Manufacturing method for secondary battery

Abstract

To provide a positive electrode active material with large charging and discharging capacity, a positive electrode active material with high charging and discharging voltage, or a positive electrode active material whose deterioration is small.SOLUTION: A positive electrode active material is manufactured through a plurality of heating steps. The heating steps after the first heating step are preferably performed at 742°C or more and 920°C or less for 1 hour or more and 10 hours or less. By this heating, magnesium, fluorine, or the like is distributed at a preferred concentration in a surface layer part of the positive electrode active material. General lithium cobaltate has the H1-3 phase type crystal structure at 4.6-V charging, so that the crystal structure is collapsed easily. However, the positive electrode active material according to the present invention has, at 4.6-V charging, less H1-3 type and has the O3' type crystal structure whose change from the discharge time is relatively small; therefore, the cycle characteristic is remarkably good.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a secondary battery using a positive electrode active material and a manufacturing method thereof, or to a portable information terminal, a vehicle, or the like having the secondary battery.

[0002] Another embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, another embodiment of the present invention relates to a process, a machine, a manufacture, or a composition of matter. Another 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 and the like, 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 and the like, 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 in the positive electrode active material have been investigated to improve the charge-discharge cycle characteristics and increase the capacity of lithium-ion secondary batteries (for example, Patent Document 1 and Non-Patent Document 1). Research on the crystal structure of the positive electrode active material has also been conducted (Non-Patent Documents 2 to 4).

[0007] Furthermore, the characteristics required of the power storage device include safety in various operating environments and improved long-term reliability. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2014-523840 [Non-patent literature]

[0009] [Non-Patent Document 1] Jae-Hyun Shim et al, “Characterization of Spinel LixCo2O4·CoatedLiCoO2 Prepared with Post-Thermal Treatment as a Cathode Material for Lithium Ion Batteries”, CEMISTRY OF MATERIALS, 2015, 27, p.3273-3279 [Non-patent document 2] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in 03-and 02·lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 3] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2 (0.0≦x≦1.0)”, Physical Review B, 80(16);165114 [Non-patent document 4] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 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 having high energy density and large charge / discharge capacity. Another object is to provide a positive electrode active material having high charge / discharge voltage. Another object is to provide a positive electrode active material with little deterioration. Another object is to provide a novel positive electrode active material. Another object is to provide a secondary battery with high energy density and large charge / discharge capacity. Another object is to provide a secondary battery with high charge / discharge voltage. Another object is to provide a secondary battery with high safety or reliability. Another object is to provide a secondary battery with little deterioration. Another object is to provide a secondary battery with a long life.

[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 secondary battery having a positive electrode, in which the positive electrode active material includes lithium, a first metal, a second metal, oxygen, and fluorine, the first metal being at least one of cobalt, nickel, and manganese, the second metal being at least one of magnesium, aluminum, titanium, zirconium, niobium, lanthanum, yttrium, and hafnium, and the second metal and fluorine are unevenly distributed in a surface layer portion of the positive electrode active material.

[0014] In the above, it is preferable that the second metal is magnesium, the magnesium concentration in the surface layer portion of the positive electrode active material is 4.5 atomic % or more, and the magnesium and fluorine have a concentration gradient such that the concentrations are higher closer to the surface of the positive electrode active material and decrease to ¼ or less from the surface to a depth of 10 nm.

[0015] Another embodiment of the present invention is a method for manufacturing a secondary battery. The secondary battery includes a positive electrode. The positive electrode includes a positive electrode active material. The positive electrode active material is manufactured through first to third manufacturing steps. The first manufacturing step is a step of mixing a lithium source, a first metal source, a second metal source, and a fluorine source to manufacture a mixture. The second manufacturing step is a step of heating the mixture obtained in the first manufacturing step to manufacture a composite oxide. The third manufacturing step is a step of heating the composite oxide obtained in the second manufacturing step.

[0016] Another embodiment of the present invention is a method for manufacturing a secondary battery. The secondary battery has a positive electrode. The positive electrode has a positive electrode active material. The positive electrode active material is manufactured through first to third manufacturing steps. The first manufacturing step is a step of mixing a lithium source, a first metal source, a second metal source, and a fluorine source to manufacture a mixture. The second manufacturing step is a step of putting the mixture obtained in the first manufacturing step into a container, covering the container, and heating the container to manufacture a composite oxide. The third manufacturing step is a step of putting the composite oxide obtained in the second manufacturing step into a container, covering the container, and heating the container.

[0017] In the above, the heating step in the second manufacturing process is preferably performed at 900°C or higher and 1100°C or lower for 5 hours or longer and 20 hours or shorter, and the heating step in the third manufacturing process is preferably performed at 742°C or higher and 920°C or lower for 1 hour or longer and 10 hours or shorter.

[0018] Another aspect of the present invention is a secondary battery having a positive electrode, wherein a lithium ion secondary battery using the positive electrode and metallic lithium as a negative electrode is charged at a constant current in a 25°C environment until the battery voltage reaches 4.6 V, and then charged at a constant voltage until the current value reaches 0.01 C. After that, the positive electrode is analyzed by powder X-ray diffraction using CuKα1 radiation, and the integrated value at 2θ of 18.00° or more and less than 19.30° is defined as an area intensity I H1-3(006) The integrated value for 2θ between 19.30° and 20.00° is the area intensity I O3’+O3(003) When the area intensity I H1-3(006) / I O3’+O3(003) It is a secondary battery with a capacity of 60% or less.

[0019] In the above, it is preferable that the half width of the peaks present at 2θ of 18.5° or more and 20° or less is 0.2° or less, and the half width of the peaks present at 2θ of 45° or more and 46° or less is 0.2° or less.

[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 having a high energy density and a large charge / discharge capacity can be provided. Alternatively, a positive electrode active material having a high energy density and 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 high energy density and 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, a novel substance, 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. 1A is a cross-sectional view of a positive electrode active material, and Fig. 1B to Fig. 1C2 are diagrams illustrating the distribution of elements contained in the positive electrode active material. [Figure 2] 2A1 to 2C2 are diagrams illustrating the distribution of elements contained in the positive electrode active material. [Figure 3] Figure 3 shows an example of a TEM image in which the crystal orientations are roughly consistent. [Figure 4] Figure 4A shows an example of a STEM image in which the crystal orientations are roughly consistent. Figure 4B shows an FFT of a region of the rock-salt-type crystal RS, and Figure 4C shows an FFT of a region of the layered rock-salt-type crystal LRS. [Figure 5]FIG. 5 is a diagram illustrating the depth of charge and the crystal structure of a positive electrode active material according to one embodiment of the present invention. [Figure 6] Figure 6 shows the XRD pattern calculated from the crystal structure. [Figure 7] FIG. 7 is a diagram illustrating the state of charge and the crystal structure of the positive electrode active material of the comparative example. [Figure 8] Figure 8 shows the XRD pattern calculated from the crystal structure. [Figure 9] 9A and 9B are diagrams illustrating a method for producing a positive electrode active material. [Figure 10] FIG. 10 is a diagram illustrating a method for producing a positive electrode active material. [Figure 11] 11A to 11D are cross-sectional views illustrating examples of the positive electrode of a secondary battery. [Figure 12] 12A is an exploded perspective view of the coin-type secondary battery, FIG. 12B is a perspective view of the coin-type secondary battery, and FIG. 12C is a cross-sectional perspective view of the coin-type secondary battery. [Figure 13] FIG. 13A is an example of a cylindrical secondary battery, FIG. 13B is an example of a cylindrical secondary battery, FIG. 13C is an example of multiple cylindrical secondary batteries, and FIG. 13D is an example of a power storage system having multiple cylindrical secondary batteries. [Figure 14] 14A and 14B are diagrams illustrating an example of a secondary battery, and FIG. 14C is a diagram showing the inside of the secondary battery. [Figure 15] 15A to 15C are diagrams illustrating an example of a secondary battery. [Figure 16] 16A and 16B are diagrams showing the external appearance of a secondary battery. [Figure 17] 17A to 17C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 18] 18A to 18C show examples of the configuration of a battery pack. [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] FIG. 22A is a perspective view of a battery pack according to one embodiment of the present invention, FIG. 22B is a block diagram of the battery pack, and FIG. 22C is a block diagram of a vehicle having a motor. [Figure 23] 23A to 23D are diagrams illustrating an example of a vehicle. [Figure 24] 24A and 24B illustrate a power storage device according to one embodiment of the present invention. [Figure 25] FIG. 25A is a diagram showing a two-wheeled electric vehicle, FIG. 25B is a diagram showing a secondary battery for an electric bicycle, and FIG. 25C is a diagram explaining an electric motorcycle. [Figure 26] 26A to 26D are diagrams illustrating an example of an electronic device. [Figure 27] FIG. 27A is an example of a wearable device, FIG. 27B is a perspective view of a wristwatch-type device, and FIG. 27C is a diagram illustrating a side view of the wristwatch-type device. [Figure 28] 28A and 28B are graphs showing the cycle characteristics of the positive electrode active materials of the examples. [Figure 29] FIG. 29 is a graph showing the XRD patterns of the positive electrode active materials of the examples. [Figure 30] 30A and 30B are graphs showing XRD patterns of the positive electrode active materials of the examples. [Figure 31] FIG. 31 is a graph showing the XRD patterns of the positive electrode active materials of the examples. [Figure 32] 32A and 32B are graphs showing XRD patterns of the positive electrode active materials of the examples. 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 positive electrode active material is a material that constitutes a positive electrode. The positive electrode active material is, for example, a material that undergoes a reaction that contributes to charge / discharge capacity. Note that the positive electrode active material may partially contain a material that does not contribute to charge / discharge capacity. In other words, the positive electrode active material does not necessarily have to have a region that has lithium sites that contribute to 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, uneven distribution refers to the non-uniformity of the concentration of a particular element in a solid composed of multiple elements, and particularly refers to the phenomenon in which the concentration of a particular element is high in a certain location.

[0030] 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).

[0031] 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.

[0032] In this specification, the depth of charge is a value that indicates the amount of capacity that has been charged based on the theoretical capacity of the positive electrode active material, in other words, the amount of lithium that has been released from the positive electrode. For example, lithium cobalt oxide (LiCoO2) and lithium nickel-cobalt-manganese oxide (LiNi x Co y Mn z In the case of a positive electrode active material with a layered rock salt structure such as O2 (x+y+z=1), the theoretical capacity is based on 274mAh / g. When the charge depth is 0, it means that no Li has been released from the positive electrode active material. When the charge depth is 0.5, it means that 137mAh / g of lithium has been released from the positive electrode. When the charge depth is 0.8, it means that 219.2mAh / g of lithium has been released from the positive electrode. a When expressing CoO2 (0≦a≦1), if the charge depth is 0, it is expressed as LiCoO2 with a of 1, and if the charge depth is 0.5, it is expressed as LiCoO2 with a of 0.5. 0.5If the charge depth is 0.8, then a is 0.2. 0.2 It is written as CoO2.

[0033] In this specification and the like, unless otherwise specified, a value in the vicinity of a certain numerical value X refers to a value of 0.9X or more and 1.1X or less.

[0034] Although the present specification and the like sometimes show examples of secondary batteries using a positive electrode and a positive electrode active material of one embodiment of the present invention, in which lithium metal is used for the negative electrode, 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 the positive electrode active material of one embodiment of the present invention, such as their resistance to crystal structure collapse even after repeated charge and discharge and their excellent cycle characteristics, are not affected by the material of the negative electrode. Although the present specification and the like sometimes show examples of secondary batteries using lithium for the negative electrode and charging and discharging the secondary battery at a voltage higher than the charge voltage of about 4.6 V, charging and discharging at a lower voltage may also be used. Charging and discharging at a lower voltage is expected to result in even better cycle characteristics than those shown in the present specification and the like.

