage becomes 4.6 V or higher based on the redox potential of lithium metal, or deep charging is performed such that the depth of charge becomes 0.8 or higher, and charging and discharging are repeated, lithium cobaltate repeats a change in crystal structure (i.e., a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m (O3) structure in the discharged state.

[0183] However, the shift of the CoO2 layer is large between these two crystal structures. As shown by the dotted lines and arrows in FIG. 9, in the H1-3 type crystal structure, the CoO2 layer is largely shifted from R-3m (O3). Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0184] Furthermore, the volume difference is also large. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.0% or more.

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

[0186] Therefore, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is presumably because when the crystal structure collapses, the sites where lithium can stably exist decrease, and it becomes difficult for lithium to be inserted and extracted.

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

[0188] (Embodiment 3) In this embodiment, an example of a secondary battery according to an aspect of the present invention will be described with reference to FIGS. 9 to 12.

[0189] <Example of the configuration of a secondary battery 1> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example.

[0190] Positive Electrode The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material and may have a conductive material and a binder. As the positive electrode active material, the positive electrode active material produced using the production method described in the previous embodiment is used.

[0191] Also, the positive electrode active material described in the previous embodiment may be mixed with other positive electrode active materials 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 dA lithium manganese composite oxide represented by the following can be used. Here, the element M is preferably a metal element selected from elements other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. Further, when measuring the entire particles of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≦ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particles of the lithium manganese composite oxide can be measured using, for example, ICP-MS (inductively coupled plasma mass spectrometer). Also, the oxygen composition of the entire particles of the lithium manganese composite oxide can be measured using, for example, EDX (energy dispersive X-ray analysis method). Further, it can be determined by using valence evaluation of melting 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, and phosphorus.

[0195] As the conductive material, a graphene compound may be used. In this 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, etc. The graphene compound refers to a substance having carbon, having a flat plate shape, a sheet shape, etc., and having a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may be referred to as a carbon sheet. The graphene compound may have a functional group. Also, the graphene compound preferably has a bent shape. Also, the graphene compound may be rounded to be like a carbon nanofiber.

[0196] In this specification and the like, graphene oxide refers to a substance that contains carbon and oxygen, has a sheet-like shape, and has functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0197] In this specification and the like, reduced graphene oxide refers to a substance that contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. It may also be referred to as a carbon sheet. Reduced graphene oxide can function even when there is a single sheet, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where 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 and oxygen concentrations, it can function as a highly conductive material even in small amounts. Also, reduced graphene oxide preferably has an intensity ratio G / D of the G band and the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0198] In the longitudinal section of the active material layer, sheet-like graphene compounds are dispersed approximately uniformly in the internal region of the active material layer. Since the plurality of graphene compounds are formed so as to partially cover the plurality of granular positive electrode active materials or adhere onto the surfaces of the plurality of granular positive electrode active materials, they are in surface contact with each other.

[0199] Here, by bonding the plurality of graphene compounds to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is covered with the graphene net, the graphene net can also function as a binder that binds the active materials to each other. Therefore, the amount of the binder can be reduced or it can be not used, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the charge and 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. That is, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in a polar solvent, for the formation of the graphene compound, the graphene compound can be dispersed approximately uniformly in the internal region of the active material layer. In order to volatilize and remove the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reduce the graphene oxide, the graphene compounds remaining in the active material layer partially overlap and are dispersed to the extent of face contact with each other, so that a three-dimensional conductive path can be formed. The reduction of 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 that make point contact with the active material, the graphene compound enables face contact with low contact resistance. Thus, the electrical conductivity between the granular positive electrode active material and the graphene compound can be improved with a smaller amount than that of ordinary conductive materials. Therefore, the ratio of the active material layer in the positive electrode active material can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

[0202] Also, in advance, by using a spray dryer device, the entire surface of the active material can be covered to form a graphene compound, which is a conductive material, as a film, and a conductive path can also be formed between the active materials with the graphene compound.

[0203] Also, together with the graphene compound, the materials used for forming the graphene compound may be mixed and used in the active material layer. For example, the particles used as a catalyst when forming the graphene compound may be mixed with the graphene compound. Examples of the catalyst used when forming the graphene compound include particles having silicon oxide (SiO2, SiO x (x < 2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. It is preferable that the D50 of the particles is 1 μm or less, and more preferably 100 nm or less.

[0204] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Further, the negative electrode active material layer may have a conductive material and a binder.

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

[0206] As the negative electrode active material, an element capable of performing a charge-discharge reaction by an 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 in particular, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, there are SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, an element capable of performing a charge-discharge reaction by an alloying / dealloying reaction with lithium, and a compound containing the element, etc. may be referred to as an alloy-based material.

[0207] In this specification etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can be expressed as SiO x It can also be expressed as. Here, x preferably has a value near 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. Alternatively, 0.2 or more and 1.2 or less is preferable. Alternatively, 0.3 or more and 1.5 or less is preferable.

[0208] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotube, graphene, carbon black, etc. 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, pitch-based artificial graphite, etc. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which may be preferable. Examples of natural graphite include flake graphite, spheroidized natural graphite, etc.

[0210] Graphite shows a potential as low as that of lithium metal when lithium ions are inserted into graphite (when forming a lithium-graphite intercalation compound) (0.05 V or more and 0.3 V or less vs. Li / Li + ). Thereby, the lithium-ion secondary battery can show a high operating voltage. Furthermore, graphite has advantages such as a relatively high charge-discharge capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal, so it is preferable.

[0211] Also, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

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

[0213] When using a complex nitride of lithium and a transition metal, since lithium ions are contained in the negative electrode active material, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, a complex nitride of lithium and a transition metal can be used as the negative electrode active material by previously desorbing the lithium ions contained in the positive electrode active material.

[0214] In addition, a material in which a conversion reaction occurs 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), may be used as the negative electrode active material. Materials in which a conversion reaction occurs further include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, 0.89 sulfides such as CoS, 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 the negative electrode active material layer can have, the same materials as the conductive material and binder that the positive electrode active material layer can have can be used.

[0216] [Negative electrode current collector] For the negative electrode current collector, the same materials as the positive electrode current collector can be used. It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0217] [Electrolyte solution] The electrolyte has a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferable. For example, 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. can be used alone, or two or more of these can be used in any combination and ratio.

[0218] Also, by using one or more ionic liquids (room temperature molten salts) that are flame-retardant and hardly volatile as the solvent of the electrolyte, it is possible to prevent short circuits in the internal region of the secondary battery, and rupture and ignition of the secondary battery when the internal region temperature rises due to overcharging, etc. An ionic liquid consists 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-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions, etc.

[0219] Also, as the electrolyte dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10, Li2B 12 Cl 12 One kind of lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, or two or more of these can be used in any combination and ratio.

[0220] For the electrolyte used in the secondary battery, it is preferable to use a highly purified electrolyte with a low content of particulate dust and elements other than the constituent elements of the electrolyte (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte is 1% or less, preferably 0.1% or less, and 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 can be added to the electrolyte. The concentration of the additive material may be, for example, 0.1 wt% or more and 5 wt% or less based on the total solvent.

[0222] Moreover, a polymer gel electrolyte in which the polymer is swollen with the electrolyte may be used.

[0223] By using the polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. Also, the secondary battery can be made thinner and lighter.

[0224] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, gels of fluorine-based polymers, etc. can be used.

