Manufacture method of cathode active material

Abstract

To provide a cathode active material with a large charge / discharge capacity, or to provide a cathode active material with a high charge / discharge voltage, or to provide a secondary battery with little deterioration, or to provide a highly safe power storage device, or to provide a novel secondary battery.SOLUTION: A cathode active material containing cobalt, oxygen, and fluorine, with cobalt-fluorine bonds at the surface or near grain boundaries. The fluorine bonds cause at least some of the cobalt to become high-spin (paramagnetic) Co2+. Therefore, in ESR analysis, the spin concentration at 113K is greater than the spin concentration at 300K by 1.1×10-5 spins / g or more.SELECTED DRAWING: Figure 1

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, or to a mobile information terminal, a vehicle, etc. that has a secondary battery.

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

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like.

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

[0005] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, as they are used in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, and next-generation clean-energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), making them indispensable in today's information society as a rechargeable energy source.

[0006] Therefore, improvements to the positive electrode active material have been investigated to improve the cycle characteristics and capacity of lithium-ion secondary batteries (for example, Patent Document 1). In addition, a technique called electron spin resonance (ESR) or electron paramagnetic resonance (EPR) is useful for analyzing the state of transition metals in positive electrode active materials (for example, Non-Patent Document 1).

[0007] Furthermore, lithium ion secondary batteries are required to have the following characteristics: safety in various operating environments, and improved long-term reliability. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-12022 [Non-patent literature]

[0009] [Non-Patent Document 1] Fe3+ and Ni3+ impurity distribution and electrochemical performance of LiCoO2 electrode materials for lithium ion batteries, R.Alcantara et al, Journal of Power Sources 194(2009)494-501 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of one embodiment of the present invention is to provide a positive electrode active material that exhibits favorable rate characteristics.An object of one embodiment of the present invention is to provide a positive electrode active material that has a large charge / discharge capacity.An object of one embodiment of the present invention is to provide a positive electrode active material that has a high charge / discharge voltage.An object of one embodiment of the present invention is to provide a positive electrode active material that is less prone to deterioration.An object of one embodiment of the present invention is to provide a novel positive electrode active material.An object of one embodiment of the present invention is to provide a secondary battery that has a large charge / discharge capacity.An object of one embodiment of the present invention is to provide a secondary battery that has a high charge / discharge voltage.An object of one embodiment of the present invention is to provide a secondary battery that is safe or highly reliable.An object of one embodiment of the present invention is to provide a secondary battery that is less prone to deterioration.An object of one embodiment of the present invention is to provide a secondary battery with a long life.An object of one embodiment of the present invention is to provide a novel secondary battery.

[0011] Another object of one embodiment of the present invention is to provide an active material, a power storage device, or a manufacturing method thereof.

[0012] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims. [Means for solving the problem]

[0013] One embodiment of the present invention is a positive electrode active material containing cobalt, oxygen, and fluorine, the positive electrode active material having a bond between cobalt and fluorine in a surface layer portion or in the vicinity of grain boundaries.

[0014] Another embodiment of the present invention is a positive electrode active material containing lithium, cobalt, oxygen, and fluorine, in which part of the cobalt is divalent in a discharged state.

[0015] Another embodiment of the present invention is a positive electrode active material that contains cobalt, oxygen, and fluorine, and at least a portion of which exhibits paramagnetism.

[0016] In addition, in the region where the g value obtained from the electron spin resonance spectrum is between 2.068 and 2.233, the spin concentration at a temperature of 113 K is 1.1 × 10 -5 It is a positive electrode active material with a spins / g or more.

[0017] In addition, in the graph above showing the reciprocal of temperature versus the spin concentration per cobalt ion, when an approximate straight line is drawn with three or more measured values ​​at temperatures between 113 K and 300 K, the slope of the line is 5 × 10 -6 Over 4×10 -5 The positive electrode active material is as follows.

[0018] Another aspect of the present invention is a positive electrode having a positive electrode active material, a conductive material, and a current collector, wherein the positive electrode active material contains cobalt, oxygen, and fluorine, and the conductive material contains carbon, and the positive electrode active material has a g value of 2.068 or more and 2.233 or less obtained by electron spin resonance spectroscopy, in a region where the spin concentration at a temperature of 113 K is 1.1 × 10 higher than the spin concentration at a temperature of 300 K. -5 spins / g or more, positive electrode.

[0019] Another embodiment of the present invention is a secondary battery including any of the above positive electrode active materials.

[0020] Another embodiment of the present invention is an electronic device including any of the above secondary batteries.

[0021] Another embodiment of the present invention is a vehicle including the above-described secondary battery. [Effects of the Invention]

[0022] According to one embodiment of the present invention, a positive electrode active material exhibiting good rate characteristics can be provided. Alternatively, according to one embodiment of the present invention, a positive electrode active material having a large charge / discharge capacity can be provided. Alternatively, a positive electrode active material having a high charge / discharge voltage can be provided. Alternatively, a positive electrode active material with little deterioration can be provided. Alternatively, a novel positive electrode active material can be provided. Alternatively, a secondary battery having a large charge / discharge capacity can be provided. Alternatively, a secondary battery with a high charge / discharge voltage can be provided. Alternatively, a secondary battery with high safety or reliability can be provided. Alternatively, a secondary battery with little deterioration can be provided. Alternatively, a secondary battery with a long life can be provided. Alternatively, a novel secondary battery can be provided.

[0023] According to one embodiment of the present invention, an active material, a power storage device, or a manufacturing method thereof can be provided.

[0024] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram illustrating the magnetism of cobalt. [Figure 2] 2A to 2B2 are diagrams illustrating a model used in calculations related to lithium desorption energy. [Figure 3] 3A to 3B2 are diagrams illustrating a model used in calculations related to lithium desorption energy. [Figure 4] FIG. 4 is a graph showing the calculation results for the lithium migration barrier. [Figure 5] 5A to 5C are diagrams illustrating a model used in calculations related to DOS. [Figure 6]6A and 6B are graphs showing the calculation results for DOS. [Figure 7] 7A and 7B are graphs showing the calculation results for DOS. [Figure 8] 8A and 8B are graphs showing the calculation results for DOS. [Figure 9] 9A and 9B are graphs showing the calculation results for DOS. [Figure 10] 10A and 10B are graphs showing the calculation results for DOS. [Figure 11] 11A and 11B are graphs showing the calculation results for DOS. [Figure 12] 12A and 12B are graphs showing the calculation results for DOS. [Figure 13] FIG. 13 is a graph showing the calculation results for DOS. [Figure 14] FIG. 14 is a diagram illustrating a method for producing a positive electrode active material. [Figure 15] FIG. 15 is a diagram illustrating a method for producing a positive electrode active material. [Figure 16] FIG. 16 is a diagram illustrating a method for producing a positive electrode active material. [Figure 17] FIG. 17 is a diagram illustrating a method for producing a positive electrode active material. [Figure 18] 18A and 18B are cross-sectional views of an active material layer in which a graphene compound is used as the conductive material. [Figure 19] 19A and 19B are diagrams illustrating an example of a secondary battery. [Figure 20] 20A to 20C are diagrams illustrating an example of a secondary battery. [Figure 21] 21A and 21B are diagrams illustrating an example of a secondary battery. [Figure 22] 22A to 22C are diagrams illustrating a coin-type secondary battery. [Figure 23] 23A to 23D are diagrams illustrating a cylindrical secondary battery. [Figure 24]24A and 24B are diagrams illustrating an example of a secondary battery. [Figure 25] 25A to 25D are diagrams illustrating an example of a secondary battery. [Figure 26] 26A and 26B are diagrams illustrating an example of a secondary battery. [Figure 27] FIG. 27 is a diagram illustrating an example of a secondary battery. [Figure 28] 28A to 28C are diagrams illustrating a laminated secondary battery. [Figure 29] 29A and 29B are diagrams illustrating a laminated secondary battery. [Figure 30] FIG. 30 is a diagram showing the appearance of a secondary battery. [Figure 31] FIG. 31 is a diagram showing the appearance of a secondary battery. [Figure 32] 32A to 32C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 33] 33A to 33H are diagrams illustrating an example of an electronic device. [Figure 34] 34A to 34C are diagrams illustrating an example of an electronic device. [Figure 35] FIG. 35 is a diagram illustrating an example of an electronic device. [Figure 36] 36A to 36C are diagrams illustrating an example of an electronic device. [Figure 37] 37A to 37C are diagrams showing an example of an electronic device. [Figure 38] 38A to 38C are diagrams illustrating an example of a vehicle. [Figure 39] FIG. 39 shows the ESR spectrum of the positive electrode active material of the example. [Figure 40] FIG. 40 shows the ESR spectrum of the positive electrode active material of the example. [Figure 41] FIG. 41 shows the ESR spectrum of the positive electrode active material of the example. [Figure 42] FIG. 42 is a graph showing the spin concentration of the positive electrode active material of the example. [Figure 43]FIG. 43 is a graph showing the spin concentration of the positive electrode active material of the example. [Figure 44] FIG. 44 is a graph showing the spin concentration per cobalt ion of the positive electrode active material of the example and the reciprocal of the temperature. [Figure 45] 45A and 45B show charge / discharge curves of the secondary battery of the example. [Figure 46] FIG. 46 shows the discharge capacity of the secondary battery of the example. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0027] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may partially contain a substance that does not contribute to the charge / discharge capacity.

[0028] In this specification and the like, the positive electrode active material of one embodiment of the present invention may be referred to as a positive electrode material, a positive electrode material for a secondary battery, a composite oxide, or the like. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a compound. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composition. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composite.

[0029] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of multiple elements (for example, A, B, and C).

[0030] In this specification, the surface layer of particles of active material or the like refers to, for example, a region within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm from the surface toward the interior. Surfaces caused by cracks or fissures may also be considered the surface. Regions deeper than the surface layer are referred to as the interior. In this specification, the term "grain boundary" refers to, for example, a region where particles adhere to each other, a region where the crystal orientation changes within a particle, a region containing many defects, or a region where the crystal structure is disordered. A grain boundary can be considered a type of planar defect. The term "vicinity of a grain boundary" refers to a region within 10 nm from a grain boundary. In this specification, the term "particle" is not limited to spherical shapes (circular cross-sectional shapes), but may also refer to cross-sectional shapes such as oval, rectangular, trapezoidal, conical, square with rounded corners, and asymmetrical shapes. Furthermore, individual particles may also have irregular shapes.

[0031] In addition, Miller indices are used to represent crystal planes and directions in this specification. Individual planes representing crystal planes are represented by ( ). In crystallography, crystal planes, directions, and space groups are represented by a superscript bar. However, due to limitations in application notation, in this specification, instead of a bar above the number, a minus sign (-) may be placed before the number. 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 with equivalent symmetry are represented by {}. Furthermore, trigonal crystals represented by the space group R-3m are generally represented as a hexagonal composite hexagonal lattice for ease of understanding the structure, and Miller indices such as (hkl) and (hkil) are sometimes used. Here, i is -(h+k).