[0035] (Embodiment 1) In this embodiment, a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS. 1A to 4. FIG.

[0036] FIG. 1A is a cross-sectional view of a positive electrode active material 100 according to one embodiment of the present invention. Enlarged views of the vicinity of AB in FIG. 1A are shown in FIGS. 1B, 1C1, and 1C2. Enlarged views of the vicinity of CD in FIG. 1A are shown in FIGS. 2A1, 2A2, 2B1, 2B2, 2C1, and 2C2. In the gradations in these figures, a darker color, i.e., closer to black, indicates a higher concentration of a certain element, and a lighter color, i.e., closer to white, indicates a lower concentration of that element.

[0037] 1A, 1B, 1C1, and 1C2, a positive electrode active material 100 has a surface layer portion 100a and an interior portion 100b. In these figures, the boundary between the surface layer portion 100a and the interior portion 100b is indicated by a dashed line. Also, in FIG. 1A, a portion of a crystal grain boundary is indicated by a dashed-dotted line.

[0038] In this specification, the surface portion 100a of the positive electrode active material 100, for example, refers to a region within 50 nm from the surface toward the interior, more preferably within 35 nm from the surface toward the interior, even more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm from the surface toward the interior. Surfaces and the interior of voids formed by cracks may also be considered the surface. The region deeper than the surface portion 100a is referred to as the interior portion 100b of the active material particle. The surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface portion 100a and the interior portion 100b. Therefore, the positive electrode active material 100 does not contain carbonic acid, hydroxyl groups, etc., chemically adsorbed after preparation. It also does not contain electrolyte, binder, conductive material, or compounds derived from these that adhere to the positive electrode active material 100. The surface of the positive electrode active material 100 in a cross-sectional STEM image, etc., refers to the surface where a metal element with an atomic number greater than that of lithium is first observed. More specifically, first, the nucleus of a metal element having an atomic number larger than that of lithium, that is, the point where a brightness peak exists in a cross-sectional STEM image or the like, is assumed.

[0039] In addition, in this specification, the term "grain boundary" refers to, for example, a portion where particles are stuck together, a portion where the crystal orientation changes inside a particle, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc. In this specification, the term "crystal defect" refers to a defect that can be observed in a TEM image, etc., that is, a structure in which other elements have entered the crystal, a cavity, etc. A grain boundary can be said to be one type of planar defect. In addition, the vicinity of a grain boundary refers to a region within 10 nm from the grain boundary. Grain boundaries can be observed, for example, by cross-sectional observation (cross-sectional TEM, cross-sectional STEM).

[0040] Furthermore, in this specification and the like, the term "particle" is not limited to referring only to spherical shapes (cross-sectional shapes of which are circles), but the cross-sectional shapes of individual particles may be elliptical, rectangular, trapezoidal, conical, quadrilateral with rounded corners, asymmetrical, etc., and further, individual particles may be irregular in shape.

[0041] <Contained elements> The positive electrode active material 100 includes lithium, a first metal M1, a second metal M2, oxygen, and fluorine. The positive electrode active material 100 may be described as a composite oxide represented by LiM1O2 to which M2 and fluorine have been added. However, the positive electrode active material of one embodiment of the present invention is sufficient as long as it includes a lithium composite oxide represented by LiM1O2, and its composition is not strictly limited to Li:M1:O=1:1:2.

[0042] The first metal M1 contained in the positive electrode active material 100 is preferably a transition metal capable of forming a layered rock-salt composite oxide belonging to the space group R-3m with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, the first metal M1 contained in the positive electrode active material 100 may be cobalt alone, nickel alone, a combination of cobalt and manganese, or a combination of cobalt and nickel, or three of cobalt, manganese, and nickel. That is, the positive electrode active material 100 may contain a composite oxide containing lithium and the first metal M1, such as lithium cobalt 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 nickel-manganese-lithium cobalt oxide.

[0043] 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 vacancies of cations or anions may also be present. Strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice.

[0044] 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.

[0045] Furthermore, when the positive electrode active material contains 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more of cobalt as the transition metal, it has many advantages such as being relatively easy to synthesize and handle, and having excellent cycle characteristics.

[0046] Furthermore, if the first metal M1 contains not only cobalt but also nickel, it may suppress the shift in the layered structure consisting of cobalt and oxygen octahedra. This is preferable because it may make the crystal structure more stable, especially in the charged state at high temperatures. This is because nickel easily diffuses deep into the lithium cobalt oxide, and while it is present on the cobalt site during discharge, it is thought to be able to occupy the lithium site during charge through cation mixing. The nickel present on the lithium site during charge is thought to function as a pillar supporting the layered structure consisting of cobalt and oxygen octahedra, contributing to the stabilization of the crystal structure.

[0047] The first metal M1 does not necessarily have to contain manganese, and does not necessarily have to contain nickel.

[0048] The second metal M2 contained in the positive electrode active material 100 is preferably at least one of magnesium, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, lanthanum, yttrium, hafnium, and zinc. Silicon, sulfur, phosphorus, boron, or arsenic may also be added together with the second metal M2. Addition of phosphorus is particularly preferable because it can improve the continuous charge durability and result in a highly safe secondary battery.

[0049] As will be described later, these second metals and fluorine may further stabilize the crystal structure of the positive electrode active material 100. That is, the positive electrode active material 100 may 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 doped with magnesium and fluorine, nickel-cobalt-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide doped with magnesium and fluorine, and nickel-manganese-cobalt oxide doped with magnesium and fluorine. In this specification and the like, the second metal M2 may be referred to as an additive, a mixture, a part of a raw material, an impurity, or the like.

[0050] Manganese, titanium, vanadium, and chromium may easily assume a stable tetravalent state, and may contribute greatly to structural stability.

[0051] The second metal M2 is preferably added in a concentration that does not significantly change the crystallinity of the composite oxide represented by LiMO, for example, in an amount that does not cause the Jahn-Teller effect, which will be described later.

[0052] The second metal does not necessarily have to include aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, lanthanum, yttrium, hafnium, or zinc.

[0053] <Elemental distribution> The surface layer portion 100a preferably has higher concentrations of the second metal M2 and fluorine than the interior portion 100b. The second metal M2 and fluorine preferably have a concentration gradient. When there are multiple second metals M2, it is preferable that the peak positions of the concentrations differ depending on the element. It can be said that the second metal M2 and fluorine are unevenly distributed in the surface layer portion 100a.

[0054] For example, it is preferable that a certain second metal M2(1) has a concentration gradient that increases from the interior 100b toward the surface, as shown by the gradation in Fig. 1C1. Examples of the second metal M2(1) that preferably has such a concentration gradient include magnesium and titanium.

[0055] It is also preferable that fluorine has a concentration gradient that increases from the interior 100b toward the surface, as shown by the gradation in FIG. 1C1.

[0056] The second metal M2(2) preferably has a concentration gradient, as shown by the gradation in FIG. 1C2, and a concentration peak in a region deeper than the second metal M2(1). The concentration peak may be present in the surface layer 100a or may be deeper than the surface layer 100a. For example, the concentration peak is preferably present in a region from 5 nm to 30 nm from the surface. Examples of the second metal M2(2) that preferably has such a concentration gradient include aluminum and manganese.

[0057] Furthermore, due to the concentration gradient of the second metal M2 and fluorine as described above, it is preferable that the crystal structure continuously change from the interior 100b toward the surface layer 100a. For example, it is preferable that the layered rock-salt crystal structure of the interior 100b becomes more characteristic of the rock-salt crystal structure toward the surface layer 100a. Furthermore, it is preferable that the crystal orientation of the surface layer 100a and the interior 100b roughly coincide.

[0058] In the positive electrode active material 100 according to one embodiment of the present invention, the layered structure consisting of the first metal M1 and oxygen octahedra is reinforced by the second metal M2 and the surface layer portion 100a having a high concentration of fluorine, i.e., the outer periphery of the particle, so that the layered structure consisting of the first metal M1 and oxygen octahedra does not collapse even when lithium is released from the positive electrode active material 100 upon charging.

[0059] Furthermore, it is preferable that the concentration gradient of the second metal M2 is uniformly present in the surface layer 100a of the positive electrode active material 100. The uniform presence of the concentration gradient of the second metal M2 in the surface layer 100a of the positive electrode active material 100 can suppress stress concentration that may occur locally in the particles. For example, if the concentration gradient of the second metal M2 is not uniformly present in the surface layer 100a, stress may concentrate in the particles from areas where there is no concentration gradient of the second metal M2. Stress concentration in a part of the particle may cause defects such as cracks, which may lead to particle breakage and a decrease in charge / discharge capacity.

[0060] However, the concentration gradient of the second metal M2 does not necessarily have to be uniform across the entire surface layer 100a of the positive electrode active material 100. Examples of the distribution of the second metal M2(1) near the CD in FIG. 1A are shown in FIGS. 2A1, 2B1, and 2C1. Examples of the distribution of the second metal M2(2) near the CD in FIG. 1A are shown in FIGS. 2A2, 2B2, and 2C2.

[0061] The surface layer portion 100a of the positive electrode active material 100 may have a region that does not have either the second metal M2(1) or the second metal M2(2), as shown in Figures 2A1 and 2A2. Alternatively, as shown in Figures 2B1 and 2B2, the surface layer portion 100a may have a region that has the second metal M2(1) but does not have the second metal M2(2). Alternatively, as shown in Figures 2C1 and 2C2, the surface layer portion 100a may have a region that does not have the second metal M2(1) but does have the second metal M2(2).

[0062] When cobalt and nickel are used as the first metal M1, it is preferable that the cobalt and nickel are uniformly dissolved in the entire positive electrode active material 100. When the concentration of a part of the first metal M1, for example, nickel, is low, it may be below the detection limit in analysis such as XPS or EDX.

[0063] For example, if the number of nickel atoms is 2% or less of the number of cobalt atoms, the nickel content in the lithium composite oxide will be 0.5 atomic % or less. Meanwhile, the detection limits of XPS and EDX are generally around 1 atomic %. In this case, if nickel is uniformly dissolved throughout the positive electrode active material 100, the results may be below the detection limit using analytical methods such as XPS and EDX. In this case, a result below the detection limit indicates that the nickel concentration is 1 atomic % or less, and that nickel is dissolved throughout the positive electrode active material 100.

[0064] On the other hand, using ICP-MS, GD-MS, etc., it is possible to quantify nickel even at concentrations of 1 atomic % or less.

[0065] A part of the first metal M1 contained in the positive electrode active material 100, for example, manganese, may have a concentration gradient that increases from the interior 100b toward the surface.

[0066] As described above, the surface portion 100a of the cathode active material 100 of one embodiment of the present invention preferably has a composition different from that of the interior portion 100b, i.e., the surface portion 100a has a higher concentration of the second metal M2 and fluorine than the interior portion 100b. Furthermore, the surface portion 100a preferably has a stable crystal structure at room temperature (25°C). Therefore, the surface portion 100a may have a crystal structure different from that of the interior portion 100b. For example, at least a portion of the surface portion 100a of the cathode active material 100 of one embodiment of the present invention may have a rock-salt crystal structure. Furthermore, when the surface portion 100a and the interior portion 100b have different crystal structures, the crystal orientations of the surface portion 100a and the interior portion 100b preferably roughly match.

[0067] Layered rock salt crystals and the anions of rock salt crystals form a cubic close-packed structure (face-centered cubic lattice structure).