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

[0226] Further, instead of the electrolytic solution, one or more selected from solid electrolytes having a sulfide-based inorganic material, solid electrolytes having an oxide-based inorganic material, and solid electrolytes having a polymer material such as a PEO (polyethylene oxide) - based material can be used. When using a solid electrolyte, it is not necessary to install a separator and a spacer. In addition, since the entire battery can be solidified, there is no risk of liquid leakage and the safety is significantly improved.

[0227] 〔Separator〕 Moreover, the secondary battery preferably has a separator. As the separator, for example, those formed of paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into an envelope shape and arranged to wrap either the positive electrode or the negative electrode.

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

[0229] Coating with a ceramic-based material improves oxidation resistance, suppresses deterioration of the separator during high-voltage charge and discharge, and can improve the reliability of the secondary battery. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere, and can improve the output characteristics. Coating with a polyamide-based material, particularly aramid, improves heat resistance, and thus can improve the safety of the secondary battery.

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

[0231] Using a separator with a multilayer structure can maintain the safety of the secondary battery even when the overall thickness of the separator is thin, and thus can increase the charge and discharge capacity per unit volume of the secondary battery.

[0232] 〔Outer package〕 As the outer package of the secondary battery, for example, one or more selected from metal materials such as aluminum and resin materials can be used. Also, a film-shaped outer package can be used. As the film, for example, a flexible metal thin film such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the outer package on the metal thin film, and a three-layer structure film can be used.

[0233] <Configuration example 2 of secondary battery> Hereinafter, as an example of the configuration of the secondary battery, the configuration of the secondary battery using a solid electrolyte layer will be described.

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

[0235] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. As the positive electrode active material 411, the positive electrode active material produced using the production method described in the previous embodiment is used. Further, the positive electrode active material layer 414 may have a conductive assistant and a binder.

[0236] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that has neither the positive electrode active material 411 nor the 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. Further, the negative electrode active material layer 434 may have a conductive assistant and a binder. When metallic lithium is used for the negative electrode 430, as shown in Fig. 10B, the negative electrode 430 that does not have the solid electrolyte 421 can be used. When metallic lithium is used for the negative electrode 430, it is preferable because the energy density of the secondary battery 400 can be improved.

[0238] As the solid electrolyte 421 included in 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] Among sulfide-based solid electrolytes, there are thiophosphosilicate-based (Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75 S4 etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2 etc.), sulfide crystallized glasses (Li7P3S 11 、Li 3.25 P 0.95It includes sulfide-based solid electrolytes (such as S4, etc.). Sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft, so the conductive path is likely to be maintained even after charge and discharge.

[0240] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (such as La 2 / 3-x Li 3x TiO3, etc.), materials having a NASICON-type crystal structure (such as Li 1-X Al X Ti 2-X (PO4)3, etc.), materials having a garnet-type crystal structure (such as Li7La3Zr2O 12 etc.), materials having a LISICON-type crystal structure (such as Li 14 ZnGe4O 16 etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (such as Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), and oxide crystallized glasses (such as 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 atmosphere.

[0241] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can be used as solid electrolytes.

[0242] Also, different solid electrolytes may be mixed and used.

[0243] Among them, Li 1+x Al x Ti 2-x(PO4)3(0 < x < 1) (hereinafter referred to as LATP) contains elements such as aluminum and titanium that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. In addition, an improvement in productivity due to reduction of processes can also be expected. In this specification and the like, the NASICON-type crystal structure refers to a compound represented by M2(AO4)3 (M: transition metal, A: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and AO4 tetrahedra 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 the electrode plate 753 is pressed by rotating the pressing screw 763 to fix the evaluation material. 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 is shown in FIG. 11B.

[0248] As an example of the evaluation material, a stack 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. Note that 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 that are electrically connected to the positive electrode 750a can be said to correspond to the positive electrode terminal. The electrode plate 753 and the upper member 762 that are electrically connected to the negative electrode 750c can be said to correspond to the negative electrode terminal. 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] Also, for the exterior body of the secondary battery according to one aspect of the present invention, it is preferable to use a package having excellent airtightness. For example, a ceramic package or a resin package can be used. Further, when sealing the exterior body, it is preferable to perform the sealing in an atmosphere that blocks outside air and is sealed, for example, inside a glove box.

[0251] FIG. 12A shows a perspective view of a secondary battery according to one aspect of the present invention having an exterior body and a shape different from those in FIG. 11. The secondary battery in FIG. 12A has external electrodes 771 and 772 and is sealed with an exterior body having a plurality of package members.

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

[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. Also, 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 can be used in appropriate combination with other embodiments.

[0255] (Embodiment 4) In this embodiment, an example of the shape of a secondary battery having a positive electrode described in the previous embodiment will be described. The materials used for the secondary battery described in this embodiment can refer to the description of the previous 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-type) secondary battery, and FIG. 13B is a cross-sectional view thereof.

[0257] In the coin-type secondary battery 300, a positive electrode can 301 also serving as a positive electrode terminal and a negative electrode can 302 also serving 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 by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0258] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layer may be formed only on one side.

[0259] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys thereof, or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolyte, it is preferable to coat one or more selected from nickel and 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, with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are pressure-bonded via the gasket 303 to manufacture a coin-shaped secondary battery 300.

[0261] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0262] Here, the flow of current during charging of the secondary battery will be described with reference to Fig. 13C. When a secondary battery using lithium is regarded as a single closed circuit, the movement of lithium ions and the flow of current are in the same direction. Note that in a secondary battery using lithium, the anode and cathode are switched between charging and discharging, and the oxidation reaction and reduction reaction are switched. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification, whether during charging, discharging, when a reverse pulse current is flowing, or when a charging current is flowing, the positive electrode will be referred to as the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode will be referred to as the "negative electrode" or the "- electrode (minus electrode)". Using the terms anode or cathode related to the oxidation reaction or reduction reaction would result in them being reversed during charging and discharging, which could cause confusion. Therefore, the terms anode or cathode will not be used in this specification. If the terms anode or cathode are used, it is necessary to specify whether it is during charging or discharging and also note which one corresponds to the positive electrode (plus electrode) or the negative electrode (minus electrode).

[0263] A charger is connected to the two terminals shown in Fig. 13C, and the secondary battery 300 is charged. 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. An external view of a cylindrical secondary battery 600 is shown in FIG. 14A. FIG. 14B is a diagram schematically 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 upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0265] Inside the 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 interposed 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, a metal such as nickel, aluminum, titanium, etc., which is corrosion-resistant to the electrolytic solution, or an alloy thereof, or an alloy of these and other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with one or more selected from nickel and aluminum, etc. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode and the separator are wound is sandwiched by a pair of opposing insulating plates 608, 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the internal region of the battery can 602 in which the battery element is provided. The non-aqueous electrolytic solution can be the same as that used in the coin-type secondary battery.

[0266] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 603 is resistance welded to the 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 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold value. Also, the PTC element 611 is a thermal sensing resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used.

[0267] Also, as shown in FIG. 14C, a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between a conductive plate 613 and a conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then further in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0268] Figure 14D is a top view of the module 615. The conductive plate 613 is shown by a dotted line for clarity. As shown in Figure 14D, the module 615 may have a conductive wire 616 that electrically connects a plurality of secondary batteries 600. A conductive plate can be provided superimposed on the conductive wire 616. Further, a temperature control device 617 may be provided between the plurality of 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 likely to be affected by the outside air temperature. The heat medium of the temperature control device 617 preferably has insulation and non-combustibility.