[0032] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0033] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0034] Layered rock salt crystals and the anions of rock salt crystals form a cubic close-packed structure (face-centered cubic lattice structure).

[0035] In this specification, if the anions have a structure in which three layers are stacked with a skew, such as ABCABC, it is called a cubic close-packed structure. Therefore, the anions do not need to be strictly cubic lattices. At the same time, since real crystals always have defects, the analysis results do not necessarily match the theoretical results. For example, in electron diffraction or FFT (fast Fourier transform) of TEM images, spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical positions is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close-packed structure.

[0036] When layered rock salt crystals come into contact with each other, there are crystal faces where the cubic close-packed structures formed by anions are oriented in the same direction.

[0037] Alternatively, it can be explained as follows: the anions on the (111) plane of the cubic crystal structure have a triangular arrangement. The layered rocksalt type has a space group of R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally represented as a compound hexagonal lattice, and the (000l) plane of the layered rocksalt type has a hexagonal lattice. The triangular lattice on the cubic (111) plane has the same atomic arrangement as the hexagonal lattice on the (000l) plane of the layered rocksalt type. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0038] However, the space group of the layered rock salt type crystal and the O3' type crystal is R-3m, which is different from the space group of the rock salt type crystal, Fm-3m (the space group of a general rock salt type crystal) and Fd-3m, and therefore the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt type crystal and the O3' type crystal and the rock salt type crystal. In this specification, when the orientations of the cubic close-packed structures formed by anions in the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal are aligned, it may be said that the crystal orientations are approximately the same.

[0039] The fact that the crystal orientations of the two regions roughly match can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscopy) images, electron diffraction, FFT of TEM images, etc. XRD (X-ray Diffraction), neutron diffraction, etc. can also be used as materials for determination.

[0040] TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc. provide images that reflect the crystal structure.

[0041] For example, in high-resolution TEM images, contrast originating from crystal planes is observed. When an electron beam is incident perpendicular to the c-axis of a layered rock-salt crystal, for example, the contrast originating from the (0003) plane appears as a repetition of bright and dark bands (bright strips) due to electron diffraction and interference. Therefore, when repetition of bright and dark lines is observed in a TEM image and the angle between the bright lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are roughly aligned, i.e., the crystal orientation is roughly aligned. Similarly, when the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can also be determined that the crystal orientation is roughly aligned.

[0042] Furthermore, HAADF-STEM images exhibit contrast dependent on atomic number, with elements with higher atomic numbers appearing brighter. For example, in the case of layered rock-salt lithium cobaltate, which belongs to the space group R-3m, cobalt (atomic number 27) has the highest atomic number, so the electron beam is strongly scattered at the cobalt atoms, resulting in the arrangement of the cobalt atoms being observed as bright lines or an array of highly luminous dots. Therefore, when lithium cobaltate with a layered rock-salt crystal structure is observed perpendicular to the c-axis, the arrangement of the cobalt atoms perpendicular to the c-axis is observed as bright lines or an array of highly luminous dots, while the arrangements of lithium and oxygen atoms are observed as dark lines or low-luminance regions. The same is true when lithium cobaltate contains fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.

[0043] Therefore, in an HAADF-STEM image, if repeated bright and dark lines are observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the atomic arrangements are roughly the same, i.e., that the crystal orientations are roughly the same. Similarly, if the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can also be determined that the crystal orientations are roughly the same.

[0044] Elements with smaller atomic numbers appear brighter in ABF-STEM, but like HAADF-STEM, contrast is obtained according to atomic number, making it possible to determine crystal orientation in the same way as with HAADF-STEM images.

[0045] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0046] In this specification, the depth of charge when all intercalable and detachable lithium has been intercalated is defined as 0, and the depth of charge when all intercalable and detachable lithium contained in the positive electrode active material has been deintercalated is defined as 1. A positive electrode active material having a depth of charge of 0.7 to 0.9 is sometimes referred to as a positive electrode active material charged at a high voltage. A positive electrode active material having a depth of charge of 0.06 or less, or a positive electrode active material that has been discharged to 90% or more of its charge capacity from a state charged at a high voltage, is referred to as a fully discharged positive electrode active material.

[0047] Discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging at a current of 2X (A), it is said to have been discharged at 2C, and when discharging at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same is true for charge rate; when charging at a current of 2X (A), it is said to have been charged at 2C, and when charging at a current of X / 5 (A), it is said to have been charged at 0.2C.

[0048] Constant current charging, for example, refers to a method of charging at a constant charge rate. Constant voltage charging, for example, refers to a method of charging at a constant voltage once the upper voltage limit is reached. Constant current discharging, for example, refers to a method of discharging at a constant discharge rate.

[0049] In this specification, a value close to a certain value A refers to a value between 0.9 A and 1.1 A.

[0050] Although this specification and the like may show examples of secondary batteries using lithium metal as a counter electrode in the positive electrode and positive electrode active material of one embodiment of the present invention, the secondary battery of one embodiment of the present invention is not limited thereto. Other materials, such as graphite and lithium titanate, may also be used for the negative electrode. The properties of the positive electrode and positive electrode active material of one embodiment of the present invention, such as their resistance to crystal structure collapse even with repeated charge and discharge and their excellent cycle characteristics, are not affected by the material of the negative electrode. Although examples of secondary batteries of one embodiment of the present invention using a lithium counter electrode and charging and discharging at a voltage higher than the typical charging voltage of about 4.6 V are shown, they may also be charged and discharged at a lower voltage. Charging and discharging at a lower voltage is expected to result in even better cycle characteristics than those shown in this specification and the like.

[0051] (Embodiment 1) In this embodiment, a positive electrode active material 100 according to one embodiment of the present invention will be described with reference to FIGS.

[0052] <Contained elements> The positive electrode active material 100 contains lithium, a transition metal M, oxygen, and an additive. The positive electrode active material 100 may be said to be a composite oxide represented by LiMO2 to which the additive has been added. However, the positive electrode active material of one embodiment of the present invention is only required to have the crystal structure of a lithium composite oxide represented by LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2.

[0053] The transition metal M contained in the positive electrode active material 100 is preferably a metal that can form a layered rock-salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In particular, using cobalt as the transition metal M contained in the positive electrode active material 100 at 75 atomic % or more, preferably at 90 atomic % or more, and more preferably at 95 atomic % or more, offers many advantages, such as relatively easy synthesis and handling, and excellent cycle characteristics.

[0054] The additive contained in the positive electrode active material 100 is preferably at least one of halogens (e.g., fluorine and chlorine), alkaline earth metals (e.g., magnesium and calcium), Group 13 elements (e.g., boron, aluminum, and gallium), Group 4 elements (e.g., titanium, zirconium, and hafnium), Group 5 elements (e.g., vanadium and niobium), Group 3 elements (e.g., scandium and yttrium), lanthanoids (e.g., lanthanum, cerium, neodymium, and samarium), iron, chromium, cobalt, arsenic, zinc, silicon, sulfur, and phosphorus. These elements may further stabilize the crystal structure of the positive electrode active material 100, as will be described later. That is, the positive electrode active material 100 can include lithium cobalt oxide doped with magnesium and fluorine, lithium cobalt oxide doped with magnesium, fluorine, and titanium, lithium nickel-cobalt oxide doped with magnesium and fluorine, lithium cobalt-aluminate doped with magnesium and fluorine, nickel-cobalt-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide doped with magnesium and fluorine, lithium nickel-manganese-cobalt oxide doped with magnesium and fluorine, etc. In this specification and the like, the term "additive" may be replaced with the term "mixture," "part of the raw material," "impurity," etc.

[0055] The additives do not necessarily have to include alkaline earth metals (e.g., magnesium and calcium), Group 13 elements (e.g., boron, aluminum and gallium), Group 4 elements (e.g., titanium, zirconium and hafnium), Group 5 elements (e.g., vanadium and niobium), Group 3 elements (e.g., scandium and yttrium), iron, chromium, cobalt, arsenic, zinc, silicon, sulfur and phosphorus.

[0056] The positive electrode active material 100 according to one embodiment of the present invention preferably contains at least cobalt as the transition metal M and at least fluorine as an additive element. In particular, it is preferable that the positive electrode active material 100 has a bond between cobalt and fluorine in the surface layer portion. That is, in the surface layer portion or in the vicinity of the grain boundary, part of the oxygen in LiCoO2 is substituted with fluorine, and LiCoO 2-x F x (0.01≦x≦1). As a result, some Co atoms adjacent to fluorine atoms 3+ Co 2+ It is preferable that the surface layer or the vicinity of the grain boundary is Co. 2+ The concentration of cobalt is preferably sufficiently high, for example, at a level at or below 100 K where spin-spin interaction occurs between the unpaired electrons of the nearest cobalt atoms. Furthermore, for cation balance, some cations may be missing, the amount corresponding to the substitution of fluorine. Unless otherwise specified, the valence of cobalt in this specification refers to the valence in a discharged state, i.e., a state in which lithium is fully inserted. A fully inserted state refers to a state in which 99% or more of the charge capacity has been discharged, for example.

[0057] <Magnetism> Co in 100% of the positive electrode active material 3+ and Co 2+ Whether or not the concentration is preferable can be analyzed by, for example, electron spin resonance (ESR) as follows.

[0058] Cobalt in layered rock salt and rock salt forms has an octahedral structure with six anions. Therefore, as shown in Figure 1, the 3d orbitals are e g Orbit and t 2g The orbitals are split into two. The two are arranged in a direction away from the anion. 2g The orbital energy is low.

[0059] Co 2+ Co has three unpaired electrons in the high spin state and is paramagnetic. 2+Co can also have a low spin, in which case it has one unpaired electron and is paramagnetic. 3+ is for low spin 2g All orbitals are filled, resulting in diamagnetism. 4+ has one unpaired electron in the low spin case and is paramagnetic.

[0060] The behavior of magnetic susceptibility χ with temperature changes differs between diamagnetism and paramagnetism. In diamagnetism, magnetic susceptibility χ does not change between room temperature (for example, around 300 K) and low temperatures (for example, around 113 K). On the other hand, in paramagnetism, magnetic susceptibility χ increases as the temperature drops from room temperature. As magnetic susceptibility χ increases, the ESR signal intensity increases. As a result, the observed spin concentration increases.

[0061] The positive electrode active material contains cobalt, and the diamagnetic Co 3+ Paramagnetic Co 2+ When there is a region where C exists at a preferred concentration, the magnetic susceptibility χ of the positive electrode active material follows the Curie-Weiss law shown below (1), where C is the Curie constant and θ is the Weiss constant.