[0068] In this specification, if the anions have a structure in which three layers are stacked with a skew, such as ABCABC, it is called cubic close-packed. 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.

[0069] 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.

[0070] Alternatively, it can be explained as follows: Anions on the (111) plane of a cubic crystal structure have a triangular lattice. Layered rocksalt has a space group of R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (000l) plane of the layered rocksalt 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. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0071] However, the space group of the layered rock salt type crystal is R-3m, which is different from the space groups Fm-3m (space groups of general rock salt type crystals) and Fd-3m of the rock salt type crystal, 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 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 and the rock salt type crystal are aligned, it may be said that the crystal orientations are approximately the same.

[0072] 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.

[0073] Figure 3 shows an example of a TEM image in which the orientation of the layered rock salt crystal LRS and the rock salt crystal RS roughly coincides. Images that reflect the crystal structure can be obtained in TEM, STEM, HAADF-STEM, ABF-STEM, etc.

[0074] For example, in high-resolution TEM images, contrast originating from crystal planes can be observed. When an electron beam is incident perpendicular to the c-axis of a layered rock-salt structure, for example, due to the diffraction and interference of the electron beam, the contrast originating from the (0003) plane is observed as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, a repetition of bright and dark lines is observed in the TEM image, and the bright lines (for example, the L shown in Figure 3) are not clearly distinguishable from each other. RS and L LRS If the angle between the dark 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., that the crystal orientations are roughly aligned. Similarly, if the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are roughly aligned.

[0075] Furthermore, HAADF-STEM images exhibit contrast dependent on the 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.

[0076] 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.

[0077] 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.

[0078] Figure 4A shows an example of a STEM image in which the orientations of the layered rock-salt-type crystal LRS and the rock-salt-type crystal RS roughly coincide. Figure 4B shows an FFT of the region of the rock-salt-type crystal RS, and Figure 4C shows an FFT of the region of the layered rock-salt-type crystal LRS. The composition, JCPDS card number, and the d-value and angle calculated from these are shown on the left of Figures 4B and 4C, and the measured values ​​are shown on the right. The spot marked O is the zeroth-order diffraction.

[0079] The spot marked A in Figure 4B is due to the 11-1 reflection of the cubic crystal. The spot marked A in Figure 4C is due to the 0003 reflection of the layered rock salt type. From Figures 4B and 4C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 4B is roughly parallel to the line passing through AO in Figure 4C. Here, roughly coincident and roughly parallel mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0080] Thus, in FFT and electron diffraction, when the orientations of the layered rock salt crystal and the rock salt crystal roughly coincide, the <0003> orientation of the layered rock salt crystal and the <11-1> orientation of the rock salt crystal may roughly coincide. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. A reciprocal lattice point that is spot-like and not continuous with other reciprocal lattice points indicates high crystallinity.

[0081] Furthermore, even if the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt crystal are roughly the same as described above, depending on the incident orientation of the electron beam, spots not originating from the 0003 reflection of the layered rock salt crystal may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt crystal. For example, the spot marked B in Figure 4C originates from the 1014 reflection of the layered rock salt crystal. This spot may be observed at an angle of 52° to 56° (i.e., ∠AOB is 52° to 56°) from the orientation of the reciprocal lattice point originating from the 0003 reflection of the layered rock salt crystal (A in Figure 4C), and at a point where d is 0.19 nm to 0.21 nm. Note that this index is merely an example and does not necessarily have to be identical. For example, equivalent reciprocal lattice points in each may be used.

[0082] Similarly, spots not originating from the 11-1 reflection of the cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of the cubic crystal is observed. For example, the spot marked B in Figure 4B is originating from the 200 reflection of the cubic crystal. This spot originating from the 200 reflection of the cubic crystal may be observed at an angle of 54° to 56° (i.e., ∠AOB is 54° to 56°) from the orientation of the reflection originating from the 11-1 reflection of the cubic crystal (A in Figure 4B). Note that this index is just an example and does not necessarily have to be the same. For example, equivalent planes in each may be used.

[0083] It is known that layered rock-salt cathode active materials, such as lithium cobalt oxide, tend to exhibit the (0003) plane and its equivalents, as well as the (10-14) plane and its equivalents, as crystal planes. Therefore, by carefully observing the shape of the cathode active material using an SEM or similar, it is possible to thin-section the observation sample using an FIB or similar technique so that the electron beam is [12-10] incident in a TEM or similar technique, making it easier to observe the (0003) plane. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock-salt cathode active material so that the (0003) plane can be easily observed.

[0084] However, if the surface layer 100a is composed of only MgO or only a solid solution of MgO and CoO(II), it becomes difficult to insert and extract lithium. Therefore, the surface layer 100a must contain at least cobalt, and in a discharged state, it must also contain lithium, providing a path for lithium insertion and extraction. It is also preferable that the concentration of cobalt be higher than that of magnesium.

[0085] <Internal crystal structure> Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries.

[0086] It is known that the strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal.

[0087] In compounds containing nickel, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the influence of the Jahn-Teller effect is suggested to be small, and it may be preferable because it may have better resistance to high-voltage charging.

[0088] The positive electrode active material will be described with reference to Figures 5 to 8. Figures 5 to 8 describe the case where cobalt is used as the first metal M1 contained in the positive electrode active material.

[0089] <Conventional positive electrode active materials> The positive electrode active material shown in Fig. 7 is lithium cobalt oxide (LiCoO) to which fluorine and magnesium are not added using a manufacturing method described later. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Fig. 7 changes depending on the depth of charge.

[0090] As shown in Figure 7, lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0091] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0092] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.76 has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes referred to as an H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 7 and other parts of this specification, for ease of comparison with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0093] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 type crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the O3' type crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' type structure and the H1-3 type structure, and that the O3' type structure changes less from the O3 type structure than the H1-3 type structure. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of XRD. In this case, the unit cell that results in the smallest goodness of fit (GOF) value should be used.

[0094] When lithium cobalt oxide is repeatedly charged and discharged at a high voltage of 4.6 V or higher, based on the redox potential of lithium metal, or at a deep charge depth of 0.8 or higher, the crystal structure of the lithium cobalt oxide changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0095] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 7, in the H1-3 crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0096] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0097] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0098] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0099] <Positive Electrode Active Material of One Embodiment of the Present Invention> The positive electrode active material 100 of one embodiment of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charge and discharge. Furthermore, the change in volume can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material of one embodiment of the present invention can have a stable crystal structure in a high-voltage charged state. Therefore, the positive electrode active material of one embodiment of the present invention may be less likely to cause a short circuit when maintained in a high-voltage charged state. In such cases, safety is further improved, which is preferable.

[0100] In the positive electrode active material of one embodiment of the present invention, the change in crystal structure and the difference in volume per the same number of transition metal atoms between a fully discharged state and a highly charged state are small.

[0101] The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown in Figure 5. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a first metal M1, and oxygen. In addition to the above, it preferably contains magnesium as a second metal M2. It also preferably contains fluorine.

[0102] The crystal structure at a charge depth of 0 (discharged state) in Figure 5 is the same as that in Figure 7, R-3m(O3). On the other hand, at high charge depths, the positive electrode active material 100 has a crystal structure different from the H1-3 type crystal structure. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium ions occupy the oxygen hexacoordination positions. The symmetry of the CoO2 layers in this structure is the same as that of the O3 type. Therefore, this structure is referred to as the O3' type crystal structure in this specification. In both the O3 type crystal structure and the O3' type crystal structure, it is preferable for magnesium to be present in a dilute form between the CoO2 layers, i.e., at the lithium sites. It is also preferable for fluorine to be present in a random and dilute form at the oxygen sites.

[0103] In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen tetracoordination position.

[0104] Although FIG. 5 shows lithium ions present at all lithium sites with equal probability, the positive electrode active material of one embodiment of the present invention is not limited to this. Li ions may be present disproportionately at some of the lithium sites. For example, Li ions belonging to the space group P2 / m may be present at some of the lithium sites. 0.5 Like CoO2, it may be present at some ordered lithium sites. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0105] It can also be said that the O3' type crystal structure is similar to the CdCl2 type crystal structure, although it has random lithium between the layers. This CdCl2 type-like crystal structure was observed when lithium nickel oxide was charged to a charge depth of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0106] In the positive electrode active material 100 according to one embodiment of the present invention, when a large amount of lithium is released during charging at a high voltage, the change in the crystal structure is suppressed more than in conventional positive electrode active materials. For example, as shown by the dotted line in Figure 5, there is almost no displacement of the CoO2 layers in these crystal structures.

[0107] More specifically, the cathode active material 100 of one embodiment of the present invention has high structural stability even at high depths of charge. For example, the R-3m(O3) crystal structure can be maintained even at a charge voltage at which a conventional cathode active material would develop an H1-3 crystal structure, such as a voltage of about 4.6 V relative to the potential of lithium metal. Furthermore, the O3' crystal structure can be maintained even at higher charge voltages, such as a voltage of about 4.65 V to 4.7 V relative to the potential of lithium metal. In some cases, the H1-3 crystal structure is finally observed when the charge voltage is further increased.

[0108] Therefore, in the positive electrode active material 100 of one embodiment of the present invention, the crystal structure is not easily broken even when charge and discharge are repeated at a high voltage.

[0109] The space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification and the like, "belonging to a certain space group" or "being a certain space group" can be rephrased as "identified with a certain space group."

[0110] Furthermore, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above by the potential of the graphite. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, even when the voltage of a secondary battery using graphite as the negative electrode active material is 4.3 V or higher and 4.5 V or lower, the positive electrode active material 100 of one embodiment of the present invention can maintain the R-3m(O3) crystal structure. Furthermore, even when the charge voltage is higher, for example, when the voltage of the secondary battery is higher than 4.5 V and lower than 4.6 V, the positive electrode active material 100 of one embodiment of the present invention can adopt the O3'-type crystal structure. Furthermore, even when the charge voltage is lower, for example, when the voltage of the secondary battery is 4.2 V or higher but lower than 4.3 V, the positive electrode active material 100 of one embodiment of the present invention can adopt the O3'-type crystal structure.

[0111] In the O3'-type crystal structure, the coordinates of the cobalt and oxygen atoms in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. Regarding the lattice constants of the unit cell, the a-axis is preferably 2.797≦a≦2.837 (Å), more preferably 2.807≦a≦2.827 (Å), typically a=2.817 (Å). The c-axis is preferably 13.681≦c≦13.881 (Å), more preferably 13.751≦c≦13.811 (Å), typically c=13.781 (Å).

[0112] A second metal M2, such as magnesium, randomly and dilutely present between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers during high-voltage charging. Therefore, the presence of magnesium between the CoO2 layers facilitates the formation of an O3'-type crystal structure. Therefore, it is preferable that magnesium be distributed at an appropriate concentration throughout the entire cathode active material 100 of one embodiment of the present invention (i.e., the surface layer 100a and the interior 100b). To distribute magnesium throughout the entire cathode active material 100, it is preferable to perform a heat treatment during the fabrication process of the cathode active material 100 of one embodiment of the present invention.

[0113] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that a second metal M2, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site is ineffective in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to a divalent state and lithium evaporating.

[0114] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute the magnesium throughout the particles. Adding the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute the magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0115] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. Additionally, unnecessary magnesium compounds (e.g., oxides and fluorides) that do not substitute for either the lithium site or the cobalt site may be unevenly distributed on the surface of the positive electrode active material, potentially becoming resistance components. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the first metal M1, more preferably more than 0.01 to less than 0.04 times, and even more preferably approximately 0.02 times. Alternatively, the number is preferably 0.001 to 0.04 times. Alternatively, the number is preferably 0.01 to 0.1 times. The magnesium concentration shown here may be a value obtained by performing elemental analysis of the entire positive electrode active material using, for example, ICP-MS, or may be based on the composition of raw materials used in the production of the positive electrode active material.