[0269] By using the positive electrode active material described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with a high charge and discharge capacity and excellent cycle characteristics can be obtained.

[0270] <Structural example of secondary battery> Another structural example of the secondary battery will be described with reference to FIGS. 15 to 18.

[0271] FIGS. 15A and 15B are views 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. Further, 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 seal 915.

[0272] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 951, the terminal 952, the antenna 914, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0273] The circuit 912 may be provided on the back surface of the circuit board 900. Note that the antenna 914 is not limited to a coil shape, and may be, for example, linear or plate-shaped. Also, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas 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. That is, the antenna 914 may function as one of the two conductors of the capacitor. Thereby, power can 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 the electromagnetic field generated by the secondary battery 913. As the layer 916, for example, a magnetic material can be used.

[0275] Note that the structure of the battery pack is not limited to that shown in FIG. 15.

[0276] For example, as shown in FIGS. 16A and 16B, antennas may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 15A and 15B. FIG. 16A is an external view showing one of the pair of surfaces, and FIG. 16B is an external view showing the other of the pair of surfaces. Note that for the same parts as the secondary battery shown in FIGS. 15A and 15B, the description of the secondary battery shown in FIGS. 15A and 15B can be appropriately incorporated.

[0277] As shown in FIG. 16A, the antenna 914 is provided with the layer 916 interposed therebetween on one of the pair of surfaces of the secondary battery 913, and as shown in FIG. 16B, the antenna 918 is provided with the layer 917 interposed therebetween on the other of the pair of surfaces of the secondary battery 913. The layer 917 has a function of, for example, shielding the electromagnetic field generated by the secondary battery 913. As the layer 917, for example, a magnetic material can be used.

[0278] By adopting the above structure, the sizes of both the antenna 914 and the antenna 918 can be increased. The antenna 918 has a function of, for example, performing data communication with an external device. For the antenna 918, an antenna having a shape applicable to the antenna 914 can be applied, for example. As a communication method between the secondary battery and other devices via the antenna 918, a response method such as NFC (Near Field Communication) that can be used between the secondary battery and other devices 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 a label 910 may not be provided at the portion where the display device 920 is provided. For the same portions as the secondary battery shown in FIGS. 15A and 15B, the description of the secondary battery shown in FIGS. 15A and 15B can be appropriately incorporated.

[0280] The display device 920 may display, for example, an image indicating whether charging is in progress, an image indicating the power storage amount, or the like. As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used. For example, by using an electronic paper, the power consumption of the display device 920 can be reduced.

[0281] Alternatively, as shown in FIG. 16D, a sensor 921 may be provided on the secondary battery 913 shown in FIGS. 15A and 15B. The sensor 921 is electrically connected to the terminal 911 via the terminal 922. For the same portions as the secondary battery shown in FIGS. 15A and 15B, the description of the secondary battery shown in FIGS. 15A and 15B can be appropriately incorporated.

[0282] As the sensor 921, for example, it may have a function capable of measuring displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. By providing the sensor 921, for example, data (such as temperature) indicating the environment where the secondary battery is placed can be detected and stored in the memory within the circuit 912.

[0283] Furthermore, a structural example of the secondary battery 913 will be described with reference to FIGS. 17 and 18.

[0284] The secondary battery 913 shown in FIG. 17A has a wound body 950 in which a terminal 951 and a terminal 952 are provided in the internal region of the housing 930. The wound body 950 is impregnated with an electrolytic solution in the internal region of the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 17A, for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0285] Note that, as shown in FIG. 17B, the housing 930 shown in FIG. 17A may be formed of 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 region surrounded by the housing 930a and the housing 930b.

[0286] As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna such as the antenna 914 may be provided in the internal region of the housing 930a. As the housing 930b, for example, a metal material can be used.

[0287] Furthermore, the structure of the wound body 950 is shown in FIG. 17C. 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 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0288] The negative electrode 931 is connected to the terminal 911 shown in FIG. 15 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG. 15 via the other of the terminals 951 and 952.

[0289] Alternatively, a secondary battery 913 having a wound body 950a as shown in FIGS. 18A to 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 that of 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. It is preferable from the viewpoint of safety that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Further, a wound body 950a having such a shape is preferable in terms of safety and productivity.

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

[0291] As shown in FIG. 18C, the wound body 950a and the electrolytic solution are covered with the housing 930 to form the secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc. in the housing 930.

[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, a secondary battery 913 with a larger charge / discharge capacity can be obtained. For other elements of the secondary battery 913 shown in FIGS. 18A and 18B, reference can be made to the description of the secondary battery 913 shown in FIGS. 17A to 17C.

[0293] By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with a high charge / discharge capacity and excellent cycle characteristics can be obtained.

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

[0295] The 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. Similar to the wound body 950 described in FIG. 18, the wound body 993 is formed by laminating the negative electrode 994 and the positive electrode 995 with the separator 996 interposed therebetween, and winding the laminated sheet.

[0296] Note that the number of laminations of the laminate composed 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 the 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, by storing the above-described winding body 993 in a space formed by thermocompression bonding or the like a film 981 serving as an exterior body and a film 982 having a recess, a secondary battery 980 as shown in FIG. 19C can be manufactured. The winding body 993 has lead electrodes 997 and 998 and is impregnated with an electrolytic solution in the internal regions of the film 981 and the film 982 having a recess.

[0298] For the film 981 and the film 982 having a recess, one or more selected from metal materials such as aluminum and resin materials can be used. If a resin material is used as the material of the film 981 and the film 982 having a recess, the film 981 and the film 982 having a recess can be deformed when a force is applied from the outside, and a flexible storage battery can be manufactured.

[0299] Also, FIGS. 19B and 19C show an example using two films, but a space may be formed by bending a single film, and the above-described winding body 993 may be stored in the space.

[0300] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 having a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0301] Also, in FIG. 19, an example of a secondary battery 980 having a winding body in a space formed by a film serving as an exterior body has been described. However, as shown in FIG. 20 for example, a secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes may be used in the space formed by the film serving as the exterior body.

[0302] The laminated secondary battery 500 shown in Fig. 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 electrolytic solution 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. Further, the interior of the exterior body 509 is filled with the electrolytic solution 508. As the electrolytic solution 508, the electrolytic solution shown in Embodiment 3 can be used.

[0303] In the laminated secondary battery 500 shown in Fig. 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, a part of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged to be exposed outside the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed outside the exterior body 509, and a lead electrode may be ultrasonically bonded to the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 so that the lead electrode is exposed outside.

[0304] In the laminated secondary battery 500, the exterior body 509 may be formed of a three-layer laminated film in which a metal thin film with excellent flexibility such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film.

[0305] Further, an example of the cross-sectional structure of the laminated secondary battery 500 is shown in Fig. 20B. In Fig. 20A, for simplicity, an example composed of two current collectors is shown, but actually, as shown in Fig. 20B, it is composed of a plurality of electrode layers.

[0306] In FIG. 20B, as an example, the number of electrode layers is 16. Even when the number of electrode layers is 16, the secondary battery 500 has flexibility. FIG. 20B shows a structure of a total of 16 layers, with 8 layers of the negative electrode current collector 504 and 8 layers of the positive electrode current collector 501. Note that FIG. 20B shows a cross-section of the extraction portion of the negative electrode, and the 8-layer negative electrode current collector 504 is ultrasonically bonded. Of course, the number of electrode layers is not limited to 16, and it may be more or less. When the number of electrode layers is large, a secondary battery having a larger charge and discharge capacity can be obtained. When the number of electrode layers is small, the battery can be made thinner and can be a secondary battery with excellent flexibility.