[0062]

number

[0063] In this case, at room temperature, i.e., around 300 K, the spins of the unpaired electrons are disordered and paramagnetic. Up to around 100 K, the magnetic susceptibility χ increases as the inverse of temperature, as in the simple Curie law. The ESR signal intensity and spin number, as well as the magnetic susceptibility χ, also increase as the inverse of temperature.

[0064] At temperatures below about 100K, Co 2+ Long-range order occurs due to the interaction between the magnetic spins of the ions. Although the ESR signal intensity increases according to Curie's law, the ESR signal becomes difficult to observe and broadens due to the strong influence of the interaction between the magnetic spins.

[0065] At even lower temperatures, complete long-range ordering occurs, and the ESR signal disappears.

[0066] In the positive electrode active material 100 of one embodiment of the present invention, the spin concentration at 113 K is preferably greater than the spin concentration at 300 K in the region of the ESR spectrum where the g value is 2.068 or more and 2.233 or less. The difference in spin concentration is 1.1×10 -5 spins / g or more is preferable, and 2.5×10 -5 spins / g or more is more preferable, and 4.0×10 -5 It is more preferable that the density is equal to or greater than spins / g.

[0067] The g-value range of 2.068 to 2.233 can also be rephrased as a range in which the magnetic field is 295 mT to 318.5 mT in the case of a microwave frequency of 9.22 GHz.

[0068] In addition, in the positive electrode active material 100 of one embodiment of the present invention, it is preferable that three or more measured values ​​form a straight line in a graph of the reciprocal of the temperature and the spin concentration per cobalt ion at temperatures of 113 K or higher and 300 K or lower. Specifically, when the measured values ​​of three or more points are approximated to a straight line, the coefficient of determination R of the approximated line is 2 It is preferable that the slope of the approximate line is 5×10 -6 It is preferable that the value is 7×10 or more. -6 It is more preferable that the slope of the approximate line is 4×10 -5 It is preferable that:

[0069] When the temperature and spin concentration have the above-mentioned relationship, the positive electrode active material 100 can be said to exhibit paramagnetism. 3+ Paramagnetic Co 2+ It can be determined that there is a region where fluorine exists at a preferred concentration. In addition, in the surface layer portion or in the vicinity of the grain boundaries of the positive electrode active material 100, part of the oxygen in LiCoO2 is substituted with fluorine, and LiCoO 2-x F xIt can be determined that (0.01≦x≦1) holds. It can also be determined that there is a bond between cobalt and fluorine in the surface layer portion or in the vicinity of the grain boundary of the positive electrode active material 100.

[0070] As shown in Figure 1, hexacoordinated cobalt is 2+ and Co 4+ Both have unpaired electrons, and Co 3+ However, Co does not have unpaired electrons. ESR is an analysis that observes the spin reversal of unpaired electrons, so ESR alone cannot be used to determine the 2+ and Co 4+ Therefore, it is preferable to determine the valence of cobalt in combination with the results of other analyses such as X-ray photoelectric spectroscopy (XPS), electron energy loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDX), and electron probe microanalyzer (EPMA). For example, when the positive electrode active material 100 has a region containing sufficient lithium and fluorine, for example, a region in which the sum of lithium and fluorine is 5 atomic % or more, and the spin reversal of the unpaired electron of cobalt is observed, it is considered to be LiCoO. 2-x F x (0.01≦x≦1) and Co 2+ On the other hand, if the spin reversal of the unpaired electrons of cobalt is observed in the positive electrode active material after charging and discharging, even though the material is poor in lithium and fluorine, it is considered that the material contains CoO2 in part and Co 4+ It can be determined that it has the following.

[0071] In addition, when lithium is significantly deficient, CoO, Co3O4, etc. are generated and Co 2+ However, in this case, the ratio of elements in the positive electrode active material as determined by ICP-MS analysis etc. changes significantly, and the charge / discharge characteristics are significantly reduced. 2-x F x (0.01≦x≦1) can be distinguished from cases where the peak corresponding to the (003) plane of the layered rock salt crystal structure is significantly reduced in XRD analysis, for example, and it can also be determined that CoO, Co3O4, etc. are present.

[0072] Whether or not there is a region having sufficient lithium and fluorine can be determined, for example, by XPS analysis of the positive electrode active material 100. XPS is capable of analyzing a region from the surface of the particle to a depth of 2 nm to 8 nm (usually about 5 nm). If the sum of lithium and fluorine in the XPS analysis is 5 atomic % or more, it can be said that there is a region having sufficient lithium and fluorine in the surface layer.

[0073] In addition, the positive electrode active material 100 according to one embodiment of the present invention contains fluorine and LiCoO in the surface layer portion or in the vicinity of the grain boundaries. 2-x F x (0.01≦x≦1) and Co 2+ It is preferable that the layered rock salt type crystal structure is sufficiently formed, but this is not necessarily the case in the interior. It is preferable that the layered rock salt type crystal structure is maintained in the interior. If the layered rock salt type crystal structure is maintained in the interior, many lithium sites that contribute to charge and discharge can be secured, which is preferable because the charge and discharge capacity of the secondary battery becomes large.

[0074] Therefore, the internal cobalt is the paramagnetic Co of LiCoO2. 3+ It is preferable that the majority of the 3+ Since does not have unpaired electrons, the excessive spin concentration suggests that there is little LiCoO2 and it is difficult to maintain the layered rock-salt crystal structure.

[0075] It is expected that the ESR spectrum will be different when analyzing only the positive electrode active material 100 and when analyzing a positive electrode active material layer containing a conductive material and a binder. For example, it is expected that the signal of the positive electrode active material 100 and the signal derived from the carbon-based material contained in the conductive material will be observed overlapping. However, the g value and g of the ESR spectrum of carbon-based materials, such as fibrous carbon materials including acetylene black, graphite, graphene, and carbon nanotubes, are different. / / , g ⊥ The ESR spectrum of acetylene black in the positive electrode active material layer had g = 2.001 and a ΔPeak-to-Peak of about 1 mT at a microwave frequency of 9.22 GHz. 2+ , Co4+ It is known that the spin of is approximately g=2.14, and Δpeak-to-peak is approximately 3 mT to 5 mT at a microwave frequency of 9.22 GHz. Therefore, by separating the signal originating from cobalt in the positive electrode active material 100 from the signal originating from the carbon-based material, it is possible to determine the magnetism of cobalt.

[0076] <Lithium desorption energy> In the surface layer portion or in the vicinity of the grain boundaries of the positive electrode active material 100, part of the oxygen in LiCoO2 is substituted with fluorine, and LiCoO 2-x F x When x satisfies the condition (0.01≦x≦1), the lithium desorption energy is small as described below, which is preferable because it improves the charge / discharge characteristics and rate characteristics when used in a secondary battery.

[0077] Figure 2A shows a model of LiCoO2 without fluorine, where all the cobalt is trivalent and low spin.

[0078] 2B1 and 2B2 show a model in which one lithium atom has been released from the structure shown in FIG. 2A. The lithium release site 90 is indicated by an arrow. At this time, one of the cobalt atoms close to the lithium release site 90 becomes tetravalent. The tetravalent cobalt atom 91 is indicated by an arrow.

[0079] Next, in Figure 3A, one of the oxygen atoms is replaced by fluorine. 2-x F x The model for (0.01≦x≦1) is shown. The fluorine substitution site 92 is indicated by an arrow. In this case, one of the cobalt atoms adjacent to the fluorine becomes divalent. The divalent cobalt atom 93 is indicated by an arrow.

[0080] Figures 3B1 and 3B2 show a model in which one lithium atom has been removed from Figure 3A. The lithium removal site 90 is indicated by an arrow. At this time, all of the cobalt becomes trivalent.

[0081] Energy was calculated for the above model. The calculation conditions are shown in Table 1. From the calculation results, the difference in energy before and after the removal of one lithium atom, i.e., the lithium removal energy, was calculated and is shown in Table 2.

[0082] [Table 1]

[0083] [Table 2]

[0084] As shown in Table 2, the model in which some of the oxygen atoms are substituted with fluorine has a lithium desorption energy 1.54 eV lower than the model without fluorine. This is because the valence of the cobalt ion changes with lithium desorption (from trivalent to tetravalent in the case without fluorine and from divalent to trivalent in the case with fluorine), and the redox potentials of these ions are different.

[0085] Therefore, in the surface layer portion of the positive electrode active material 100, LiCoO 2-x F x When the x satisfies (0.01≦x≦1), it can be said that the lithium ions near the fluorine atoms can be easily released, which is preferable because it improves the charge / discharge characteristics and rate characteristics when used in secondary batteries.

[0086] While the difference in stabilization energy before and after lithium desorption was referred to above as the lithium desorption energy, a similar energy difference occurs when lithium is inserted. Therefore, improvements in charge / discharge characteristics and rate characteristics can be expected not only during charging but also during discharging.

[0087] <Lithium migration barrier> Next, in the surface layer portion or in the vicinity of the grain boundaries of the positive electrode active material 100, there is LiCoO2 that does not contain fluorine, and there is LiCoO2 that has a structure in which part of the oxygen in LiCoO2 is replaced with fluorine. 2-x F xWe calculated the difference in the conductivity of lithium ions, i.e., the difference in the lithium migration barrier, between the case where (0.01≦x≦1) and the case where (0.01≦x≦1).

[0088] When a lithium ion at a certain position moves (diffuses) to a nearby stable site, it must overcome an energy barrier caused by the repulsive and attractive forces of electrons from surrounding ions (such as cobalt ions and oxygen ions). Therefore, we calculated the energy at each position during lithium migration using a method called Nudged Elastic Band (NEB). The highest energy corresponds to the barrier.

[0089] The process by which lithium ions overcome an energy barrier from their initial position to reach the end of their migration is called lithium ion hopping. Lithium conductivity is generated by repeating this lithium ion hopping. Here, the energy barrier for one lithium ion hopping was calculated to evaluate the ease of lithium ion migration. A lower barrier (height of the energy peak) is advantageous for lithium ion conductivity.

[0090] The calculation conditions are shown in Table 3.

[0091] [Table 3]

[0092] The calculation results are shown in Figure 4. As shown in Figure 4, LiCoO2 (without F) and LiCoO 2-x F x The lithium ion migration barriers were almost the same for (0.01≦x≦1) (with F). This indicates that the presence of fluorine in the surface layer or near the grain boundaries of the positive electrode active material 100 does not inhibit lithium ion conduction.

[0093] <Density of States (DOS)> Next, the case of LiCoO2 (without F) and LiCoO 2-x F x (0.01≦x≦1) (with F) and LiCoO 2-x Fx The partial density of states (PDOS) was calculated for the cases where one lithium atom is removed from (0.01≦x≦1) (with F) and for the cases where one lithium atom is removed from (0.01≦x≦1) (with F).

[0094] Figure 5A shows a model of LiCoO2 (without F) without any particular substitution. Figure 5B shows a model of LiCoO2 with one oxygen atom substituted with fluorine. 2-x F x A model with (0.01≦x≦1) (with F) is shown. The fluorine substitution site 92 is indicated by an arrow. Figure 5C shows a model in which one more lithium atom has been removed from Figure 5B. The lithium removal site 90 is indicated by an arrow.