[0116] As shown in the legend in Figure 5, nickel is preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0117] As the magnesium concentration of the cathode active material 100 of one embodiment of the present invention increases, the charge / discharge capacity of the cathode active material 100 may decrease. For example, this may be due to magnesium entering lithium sites, reducing the amount of lithium contributing to charge / discharge. Excess magnesium may also produce magnesium compounds that do not contribute to charge / discharge. The cathode active material 100 of one embodiment of the present invention may contain nickel, which may increase the charge / discharge capacity per weight and per volume. The cathode active material 100 of one embodiment of the present invention may contain aluminum, which may increase the charge / discharge capacity per weight and per volume. The cathode active material 100 of one embodiment of the present invention may contain nickel and aluminum, which may increase the charge / discharge capacity per weight and per volume.

[0118] Hereinafter, the concentrations of nickel and aluminum elements contained in the positive electrode active material of one embodiment of the present invention will be expressed in terms of the number of atoms.

[0119] The number of nickel atoms in the positive electrode active material of one embodiment of the present invention is preferably more than 0% but not more than 7.5%, preferably 0.05% or more but not more than 4%, and more preferably 0.1% or more but not more than 2%, relative to the number of cobalt atoms, where the number of cobalt atoms is taken as 100%. Alternatively, it is preferably more than 0% but not more than 4%. Alternatively, it is preferably more than 0% but not more than 2%. Alternatively, it is preferably 0.05% or more but not more than 7.5%. Alternatively, it is preferably 0.05% or more but not more than 2%. Alternatively, it is preferably 0.1% or more but not more than 7.5%. Alternatively, it is preferably 0.1% or more but not more than 4%. The nickel concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0120] The number of aluminum atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, and more preferably 0.1% to 2% of the number of cobalt atoms, when the number of cobalt atoms is taken as 100%. Alternatively, the number is preferably 0.05% to 2% of the number of cobalt atoms. Alternatively, the number is preferably 0.1% to 4% of the number of cobalt atoms. The aluminum concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0121] Magnesium is preferably distributed throughout the entire positive electrode active material 100 (i.e., the surface layer 100a and the interior 100b) of one embodiment of the present invention, and in addition, as described above, the concentrations of the second metal M2 and fluorine in the surface layer 100a are preferably higher than the average concentrations throughout the particle. More specifically, the concentrations of the second metal M2 and fluorine in the surface layer 100a measured by XPS or the like are preferably higher than the average concentrations of the second metal M2 and fluorine throughout the particle measured by ICP-MS or the like.

[0122] It is more preferable that the second metal M2 and some of the fluorine contained in the positive electrode active material 100 of one embodiment of the present invention are unevenly distributed in the crystal grain boundaries 101 as shown in FIG. 1A.

[0123] In other words, the concentrations of the second metal M2 and fluorine at and near the grain boundaries 101 of the positive electrode active material 100 of one embodiment of the present invention are preferably higher than those in other regions inside the grain boundaries 101.

[0124] The grain boundary 101 is a type of planar defect. Therefore, like the grain surface, it is prone to instability and changes in the crystal structure are likely to occur. Therefore, if the concentrations of the second metal M2 and fluorine at and near the grain boundary 101 are high, changes in the crystal structure can be more effectively suppressed.

[0125] Furthermore, when the concentrations of the second metal M2 and fluorine are high at and near the grain boundaries, even if cracks 102 occur along grain boundaries 101 of particles of positive electrode active material 100 of one embodiment of the present invention, the concentrations of the second metal M2 and fluorine become high near the surfaces formed by cracks 102. Therefore, the corrosion resistance to hydrofluoric acid of the positive electrode active material after cracks 102 occur can be improved.

[0126] In this specification and the like, the vicinity of the grain boundary 101 refers to the region up to about 10 nm from the grain boundary.

[0127] <Particle size> If the particle size of the positive electrode active material 100 of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector may occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte may occur. Therefore, the average particle size (D50: also referred to as median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Alternatively, 1 μm or more and 40 μm or less is preferable. Alternatively, 1 μm or more and 30 μm or less is preferable. Alternatively, 2 μm or more and 100 μm or less is preferable. Alternatively, 2 μm or more and 30 μm or less is preferable. Alternatively, 5 μm or more and 100 μm or less is preferable. Alternatively, 5 μm or more and 40 μm or less is preferable.

[0128] Alternatively, two or more positive electrode active materials 100 having different particle sizes may be mixed and used. In other words, a positive electrode active material that exhibits multiple peaks when the particle size distribution is measured by a laser diffraction / scattering method may be used. In this case, a mixing ratio that increases the powder packing density is preferable, because this increases the capacity per volume of the secondary battery.

[0129] <Analysis method> Whether a certain cathode active material is the cathode active material 100 of one embodiment of the present invention that exhibits an O3'-type crystal structure at a high depth of charge can be determined by analyzing a cathode having the cathode active material at a high depth of charge using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the cathode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a cathode obtained by disassembling a secondary battery.

[0130] As described above, the positive electrode active material 100 according to one embodiment of the present invention is characterized by little change in crystal structure between a state of deep charge and a discharged state. Materials in which 50 wt% or more of a crystal structure that changes significantly between a state of deep charge and a discharged state when charged at a high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It should be noted that the desired crystal structure may not be achieved simply by adding the second metal M2 and fluorine. For example, lithium cobalt oxide containing magnesium and fluorine has a common feature, but when charged at a high voltage, the area intensity I of the H1-3 type is low. H1-3 In some cases, the O3'-type crystal structure exceeds 60% by weight, and in other cases, it does not. At a certain voltage, the O3'-type crystal structure becomes nearly 100 wt %, and further increasing the voltage may result in the H1-3-type crystal structure. Therefore, to determine whether a cathode active material 100 according to one embodiment of the present invention is a cathode active material 100, analysis of the crystal structure, including XRD, is required.

[0131] However, when positive electrode active materials are charged or discharged at high voltage, their crystal structure may change when exposed to air. For example, they may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is recommended that all samples be handled in an inert atmosphere such as an argon atmosphere.

[0132] ≪Charging method≫ High-voltage charging for determining whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using lithium as the negative electrode.

[0133] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive additive, and a binder.

[0134] Lithium metal can be used for the negative electrode. When a material other than lithium metal is used for the negative electrode, the voltage of the secondary battery and the potential of the positive electrode are different. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0135] The electrolyte used in the electrolytic solution is 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution can be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC).

[0136] The separator can be a 25 μm thick porous polypropylene film.

[0137] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0138] The coin cell fabricated under the above conditions was charged at a constant current of 4.6 V and 0.5 C, followed by constant voltage charging until the current reached 0.01 C. Here, 1 C corresponds to 137 mA / g. Therefore, if the amount of positive electrode active material in one coin cell is 10 mg, charging at 0.685 mA is equivalent to charging at such a low current. To observe the phase change of the positive electrode active material, charging at such a low current is desirable. The temperature is 25°C. After charging in this manner, the coin cell is disassembled in an argon-atmosphere glove box and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. For subsequent analyses, it is preferable to seal the disassembled positive electrode in an argon atmosphere to prevent reactions with external components. For example, XRD can be performed by sealing the disassembled positive electrode in an airtight container for XRD measurement in an argon atmosphere. It is also preferable to remove the positive electrode promptly after charging is complete and perform analysis. Specifically, within 1 hour after charging is complete, and even more preferably within 30 minutes.

[0139] The 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 the 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.

[0140] Constant current charging refers to a method of charging at a constant charge rate, constant voltage charging refers to a method of charging at a constant voltage once the upper voltage limit is reached, and constant current discharging refers to a method of discharging at a constant discharge rate.

[0141] <XRD> The XRD measurement apparatus and conditions are not particularly limited. For example, the measurement can be performed using the following apparatus and conditions. XRD equipment: Bruker AXS, D8 ADVANCE X-ray source:CuKα ray Output: 40KV, 40mA Slit type: Div.Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0142] If the measurement sample is a powder, it can be set by placing it in a glass sample holder, or by sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.

[0143] Figures 6 and 8 show ideal powder XRD patterns calculated from the O3'-type crystal structure and the H1-3-type crystal structure model using CuKα1 radiation. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) at a charge depth of 0 and CoO2(O1) at a charge depth of 1 are also shown. The LiCoO2(O3) and CoO2(O1) patterns were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 5). The 2θ range was 15° to 75°, with a step size of 0.01 and a wavelength of λ1 of 1.540562×10. -10m and λ2 were not set, and Monochromator was set to single. The pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 3. The pattern of the O3' type crystal structure was created by estimating the crystal structure from the XRD pattern of a positive electrode active material of one embodiment of the present invention and fitting it using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and an XRD pattern was created in the same way as for O3, O1, and H1-3.

[0144] As shown in Figure 6, the O3'-type crystal structure exhibits diffraction peaks at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 8, the H1-3-type crystal structure and CoO2(P-3m1, O1) do not exhibit peaks at these positions. Therefore, the appearance of peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0145] This can also be said to mean that the positions at which XRD diffraction peaks appear are close between the crystal structure at a charge depth of 0 and the crystal structure after high-voltage charging. More specifically, the difference in the positions at which two or more, preferably three or more, of the main diffraction peaks of both structures appear is 2θ=0.7° or less, more preferably 2θ=0.5° or less.

[0146] Furthermore, the sharpness of diffraction peaks in an XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, i.e., has a narrow half-width. The half-width varies depending on the XRD measurement conditions and the value of 2θ, even for peaks arising from the same crystalline phase. Under the measurement conditions described above, for peaks observed at 2θ between 43° and 46°, the half-width is preferably 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of that crystalline phase is high. This contributes to the stabilization of the crystalline structure after charging.

[0147] Although the positive electrode active material 100 of one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage, not all of the particles may have the O3'-type crystal structure. Other crystal structures may be included, or a portion may be amorphous.

[0148] For example, when comparing the area intensity ratio of the H1-3 type peak and the O3' type peak in the XRD pattern after charging to 4.6 V, it is sufficient if the area intensity ratio of the H1-3 type peak is below a certain level, or if the area intensity ratio of the H1-3 type peak to the area intensity ratio of the O3' type and O3 type peaks is above a certain level.

[0149] For example, the H1-3 type has a peak corresponding to the (006) plane at 2θ=19.69°±0.2°. The O3' type and the O3 type of LiCoO2 have a peak corresponding to the (003) plane at 2θ=19.30±0.20°. Therefore, among the integrated intensities in the 2θ range of 18° to 20°, the area below 19.30° can be considered to be the integrated intensities of the O3' type and O3 type peaks. The integrated intensity ratio I H1-3(006) / I O3’+O3(003) is preferably 60% or less, more preferably 50% or less, and even more preferably 40% or less. With such an area intensity ratio, a positive electrode active material having sufficiently excellent charge-discharge cycle characteristics can be obtained.

[0150] Furthermore, for the H1-3 type, a peak corresponding to the (107) plane is observed at 2θ = 43.83° ± 0.2°. For the O3' and O3 types, a peak corresponding to the (104) plane is observed at 2θ = 45.55° ± 0.2°. Therefore, of the area intensities in the 2θ range of 43° to 46°, the area above 44.50° can be considered to be the area intensities of the O3' and O3 type peaks. These area intensity ratios I H1-3(107) / I O3’+O3(104) is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. With such an area intensity ratio, a positive electrode active material having sufficiently excellent charge-discharge cycle characteristics can be obtained.