[0307] Here, an example of the external view of the laminate type secondary battery 500 is shown in FIGS. 21 and 22. FIGS. 21 and 22 include 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.

[0308] FIG. 23A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. Also, 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 the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. Also, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. The area and shape of the tab regions of the positive electrode and the negative electrode are not limited to the example shown in FIG. 23A.

[0309] <Manufacturing method of laminate type secondary battery> Here, an example of the manufacturing method of 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, separator 507, and positive electrode 503. Here, an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like may be used. Similarly, the tabs of the negative electrode 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 arranged on the exterior body 509.

[0312] Next, as shown in FIG. 23C, the exterior body 509 is bent at the portion indicated by the dashed line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, a region that is not joined to a part (or one side) of the exterior body 509 (hereinafter referred to as an inlet) is provided so that the electrolytic solution 508 can be put in later.

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

[0314] By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery 500 with a high charge-discharge capacity and excellent cycle characteristics can be obtained.

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

[0316] FIG. 24A shows a schematic top view of a bendable secondary battery 250. FIGS. 24B, 24C, and 24D are schematic cross-sectional views taken along cutting lines C1-C2, C3-C4, and A1-A2 in FIG. 24A, respectively. The secondary battery 250 includes an exterior body 251 and an electrode laminate 210 housed in an inner 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 form the electrode laminate 210. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior body 251. In addition, an electrolytic solution (not shown) is enclosed in a region surrounded by the exterior body 251 in addition to the positive electrode 211a and the negative electrode 211b.

[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 for explaining the lamination order of the positive electrode 211a, the negative electrode 211b, and the separator 214. FIG. 25B is a perspective view showing the leads 212a and 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0318] As shown in FIG. 25A, the secondary battery 250 has a plurality of strip-shaped positive electrodes 211a, a plurality of strip-shaped negative electrodes 211b, and a plurality of separators 214. The positive electrode 211a and the 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 a portion other than the tab on one surface of the positive electrode 211a, and a negative electrode active material layer is formed on a portion other than the tab on one surface of the negative electrode 211b.

[0319] The positive electrode 211a and the negative electrode 211b are laminated such that surfaces of the positive electrode 211a where the positive electrode active material layer is not formed contact each other, and surfaces of the negative electrode 211b where the negative electrode active material is not formed contact each other.

[0320] In addition, a separator 214 is provided between the surface of the positive electrode 211a where the positive electrode active material is formed and the surface of the negative electrode 211b where the negative electrode active material is formed. The separator 214 is shown by a dotted line in FIGS. 25A and 25B for easy viewing.

[0321] Also, as shown in FIG. 25B, a plurality of positive electrodes 211a and leads 212a are electrically connected at a joint portion 215a. Also, a plurality of negative electrodes 211b and leads 212b are electrically connected at a joint portion 215b.

[0322] Next, the 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 bent into two parts so as to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a bent portion 261, a pair of seal portions 262, and a seal portion 263. The pair of seal portions 262 are provided with the positive electrode 211a and the negative electrode 211b sandwiched therebetween and can also be called side seals. Also, the seal portion 263 has a portion overlapping the leads 212a and 212b and can also be called a top seal.

[0324] The exterior body 251 preferably has a wavy shape in which ridge lines 271 and valley lines 272 are alternately arranged in a portion overlapping the positive electrode 211a and the negative electrode 211b. Also, the seal portions 262 and 263 of the exterior body 251 are preferably flat.

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

[0326] Here, let the distance between the end portions in the width direction of the positive electrode 211a and the negative electrode 211b, that is, the end portions of the positive electrode 211a and the negative electrode 211b and the seal portion 262 be the distance La. When the secondary battery 250 is deformed such as being bent, as will be described later, the positive electrode 211a and the negative electrode 211b are deformed so as to shift from each other in the length direction. At this 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, when the metal film of the exterior body 251 is exposed, there is a risk that the metal film will be corroded by the electrolytic solution. 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 will increase.

[0327] Also, the thicker the total thickness of the stacked positive electrode 211a and negative electrode 211b, the more preferably the distance La between the positive electrode 211a and negative electrode 211b and the seal portion 262 is increased.

[0328] More specifically, when the total thickness of the stacked positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is t, the distance La is preferably 0.8 times or more and 3.0 times or less, preferably 0.9 times or more and 2.5 times or less, more preferably 1.0 times or more and 2.0 times or less of the thickness t. Or preferably 0.8 times or more and 2.5 times or less. Or preferably 0.8 times or more and 2.0 times or less. Or preferably 0.9 times or more and 3.0 times or less. Or preferably 0.9 times or more and 2.0 times or less. Or preferably 1.0 times or more and 3.0 times or less. Or preferably 1.0 times or more and 2.5 times or less. By setting the distance La within this range, a compact and highly reliable battery against bending can be realized.

[0329] Also, when the distance between the pair of seal portions 262 is defined as distance Lb, it is preferable that the distance Lb is sufficiently larger than the widths of the positive electrode 211a and the negative electrode 211b (here, the width Wb of the negative electrode 211b). Thereby, when the secondary battery 250 is repeatedly deformed such as being bent, even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251, a part of the positive electrode 211a and the negative electrode 211b can be displaced in the width direction, so that it is possible to effectively prevent the positive electrode 211a and the negative electrode 211b from rubbing against the exterior body 251.

[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 satisfies 1.6 times or more and 6.0 times or less, preferably 1.8 times or more and 5.0 times or less, more preferably 2.0 times or more and 4.0 times or less of the thickness t of the positive electrode 211a and the negative electrode 211b. Or 1.6 times or more and 5.0 times or less is preferable. Or 1.6 times or more and 4.0 times or less is preferable. Or 1.8 times or more and 6.0 times or less is preferable. Or 1.8 times or more and 4.0 times or less is preferable. Or 2.0 times or more and 6.0 times or less is preferable. Or 2.0 times or more and 5.0 times or less is preferable.

[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 it satisfies 0.8 or more and 2.5 or less. Or it satisfies 0.8 or more and 2.0 or less. Or it satisfies 0.9 or more and 3.0 or less. Or it satisfies 0.9 or more and 2.0 or less. Or it satisfies 1.0 or more and 3.0 or less. Or it satisfies 1.0 or more and 2.5 or less.

[0332] Also, FIG. 24D is a cross section including the lead 212a and corresponds to a cross section in the longitudinal direction of the secondary battery 250, the positive electrode 211a, and the negative electrode 211b. As shown in FIG. 24D, in the bent portion 261, it is preferable to have a space 273 between the longitudinal ends of the positive electrode 211a and the negative electrode 211b and the exterior body 251.

[0333] FIG. 24E shows a schematic cross-sectional view when the secondary battery 250 is bent. FIG. 24E corresponds to a 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 outer side of the bend extends, and another part located on the inner side deforms so as to contract. More specifically, the portion located on the outer side of the exterior body 251 deforms such that the amplitude of the wave is small and the period of the wave is large. On the other hand, the portion located on the inner side of the exterior body 251 deforms such that the amplitude of the wave is large and the period of the wave is small. Thus, when the exterior body 251 deforms, the stress applied to the exterior body 251 due to the bending is relaxed, so that the material itself constituting the exterior body 251 does not need to expand and contract. As a result, the secondary battery 250 can be bent with a small force without the exterior body 251 being damaged.