[0095] The calculation conditions are shown in Table 4. In all cases, the Fermi level was set to 0. The Fermi levels of each model are shown in Table 5.

[0096] [Table 4]

[0097] [Table 5]

[0098] The calculation results are shown in FIGS. 6A to 13.

[0099] 6A to 7B show the PDOS of unsubstituted LiCoO2. Fig. 6A shows the PDOS of total, Fig. 6B shows the PDOS of cobalt (Co), Fig. 7A shows the PDOS of oxygen (O), and Fig. 7B shows the PDOS of lithium (Li).

[0100] 8A to 10B show LiCoO in which one of the oxygen atoms is substituted with fluorine. 2-x F x (0.01≦x≦1) Fig. 8A shows the PDOS of the whole, Fig. 8B shows the PDOS of cobalt, Fig. 9A shows the PDOS of oxygen, Fig. 9B shows the PDOS of lithium, and Fig. 10A shows the PDOS of divalent cobalt (Co 2+ ), and Figure 10B shows the PDOS of fluorine (F). Figures 10A and 10B have different vertical scales than the other graphs.

[0101] 11A to 13 show LiCoO in which one of the oxygen atoms is substituted with fluorine. 2-x F x The DOS for the case where one lithium atom is removed from (0.01≦x≦1) is shown in Figure 11A. Figure 11B shows the PDOS for cobalt, Figure 12A for oxygen, Figure 12B for lithium, and Figure 13 for fluorine.

[0102] As shown in Figure 6B, in LiCoO2, the bands originating from cobalt are symmetrical with up-spin and down-spin, and cobalt is 3+ It was shown to be a low-spin diamagnetic material.

[0103] On the other hand, as shown in Fig. 8(B) and Fig. 10(A), LiCoO 2-x F x In the case of (0.01≦x≦1), the bands originating from cobalt are asymmetric between up-spin and down-spin, which is due to the fact that one cobalt is Co 2+ This is due to the high spin paramagnetism of Co. 2+ is e g It has been shown that the Fermi level increases due to the presence of electrons in the orbital, as shown in Table 5.

[0104] Furthermore, as shown in Figure 11B, LiCoO 2-x F x When one lithium atom leaves (0.01≦x≦1), the bands derived from cobalt are symmetrical with up-spin and down-spin, and cobalt is Co 3+ 8B, 10A, and 11B, when one lithium atom is removed, the Co 2+ Co 3+ It was shown that the

[0105] This embodiment can be used in combination with other embodiments.

[0106] (Embodiment 2) In this embodiment, an example of a method for manufacturing a positive electrode active material 100 according to one embodiment of the present invention will be described with reference to FIGS.

[0107] <Step S11> In step S11 of FIG. 14, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen.

[0108] As the lithium source, for example, lithium carbonate, lithium fluoride, etc. can be used.

[0109] As described in the previous embodiment, 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 M. For example, at least one of manganese, cobalt, and nickel can be used. In particular, using cobalt as the transition metal M at 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more, has many advantages, such as relatively easy synthesis and handling, and excellent cycle characteristics.

[0110] As the transition metal M source, oxides, hydroxides, etc. of the metals exemplified above as the transition metal M can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. As the manganese source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0111] <Step S12> Next, in step S12, the lithium source and the transition metal M source are mixed. Mixing can be performed by a dry method or a wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0112] <Step S13> Next, in step S13, the mixed materials are heated. This step is sometimes referred to as calcination or first heating to distinguish it from subsequent heating steps. Heating is preferably carried out at a temperature of 800°C or higher but lower than 1100°C, more preferably 900°C or higher but 1000°C or lower, and even more preferably around 950°C. Alternatively, 800°C or higher but 1000°C or lower is preferred. Alternatively, 900°C or higher but 1100°C or lower is preferred. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal used as the transition metal M, which is responsible for the redox reaction, or lithium evaporation.

[0113] The heating time can be, for example, from 1 hour to 100 hours, preferably from 2 hours to 20 hours. Alternatively, from 1 hour to 20 hours is preferred. Alternatively, from 2 hours to 100 hours is preferred. Firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or less, more preferably -100°C or less). For example, heating is preferably carried out at 1000°C for 10 hours, with a temperature increase rate of 200°C / h and a flow rate of the dry atmosphere of 10 L / min. The heated material can then be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably from 10 hours to 50 hours.

[0114] However, cooling to room temperature in step S13 is not essential, and cooling to a temperature higher than room temperature may be performed if there is no problem in carrying out the subsequent steps S41 to S44.

[0115] <Step S14> Next, in step S14, the calcined material is recovered to obtain a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen. Specifically, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is substituted with manganese, lithium cobalt oxide in which some of the cobalt is substituted with nickel, or lithium nickel-manganese-cobalt oxide is obtained.

[0116] Alternatively, a composite oxide containing lithium, a transition metal M, and oxygen that has been synthesized in advance may be used in step S14, in which case steps S11 to S13 can be omitted.

[0117] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as a pre-synthesized composite oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0118] Alternatively, lithium cobalt oxide particles (product name: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This is lithium cobalt oxide with an average particle size (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0119] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0120] <Step S21> Next, in step S21, a fluorine source is prepared. Although not shown, it is preferable to also prepare a lithium source.

[0121] Examples of fluorine sources that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, 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), and sodium aluminum hexafluoride (Na3AlF6). The fluorine source is not limited to a solid, and may be, for example, fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), which may be mixed into the atmosphere during the heating step described below. A mixture of multiple fluorine sources may also be used. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the annealing step described below.

[0122] Examples of lithium sources that can be used include lithium fluoride and lithium carbonate. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0123] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source and the lithium source.

[0124] If the subsequent mixing and grinding steps are performed wet, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used.

[0125] It is preferable that the fluorine source be sufficiently finely pulverized. For example, the D50 (median diameter) is preferably 10 nm to 20 μm, more preferably 100 nm to 5 μm. Alternatively, 10 nm to 5 μm is preferable. Alternatively, 100 nm to 20 μm is preferable. If the fluorine source is finely pulverized in this manner, when it is mixed with a composite oxide containing lithium, a transition metal M, and oxygen in a subsequent process, the fluorine source can be easily uniformly attached to the surface of the composite oxide particles. Uniform attachment of the fluorine source to the surface of the composite oxide particles is preferable because it makes it easier to distribute fluorine thoroughly throughout the near-surface region of the composite oxide particles after heating.

[0126] <Step S41> Next, in step S41, the LiMO2 obtained in step S14 is mixed with a fluorine source. The ratio of the number of transition metal atoms M in the composite oxide containing lithium, transition metal, and oxygen to the number of fluorine atoms F in the fluorine source is preferably M:F=100:y (0.1≦y≦10), more preferably M:F=100:y (0.2≦y≦5), and even more preferably M:F=100:y (0.3≦y≦3).

[0127] The mixing in step S41 is preferably performed under milder conditions than those in step S12 so as not to destroy the composite oxide particles. For example, it is preferable to perform the mixing under conditions with a lower rotation speed or shorter time than those in step S12. It can also be said that a dry method is less likely to destroy particles than a wet method. For example, a ball mill, a bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0128] <Step S42> Next, in step S42, the mixed materials are collected to obtain a mixture 903.

[0129] Although this embodiment describes a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities, one embodiment of the present invention is not limited thereto. Instead of the mixture 903 in step S42, a starting material of lithium cobalt oxide to which a fluorine source or the like has been added and which has been fired may be used. In this case, there is no need to separate steps S11 to S14 from steps S21 to S23, resulting in a simple and highly productive process.

[0130] Alternatively, lithium cobalt oxide to which fluorine has been added in advance may be used. If lithium cobalt oxide to which fluorine has been added is used, the steps up to step S42 can be omitted, which is simpler.

[0131] Furthermore, a fluorine source may be further added to lithium cobalt oxide to which fluorine has been added in advance.

[0132] <Step S43> Next, in step S43, the mixture 903 is heated in an atmosphere containing oxygen. It is more preferable that the heating be performed in a manner that suppresses adhesion so as to prevent the particles of the mixture 903 from adhering to each other. This step is sometimes called annealing to distinguish it from the previous heating step.

[0133] Examples of heating that has the effect of suppressing adhesion include heating while stirring the mixture 903, heating while vibrating the container containing the mixture 903, and the like.

[0134] The heating temperature in step S43 must be equal to or higher than the temperature at which the reaction between LiMO2 and the mixture 902 proceeds. The temperature at which the reaction proceeds here is any temperature at which mutual diffusion of elements contained in LiMO2 and the mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in the case of oxides, the melting temperature T m 0.757 times (Tanman temperature T d ) solid-state diffusion occurs. Therefore, for example, a temperature of 500°C or higher is sufficient, and 830°C or higher is more preferable.

[0135] A higher annealing temperature is preferable because the reaction proceeds more easily, the annealing time can be shortened, and productivity is high.

[0136] However, the annealing temperature must be below the decomposition temperature of LiMO2 (1130°C for LiCoO2). At temperatures close to the decomposition temperature, there is concern that LiMO2 may decompose, albeit in trace amounts. Therefore, the annealing temperature is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0137] Therefore, the annealing temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, it is preferably 742°C to 1130°C, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, it is preferably 830°C to 1130°C, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0138] Because lithium fluoride is lighter than oxygen, it may volatilize when heated, resulting in a decrease in the amount of lithium fluoride in mixture 903. Therefore, when heating mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range. For example, one method is to cover the heating crucible.

[0139] The annealing is preferably performed for an appropriate time, which varies depending on conditions such as the annealing temperature, the size and composition of the LiMO2 particles in step S14, etc. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large.

[0140] For example, when the average particle size (D50) of the particles in step S14 is about 12 μm, the annealing temperature is preferably, for example, 600° C. or more and 950° C. or less. The annealing time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0141] On the other hand, when the average particle size (D50) of the particles in step S24 is about 5 μm, the annealing temperature is preferably, for example, 600° C. to 950° C. The annealing time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0142] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0143] <Step S44> Next, in step S44, the annealed material is recovered to produce the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. By sieving, if particles of the positive electrode active material 100 are stuck together, this can be resolved.

[0144] Next, an example of a manufacturing method different from that shown in Fig. 14 will be described with reference to Fig. 15 to Fig. 17. Note that since there are many common parts with Fig. 14, the different parts will be mainly described. For the common parts, the description of Fig. 14 can be referred to.

[0145] Although the production method in which LiMO2 and a fluorine source are mixed in step S41 has been described in FIG. 14, other additives may be further mixed as shown in steps S21, S31, and S32 in FIGS. 15 to 17.