[0151] Peaks with 2θ between 43° and 46° tend to be broad, but peaks with 2θ between 18° and 20° tend to be relatively sharp. Therefore, it is preferable to use peaks with 2θ between 18° and 20° for the analysis of area intensity ratios.

[0152] As described above, the positive electrode active material 100 of one embodiment of the present invention preferably has a small influence of the Jahn-Teller effect. The positive electrode active material 100 of one embodiment of the present invention preferably has a layered rock-salt crystal structure and contains cobalt as a transition metal. Furthermore, the positive electrode active material 100 of one embodiment of the present invention may contain the second metal M2, nickel, and manganese described above in addition to cobalt, as long as the influence of the Jahn-Teller effect is small.

[0153] The peaks appearing in the powder XRD pattern reflect the crystalline structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100. The crystalline structure of the surface layer 100a can be analyzed by electron beam diffraction or the like of a cross section of the positive electrode active material 100.

[0154] XPS X-ray photoelectron spectroscopy (XPS) can analyze a region from the surface to a depth of approximately 2 to 8 nm (usually approximately 5 nm), allowing quantitative analysis of the concentration of each element in a region approximately halfway down to the surface layer 100a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is often approximately ±1 atomic %, and the lower detection limit is approximately 1 atomic %, depending on the element.

[0155] When XPS analysis was performed on the positive electrode active material 100 of one embodiment of the present invention, the number of atoms of the second metal M2 was preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of atoms of the first metal M1. When the second metal M2 is magnesium and the first metal M1 is cobalt, the number of magnesium atoms was preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of cobalt atoms. Furthermore, the number of halogen atoms such as fluorine atoms was preferably 0.2 to 6.0 times, and more preferably 1.2 to 4.0 times, the number of atoms of the first metal M1.

[0156] When performing XPS analysis, for example, monochromated aluminum can be used as the X-ray source. The take-off angle can be set to, for example, 45°. For example, measurement can be performed using the following equipment and conditions. Measurement equipment: PHI Quantera II X-ray source: Monochromatic Al Kα (1486.6eV) Detection area: 100 μmφ Detection depth: Approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: Wide scan, narrow scan for each detected element

[0157] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is analyzed by XPS, the peak showing the bond energy between fluorine and other elements is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably about 684.3 eV. This value is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV). In other words, when the positive electrode active material 100 of one embodiment of the present invention contains fluorine, the bond is preferably other than that of lithium fluoride or magnesium fluoride.

[0158] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 of one embodiment of the present invention contains magnesium, the bond is preferably other than that of magnesium fluoride.

[0159] The second metal M2, such as magnesium and aluminum, which is preferably present in large amounts in the surface layer 100a, preferably has a concentration measured by XPS or the like that is higher than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0160] When a cross section of magnesium and aluminum is exposed by processing and analyzed using TEM-EDX, the concentration of magnesium and aluminum in the surface layer 100a is preferably higher than the concentration in the interior 100b. For example, in TEM-EDX analysis, the magnesium concentration preferably decays to 60% or less of the peak at a point 1 nm deep from the peak top. Also, it preferably decays to 30% or less of the peak at a point 2 nm deep from the peak top. Processing can be performed using, for example, a FIB (Focused Ion Beam).

[0161] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms, while the ratio of the number of magnesium atoms Mg / Co in ICP-MS analysis is preferably 0.001 to 0.06.

[0162] ESR As described above, the positive electrode active material of one embodiment of the present invention preferably contains cobalt and nickel as the transition metals and magnesium as the second metal M2. 3+ Ni 3+ and some Li + Mg 2+ It is preferred that Li be substituted. + Mg 2+ With the replacement of Ni 3+ is reduced to Ni 2+ In addition, some Li + Mg 2+ is substituted by Co 3+ is reduced to Co 2+ In addition, some Co 3+ Mg 2+ is substituted by Co 3+ is oxidized to Co 4+ This may occur.

[0163] Therefore, the positive electrode active material according to one embodiment of the present invention is Ni 2+ , Ni 3+ , Co 2+ and Co 4+ It is preferable that the positive electrode active material contains at least one of the following: 2+ , Ni 3+ , Co 2+ and Co 4+ The spin density due to one or more of the following is 2.0×10 17 spins / g or more 1.0×10 21It is preferable that the positive electrode active material has the above-mentioned spin density, because the crystal structure is stable especially in the charged state. 2+ , Ni 3+ , Co 2+ and Co 4+ The spin density may be reduced due to one or more of the above.

[0164] The spin density in the positive electrode active material can be analyzed using, for example, electron spin resonance (ESR) or the like.

[0165] EPMA EPMA (Electron Probe Microanalysis) can quantify elements, and area analysis can analyze the distribution of each element.

[0166] EPMA analyzes a region from the surface to a depth of about 1 μm. Therefore, the concentration of each element may differ from the results measured using other analytical methods. For example, when performing a surface analysis of the positive electrode active material 100, the concentration of the second metal M2 present in the surface layer 100a may be lower than the results obtained by XPS. Furthermore, the concentration of the second metal M2 present in the surface layer 100a may be higher than the results obtained by ICP-MS or the value obtained from the raw material composition used in the production of the positive electrode active material.

[0167] When EPMA surface analysis is performed on a cross section of the positive electrode active material 100 according to one embodiment of the present invention, the concentration of the second metal M2 preferably has a concentration gradient that increases from the interior toward the surface layer 100a. More specifically, as shown in FIG. 1C1, magnesium, fluorine, and titanium preferably have concentration gradients that increase from the interior toward the surface. Furthermore, as shown in FIG. 2C2, aluminum preferably has a concentration peak in a region deeper than the concentration peaks of the above elements. The aluminum concentration peak may be present in the surface layer 100a or may be deeper than the surface layer 100a.

[0168] The surface and surface layer 100a of the cathode active material 100 according to one embodiment of the present invention are assumed to be free of carbonic acid, hydroxyl groups, and the like that are chemically adsorbed after the cathode active material is prepared. The surface also is assumed to be free of electrolyte, binder, conductive material, and compounds derived therefrom that adhere to the surface of the cathode active material. Therefore, when quantifying the elements contained in the cathode active material 100, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, and the like that can be detected by surface analysis such as XPS and EPMA. For example, XPS can separate the types of bonds by analysis, and corrections may be made to exclude C—F bonds derived from the binder.

[0169] Furthermore, before subjecting the sample to various analyses, the sample of the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived therefrom adhering to the surface of the positive electrode active material. In this case, lithium may dissolve in the solvent used for washing, but even in this case, the first metal M1 and the second metal M2 are unlikely to dissolve, and therefore the atomic ratio of the first metal M1 and the second metal M2 is not affected.

[0170] <Surface roughness and specific surface area> The positive electrode active material 100 of one embodiment of the present invention preferably has a smooth surface with few irregularities. A smooth surface with few irregularities is one factor indicating that the second metal M2 is well distributed in the surface layer portion 100a.

[0171] Whether the surface is smooth and has few irregularities can be determined from, for example, a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of ​​the positive electrode active material 100, or the like.

[0172] For example, the surface smoothness can be quantified from a cross-sectional SEM image or a cross-sectional TEM image of the positive electrode active material 100 as follows.

[0173] First, the cathode active material 100 is processed using FIB or the like to expose its cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, Gaussian blurring (σ=2) is performed, followed by binarization. The interface is then extracted using image processing software. The interface line between the protective film or the like and the cathode active material 100 is selected using a magic hand tool or the like, and the data is extracted into a spreadsheet or the like. Using a function in the spreadsheet or the like, correction is performed from a regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after slope correction. The root mean square surface roughness (RMS) is calculated by calculating the standard deviation. This surface roughness is the surface roughness over a 400 nm square area of ​​the cathode active material, including at least the particle surface layer.

[0174] On the particle surfaces of the positive electrode active material 100 of this embodiment, the roughness (RMS: root mean square surface roughness), which is an index of roughness, is preferably less than 3 nm, more preferably less than 1 nm, and even more preferably less than 0.5 nm.

[0175] The image processing software used for noise processing, boundary extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

[0176] For example, the actual specific surface area A measured by the gas adsorption method using the constant volume method R and the ideal specific surface area A i The smoothness of the surface of the positive electrode active material 100 can also be quantified from the ratio of the surface roughness to the surface smoothness.

[0177] Ideal specific surface area A i is calculated assuming that all particles have the same diameter as D50, the same weight, and an ideal spherical shape.

[0178] The median diameter D50 can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. The specific surface area can be measured by a specific surface area measuring device using a gas adsorption method based on a constant volume method, for example.

[0179] The positive electrode active material 100 according to one embodiment of the present invention has an ideal specific surface area A calculated from the median diameter D50. i and the actual specific surface area A R Ratio A R / A i is preferably 2 or less.

[0180] This embodiment mode can be used in combination with other embodiments mode.

[0181] (Embodiment 2) In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS. 9A, 9B, and 10. FIG.

[0182] <Step S11> In step S11 of FIG. 9A, a lithium source, a first metal M1 source, a second metal M2 source, and a fluorine source are prepared.

[0183] As the lithium source, for example, lithium carbonate, lithium fluoride, etc. can be used.

[0184] 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 first metal M. For example, at least one of manganese, cobalt, and nickel can be used.

[0185] As the first metal M1 source, oxides, hydroxides, etc. of the metals exemplified above as the first metal M1 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.

[0186] As described in the previous embodiment, the second metal M2 may be magnesium, aluminum, titanium, zirconium, niobium, lanthanum, yttrium, hafnium, or the like.

[0187] As the source of the second metal M2, oxides, hydroxides, fluorides, alkoxides, etc. of the metals exemplified above as the second metal M2 can be used.

[0188] Examples of magnesium sources that can be used include magnesium fluoride, magnesium oxide, magnesium hydroxide, and magnesium carbonate. Examples of aluminum sources that can be used include aluminum alkoxides such as aluminum oxide, aluminum hydroxide, aluminum fluoride, and aluminum isopropoxide. Examples of titanium sources that can be used include titanium alkoxides such as titanium oxide, titanium hydroxide, titanium fluoride, and titanium isopropoxide. Examples of zirconium sources that can be used include zirconium alkoxides such as zirconium oxide, zirconium hydroxide, zirconium fluoride, and zirconium isopropoxide. Examples of niobium sources that can be used include niobium oxide, niobium hydroxide, niobium fluoride, and niobium alkoxides. Examples of lanthanum sources that can be used include lanthanum oxide, lanthanum hydroxide, lanthanum fluoride, and lanthanum alkoxides.

[0189] <Step S12> Next, in step S12, the lithium source, the first metal M1 source, the second metal M2 source, and the fluorine source are mixed. Mixing can be performed by dry or wet methods. 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 zirconium oxide balls as the grinding media. When using an alkoxide as the second metal M2 source, mixing can be performed after gelling the alkoxide. In this case, grinding media is not necessary.

[0190] <Step S13> The mixed materials are collected to obtain a mixture 900.

[0191] <Step S14> Next, in step S14, the mixture 900 is heated. This step may be referred to as the first heating step to distinguish it from the subsequent heating step.

[0192] In this case, some element sources, for example, LiF, which can be used as a fluorine source and a lithium source, are lighter than oxygen, and therefore, heating may volatilize LiF, resulting in a decrease in the amount of LiF in the mixture 900. Therefore, when heating the mixture 900, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range. For example, one method for doing this is to cover the heating crucible.