[0335] Also, as shown in FIG. 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 on the seal portion 263 side of the plurality of stacked positive electrodes 211a and negative electrodes 211b is fixed by the fixing member 217, they are each displaced such that the amount of displacement increases as they are closer to the bent portion 261. Thereby, the stress applied to the positive electrode 211a and the negative electrode 211b is relaxed, and the positive electrode 211a and the negative electrode 211b themselves do not need to expand and contract. As a result, the secondary battery 250 can be bent without the positive electrode 211a and the negative electrode 211b being damaged.

[0336] Further, since there is a space 273 between the positive electrode 211a and the negative electrode 211b and the exterior body 251, the positive electrode 211a and the negative electrode 211b located on the inner side when bent can be displaced relative to each other without contacting the exterior body 251.

[0337] The secondary battery 250 illustrated in FIGS. 24 and 25 is a battery in which damage to the exterior body, damage to the positive electrode 211a and the negative electrode 211b, etc. are unlikely to occur even when repeated bending and stretching are performed, 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 included in the secondary battery 250, a battery with even more excellent cycle characteristics can be obtained.

[0338] In a all-solid-state battery, by laminating a positive electrode and a negative electrode and applying a predetermined pressure in the lamination direction, the contact state of the interfaces in the internal region can be kept good. By applying a predetermined pressure in the lamination direction of the positive electrode and the negative electrode, it is possible to suppress expansion in the lamination direction due to charge and discharge of the all-solid-state battery, and the reliability of the all-solid-state battery can be improved.

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

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

[0341] First, examples of mounting the bendable secondary battery described in the previous embodiment on an electronic device are shown in FIGS. 26A to 26G. Examples of electronic devices to which the bendable secondary battery is applied include, for example, a television device (also referred to as a television or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a mobile phone or a mobile phone device), a portable game machine, a portable information terminal, an audio reproduction device, and a large game machine such as a pachinko machine.

[0342] In addition, it is also possible to incorporate a secondary battery having a flexible shape 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 the interior of an automobile, or the curved surface of the exterior of an automobile.

[0343] FIG. 26A shows an example of a mobile phone. The mobile phone 7400 includes, in addition to a display unit 7402 incorporated in a housing 7401, an operation button 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 has a secondary battery 7407. By using the secondary battery of one aspect of the present invention for the secondary battery 7407, a lightweight and long-life mobile phone can be provided.

[0344] FIG. 26B shows the 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 its internal region is also bent. At that time, the state of the bent secondary battery 7407 is shown in FIG. 26C. The secondary battery 7407 is a thin rechargeable battery. The secondary battery 7407 is fixed in the bent state. Note that the secondary battery 7407 has a lead electrode electrically connected to a current collector. For example, the current collector is a copper foil, which is alloyed with a part of gallium to improve the adhesion to the active material layer in contact with the current collector, and has a configuration with high reliability in the state where the secondary battery 7407 is bent.

[0345] FIG. 26D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Further, FIG. 26E shows the state of the bent secondary battery 7104. When the secondary battery 7104 is bent and worn on the user's arm, the housing deforms and the curvature of part or all of the secondary battery 7104 changes. Note that the degree of bending at an arbitrary point on a curve represented by the value of the radius of a corresponding circle is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or the secondary battery 7104 changes within a range where the radius of curvature is 40 mm or more and 150 mm or less. If the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm or more and 150 mm or less, high reliability can be maintained. By using the secondary battery according to one aspect of the present invention for the secondary battery 7104 described above, a lightweight and long-life portable display device can be provided.

[0346] FIG. 26F shows an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

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

[0348] The display unit 7202 is provided with a curved display surface and can perform displays along the curved display surface. In addition, the display unit 7202 is equipped with a touch sensor and can be operated by touching the screen with a finger or a stylus. For example, an application can be launched by touching the icon 7207 displayed on the display unit 7202.

[0349] In addition to time setting, the operation button 7205 can have various functions such as turning on and off the power, turning on and off wireless communication, executing and canceling the silent mode, and executing and canceling the power-saving mode. For example, the functions of the operation button 7205 can also be freely set by the operating system incorporated in the portable information terminal 7200.

[0350] In addition, the portable information terminal 7200 is capable of performing short-range wireless communication compliant with communication standards. For example, it can also make hands-free calls by communicating with a wireless communication-capable headset. The portable information terminal 7200 may have an antenna. Also, the antenna may be used for wireless communication.

[0351] In addition, the portable information terminal 7200 is provided with an input / output terminal 7206 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal 7206. Note that the charging operation may also be performed by wireless power supply without passing through the input / output terminal 7206.

[0352] The display unit 7202 of the portable information terminal 7200 has a secondary battery according to one aspect of the present invention. By using the secondary battery according to one aspect of the present invention, a lightweight and long-life portable information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 26E can be incorporated in a curved state in the internal area of the housing 7201 or in a state where it can be curved in the internal area of the band 7203.

[0353] The mobile information terminal 7200 preferably has sensors. As sensors, for example, one or more selected from human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, as well as touch sensors, pressure sensors, and acceleration sensors, etc. are preferably mounted.

[0354] Figure 26G shows an example of a wristband-type display device. The display device 7300 has a display unit 7304 and has a secondary battery according to one aspect of the present invention. Further, the display device 7300 can also be provided with a touch sensor on the display unit 7304 and can also function as a mobile information terminal.

[0355] The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. Further, the display device 7300 can change the display status by means of communication-standardized short-range wireless communication or the like.

[0356] Further, the display device 7300 is provided with input / output terminals and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminals. Note that the charging operation may be performed by wireless power supply without passing through the input / output terminals.

[0357] By using the secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0358] Also, an example of mounting the secondary battery shown in the previous embodiment on an electronic device will be described with reference to FIGS. 26H, 27, and 28.

[0359] By using the secondary battery according to one aspect of the present invention as the secondary battery of a consumer electronic device, a lightweight and long-life product can be provided. For example, consumer electronic devices include electric toothbrushes, electric shavers, electric beauty devices, etc. As the secondary batteries for these products, considering the ease of use by the user, a secondary battery having a stick shape, being small, lightweight, and having a large charge / discharge capacity is desired.

[0360] FIG. 26H is a perspective view of a device also called a tobacco-containing 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 and a sensor. To enhance safety, a protection circuit that prevents overcharging, over-discharging, or both of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 26H has external terminals so that it can be connected to a charging device. Since the secondary battery 7504 becomes the tip portion when held, it is desirable that the total length is short and the weight is light. The secondary battery according to one aspect of the present invention has a high charge-discharge capacity and good cycle characteristics, so it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period.

[0361] Next, FIGS. 27A and 27B show an example of a foldable tablet terminal. The tablet terminal 9600 shown in FIGS. 27A and 27B includes a housing 9630a, a housing 9630b, a movable part 9640 that connects the housing 9630a and the housing 9630b, a display part 9631 including a display part 9631a and a display part 9631b, switches 9625, 9626, and 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] Further, the tablet terminal 9600 has a power storage body 9635 in the internal regions of the housing 9630a and the housing 9630b. The power storage body 9635 is provided across the housing 9630a and the housing 9630b through the movable part 9640.