[0146] The additive may be, for example, one or more selected from halogens other than fluorine (e.g., chlorine), alkaline earth metals (e.g., magnesium, calcium), Group 13 elements (e.g., boron, aluminum, gallium), Group 4 elements (e.g., titanium, zirconium, hafnium), Group 5 elements (e.g., vanadium, niobium), Group 3 elements (e.g., scandium, yttrium), lanthanoids (e.g., lanthanum, cerium, neodymium, samarium), iron, chromium, cobalt, arsenic, zinc, silicon, sulfur, and phosphorus.

[0147] An example in which two kinds of additives, a magnesium source and a fluorine source, are used in step S21, a nickel source in step S31, and an aluminum source in step S32, will be described with reference to FIGS.

[0148] These additives are preferably used in the form of finely pulverized oxides, hydroxides, fluorides, etc. of the respective elements. The fine pulverization can be carried out, for example, by a wet method.

[0149] For example, the magnesium source may be, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. In this embodiment, magnesium fluoride (MgF2) is prepared as the magnesium source.

[0150] When LiF is used as the fluorine source and MgF2 is used as the magnesium source, the melting point is most effectively lowered when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive, resulting in poor cycle performance. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0≦x≦1.9), more preferably LiF:MgF2 = x:1 (0.1≦x≦0.5), and even more preferably LiF:MgF2 = x:1 (x = approximately 0.33).

[0151] <Step S22> When mixing other additives such as a magnesium source together with the fluorine source, it is preferable to mix and crush them in step S22. Mixing can be performed by either a dry method or a wet method, but a wet method is preferable because it allows for finer grinding. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media. It is preferable to thoroughly perform this mixing and crushing process to obtain fine powders.

[0152] <Step S23> Next, in step S23, the mixed and crushed materials are collected and designated as mixture 902.

[0153] 15, the nickel source and the aluminum source can be mixed in step S42 at the same time as the mixture 902. This method is preferable because it requires fewer annealing cycles and therefore has high productivity.

[0154] 16, annealing may be performed multiple times in steps S53 and S55, with the adhesion suppression operation step S54 being performed between them. The annealing conditions in steps S53 and S55 can be determined by referring to the description of step S43. Examples of the adhesion suppression operation include crushing with a pestle, mixing using a ball mill, mixing using a centrifugal mixer, sieving, and vibrating the container containing the composite oxide.

[0155] 17, LiMO and mixture 902 may be mixed and annealed in step S41, and then a nickel source and an aluminum source may be mixed in step S61. This mixture is called mixture 904. In step S63, mixture 904 is annealed again. The annealing conditions can be determined by referring to the description of step S43.

[0156] In this way, by separating the steps of introducing the transition metal M and the additive, it may be possible to change the depth profile of each element. For example, the concentration of the additive can be increased in the near-surface region of the particle compared to the internal region. Furthermore, the ratio of the number of atoms of the additive element to the reference number of atoms of the transition metal M can be made higher in the near-surface region than in the internal region.

[0157] This embodiment can be used in combination with other embodiments.

[0158] (Embodiment 3) In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS.

[0159] <Configuration example 1 of secondary battery> The following description will be given taking as an example a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.

[0160] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may include a conductive material and a binder. The positive electrode active material 100 manufactured by the manufacturing method described in the above embodiment is used as the positive electrode active material.

[0161] Furthermore, the positive electrode active material 100 described in the previous embodiment may be mixed with other positive electrode active materials.

[0162] Other examples of positive electrode active materials include composite oxides with an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure, such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2.

[0163] In addition, other positive electrode active materials include lithium-containing materials with a spinel-type crystal structure containing manganese, such as LiMn2O4, and lithium nickel oxide (LiNiO2 and LiNi 1-x M xIt is preferable to mix O2(0 < x < 1)(M = Co, Al, etc.). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0164] Also, as another positive electrode active material, a lithium manganese composite oxide represented by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. Further, when measuring the entire particle 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. Note that the composition of metals, silicon, phosphorus, etc. in the entire particle 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 particle of the lithium manganese composite oxide can be measured using, for example, EDX (Energy Dispersive X-ray Analysis Method). Further, it can be obtained by using the valence evaluation of melting gas analysis and XAFS (X-ray Absorption Fine Structure) analysis in combination with ICPMS analysis. Note that 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.

[0165] Hereinafter, as an example, a cross-sectional configuration example when graphene or a graphene compound is used as the conductive material in the active material layer 200 will be described.

[0166] FIG. 18A shows a longitudinal sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 100, graphene or graphene compound 201 as the conductive material, and a binder (not shown).

[0167] In this specification and the like, graphene compounds include multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Graphene compounds contain carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a curved shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0168] In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0169] In this specification, reduced graphene oxide refers to a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. It may also be called a carbon sheet. Although a single sheet of reduced graphene oxide can function, multiple sheets may also be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is between 2 atomic % and 15 atomic %. By achieving these carbon and oxygen concentrations, reduced graphene oxide can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D between the G band and the D band in a Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0170] In a longitudinal cross section of the active material layer 200, as shown in FIG. 18B, sheet-like graphene or graphene compound 201 is dispersed approximately uniformly within the active material layer 200. While the graphene or graphene compound 201 is schematically represented by a thick line in FIG. 18B, it is actually a thin film having a thickness equivalent to a single layer or multiple layers of carbon molecules. The multiple graphene or graphene compounds 201 are formed so as to partially cover the multiple granular positive electrode active material 100 or to adhere to the surfaces of the multiple granular positive electrode active material 100, and are in surface contact with each other. It is preferable that the graphene or graphene compound 201 is clinging to at least a portion of the active material. It is also preferable that the graphene or graphene compound 201 overlaps at least a portion of the active material. It is also preferable that the shape of the graphene or graphene compound 201 matches at least a portion of the shape of the active material. The shape of the active material refers to, for example, the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that at least a part of the active material is surrounded by the graphene or graphene compound 201. The graphene or graphene compound 201 may have holes.

[0171] Here, a plurality of graphene compounds are bonded together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When an active material is covered with a graphene net, the graphene net can also function as a binder that binds the active materials together. This allows the amount of binder to be reduced or eliminated, thereby improving the ratio of the active material to the electrode volume or weight. In other words, the charge / discharge capacity of a secondary battery can be increased.

[0172] Here, it is preferable to use graphene oxide as the graphene or graphene compound 201, mix it with an active material to form a layer that will become the active material layer 200, and then reduce it. That is, the completed active material layer preferably contains reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene or graphene compound 201, it is possible to substantially uniformly disperse the graphene or graphene compound 201 within the active material layer 200. The solvent is volatilized and removed from the dispersion medium containing the uniformly dispersed graphene oxide, and the graphene oxide is reduced. Therefore, the graphene or graphene compound 201 remaining in the active material layer 200 partially overlaps with each other and is dispersed to such an extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of the graphene oxide may be performed, for example, by heat treatment or using a reducing agent.

[0173] Therefore, unlike granular conductive materials such as acetylene black that make point contact with the active material, graphene or the graphene compound 201 enables surface contact with low contact resistance, and therefore can improve the electrical conductivity between the granular positive electrode active material 100 and the graphene or the graphene compound 201 with a smaller amount than that of a typical conductive material. This allows the ratio of the positive electrode active material 100 in the active material layer 200 to be increased, thereby increasing the discharge capacity of the secondary battery.

[0174] Furthermore, by using a spray dryer in advance, a graphene compound, which is a conductive material, can be formed as a coating that covers the entire surface of the active material, and further a conductive path can be formed between the active material particles by the graphene compound.

[0175] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer 200. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO2, SiO x(x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a D50 of 1 μm or less, more preferably 100 nm or less.

[0176] <Binder> As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0177] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of water-soluble polymers that can be used include polysaccharides. Examples of polysaccharides that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0178] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0179] The binder may be used in combination with two or more of the above.

[0180] For example, a material with particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjusting effect. Furthermore, as water-soluble polymers with particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch may be used.

[0181] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium salts or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials and other components when preparing electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0182] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials and other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl groups and carboxyl groups. Because of these functional groups, the polymers are expected to interact with each other and widely cover the surface of the active material.

[0183] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and suppress the decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress the decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0184] <Positive electrode current collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable that the current collector have a thickness of 5 μm to 30 μm.

[0185] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive material and a binder.

[0186] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0187] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a higher charge-discharge capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. For this reason, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called alloy-based materials.

[0188] In this specification, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO x Here, x preferably has a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less, or preferably 0.2 or more and 1.2 or less, or preferably 0.3 or more and 1.5 or less.

[0189] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0190] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0191] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high charge / discharge capacity per unit volume, relatively little volume expansion, low cost, and higher safety compared to lithium metal.

[0192] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0193] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type. 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0194] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0195] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0196] The conductive material and binder that can be contained in the negative electrode active material layer can be the same as the conductive material and binder that can be contained in the positive electrode active material layer.

[0197] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0198] [Electrolyte] The electrolytic solution contains a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent, such as 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, or sultone, or any combination and ratio of two or more of these.

[0199] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the secondary battery. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0200] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these.

[0201] The electrolyte used in the secondary battery is preferably a highly purified electrolyte with a low content of granular dust and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0202] The electrolyte may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0203] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0204] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0205] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0206] Examples of polymers that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0207] In addition, instead of an electrolyte solution, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymer materials such as polyethylene oxide (PEO) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.

[0208] [Separator] The secondary battery preferably has a separator. Examples of the separator include paper, nonwoven fabric, glass fiber, ceramics, and synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably envelope-shaped and disposed so as to encase either the positive electrode or the negative electrode.

[0209] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0210] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0211] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0212] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the charge / discharge capacity per volume of the secondary battery can be increased.

[0213] [Exterior body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film 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 resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0214] <Configuration example 2 of secondary battery> As an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte layer will be described below.

[0215] As shown in FIG. 19A, a secondary battery 400 according to one embodiment of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0216] The positive electrode 410 includes a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 includes a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is formed using the positive electrode active material formed by the method described in the above embodiment. The positive electrode active material layer 414 may include a conductive additive and a binder.

[0217] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0218] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 19B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0219] As the solid electrolyte 421 of the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0220] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0221] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON-type crystal structure (Li 1-X Al X Ti 2-X (PO4)3, etc.), materials with garnet-type crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON-type crystal structure (Li 14 ZnGeO 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide glass-ceramics (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0222] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0223] Also, different solid electrolytes may be mixed and used.

[0224] Among them, Li with NASICON type crystal structure 1+x Al x Ti 2-x(PO4)3 (0≦x≦1) (hereinafter, LATP) contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and is therefore expected to have a synergistic effect in improving cycle characteristics, making it preferable. It is also expected to improve productivity by reducing the number of steps. In this specification and elsewhere, the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra are arranged three-dimensionally with vertices shared.

[0225] [Shapes of exterior body and secondary battery] The exterior of the secondary battery 400 of one embodiment of the present invention can be made of various materials and in various shapes, but preferably has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0226] For example, Figure 20 shows an example of a cell for evaluating materials for all-solid-state batteries.