[0193] The heating temperature is preferably between two-thirds and the melting point of the composite oxide 901. For example, when 80 atomic % or more of the first metal M1 contained in the composite oxide 901 is cobalt, the heating is preferably performed at a temperature of 800°C or higher but lower than 1100°C, more preferably at a temperature of 900°C or higher but 1000°C or lower, and even more preferably at about 950°C. Alternatively, a temperature of 800°C or higher but 1000°C or lower is preferable. Alternatively, a temperature of 900°C or higher but 1100°C or lower is preferable. If the temperature is too low, the decomposition and melting of the mixture 900 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 first metal M1, which is responsible for the redox reaction, or evaporation of lithium.

[0194] The heating time refers to the time after the target heating temperature is reached. 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. The first heating 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 dry atmosphere flow rate 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.

[0195] However, cooling to room temperature in step S14 is not essential. Cooling to a temperature higher than room temperature may be performed as long as there is no problem in performing the subsequent steps S15 and S16. For example, cooling to 100°C or below is preferable because the subsequent steps are possible and there is little risk of damaging the heating device.

[0196] <Step S15> The composite oxide 901 is obtained by the above process.

[0197] <Step S16> Next, in step S16, the composite oxide 901 is heated. This step may be referred to as the second heating step to distinguish it from the previous heating step.

[0198] By undergoing the heating in this step, the second metal M2 and fluorine can be distributed in the surface layer portion 100a of the positive electrode active material 100 at an appropriate concentration.

[0199] Because the positive electrode active material 100 is produced through two heating steps, this production method can also be called a two-step method.

[0200] The reason why the second metal M2 such as magnesium and fluorine are distributed at an appropriate concentration through this process can be divided into two aspects: first, why they do not dissolve throughout the particles including the interior 100b of the positive electrode active material 100; and second, why they remain in the surface layer even after heating.

[0201] First, the reason why the second metal M2 and fluorine are difficult to dissolve in the entire particle is because they are energetically unstable in the layered rock-salt crystal structure of lithium cobalt oxide and other elements. However, even though they are unstable, the difference in stabilization energy between the second metal M2 and other elements (the first metal M1, such as lithium and cobalt) is small. Therefore, if the second heating temperature is too high, the entropy gain will be greater, resulting in the formation of other compounds such as MgCo2O4. Therefore, the second heating temperature in this process is extremely important.

[0202] Next, the reason why the second metal M2 and fluorine remain in the surface layer is because the bond distance between the second metal M2 and oxygen is longer than the bond distance between the metal and oxygen in lithium cobalt oxide. Therefore, even if interdiffusion of elements occurs after multiple heating processes, or even if part of the particles melts, the second metal M2 and fluorine are more stable when they remain on the surface and in the surface layer 100a. Furthermore, in the surface layer, monovalent lithium is replaced by a divalent second metal M2, such as magnesium. Therefore, replacing some of the divalent oxygen with monovalent fluorine is preferable because it balances the charge and stabilizes the crystal structure.

[0203] In step S16, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range for the same reason as in step S14. For example, it is preferable to heat the heating crucible with a lid on.

[0204] The heating temperature in step S16 must be a temperature at which mutual diffusion of elements contained in the composite oxide 901 occurs. For example, 500° C. or higher is sufficient, 742° C. or higher is preferable, and 830° C. or higher is more preferable. The higher the second heating temperature, the more easily the reaction proceeds, the shorter the second heating time can be, and the higher the productivity is, which is preferable.

[0205] However, the temperature of the second heating must be at least the decomposition temperature of LiM1O2 (1130°C in the case of LiCoO2) or lower. At temperatures near the decomposition temperature, there is a concern that LiMO2 may decompose, albeit in a small amount. Therefore, the second heating temperature is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0206] Therefore, the second heating temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, 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.

[0207] The second heating is preferably performed for an appropriate time. The appropriate second heating time varies depending on conditions such as the temperature, the particle size and composition of the composite oxide 901, etc. When the particles are small, a lower temperature or a shorter time may be more preferable than when the particles are large.

[0208] For example, when the average particle size (D50) of the composite oxide 901 is about 12 μm, the second heating temperature is preferably, for example, 600° C. or more and 950° C. or less. The second heating time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0209] On the other hand, when the average particle diameter (D50) of the composite oxide 901 is about 5 μm, the second heating temperature is preferably, for example, from 600° C. to 950° C. The second heating time is preferably, for example, from 1 hour to 10 hours, more preferably about 2 hours.

[0210] The temperature-lowering time after the second heating is preferably, for example, 10 hours or more and 50 hours or less.

[0211] <Step S17> The heated material is recovered to obtain the positive electrode active material 100 .

[0212] Next, a manufacturing method different from that of Figure 9A will be described using Figure 9B. Note that since there are many commonalities between this method and Figure 9A, the differences will be mainly described. For the commonalities, the description of Figure 9A can be referred to.

[0213] As shown in steps S26 and S28 of Fig. 9B, the second heating may be performed once or multiple times. Furthermore, it is preferable to perform a sticking prevention procedure before the second heating. Examples of sticking prevention procedures include crushing with a pestle, mixing using a ball mill, mixing using a centrifugal mixer, sieving, and vibrating the container containing the composite oxide.

[0214] Such a production method involving multiple cycles of second heating is particularly effective when a large amount is heated at one time (for example, when the amount of composite oxide 901 is 5 g or more). This is because when a large amount is heated at one time, the particles tend to adhere to each other, which may result in an undesirable distribution of the second metal M2 and fluorine in the surface layer portion 100a.

[0215] Fig. 10 shows a more specific manufacturing method than Fig. 9A, which uses cobalt as the first metal and magnesium as the second metal.

[0216] This embodiment can be used in combination with other embodiments.

[0217] (Embodiment 3) In this embodiment, a lithium-ion secondary battery including a positive electrode active material according to one embodiment of the present invention will be described. The secondary battery includes at least an outer casing, a current collector, an active material (a positive electrode active material or a negative electrode active material), a conductive additive, and a binder. The secondary battery also includes an electrolyte solution containing a lithium salt or the like dissolved therein. In the case of a secondary battery using an electrolyte solution, a positive electrode, a negative electrode, and a separator are provided between the positive electrode and the negative electrode.

[0218] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer preferably includes the positive electrode active material described in Embodiment 1, and may further include a binder, a conductive additive, and the like.

[0219] Furthermore, after the positive electrode is fabricated, the positive electrode active material layer is thoroughly impregnated with an electrolyte during the process of incorporating the positive electrode into a secondary battery. Therefore, the positive electrode active material layer in the secondary battery contains an electrolyte. When the electrolyte is sufficiently impregnated into the positive electrode active material layer, elements contained in the electrolyte can be detected in the gaps between the positive electrode active materials, on the surface of the positive electrode active material, on the surface of the current collector, and so on. For example, when the electrolyte contains LiPF6, phosphorus can be detected in these locations.

[0220] FIG. 11A shows an example of a cross-sectional view of a positive electrode.

[0221] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry to the metal foil and drying it. After drying, the metal foil may be further pressed. The positive electrode is formed by forming an active material layer on the current collector 550.

[0222] The slurry is a material liquid used to form an active material layer on the current collector 550, and refers to a material containing at least an active material, a binder, and a solvent, and preferably further mixed with a conductive additive. The slurry is also called an electrode slurry or an active material slurry, and is sometimes called a positive electrode slurry when forming a positive electrode active material layer, and a negative electrode slurry when forming a negative electrode active material layer.

[0223] The conductive additive, also called a conductivity-imparting agent or conductive material, is made of a carbon material. By attaching the conductive additive between multiple active materials, the active materials are electrically connected to each other, thereby increasing their conductivity. Note that "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covering part of the surface of the active material, the conductive additive fitting into the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0224] Carbon black (furnace black, acetylene black, graphite, etc.) is a typical carbon material used as a conductive additive.

[0225] FIG. 11A illustrates acetylene black 553 as a conductive additive. FIG. 11A also illustrates an example in which a second active material 562 having a particle size smaller than that of the positive electrode active material 100 shown in Embodiment 1 is mixed. Mixing particles of different sizes can provide a high-density positive electrode active material layer, thereby increasing the charge / discharge capacity of the secondary battery. Note that the positive electrode active material 100 shown in Embodiment 1 corresponds to the active material 561 in FIG. 11A.

[0226] A binder (resin) is mixed to bond the active material to a current collector 550 such as a metal foil as the positive electrode of a secondary battery. The binder is also called a binding agent. The binder is a polymer material, and if a large amount of binder is added, the proportion of active material in the positive electrode decreases, thereby reducing the discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum. In FIG. 11A, the areas not filled with the active material 561, second active material 562, and acetylene black 553 indicate voids or binder.

[0227] 11A shows an example in which active material 561 is spherical, but the shape is not particularly limited and various shapes are possible. The cross-sectional shape of active material 561 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0228] 11B shows an example in which the active material 561 has various shapes. FIG. 11B shows an example different from FIG. 11A.

[0229] In the positive electrode in FIG. 11B, graphene 554 is used as a carbon material used as a conductive additive.

[0230] Graphene is a carbon material that has amazing electrical, mechanical, and chemical properties and is expected to be applied in a variety of fields, including field-effect transistors and solar cells.

[0231] Furthermore, 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.

[0232] 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.

[0233] 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 greater. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0234] Graphene compounds may have excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds may also have a sheet-like shape. Graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. Even when thin, they may have very high conductivity, allowing a small amount to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive material can increase the contact area between the active material and the conductive material. It is preferable that the graphene compound clings to at least a portion of the active material particles. It is also preferable that the graphene compound overlaps at least a portion of the active material particles. It is also preferable that the shape of the graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a portion of the active material particles. The graphene compound may also have holes.

[0235] Furthermore, by bonding multiple graphenes or graphene compounds together, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed. When an active material is covered with a graphene net, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or can be eliminated, thereby improving the ratio of active material to the electrode volume or weight. In other words, the charge / discharge capacity of a secondary battery can be increased.

[0236] 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.

[0237] In FIG. 11B, a positive electrode active material layer including an active material 561, graphene 554, and acetylene black 553 is formed on a current collector 550.

[0238] In the step of mixing graphene 554 and acetylene black 553 to obtain electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of graphene.

[0239] Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, the dispersion stability of acetylene black 553 is excellent and aggregation is unlikely to occur during slurry preparation. Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 553 as a conductive additive. Increasing the electrode density can increase the capacity per unit weight. Specifically, the density of the positive electrode active material layer measured by weight can be increased to more than 3.5 g / cc. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is within the above range, a synergistic effect can be expected in terms of increasing the capacity of the secondary battery, which is preferable.

[0240] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive additive, rapid charging can be achieved by mixing the first carbon material (graphene) and the second carbon material (acetylene black) in the above range. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is in the above range, the secondary battery is more stable and a synergistic effect of being able to handle even faster charging can be expected, which is preferable.

[0241] These features are effective for use as a secondary battery for vehicles.

[0242] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0243] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0244] By using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery for vehicle use having high energy density and favorable output characteristics can be obtained.

[0245] This configuration is also effective in a portable information terminal, and the secondary battery can be miniaturized and have a high capacity by using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and by setting the mixture ratio of acetylene black and graphene in an optimal range. In addition, by setting the mixture ratio of acetylene black and graphene in an optimal range, the portable information terminal can be rapidly charged.

[0246] 11B, the regions not filled with the active material 561, graphene 554, and acetylene black 553 indicate voids or binders. The voids are necessary for the electrolyte to penetrate, but if there are too many voids, the electrode density decreases, and if there are too few voids, the electrolyte cannot penetrate, and if the voids remain even after the secondary battery is fabricated, the energy density decreases.