[0363] The display unit 9631 can have all or part of its area as the touch panel area, and data can be input by touching an image, character, input form, etc. including the icons displayed in the area. For example, keyboard buttons can be displayed on the entire surface of the display unit 9631a on the housing 9630a side, and information such as characters and images can be displayed and used on the display unit 9631b on the housing 9630b side.

[0364] Alternatively, a keyboard can be displayed on the display unit 9631b on the housing 9630b side, and information such as characters and images can be displayed and used on the display unit 9631a on the housing 9630a side. Also, a keyboard display switch button for the touch panel can be displayed on the display unit 9631, and the keyboard can be displayed on the display unit 9631 by touching the button with a finger or a stylus.

[0365] Also, touch input can be simultaneously performed on the touch panel areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side.

[0366] Also, the switches 9625 to 9627 may be interfaces not only for operating the tablet terminal 9600 but also for switching various functions. For example, at least one of the switches 9625 to 9627 may function as a switch for turning on and off the power of the tablet terminal 9600. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display orientation such as vertical display or horizontal display, or a function of switching between black-and-white display and color display. Also, for example, at least one of the switches 9625 to 9627 may have a function of adjusting the brightness of the display unit 9631. Also, the brightness of the display unit 9631 can be optimized according to the amount of external light detected by the optical sensor built into the tablet terminal 9600 during use. Note that the tablet terminal may incorporate other detection devices such as a gyro and an acceleration sensor for detecting inclination in addition to the optical sensor.

[0367] Also, in FIG. 27A, an example is shown in which the display areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side are substantially the same. However, the respective display areas of the display unit 9631a and the display unit 9631b are not particularly limited, and the size of one may be different from that of the other, and the display quality may also be different. For example, one may be a display panel capable of performing a higher-definition display than the other.

[0368] FIG. 27B shows a state in which the tablet terminal 9600 is closed in a two-fold manner. The tablet terminal 9600 has a charging / discharging control circuit 9634 including a housing 9630, a solar cell 9633, and a DCDC converter 9636. Further, as the power storage body 9635, a power storage body according to one aspect of the present invention is used.

[0369] As described above, since the tablet terminal 9600 can be folded in two, the housing 9630a and the housing 9630b can be folded so as to overlap each other when not in use. By folding, the display unit 9631 can be protected, so that the durability of the tablet terminal 9600 can be enhanced. In addition, since the power storage body 9635 using the secondary battery according to one aspect of the present invention has a high charge / discharge capacity and good cycle characteristics, a tablet terminal 9600 that can be used for a long time over a long period can be provided.

[0370] In addition, the tablet terminal 9600 shown in FIGS. 27A and 27B can also have functions such as a function of displaying various information (still images, moving images, text images, etc.), a function of displaying a calendar, a date, or a time on the display unit, a touch input function of touch-inputting or editing the information displayed on the display unit, and a function of controlling processing by various software (programs).

[0371] Power can be supplied to a touch panel, a display unit, a video signal processing unit, etc. by a solar cell 9633 mounted on the surface of a tablet terminal 9600. Note that the solar cell 9633 can be provided on one or both sides of a housing 9630, and can be configured to efficiently charge a power storage body 9635. As the power storage body 9635, using a lithium-ion battery has advantages such as enabling miniaturization.

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

[0373] First, an example of the operation when power is generated by the solar cell 9633 due to external light will be described. The power generated by the solar cell is stepped up or down by a DCDC converter 9636 so as to become a voltage for charging the power storage body 9635. When the power from the solar cell 9633 is used for the operation of the display unit 9631, switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the voltage required for the display unit 9631. Also, when the display on the display unit 9631 is not performed, SW1 may be turned off and SW2 may be turned on to charge the power storage body 9635.

[0374] Note that although the solar cell 9633 has been shown as an example of a power generation means, it is not particularly limited, and a configuration may be adopted in which the power storage body 9635 is charged by other power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a configuration having a contactless power transmission module that wirelessly (non-contact) transmits and receives power for charging or a configuration that combines power generation by a solar cell and other charging means may also be adopted.

[0375] FIG. 28 shows 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 an aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to an aspect of the present invention is provided in an internal area of the housing 8001. The display device 8000 can receive power supply from a commercial power source or use the power stored in the secondary battery 8004. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to an aspect of the present invention as an uninterruptible power supply.

[0376] The display unit 8002 can use a semiconductor display device such as 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 DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or a FED (Field Emission Display).

[0377] Note that the display device includes all display devices for information display, such as those for personal computers and advertisement displays, in addition to those for receiving TV broadcasts.

[0378] In FIG. 28, the installed lighting device 8100 is an example of an electronic device using the secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. In FIG. 28, the case where the secondary battery 8103 is provided in the internal area of the ceiling 8104 where the housing 8101 and the light source 8102 are installed is illustrated. However, the secondary battery 8103 may be provided in the internal area of the housing 8101. The lighting device 8100 can receive power supply from a commercial power source or use the power stored in the secondary battery 8103. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power supply, the lighting device 8100 can be used.

[0379] Note that, in FIG. 28, the installed lighting device 8100 provided on the ceiling 8104 is illustrated. However, the secondary battery according to one aspect of the present invention can also be used for installed lighting devices provided on, for example, side walls 8105, floors 8106, windows 8107, etc., other than the ceiling 8104, or for desktop lighting devices.

[0380] In addition, as the light source 8102, an artificial light source that artificially obtains light using power can be used. Specifically, an incandescent bulb, a discharge lamp such as a fluorescent lamp, a light-emitting element such as an LED or an organic EL element can be cited as an example of the artificial light source.

[0381] In FIG. 28, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. In FIG. 28, the case where the secondary battery 8203 is provided in the indoor unit 8200 is illustrated, 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 supply from a commercial power source or use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8203 according to one aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0382] Note that in FIG. 28, a separate type air conditioner composed of an indoor unit and an outdoor unit is illustrated, but the secondary battery according to one aspect of the present invention can also be used in an integrated type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0383] In FIG. 28, an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one aspect 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 the internal area of the housing 8301. The electric refrigerator-freezer 8300 can receive power supply from a commercial power source or use the power stored in the secondary battery 8304. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8304 according to one aspect of the present invention as an uninterruptible power supply, the electric refrigerator-freezer 8300 can be used.

[0384] Among the electronic devices described above, high-frequency heating devices such as microwave ovens and electronic devices such as electric rice cookers require high power in a short time. Therefore, by using the secondary battery according to one aspect of the present invention as an auxiliary power source to supplement the power that cannot be covered by the commercial power supply, it is possible to prevent the breaker of the commercial power supply from tripping when the electronic device is in use.

[0385] Also, during the time when the electronic device is not in use, especially during the time when the ratio of the actually used power amount to the total power amount that can be supplied by the commercial power supply source (referred to as the power usage rate) is low, by storing power in the secondary battery, it is possible to suppress the increase in the power usage rate outside the above time period. For example, in the case of the electric refrigerator 8300, at night when the temperature is low and the doors 8302 and 8303 of the refrigerator and freezer are not opened or closed, power is stored in the secondary battery 8304. Then, during the day when the temperature rises and the doors 8302 and 8303 of the refrigerator and freezer are opened and closed, by using the secondary battery 8304 as an auxiliary power source, the power usage rate during the day can be kept low.