[0227] 20A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw and wing nut 764 that fix them in place, and electrode plate 753 is pressed by rotating a holding screw 763 to fix the evaluation material. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is provided between upper member 762 and holding screw 763 to provide a tight seal.

[0228] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 20B.

[0229] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 20C. Note that the same reference numerals are used for the same parts in Figs. 20A, 20B, and 20C.

[0230] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0231] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0232] Fig. 21A shows a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 20. The secondary battery in Fig. 21A has external electrodes 771 and 772 and is sealed in an exterior body having multiple package members.

[0233] An example of a cross section taken along the dashed line in Figure 21A is shown in Figure 21B. A laminate including positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is enclosed and sealed within package member 770a, which is a flat plate with electrode layer 773a provided thereon, frame-shaped package member 770b, and package member 770c, which is a flat plate with electrode layer 773b provided thereon. Package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[0234] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0235] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0236] (Fourth embodiment) In this embodiment, an example of the shape of a secondary battery having the positive electrode described in the previous embodiment will be described. The description in the previous embodiment can be referred to for materials used in the secondary battery described in this embodiment.

[0237] <Coin-type secondary battery> First, an example of a coin-type secondary battery will be described. Fig. 22A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 22B is a cross-sectional view thereof.

[0238] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0239] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0240] Positive electrode can 301 and negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, it is preferable to coat them with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0241] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 22B, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-type secondary battery 300.

[0242] By using the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can have high charge / discharge capacity and excellent cycle characteristics.

[0243] Here, we will use Figure 22C to explain the current flow during charging of a secondary battery. When a lithium-ion secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In lithium-ion secondary batteries, the anode (positive electrode) and cathode (negative electrode) are interchanged during charging and discharging, and the oxidation and reduction reactions are alternated. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Therefore, in this specification, the positive electrode will be called the "positive electrode" or "+ electrode (plus electrode)," and the negative electrode will be called the "negative electrode" or "- electrode (minus electrode)," regardless of whether the battery is being charged or discharged, whether a reverse pulse current is being applied, or whether a charging current is being applied. Using the terms anode (positive electrode) and cathode (negative electrode), which are related to oxidation and reduction reactions, may lead to confusion because their meanings are reversed during charging and discharging. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode and cathode are used, it should be clearly stated whether they are used during charging or discharging, and whether they correspond to the positive or negative pole.

[0244] A charger is connected to the two terminals shown in Fig. 22C to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0245] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to Fig. 23. Fig. 23A shows an external view of a cylindrical secondary battery 600. Fig. 23B is a schematic diagram showing a cross section of the cylindrical secondary battery 600. As shown in Fig. 23B, the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0246] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal that is corrosion-resistant to the electrolyte, such as nickel, aluminum, or titanium, or an alloy of these or an alloy of these with another metal (e.g., stainless steel). To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0247] Because the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active materials on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO3) based semiconductor ceramics or the like can be used for the PTC element.

[0248] 23C, a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between conductive plates 613 and 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in series after being connected in parallel. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0249] FIG. 23D is a top view of module 615. For clarity, conductive plate 613 is shown with dotted lines. As shown in FIG. 23D, module 615 may have conductors 616 that electrically connect multiple secondary batteries 600. A conductive plate can be superimposed on the conductors 616. Furthermore, a temperature control device 617 may be provided between multiple secondary batteries 600. When a secondary battery 600 overheats, it can be cooled by the temperature control device 617, and when a secondary battery 600 is too cold, it can be heated by the temperature control device 617. This makes the performance of module 615 less susceptible to the influence of the outside air temperature. It is preferable that the heat medium in temperature control device 617 is insulating and non-flammable.

[0250] By using the positive electrode active material described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 can have high charge / discharge capacity and excellent cycle characteristics.

[0251] <Example of secondary battery structure> Another structural example of the secondary battery will be described with reference to FIGS.

[0252] 24A and 24B are diagrams showing the appearance of a battery pack. The battery pack has a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to an antenna 914 via the circuit board 900. A label 910 is attached to the secondary battery 913. Furthermore, as shown in FIG. 24B, the secondary battery 913 is connected to terminals 951 and 952. The circuit board 900 is fixed with a sticker 915.

[0253] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to a terminal 951, a terminal 952, an antenna 914, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0254] The circuit 912 may be provided on the back surface of the circuit board 900. The antenna 914 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Also, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0255] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 913. The layer 916 can be made of, for example, a magnetic material.

[0256] The structure of the battery pack is not limited to that shown in FIG.

[0257] For example, as shown in Figures 25A and 25B, an antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 24A and 24B. Figure 25A is an external view showing one of the pair of surfaces, and Figure 25B is an external view showing the other of the pair of surfaces. Note that the description of the secondary battery shown in Figures 24A and 24B can be used as appropriate for the same parts as those of the secondary battery shown in Figures 24A and 24B.

[0258] 25A, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in Fig. 25B, an antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The layer 917 has a function of, for example, being able to shield an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0259] The above structure allows the sizes of both the antenna 914 and the antenna 918 to be increased. The antenna 918 has a function of, for example, performing data communication with an external device. For example, an antenna having a shape applicable to the antenna 914 can be used as the antenna 918. As a communication method between the secondary battery and other devices via the antenna 918, a response method that can be used between the secondary battery and other devices, such as NFC (near field wireless communication), can be used.

[0260] Alternatively, as shown in Fig. 25C, a display device 920 may be provided on the secondary battery 913 shown in Figs. 24A and 24B. The display device 920 is electrically connected to the terminal 911. Note that the label 910 does not need to be provided on the portion where the display device 920 is provided. Note that the description of the secondary battery shown in Figs. 24A and 24B can be used as appropriate for the same portions as those of the secondary battery shown in Figs. 24A and 24B.

[0261] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored power. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0262] 25D, a sensor 921 may be provided in the secondary battery 913 shown in Figures 24A and 24B. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. Note that the description of the secondary battery shown in Figures 24A and 24B can be used as appropriate for the same parts as those in the secondary battery shown in Figures 24A and 24B.

[0263] The sensor 921 may have a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared ray. By providing the sensor 921, for example, data indicating the environment in which the secondary battery is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0264] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0265] A secondary battery 913 shown in Fig. 26A has a wound body 950 in which terminals 951 and 952 are provided inside a housing 930. The wound body 950 is impregnated with an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in Fig. 26A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (such as aluminum) or a resin material.

[0266] 26B, the housing 930 shown in Fig. 26A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 26B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0267] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, an antenna such as the antenna 914 may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0268] 27 shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is formed by stacking the negative electrode 931 and the positive electrode 932 on top of each other with the separator 933 sandwiched therebetween, and winding the laminated sheet. Note that multiple stacks of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0269] 24 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG.

[0270] By using the positive electrode active material described in the above embodiment for the positive electrode 932, the secondary battery 913 can have high charge / discharge capacity and excellent cycle characteristics.

[0271] <Laminated secondary battery> Next, examples of laminated secondary batteries will be described with reference to Figures 28 to 32. If a laminated secondary battery has a flexible configuration, and is mounted in an electronic device having at least a flexible portion, the secondary battery can also be bent in accordance with deformation of the electronic device.

[0272] A laminated secondary battery 980 will be described using Fig. 28. The laminated secondary battery 980 has a wound body 993 shown in Fig. 28A. 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. 27, the wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 on top of each other with the separator 996 sandwiched therebetween, and winding the laminated sheet.

[0273] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed depending on the required charge / discharge capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0274] 28B, a film 981 serving as an exterior body and a film 982 having a recess are bonded together by thermocompression or the like to form a space, and the above-described wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 28C. The wound body 993 has lead electrodes 997 and 998, and is impregnated with an electrolyte solution between the film 981 and the film 982 having a recess.

[0275] For example, a metal material such as aluminum or a resin material can be used for film 981 and film 982 having recesses. If a resin material is used as the material for film 981 and film 982 having recesses, film 981 and film 982 having recesses can be deformed when an external force is applied, and a flexible storage battery can be produced.

[0276] Although an example using two films is shown in FIGS. 28B and 28C, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0277] By using the positive electrode active material described in the above embodiment for the positive electrode 995, the secondary battery 980 can have high charge / discharge capacity and excellent cycle characteristics.

[0278] Furthermore, although Figure 28 describes an example of a secondary battery 980 having a wound body in a space formed by a film that serves as an outer casing, it may also be a secondary battery having multiple rectangular positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing, as shown in Figure 29, for example.

[0279] 29A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte 508, and an exterior body 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. The interior of the exterior body 509 is filled with the electrolyte 508. The electrolyte solution described in Embodiment 3 can be used as the electrolyte 508.

[0280] 29A , positive electrode current collector 501 and negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, positive electrode current collector 501 and negative electrode current collector 504 may be arranged so as to be partially exposed to the outside from outer casing 509. Alternatively, positive electrode current collector 501 and negative electrode current collector 504 may not be exposed to the outside from outer casing 509, and lead electrodes may be used to ultrasonically bond positive electrode current collector 501 or negative electrode current collector 504 to the lead electrodes so as to be exposed to the outside.

[0281] In the laminated secondary battery 500, the exterior body 509 can be a three-layer laminate film having a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and further having an insulating synthetic resin film made of polyamide-based resin, polyester-based resin, or the like provided on the metal thin film as the outer surface of the exterior body.

[0282] 29B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 29A shows an example configured with two current collectors, but in reality, as shown in Fig. 29B, it is configured with multiple electrode layers.

[0283] In FIG. 29B, the number of electrode layers is 16 as an example. Note that even if the number of electrode layers is 16, the secondary battery 500 remains flexible. FIG. 29B shows a structure with a total of 16 layers, including eight layers of negative electrode current collectors 504 and eight layers of positive electrode current collectors 501. Note that FIG. 29B also shows a cross section of the negative electrode lead-out portion, in which eight layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16 and may be more or less. When the number of electrode layers is large, a secondary battery with a larger charge / discharge capacity can be obtained. Furthermore, when the number of electrode layers is small, a secondary battery can be made thinner and have excellent flexibility.

[0284] 30 and 31 show an example of an external view of a laminated secondary battery 500. The battery 500 includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0285] FIG. 32A shows the appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The areas and shapes of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 32A.

[0286] <Method for manufacturing laminated secondary batteries> Here, an example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 30 will be described with reference to FIGS. 32B and 32C.

[0287] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 32B shows the stacked negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions 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.

[0288] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0289] Next, as shown in Fig. 32C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that electrolyte 508 can be introduced later.

[0290] Next, electrolyte 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolyte 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, laminated secondary battery 500 can be produced.

[0291] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have high charge / discharge capacity and excellent cycle characteristics.