[0247] By using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode and by adjusting the mixture ratio of acetylene black and graphene to an optimal range, it is possible to achieve both high electrode density and the creation of appropriate gaps necessary for ion conduction, thereby obtaining a secondary battery with high energy density and good output characteristics.

[0248] 11C illustrates an example of a positive electrode in which carbon nanotubes 555 are used instead of graphene. Fig. 11C shows an example different from Fig. 11B. The use of carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and improve dispersibility.

[0249] In FIG. 11C, the regions not filled with active material 561, carbon nanotubes 555, and acetylene black 553 indicate voids or binders.

[0250] Another example of a positive electrode is shown in Fig. 11D. Fig. 11C shows an example in which carbon nanotubes 555 are used in addition to graphene 554. Using both graphene 554 and carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and further improve dispersibility.

[0251] In FIG. 11D, the regions not filled with the active material 561, the carbon nanotubes 555, the graphene 554, and the acetylene black 553 indicate voids or binders.

[0252] A secondary battery can be produced by using any one of the positive electrodes shown in Figures 11A to 11D, placing a separator on the positive electrode, placing the laminate in which the negative electrode is placed on the separator, in a container (exterior body, metal can, etc.) that houses the laminate, and filling the container with an electrolyte.

[0253] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0254] For example, the positive electrode active material 100 shown in the first embodiment can be used to fabricate a semi-solid battery or an all-solid battery.

[0255] In this specification, a semi-solid battery refers to a battery that has a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. The term "semi-solid" does not mean that the ratio of solid material is 50%. Semi-solid means that the battery has solid properties, such as small volume change, while also possessing some liquid-like properties, such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, the battery may be made by infiltrating a porous solid material with a liquid material.

[0256] In this specification and the like, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive electrode and the negative electrode. The polymer electrolyte secondary battery includes a dry (or solid) polymer electrolyte battery and a polymer gel electrolyte battery. The polymer electrolyte secondary battery may also be referred to as a semi-solid battery.

[0257] When a semi-solid battery is fabricated using the positive electrode active material 100 shown in Embodiment 1, the semi-solid battery becomes a secondary battery with a large charge-discharge capacity. Also, a semi-solid battery with a high charge-discharge voltage can be obtained. Alternatively, a semi-solid battery with high safety or reliability can be realized.

[0258] Also, the positive electrode active material described in Embodiment 1 may be mixed with other positive electrode active materials and used.

[0259] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O = 5, Cr2O = 5, and MnO2 can be mentioned.

[0260] [[ID=!5]] Also, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0261] Also, as another positive electrode active material, a composition formula Li a Mn b M c O dA lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire <a / (b+c)<2、かつc>lithium-manganese composite oxide particle, it is preferable that the composition be 0 0 during discharge and satisfy 0.26≦(b+c) / d<0.5. The composition of metals, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured using, for example, an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen composition in the entire lithium-manganese composite oxide particle can be measured using, for example, energy dispersive X-ray spectroscopy (EDX). In addition, the composition can be determined by valence evaluation using fusion gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.

[0262] <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.

[0263] 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. ​

[0264] 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.

[0265] The binder may be used in combination with two or more of the above.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] 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 have the effect of suppressing decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0270] <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.

[0271] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and may further include a conductive additive and a binder.

[0272] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0273] 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 larger 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.

[0274] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO x Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0275] 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.

[0276] 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.

[0277] 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 (0.05V to 0.3V vs. Li / Li + ) This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0278] 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.

[0279] 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.

[0280] 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.

[0281] 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.

[0282] As the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0283] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0284] [Separator] A separator is placed between the positive electrode and the negative electrode. The separator can be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0285] 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).

[0286] 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.

[0287] 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.

[0288] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0289] [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.

[0290] 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 electricity storage device from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the electricity storage device. 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.

[0291] 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, lithium bis(oxalato)borate (Li(C2O4)2, LiBOB), etc. can be used alone or in any combination and ratio of two or more of these.

[0292] The electrolyte used in the electricity storage device 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.

[0293] 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.

[0294] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0295] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0296] 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. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0297] 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.

[0298] Therefore, the positive electrode active material 100 obtained in the first embodiment can also be applied to an all-solid-state battery. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and excellent characteristics can be obtained.

[0299] [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.

[0300] This embodiment can be used in combination with other embodiments.

[0301] (Fourth embodiment) In this embodiment mode, examples of a plurality of shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0302] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 12A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 12B is an external view, and Fig. 12C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0303] 12A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 12A and 12B are not completely identical corresponding views.

[0304] In Fig. 12A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked together. These are sealed between a negative electrode can 302 and a positive electrode can 301. Note that a gasket for sealing is not shown in Fig. 15A. The spacer 322 and the washer 312 are used to protect the interior or to fix the position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0305] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0306] To prevent short-circuiting between the positive electrode and the negative electrode, a separator 310 and a ring-shaped insulator 313 are arranged so as to cover the side and top surfaces of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0307] FIG. 12B is a perspective view of the completed coin-type secondary battery.

[0308] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed 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. The negative electrode 307 is not limited to a laminated structure, and may be made of lithium metal foil or a lithium-aluminum alloy foil.

[0309] 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.

[0310] 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, etc., it is preferable to coat them with nickel, aluminum, etc. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0311] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 12C, positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with positive electrode can 301 facing downwards, and positive electrode can 301 and negative electrode can 302 are crimped together via gasket 303 to produce coin-type secondary battery 300.

[0312] By using it as a secondary battery, it is possible to obtain a coin-type secondary battery 300 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that when a secondary battery is formed between the negative electrode 307 and the positive electrode 304, the separator 310 may not be necessary.

[0313] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 13A. As shown in Fig. 13A, a cylindrical secondary battery 616 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 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0314] Fig. 13B is a schematic diagram showing the cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 13B 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.

[0315] 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 central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel). To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the 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.

[0316] Since the positive and negative electrodes used in a cylindrical storage battery are wound up, it is preferable to form active materials on both sides of the current collector.

[0317] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0318] 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 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases with an increase in temperature. This increase in resistance limits the amount of current and prevents abnormal heat generation. The PTC element can be made of a barium titanate (BaTiO3)-based semiconductor ceramic or the like.

[0319] 13C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via wiring 626. The control circuit 620 may be a charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging or overdischarging.

[0320] 13D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 615 to have a plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0321] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0322] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the outside temperature.

[0323] 13D, power storage system 615 is electrically connected to control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive electrodes of multiple secondary batteries via conductive plate 628, and wiring 622 is electrically connected to the negative electrodes of multiple secondary batteries via conductive plate 614.

[0324] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0325] A secondary battery 913 shown in Fig. 14A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in 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. 14A, 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.

[0326] 14B, the housing 930 shown in Fig. 14A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 14B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0327] 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 effect of the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0328] 14C shows the structure of wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the stacked sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0329] Alternatively, a secondary battery 913 may be provided having a wound body 950a as shown in Fig. 15. The wound body 950a shown in Fig. 15A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0330] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 932, the secondary battery 913 can have a large capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0331] The separator 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable because of its high safety and productivity.

[0332] 15B, negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. Positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0333] 15C, wound body 950a and the electrolyte are covered by casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of casing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0334] As shown in Fig. 15B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a secondary battery 913 with a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 15A and 15B, the descriptions of the secondary battery 913 shown in Figs. 14A to 14C can be referred to.

[0335] <Laminated secondary battery> 16A and 16B show examples of external views of a laminated secondary battery, which 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.

[0336] FIG. 17A shows an external view of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area and shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 17A.

[0337] <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. 16A will be described with reference to FIGS. 17B and 17C.

[0338] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 17B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0339] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0340] Next, as shown in Fig. 17C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for the joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0341] Next, an electrolyte solution (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0342] By using the positive electrode active material 100 obtained in the first embodiment for the positive electrode 503, the secondary battery 500 can be made to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0343] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be described with reference to FIG.

[0344] FIG. 18A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (which can also be called a thick flat plate shape). FIG. 18B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is attached to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0345] The inside of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0346] 18B, the secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to the terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one 551 of the positive electrode lead and the negative electrode lead of the secondary battery 513, and the other 552 of the positive electrode lead and the negative electrode lead of the secondary battery 513.

[0347] Alternatively, as shown in FIG. 18C, the circuit system 590 may include a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via the terminal 514.

[0348] The antenna 517 is not limited to a coil shape, and may be, for example, a wire or 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 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 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.

[0349] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field caused by the secondary battery 513. The layer 519 can be made of, for example, a magnetic material.

[0350] This embodiment mode can be freely combined with other embodiment modes.

[0351] (Embodiment 5) In this embodiment, an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in the first embodiment will be described.

[0352] 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.

[0353] Positive electrode 410 includes positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 includes positive electrode active material 411 and solid electrolyte 421. Positive electrode active material 411 is made of positive electrode active material 100 obtained in Embodiment 1, and the boundary between the core region and the shell region is indicated by a dotted line. Positive electrode active material layer 414 may also include a conductive additive and a binder.

[0354] 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.

[0355] 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.

[0356] 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.

[0357] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0358] 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-Y Al Y Ti 2-Y (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.

[0359] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. In addition, composite materials obtained by filling pores of porous alumina or porous silica with these halide-based solid electrolytes can also be used as solid electrolytes.

[0360] Also, different solid electrolytes may be mixed and used.

[0361] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving cycle characteristics, which is preferable. In addition, an improvement in productivity due to reduction of processes can also be expected. In this specification and the like, the NASICON-type crystal structure refers to a compound represented by M₂(XO₄)₃ (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO₆ octahedra and XO₄ tetrahedra share vertices and are three-dimensionally arranged.

[0362] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, those of various materials and shapes can be used, but it is preferable to have a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0363] For example, FIG. 20 shows an example of a cell for evaluating materials of an all-solid-state battery.

[0364] FIG. 20A is a cross-sectional view of the evaluation cell. The evaluation cell has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 for fixing them. By rotating the pressing screw 763, the electrode plate 753 is pressed to fix the evaluation material. An insulator 766 is provided between the lower member 761 and the upper member 762 made of a stainless steel material. Also, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0365] 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.

[0366] 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 to 20C.

[0367] 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.

[0368] 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.

[0369] 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.

[0370] 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.

[0371] 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.

[0372] By using the positive electrode active material 100 obtained in the first embodiment, an all-solid-state secondary battery having high energy density and good output characteristics can be realized.

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

[0374] (Embodiment 6) This embodiment is an example different from the cylindrical secondary battery shown in Fig. 13D, and an example of application to an electric vehicle (EV) is shown using Fig. 22C.

[0375] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0376] The internal structure of the first battery 1301a may be a wound type as shown in Fig. 14A or 15C, or a stacked type as shown in Fig. 16A or 16B. The first battery 1301a may use the all-solid-state battery of Embodiment 5. Using the all-solid-state battery of Embodiment 5 for the first battery 1301a allows for a high capacity, improved safety, and reduction in size and weight.

[0377] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0378] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0379] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0380] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0381] The first battery 1301a will be described with reference to FIG. 22A.

[0382] FIG. 22A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to vibrations or shaking from the outside (such as the road surface), it is preferable to fix multiple secondary batteries by fixing portions 1413 and 1414 or a battery housing box. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0383] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor.