[0386] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the reliability can be enhanced. Also, according to one aspect of the present invention, a secondary battery with a high charge-discharge capacity can be obtained. Therefore, the characteristics of the secondary battery can be improved, and thus the secondary battery itself can be made smaller and lighter. Therefore, by mounting the secondary battery, which is one aspect of the present invention, on the electronic device described in this embodiment, an electronic device with a longer lifespan and lighter weight can be obtained.

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

[0388] (Embodiment 6) In this embodiment, an example of an electronic device using the secondary battery described in the previous embodiment will be described with reference to FIGS. 29 to 30.

[0389] FIG. 29A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Also, when the user uses it in daily life or outdoors, a wearable device that can perform not only wired charging with an exposed connector part to enhance anti-splash performance, water resistance performance, or dustproof performance but also wireless charging is desired.

[0390] For example, a secondary battery according to one aspect 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 the secondary battery on the temple part of the frame 4000a having a curvature, a lightweight glasses-type device 4000 with a good weight balance and a long continuous use time can be obtained. By providing a secondary battery according to one aspect of the present invention, a configuration that can cope with space saving due to miniaturization of the housing can be realized.

[0391] Also, a secondary battery according to one aspect of the present invention can be mounted on a headset-type device 4001. The headset-type device 4001 has at least a microphone part 4001a, a flexible pipe 4001b, and an earphone part 4001c. One or more secondary batteries can be provided inside the flexible pipe 4001b and inside the earphone part 4001c. By providing a secondary battery according to one aspect of the present invention, a configuration that can cope with space saving due to miniaturization of the housing can be realized.

[0392] Also, a secondary battery according to one aspect of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. By providing a secondary battery according to one aspect of the present invention, a configuration that can cope with space saving due to miniaturization of the housing can be realized.

[0393] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided inside a thin housing 4003a of the device 4003. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving associated with miniaturization of the housing.

[0394] In addition, a secondary battery according to one aspect of the present invention can be mounted on a belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply / reception portion 4006b, and a secondary battery can be mounted in an internal region of the belt portion 4006a. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving associated with miniaturization of the housing.

[0395] Moreover, a secondary battery according to one aspect of the present invention can be mounted on a wristwatch-type device 4005. The wristwatch-type device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided in the display portion 4005a or the belt portion 4005b. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving associated with miniaturization of the housing.

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

[0397] In addition, since the wristwatch-type device 4005 is a wearable device of a type that can be directly wound around the wrist, a sensor for measuring the user's pulse, blood pressure, etc. may be mounted. Data regarding the user's exercise amount and health can be accumulated to manage the health.

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

[0399] Further, a side view is shown in FIG. 29C. FIG. 29C shows a state in which the secondary battery 913 is built in the internal area. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is provided at a position overlapping the display unit 4005a, and is small and lightweight.

[0400] FIG. 30A shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 disposed on the upper surface of the housing 6301, a plurality of cameras 6303 disposed 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 automatically, detect dust 6310, and suck dust from the suction port provided on the lower surface.

[0401] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Further, when an object likely to be entangled with the brush 6304 such as wiring 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 an aspect of the present invention and a semiconductor device or electronic components in its internal area. By using the secondary battery 6306 according to an aspect of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be made an electronic device with a 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, an arithmetic unit, and the like.

[0403] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user by 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 the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer are enabled.

[0405] The upper camera 6403 and the lower camera 6406 have a function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely by 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 an aspect of the present invention and semiconductor devices or electronic components in its internal area. By using the secondary battery according to an aspect of the present invention in the robot 6400, the robot 6400 can be made into an electronic device with a long operating time and high reliability.

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

[0408] For example, the image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of obstacles when moving. Also, from the change in the power storage capacity of the secondary battery 6503 by the electronic component 6504, the remaining battery level can be estimated. The aircraft 6500 includes a secondary battery 6503 according to one aspect of the present invention in its internal region. By using the secondary battery according to one aspect of the present invention in the aircraft 6500, the aircraft 6500 can be made into an electronic device with a long operating time and high reliability.

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

[0410] (Embodiment 7) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on a vehicle is shown.

[0411] When a secondary battery is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized.

[0412] In FIG. 31, a vehicle using a secondary battery according to one aspect of the present invention is illustrated. The automobile 8400 shown in FIG. 31A is an electric vehicle that uses an electric motor as a power source for running. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. The automobile 8400 also has a secondary battery. For the secondary battery, the modules of the secondary battery shown in FIGS. 14C and 14D may be arranged side by side with respect to the floor portion inside the vehicle. Alternatively, a battery pack in which a plurality of secondary batteries shown in FIG. 17 are combined may be installed with respect to the floor portion inside 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 aspect of the present invention preferably has a secondary battery according to one aspect of the present invention, an electric motor, and a control device. Further, the control device preferably has a function of supplying power from the secondary battery to the electric motor.

[0413] In addition, the secondary battery can supply power to a display device such as a speedometer and a tachometer that the automobile 8400 has. Further, the secondary battery can supply power to a semiconductor device such as a navigation system that the automobile 8400 has.

[0414] The motor vehicle 8500 shown in Fig. 31B can be charged by receiving power supply from an external charging facility by one or more selected from a plug-in method, a non-contact power supply method, etc. from the secondary battery of the motor vehicle 8500. Fig. 31B shows a state where charging is being performed from a ground-installed charging device 8021 to a secondary battery 8024 mounted on the motor vehicle 8500 via a cable 8022. When charging, the charging method, the specifications of the connector, etc. may be appropriately performed in a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility or may be a household power source. For example, by plug-in technology, the secondary battery 8024 mounted on the motor vehicle 8500 can be charged by external power supply. Charging can be performed by converting AC power into DC power via a conversion device such as an AC-DC converter.

[0415] Also, although not shown, a power receiving device can be mounted on the vehicle, and power can be supplied non-contact from a power transmission device on the ground for charging. In the case of this non-contact power supply method, by incorporating the power transmission device into one or both of the road and the outer wall, charging can be performed not only while the vehicle is stopped but also while it is running. Also, power transmission and reception can be performed between vehicles using this non-contact power supply method. Furthermore, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or running. For such non-contact power supply, one or more of an electromagnetic induction method and a magnetic field resonance method can be used.

[0416] Fig. 31C is an example of a two-wheeled vehicle using a secondary battery according to an aspect of the present invention. The scooter 8600 shown in Fig. 31C includes a secondary battery 8602, a side mirror 8601, and a direction indicator lamp 8603. The secondary battery 8602 can supply electricity to the direction indicator lamp 8603.

[0417] In addition, for the scooter 8600 shown in FIG. 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. When charging, the secondary battery 8602 can be carried indoors for charging and then stored before driving.

[0418] According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved, and the charge-discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it contributes to the weight reduction of the vehicle, so the cruising range can be improved. In addition, the secondary battery mounted on the vehicle can also be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using the commercial power supply during the peak of power demand. If it is possible to avoid using the commercial power supply during the peak of power demand, it can contribute to energy saving and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long time, so the amount of use of rare metals such as cobalt can be reduced.

[0419] This embodiment can be implemented in appropriate combination with other embodiments.

Example

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

[0421] <Preparation of Cobalt-Containing Material> First, along the flow shown in FIG. 5, the cobalt-containing material prepared in step S26 of FIG. 3 was prepared.

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

[0423] As step S14, first, magnesium fluoride, lithium fluoride, aluminum hydroxide, and nickel hydroxide were mixed to prepare a mixture. Lithium cobaltate was mixed with the prepared mixture and recovered (step S15) to obtain a mixture 804 (step S16).