[0292] In an all-solid-state battery, applying a predetermined pressure in the stacking direction of the stacked positive and negative electrodes can maintain good contact at the internal interfaces. Applying a predetermined pressure in the stacking direction of the positive and negative electrodes can suppress expansion in the stacking direction due to charging and discharging of the all-solid-state battery, thereby improving the reliability of the all-solid-state battery.

[0293] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0294] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on an electronic device will be described.

[0295] 33A to 33G show examples of electronic devices incorporating the bendable secondary battery described in the previous embodiment. Examples of electronic devices that use the bendable secondary battery include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.

[0296] Furthermore, a secondary battery having a flexible shape can be incorporated into the inner or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0297] 33A illustrates an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.

[0298] FIG. 33B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 installed inside is also bent. FIG. 33C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.

[0299] FIG. 33D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. FIG. 33E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing deforms, causing a change in the curvature of part or the entire secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or the entire main surface of the housing or the secondary battery 7104 changes when the radius of curvature is 40 mm to 150 mm. High reliability can be maintained when the radius of curvature of the main surface of the secondary battery 7104 is 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0300] 33F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0301] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0302] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with a touch sensor, and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0303] The operation button 7205 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0304] The mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is also possible by communicating with a wirelessly enabled headset.

[0305] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0306] The display portion 7202 of the mobile information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight mobile information terminal with a long life can be provided. For example, the secondary battery 7104 shown in FIG. 33E can be installed in a curved state inside the housing 7201 or in a bendable state inside the band 7203.

[0307] The portable information terminal 7200 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or other human body sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0308] 33G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0309] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0310] The display device 7300 also includes an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may also be performed by wireless power supply without using the input / output terminal.

[0311] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0312] An example in which the secondary battery having good cycle characteristics shown in the above embodiment is mounted in an electronic device will be described with reference to FIGS. 33H, 34, and 35. FIG.

[0313] By using a secondary battery of one embodiment of the present invention as a secondary battery in daily electronic devices, products that are lightweight and have a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For secondary batteries in these products, a stick-shaped secondary battery that is easy for users to hold, small, lightweight, and has a large charge / discharge capacity is desired.

[0314] FIG. 33H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 33H, electronic cigarette 7500 includes atomizer 7501 including a heating element, secondary battery 7504 that supplies power to the atomizer, and cartridge 7502 including a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and overdischarging of secondary battery 7504 may be electrically connected to secondary battery 7504. Secondary battery 7504 shown in FIG. 33H has external terminals so that it can be connected to a charging device. Because secondary battery 7504 is the tip portion when held, it is desirable that its total length be short and its weight be light. The secondary battery of one embodiment of the present invention has a high charge / discharge capacity and favorable cycle characteristics, making it possible to provide a compact and lightweight electronic cigarette 7500 that can be used for a long period of time.

[0315] Next, an example of a foldable tablet terminal is shown in FIGS. 34A and 34B. The tablet terminal 9600 shown in FIGS. 34A and 34B includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display portion 9631 having display portions 9631a and 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. A flexible panel can be used for the display portion 9631 to provide a tablet terminal with a larger display area. FIG. 34A shows the tablet terminal 9600 in an open state, and FIG. 34B shows the tablet terminal 9600 in a closed state.

[0316] The tablet terminal 9600 also includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housing 9630a and the housing 9630b.

[0317] The entire or part of the display portion 9631 can be a touch panel area, and data can be input by touching an image including an icon, text, an input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display portion 9631a on the housing 9630a side, and information such as text and images may be displayed on the display portion 9631b on the housing 9630b side.

[0318] A keyboard may be displayed on the display portion 9631b of the housing 9630b, and information such as text and images may be displayed on the display portion 9631a of the housing 9630a. A keyboard display switch button of a touch panel may be displayed on the display portion 9631, and the keyboard may be displayed on the display portion 9631 by touching the button with a finger, a stylus, or the like.

[0319] In addition, touch input can be simultaneously performed on the touch panel area of ​​the display portion 9631a on the housing 9630a side and the touch panel area of ​​the display portion 9631b on the housing 9630b side.

[0320] The switches 9625 to 9627 may be interfaces capable of switching various functions in addition to interfaces for operating the tablet terminal 9600. For example, at least one of the switches 9625 to 9627 may function as a switch for turning the tablet terminal 9600 on and off. For example, at least one of the switches 9625 to 9627 may have a function for switching the display orientation, such as portrait or landscape, or a function for switching between monochrome and color display. For example, at least one of the switches 9625 to 9627 may have a function for adjusting the brightness of the display unit 9631. The brightness of the display unit 9631 can be optimized depending on the amount of external light detected by an optical sensor built into the tablet terminal 9600 during use. The tablet terminal may also have built-in not only an optical sensor but also other detection devices, such as a gyroscope, an acceleration sensor, or other sensors for detecting tilt.

[0321] 34A shows an example in which the display area of ​​the display portion 9631a on the housing 9630a side and the display portion 9631b on the housing 9630b side are substantially the same, the display areas of the display portion 9631a and the display portion 9631b are not particularly limited, and one size may be different from the other size, and the display quality may also be different. For example, one may be a display panel that can display at a higher resolution than the other.

[0322] 34B shows a tablet terminal 9600 in a folded state, and the tablet terminal 9600 includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. The power storage unit 9635 is a power storage unit of one embodiment of the present invention.

[0323] As described above, the tablet terminal 9600 can be folded in half, and therefore, the housing 9630a and the housing 9630b can be folded together when not in use. By folding, the display portion 9631 can be protected, thereby improving durability of the tablet terminal 9600. Furthermore, the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high charge / discharge capacity and favorable cycle characteristics; therefore, the tablet terminal 9600 can be used for a long period of time.

[0324] In addition, the tablet terminal 9600 shown in Figures 34A and 34B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch input operations or editing information displayed on the display unit, and controlling processing using various software (programs).

[0325] A solar cell 9633 attached to the surface of the tablet terminal 9600 can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 9633 can be provided on one or both sides of the housing 9630, and can be configured to efficiently charge the power storage unit 9635. Use of a lithium-ion battery as the power storage unit 9635 has the advantage of enabling miniaturization.

[0326] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 34B will be described with reference to a block diagram in Fig. 34C. Fig. 34C shows a solar cell 9633, a power storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 34B.

[0327] First, an example of operation when power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 9636 to a voltage for charging a power storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, a switch SW1 is turned on, and the converter 9637 steps up or steps down the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, SW1 is turned off and SW2 is turned on to charge the power storage unit 9635.

[0328] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and the power storage unit 9635 may be charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be used.

[0329] FIG. 35 illustrates an example of another electronic device. In FIG. 35, a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one embodiment of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power source.

[0330] The display unit 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0331] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0332] 35 , a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. Although FIG. 35 illustrates the case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0333] Note that although Figure 35 illustrates an example of a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided in places other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device.

[0334] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include discharge lamps such as incandescent lamps and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0335] 35 , an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 of one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although FIG. 35 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or can use power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0336] Note that although FIG. 35 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, a secondary battery according to one embodiment of the present invention can also be used in an integrated air conditioner that has the functions of both the indoor unit and the outdoor unit in a single housing.

[0337] 35 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 35 , the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 of one embodiment of the present invention as an uninterruptible power source.

[0338] Among the electronic devices described above, electronic devices such as microwave ovens and other high-frequency heating devices and electric rice cookers require a large amount of power for a short period of time. Therefore, by using a secondary battery according to one embodiment of the present invention as an auxiliary power source for supplementing the power that cannot be supplied by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0339] Furthermore, by storing power in the secondary battery during time periods when electronic devices are not in use, particularly during time periods when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these time periods. For example, in the case of electric refrigerator-freezer 8300, power is stored in secondary battery 8304 during the night when the temperature is low and refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature rises and refrigerator door 8302 and freezer door 8303 are opened and closed, secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0340] According to one embodiment of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be improved. Furthermore, according to one embodiment of the present invention, a secondary battery with high charge / discharge capacity can be obtained, thereby improving the characteristics of the secondary battery, and thus the secondary battery itself can be made smaller and lighter. Therefore, by incorporating the secondary battery according to one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and be lighter.

[0341] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0342] (Embodiment 6) In this embodiment, examples of electronic devices using the secondary battery described in the above embodiment will be described with reference to FIGS.

[0343] Figure 36A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0344] For example, a secondary battery according to one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 36A . The eyeglasses-type device 4000 includes a frame 4000a and a display unit 4000b. Mounting a secondary battery on temples of the curved frame 4000a makes it possible to provide an eyeglasses-type device 4000 that is lightweight, has a good weight balance, and can be used for a long time. The inclusion of a secondary battery according to one embodiment of the present invention makes it possible to realize a configuration that can accommodate space saving associated with a smaller housing.

[0345] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0346] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery according to one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0347] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By providing the secondary battery according to one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0348] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted inside the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0349] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0350] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0351] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0352] FIG. 36B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0353] 36C shows a side view of the display portion 4005a. FIG. 36C shows that a secondary battery 913 is built in the display portion 4005a. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0354] 37A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, multiple cameras 6303 arranged on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0355] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be a highly reliable electronic device with a long operating time.

[0356] Fig. 37B shows an example of a robot. A robot 6400 shown in Fig. 37B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0357] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0358] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0359] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0360] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component inside the robot 6400. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be a highly reliable electronic device with a long operating time.

[0361] Fig. 37C shows an example of an aircraft. Aircraft 6500 shown in Fig. 37C has propeller 6501, camera 6502, secondary battery 6503, etc., and has the function of flying autonomously.

[0362] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of an obstacle when moving. Furthermore, the electronic component 6504 can estimate the remaining battery charge from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention therein. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the flying object 6500 can be an electronic device with a long operating time and high reliability.

[0363] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0364] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0365] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.

[0366] FIG. 38 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 illustrated in FIG. 38A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery. The secondary battery may be arranged in the form of secondary battery modules shown in FIGS. 23C and 23D on the floor of the vehicle. Alternatively, a battery pack including a combination of a plurality of secondary batteries as shown in FIG. 26 may be installed on the floor of the vehicle. The secondary battery not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0367] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0368] The automobile 8500 shown in FIG. 38B can charge its secondary battery by receiving power from an external charging facility using a plug-in system, a wireless power supply system, or the like. FIG. 38B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged via a cable 8022 from a ground-mounted charging device 8021. The charging method and connector specifications may be determined appropriately using a predetermined system such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0369] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0370] 38C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 38C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0371] 38C, the secondary battery 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0372] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the charge / discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. Reducing the size and weight of the secondary battery itself contributes to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery installed in the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand periods. Avoiding the use of a commercial power source during peak power demand periods can contribute to energy conservation and the reduction of carbon dioxide emissions. Furthermore, good cycle characteristics allow the secondary battery to be used for a long period of time, thereby reducing the amount of rare metals used, such as cobalt.