[0424] Next, as step S17, the mixture 804 was placed in an alumina container, covered, and placed in a muffle furnace. Then, the mixture 804 was heated and recovered (step S18) to obtain a cobalt-containing material 808 (step S19). Specifically, heating at 900 ° C for 10 hours was repeated three times in an oxygen atmosphere. After each heating, crushing was performed using a mortar.

[0425] <Fabrication of Cathode Active Material 1> Next, a cathode active material was fabricated according to the flow shown in FIG. 3.

[0426] As the titanium compound 806 in step S21, titanium oxide (TiO2) was prepared, and as the lithium compound 807 in step S22, lithium oxide (Li2O) was prepared. When the sum of the number of cobalt, nickel, and aluminum atoms contained in the cobalt-containing material 808 prepared in step S26 described later was set to 100, each material was prepared so that the number of moles of titanium oxide was 0.5 and the number of moles of lithium oxide was 1.7.

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

[0428] Next, as step S24, the mixed mixture was recovered, the solvent was volatilized, and mixture 809 was obtained (step S25).

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

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

[0431] Next, as step S28, the mixed mixture was recovered, and mixture 810 was obtained (step S29).

[0432] Next, as step S51, mixture 810 was heated. The heating conditions were set. After heating, it was recovered (step S52), and sample Sa1 and sample Sa2 were obtained as two cathode active materials with different heating conditions.

[0433] Sample Sa1 is a cathode active material obtained by heating at 850 °C for 2 hours in an oxygen atmosphere in step S51.

[0434] Sample Sa2 is a cathode active material obtained by heating at 1050 °C for 2 hours in an oxygen atmosphere in step S51.

[0435] <Fabrication of Cathode Active Material 2> Next, a cathode active material was fabricated without using lithium compound 807.

[0436] First, the titanium compound 806 and the cobalt-containing material 808 were mixed to prepare a mixture. The prepared mixture was heated. The heating conditions were varied. After heating, the mixture was collected to obtain sample Sa3 and sample Sa4 as two positive electrode active materials with different heating conditions.

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

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

[0439] <SEM像> The prepared samples were observed with a scanning electron microscope (SEM) and analyzed by EDX using a Hitachi High-Technologies Corporation SU8030.

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

[0441] In sample Sa2, the surface of the particulate positive electrode active material was smooth. In sample Sa1, which was heated at a low temperature, the surface was uneven compared to sample Sa2, and multiple protrusions were observed as shown in FIG. 32A. In samples Sa3 and Sa4, which were positive electrode active materials prepared without using lithium compound 807, the surface was significantly uneven, and in sample Sa3, which was heated at a low temperature, multiple protrusions were observed as shown in FIG. 33A.

[0442] <edx> EDX analysis was performed on sample Sa3 with large surface irregularities and multiple convex portions observed. The acceleration voltage was set to 15 keV. An SEM image is shown in Fig. 34A. The EDX surface analysis results of cobalt, oxygen, aluminum, titanium, and magnesium are shown in Figs. 34B, 34C, 34D, 34E, and 34F, respectively. From the analysis results, it was suggested that the multiple convex portions observed on the particle surface contain a large amount of titanium and magnesium. Therefore, it is suggested that a reaction or interaction, etc. between titanium and magnesium occurs during the heating in step S51.

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

[0444] First, samples Sa1, Sa2, and Sa4 were used as the positive electrode active material to fabricate a positive electrode. The positive electrode active material, AB, and PVDF were mixed at a weight ratio of positive electrode active material:AB:PVDF = 95:3:2 to prepare a slurry, and the slurry was coated on an aluminum current collector. NMP was used as the solvent for the slurry.

[0445] After coating the slurry on the current collector, the solvent was volatilized. Then, pressure was applied at 210 kN / m and then further at 1467 kN / m. Through the above steps, a positive electrode was obtained. The loading amount of the fabricated positive electrode was approximately 7 mg / cm 2 and the density of the positive electrode active material layer was higher than 3.8 g / cc.

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

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

[0448] As the electrolyte for the electrolytic solution, lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L was used. For the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was added at 2 wt%.

[0449] A separator made of polypropylene with a thickness of 25 μm was used.

[0450] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

[0451] <Cycle characteristics> Next, the cycle characteristics of the fabricated secondary battery were evaluated. For charging, constant current charging was performed at a rate of 0.5C up to a maximum voltage of 4.6V, followed by constant voltage charging at 4.6V up to a rate of 0.05C. For discharging, constant current discharging was performed at a rate of 0.5C down to a minimum voltage of 2.5V. 200 mA / g was converted with 1C rate as the reference. The measurements were carried out at 45°C.

[0452] The cycle characteristics are shown in Fig. 35. The secondary battery using Sample Sa2 as the positive electrode active material exhibited the best characteristics.

[0453] From the cycle characteristics shown in Fig. 35 and the results of the above SEM images, in the process of preparing the positive electrode active material by mixing the mixture 809 of the titanium compound 806 and the lithium compound 807 with the cobalt-containing material 808 and heating, a eutectic mixture of the titanium compound 806 and the lithium compound 807 is generated during heating, so that the eutectic mixture can be uniformly distributed on the surface of the cobalt-containing material 808, and reactions with magnesium etc. are suppressed, enabling the production of a good positive electrode active material.

Explanation of symbols

[0454] 102: Heating furnace interior space, 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: Junction, 215b: Junction, 217: Fixing member, 250: Secondary battery, 251: Exterior body, 261: Bending 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 solution, 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: Conductive wire, 617: Temperature control device, 750a: Positive electrode, 750b: Solid electrolyte layer, 750c: Negative electrode, 751: Electrode plate, 752: Insulating tube, 753: Electrode plate, 761: Lower member, 762: Upper member, 764: Wing nut, 765: O-ring, 766: Insulator, 770a: Package member, 770b: Package member, 770c: Package member, 771: External electrode, 772: External electrode, 773a: Electrode layer, 773b: Electrode layer, 801: 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 part, 4006: Belt-type device, 4006a: Belt part, 4006b: Wireless power supply and power reception 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: Aircraft, 6501: Propeller, 6502: Camera, 6503: Secondary battery, 6504: Electronic component, 7100: Portable display device, 7101: Housing, 7102: Display unit, 7103: Operation button, 7104: Secondary battery, 7200: Portable information terminal, 7201: Housing, 7202: Display unit, 7203: Band, 7204: Buckle, 7205: Operation button, 7206: Input / output terminal, 7207: Icon, 7300: Display device, 7304: Display unit, 7400: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation button, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Secondary battery, 7500: Electronic cigarette, 7501: Atomizer, 7502: Cartridge, 7504: Secondary battery,8000: Display device, 8001: Housing, 8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8021: Charging device, 8022: Cable, 8024: Secondary battery, 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: Headlight, 8406: Electric motor, 8500: Automobile, 8600: Scooter, 8601: Side mirror, 8602: Secondary battery, 8603: Direction indicator, 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: Energy storage element, 9636: DC-DC converter, 9637: Converter, 9640: Movable part,< / edx>

Claims

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

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

3. In claim 1 or claim 2, A method for producing a positive electrode active material, wherein the cobalt-containing material has fluorine.

4. In any one of claims 1 to 3, A method for producing a positive electrode active material, wherein the titanium compound and the lithium compound have a eutectic point at 780°C or higher and 1150°C or lower.

Images