[0373] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0374] In this example, a positive electrode active material according to one embodiment of the present invention was fabricated and its magnetic properties were analyzed. A secondary battery was fabricated using the positive electrode active material and its characteristics were evaluated.

[0375] <Preparation of positive electrode active material> The sample produced in this example will be described with reference to the production method shown in FIG.

[0376] In step S14, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M and no additives was prepared as LiMO2. In step S21, lithium fluoride was prepared as the fluorine source. In steps S41 and S42, the lithium cobalt oxide and lithium fluoride were mixed using a solid-phase method. The molecular weight of the lithium fluoride was adjusted to 0.5 or 1.7, assuming the number of cobalt atoms to be 100. This mixture was designated mixture 903.

[0377] Next, in step S43, the mixture 903 was annealed. Approximately 1.5 g to 2 g of the mixture 903 was placed in an alumina crucible, and the crucible was covered and heated in a muffle furnace. The atmosphere was oxygen, and the oxygen flow rate was 10 L / min. The annealing temperature was 850°C, and the annealing time was 20 hours or 60 hours.

[0378] Furthermore, lithium cobalt oxide that was annealed without adding lithium fluoride was prepared as Comparative Example 1. Furthermore, as Comparative Examples 2 and 3, lithium cobalt oxide and lithium fluoride were mixed but not annealed.

[0379] The preparation conditions are shown in Table 6.

[0380] [Table 6]

[0381] <esr> The positive electrode active material prepared above was analyzed by ESR. Using an electron spin resonance apparatus JES-FA300 manufactured by JEOL, powdered samples were placed in quartz tubes with an outer diameter of 5 mm and measured at normal pressure. All samples were 5 mg in weight. Each sample was measured at 300 K, 250 K, 200 K, 150 K, and 113 K. The Q value for all measurements was 1.0 × 10 4 That was all.

[0382] As examples of measurement results, ESR spectra at 300 K are shown in Fig. 39 for sample 1, Fig. 40 for sample 3, and Fig. 41 for sample 6. The area around g=2 is where Co in lithium cobalt oxide is located. 2+ , Co 4+ It is known that a signal originating from the cobalt ion appears. The signal with a ΔPeak-to-Peak of 4 mT, centered at g=2.14 (307 mT), i.e., peaks at 305 mT and 309 mT, originates from the S=±1 / 2 spin of the cobalt ion.

[0383] According to Non-Patent Document 1, the signals observed around 33 mT and 340 mT are due to the impurity Fe 2+ It is thought to originate from

[0384] Also, the gentle signal seen in Figure 40 with a ΔPeak-to-Peak of 176 mT centered around 153 mT, or g = 4.3, is thought to be derived from S = ±3 / 2 of the cobalt ion.

[0385] The spin concentration per weight of the positive electrode active material at a microwave frequency of 9.22 GHz in the range of 295 mT to 318.5 mT, or in g-value terms, 2.068 to 2.233 (g = approximately 2.14), is shown in Figures 42 and 43. Figures 42 and 43 show the integrated values ​​of the cobalt ion signals shown in Figures 39 to 41. Figure 42 shows the spin concentrations of Samples 1 to 3, which are comparative examples, and Figure 43 shows the spin concentrations of Samples 4 to 6, which are embodiments of the present invention.

[0386] In Samples 1 to 3, the spin concentration did not change significantly even when the temperature changed, and the difference in spin concentration between 300 K and 113 K was 1.1 × 10 -5 Therefore, it can be said that most of Samples 1 to 3 are diamagnetic. In other words, most of the cobalt in Samples 1 to 3 is hexacoordinated Co +3 It can be said that most of the LiCoO2 has a layered rock salt type crystal structure.

[0387] On the other hand, in Samples 4 to 6, the spin concentration increases as the temperature decreases, and the difference in spin concentration between 300 K and 113 K is 2.0 × 10 -5 spins / g or more, more specifically 4.0×10 -5 Therefore, it can be said that Samples 4 to 6 exhibit paramagnetism. In other words, part of the cobalt in Samples 4 to 6 is hexacoordinated Co +2 In addition to adding lithium fluoride, LiCoO 2-x F x (0.01≦x≦1) and is thought to have cobalt and fluorine bonds. 2-x F x (0.01≦x≦1) is presumed to be more prevalent in the surface layer.

[0388] More specifically, the difference in spin concentration between 300 K and 113 K is 0.6 × 10 in sample 1. -5 spins / g (6.0 × 10 -6 spins / g), and 0.7 × 10 for sample 2. -5 spins / g (7.0 × 10 -6 spins / g), and 1.1 × 10 for sample 3. -5 spins / g, 7.1 × 10 for sample 4 -5 spins / g, 5.7 × 10 for sample 5 -5 spins / g, 4.6 × 10 for sample 6 -5 spins / g.

[0389] <Inverse temperature and spin number> Figure 44 shows the results of the ESR measurements at 300K to 113K, plotted as a graph of the reciprocal of the temperature and the spin concentration per cobalt ion. For each sample series, measurements were taken at 300K, 250K, 200K, 150K, and 113K. The approximate line, the formula, and the R 2 The values ​​are also shown.

[0390] As shown in Fig. 44, the gradient of the approximation line is small for Samples 1 to 3, which means that they are diamagnetic. The gradient of the approximation line for Samples 1 to 3 is 2 × 10 -6 The R of Samples 1 to 3 was 2 was between 0.8 and 0.85, and although there was a strong correlation, it was a lower value than samples 4 to 6.

[0391] On the other hand, the slope of the approximation line for Samples 4 to 6 is large, and it can be said that they are also paramagnetic. -6 More details: 8x10 -6 The slope of the linear approximation for Samples 4 to 6 was all 4×10 -5 In addition, the R 2 was over 0.97, was nearly linear, and behaved in accordance with Curie's law.

[0392] From the above, it was confirmed by ESR analysis that lithium cobalt oxide and a mixture of lithium cobalt oxide and lithium fluoride that was not annealed exhibit diamagnetism. Furthermore, it was confirmed by ESR analysis that the positive electrode active material of the present invention, which was a mixture of lithium cobalt oxide and lithium fluoride and then annealed, exhibits paramagnetism. Furthermore, in the positive electrode active material of the present invention, part of the oxygen in lithium cobalt oxide is replaced by fluorine, resulting in LiCoO 2-x F x It was suggested that (0.01≦x≦1). It was also suggested that the positive electrode active material of the present invention has a bond between cobalt and fluorine.

[0393] As described above, the positive electrode active material of the present invention has a spin concentration at 113 K that is 1.1×10 higher than that at 300 K. -5 The results of ESR measurements at 300 K to 113 K were plotted against the reciprocal of the temperature and the spin concentration per cobalt ion. In the case of the positive electrode active material of the present invention, the slope of the approximate line was 5×10 -6 Over 4×10 -5 It was as follows.

[0394] <Preparation of secondary battery> Next, secondary batteries were fabricated using the positive electrode active materials of Sample 1 and Sample 6.

[0395] First, the positive electrode active material, AB, and PVDF were mixed in a weight ratio of 95:3:2 to prepare a slurry, which was then applied to an aluminum current collector using NMP as the solvent.

[0396] After the slurry was applied to the current collector, the solvent was evaporated. After that, a pressure of 210 kN / m was applied, and then a pressure of 1467 kN / m was applied. A positive electrode was obtained through these steps. The loading amount of the positive electrode was approximately 7 mg / cm. 2 The density was 3.8 g / cc or more.

[0397] Using the prepared positive electrode, a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0398] The counter electrode was made of lithium metal.

[0399] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7.

[0400] The separator was made of polypropylene with a thickness of 25 μm.

[0401] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0402] <Rate characteristics> The discharge rate characteristics of the secondary battery prepared above were evaluated. The charging voltage was 4.2 V. The measurement temperature was 25°C. The charging was CC / CV (0.2 C, 0.02 C cut), and the discharging was CC (0.2 C, 0.5 C, 1 C, 2 C, 3 C, 4 C, or 5 C, 2.5 V cut), with a 10-minute rest period before the next charge. In this example, 1 C was 200 mA / g.

[0403] Figure 45A shows charge-discharge curves for Sample 1 at 0.2C, 0.5C, 1C, 2C, 3C, 4C, and 5C. Figure 45B shows charge-discharge curves for Sample 6 at 0.2C, 0.5C, 1C, 2C, 3C, 4C, and 5C. Figure 46 shows a graph in which the discharge capacities of Sample 1 and Sample 6 at each discharge rate are normalized by the discharge capacity at 0.2C. Table 7 also shows the discharge capacities of Sample 1 and Sample 6 at each discharge rate. n=2 for both Figure 46 and Table 7.

[0404] [Table 7]

[0405] As shown in Figures 45A, 45B, and 46, Sample 6, which was annealed after adding a fluorine source, showed a suppressed decrease in discharge capacity at high discharge rates. This effect was clear compared to Sample 1, which was annealed without adding any fluorine source. This suggests that the presence of fluorine in the surface layer reduces the lithium desorption energy.

[0406] The spin concentration at 113K is 1.1×10 -5 It was revealed that a positive electrode active material having a spin density of at least 100 spins / g exhibits good rate characteristics. In addition, when the results of ESR measurements at 300 K to 113 K were plotted as a graph of the reciprocal of temperature versus the spin density per cobalt ion, the slope of the approximate line for the positive electrode active material of the present invention was 5×10 -6 It was clear that the above positive electrode active material exhibited good rate characteristics. [Explanation of symbols]

[0407] 90: Lithium detachment site, 91: Tetravalent cobalt, 92: Fluorine substitution site, 93: Divalent cobalt, 100: Positive electrode active material< / esr>

Claims

1. A method for producing a positive electrode active material containing lithium, cobalt, oxygen, and fluorine, comprising the steps of: a portion of the cobalt is divalent in a discharged state; The concentration of fluorine in the surface layer is higher than the concentration of fluorine in the inner region, A method for producing a positive electrode active material, comprising mixing lithium cobalt oxide and lithium fluoride and heating the mixture at a temperature of 830°C or higher and 900°C or lower.

2. Cobalt, oxygen, and fluorine are contained therein; At least a portion of the material exhibits paramagnetism, The concentration of fluorine in the surface layer is higher than the concentration of fluorine in the inner region, A method for producing a positive electrode active material, comprising mixing lithium cobalt oxide and lithium fluoride and heating the mixture at a temperature of 830°C or higher and 900°C or lower.

3. In claim 2, In the region where the g value obtained by the electron spin resonance spectrum is between 2.068 and 2.233, the spin concentration at a temperature of 113 K is 1.1 × 10 －５ A method for producing a positive electrode active material having a capacitance of at least spins / g.

4. In claim 2, In a graph of the reciprocal of temperature versus the spin concentration per cobalt ion, when an approximate straight line having three or more measured values ​​at temperatures between 113 K and 300 K is drawn, the slope of the line is 5×10 －６ 4 x 10 or more －５ The following is a method for producing a positive electrode active material.

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