[0384] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) can be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In-Ga oxide or an In-Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each of which has a c-axis aligned in a specific direction. The specific direction may be the thickness direction of the CAAC-OS film, a normal direction to the surface on which the CAAC-OS film is formed, or a normal direction to the surface of the CAAC-OS film. A crystalline region is a region in which the atomic arrangement is periodic. Considering the atomic arrangement as a lattice arrangement, a crystalline region is also a region in which the lattice arrangement is uniform. Furthermore, a CAAC-OS has a region in which multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a point in the region in which multiple crystalline regions are connected, where the lattice arrangement changes direction between a region with a uniform lattice arrangement and another region with a different uniform lattice arrangement. In other words, a CAAC-OS is an oxide semiconductor that is c-axis oriented but not clearly oriented in the ab-plane direction. A CAC-OS is, for example, a material in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range. Hereinafter, a metal oxide in which one or more metal elements are unevenly distributed and the regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range, is also referred to as a mosaic or patch structure.

[0385] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0386] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0387] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0388] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0389] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0390] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0391] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0392] Furthermore, because the control circuit unit 1320 can be used in high-temperature environments, it is preferable to use transistors using oxide semiconductors. To simplify the process, the control circuit unit 1320 may be formed using unipolar transistors. Transistors using oxide semiconductors in the semiconductor layer have a wider operating ambient temperature range than single-crystal silicon, from -40°C to 150°C, and their characteristics change less when the secondary battery is heated than single-crystal silicon. The off-current of transistors using oxide semiconductors is below the lower limit of measurement regardless of temperature, even at 150°C, whereas the off-current characteristics of single-crystal silicon transistors are highly temperature-dependent. For example, at 150°C, the off-current of single-crystal silicon transistors increases, and the current on / off ratio is not sufficiently large. The control circuit unit 1320 can improve safety. Furthermore, combining the control circuit unit 1320 with a secondary battery using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode can achieve a synergistic effect in terms of safety. A secondary battery using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode and the control circuit unit 1320 can significantly contribute to eliminating accidents, such as fires, caused by secondary batteries.

[0393] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for secondary batteries can be miniaturized.

[0394] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0395] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0396] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0397] FIG. 22B shows an example of a block diagram of the battery pack 1415 shown in FIG. 22A.

[0398] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside and the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0399] The switch unit 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch unit 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, facilitating integration. Furthermore, OS transistors can be fabricated using the same manufacturing equipment as Si transistors, allowing for low-cost fabrication. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The control circuit unit 1320 occupies a smaller volume, enabling miniaturization.

[0400] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle devices, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle devices. Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Lead-acid batteries have a higher self-discharge rate than lithium-ion secondary batteries and are prone to degradation due to a phenomenon called sulfation. Using a lithium-ion secondary battery as the second battery 1311 offers the advantage of being maintenance-free, but after prolonged use (e.g., three years or more), there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, even if the first batteries 1301a and 1301b still have remaining capacity, the motor cannot be started. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery, and the second battery is constantly charged to maintain a fully charged state.

[0401] In this embodiment, an example in which lithium ion secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown. A lead storage battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, high capacity can be achieved, and miniaturization and weight reduction are possible.

[0402] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 or the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0403] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions according to the charging characteristics of the secondary battery used, and can perform rapid charging.

[0404] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU and a GPU.

[0405] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW. Charging is also possible by receiving power from external charging equipment using a wireless power supply system.

[0406] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0407] Moreover, the secondary battery of the present embodiment described above has a high-density positive electrode by using the positive electrode active material 100 obtained in the first embodiment. Furthermore, by using graphene as a conductive additive, a secondary battery with significantly improved electrical characteristics can be realized, as a synergistic effect of suppressing capacity reduction and maintaining high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and can provide a vehicle with a long driving range, specifically, a driving range of 500 km or more per charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0408] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material 100 described in embodiment 1, and the usable capacity can be increased as the charging voltage increases. Furthermore, by using the positive electrode active material 100 described in embodiment 1 for the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0409] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0410] 13D, 15C, and 22A, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, secondary batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0411] 23A to 23D illustrate examples of transportation vehicles using one embodiment of the present invention. An automobile 2001 shown in FIG. 23A is an electric automobile that uses 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. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 4 is installed in one or more locations. The automobile 2001 shown in FIG. 23A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0412] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method, connector standards, or the like, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station provided in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electricity storage device mounted on automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0413] Furthermore, 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 two vehicles. Furthermore, solar cells 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.

[0414] 23B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series for a maximum voltage of 170 V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 23A, and therefore a description thereof will be omitted.

[0415] FIG. 23C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, which is obtained by connecting in series one hundred or more secondary batteries with a nominal voltage of 3.0 V to 5.0 V. Therefore, a secondary battery with little variation in characteristics is required. By using a secondary battery in which the positive electrode active material 100 described in the first embodiment is used for the positive electrode, a secondary battery with stable battery characteristics can be manufactured, and from the viewpoint of yield, mass production at low cost is possible. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those shown in FIG. 23A are provided, and therefore a description thereof will be omitted.

[0416] As an example, Fig. 23D shows an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 23D has wheels for takeoff and landing, it can also be said to be part of a transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and includes the secondary battery module and a charge control device.

[0417] The secondary battery module of the aircraft 2004 has, for example, eight 4V secondary batteries connected in series to produce a maximum voltage of 32V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in Fig. 23A, and therefore a description thereof will be omitted.

[0418] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0419] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 24A and 24B.

[0420] 24A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 through a wiring 2611 or the like. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The power storage device 2612 can be charged with power obtained by the solar panel 2610. The power stored in the power storage device 2612 can also be charged to a secondary battery included in a vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0421] The power stored in the power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0422] 24B illustrates an example of a power storage device 700 according to one embodiment of the present invention. As illustrated in FIG. 24B, a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. The control circuit described in Embodiment 6 may be provided in the power storage device 791. A synergistic effect on safety can be obtained by using a secondary battery in which the positive electrode active material 100 obtained in Embodiment 1 is used for the positive electrode of the power storage device 791. The control circuit described in Embodiment 6 and the secondary battery in which the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode can greatly contribute to preventing accidents such as fires caused by the power storage device 791 including a secondary battery.

[0423] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also called a control device), a display 706, and a router 709 by wiring.

[0424] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via an outlet (not shown).

[0425] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0426] The power storage controller 705 has a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (for example, from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day, based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791, based on the amount of power demand predicted by the prediction unit 712.

[0427] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, or the mobile electronic device.

[0428] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0429] (Embodiment 8) In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

[0430] 25A is an example of an electric bicycle using the power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 shown in FIG. 25A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0431] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 25B. The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery, an example of which is shown in Embodiment 6. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. The control circuit 8704 may be provided with the small-sized solid-state secondary battery shown in FIGS. 21A and 21B. By providing the small-sized solid-state secondary battery shown in FIGS. 21A and 21B in the control circuit 8704, power can be supplied to retain data in a memory circuit included in the control circuit 8704 for a long time. Furthermore, a synergistic effect in terms of safety can be obtained by combining it with a secondary battery using, as its positive electrode, positive electrode active material 100 obtained in embodiment 1. The secondary battery using, as its positive electrode, positive electrode active material 100 obtained in embodiment 1 and control circuit 8704 can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0432] 25C illustrates an example of a two-wheeled vehicle using the power storage device of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 25C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602 includes a plurality of secondary batteries each using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode, and thus can have a high capacity, which can contribute to miniaturization.

[0433] 25C, the power storage device 8602 can be stored in the under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0434] (Embodiment 9) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a secondary battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0435] 26A shows an example of a mobile phone. Mobile phone 2100 includes a display unit 2102 built into housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that mobile phone 2100 also includes secondary battery 2107. By including secondary battery 2107 using positive electrode active material 100 described in Embodiment 1 as a positive electrode, high capacity can be achieved, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0436] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0437] The operation button 2103 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 2103 can be freely set by an operating system built into the mobile phone 2100.

[0438] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0439] The mobile phone 2100 also has an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Charging may also be performed by wireless power supply without using the external connection port 2104.

[0440] The mobile phone 2100 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.

[0441] FIG. 26B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be installed in the unmanned aerial vehicle 2300.

[0442] Fig. 26C shows an example of a robot. A robot 6400 shown in Fig. 26C 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.

[0443] 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.

[0444] 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.

[0445] 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.

[0446] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6409 is suitable for the robot 6400.

[0447] 26D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0448] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and 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 the 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 in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0449] Figure 27A 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.

[0450] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 27A. The eyeglasses-type device 4000 includes a frame 4000a and a display portion 4000b. By mounting the secondary battery on temple portions of the curved frame 4000a, the eyeglasses-type device 4000 can be lightweight, well-balanced in weight, and has a long continuous use time. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[0451] 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. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and can achieve a space-saving configuration that can be achieved by miniaturizing the housing.

[0452] 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. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0453] 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. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0454] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an inner region of the belt portion 4006a. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a configuration that can accommodate space saving associated with miniaturization of the housing can be realized.

[0455] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on a wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided in the display portion 4005a or the belt portion 4005b. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and can achieve a space-saving configuration that can be achieved by miniaturizing a housing.

[0456] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0457] 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.

[0458] FIG. 27B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0459] 27C shows a side view of the display portion 4005a. FIG. 27C shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and can have high density and high capacity, and is small and lightweight.

[0460] Since the wristwatch-type device 4005 is required to be small and lightweight, by using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode of the secondary battery 913, the secondary battery 913 can have a high energy density and be small.

[0461] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0462] In this example, a positive electrode active material of one embodiment of the present invention was prepared, and elemental analysis was performed using XPS to evaluate cycle characteristics and analyze the crystal structure after charge.

[0463] <Preparation of positive electrode active material> The sample produced in this example will be described with reference to the production method shown in FIG.

[0464] In step S11, lithium carbonate was used as the lithium source, cobalt carbonate as the cobalt source, magnesium oxide as the magnesium source, and lithium fluoride as the fluorine source and lithium source. 1.02 Co 0.99 Mg 0.01 O 1.98 F 0.02 Next, as shown in step S12, these were mixed to obtain a mixture 900 (step S13).

[0465] Next, as shown in step S14, the mixture 900 was subjected to a first heating. The mixture 900 was placed in an aluminum oxide crucible, which was then covered and heated in a muffle furnace. The heating temperature was 1000°C, the heating time was 10 hours, and the heating was performed while flowing dry air into the muffle furnace at 10 L / min. The temperature increase rate was 200°C / hour. After heating was completed, the mixture was slowly cooled to room temperature over 10 hours or more. In this way, a composite oxide 901 was obtained (step S15). The sample that had only been subjected to this first heating was designated as Sample 1 (Comparative Example).

[0466] Next, as shown in step S16, composite oxide 901 was subjected to a second heating. Composite oxide 901 was placed in an aluminum oxide crucible, which was then covered and heated in a muffle furnace. The heating temperature was 800°C for 2 hours, and dry air was flowed into the muffle furnace at 10 L / min. After heating, the mixture was slowly cooled to room temperature over 10 hours or more. In this way, positive electrode active material 100 was obtained (step S17). The sample that had undergone the first and second heating processes was designated as Sample 2.

[0467] Also, Li 1.01 Co 0.995 Mg 0.005 O 1.99 F 0.01 Sample 3 was prepared by the same heating process as Sample 1 except that the weight was weighed to have the composition of 1.01 Co 0.995 Mg 0.005 O 1.99 F 0.01 Sample 4 was prepared by carrying out the heating process twice in the same manner as Sample 2, except that the weight was weighed so as to have the composition shown below.

[0468] Also, Li 1.04 Co 0.98 Mg 0.02 O 1.96 F 0.04 Sample 5 was prepared in the same manner as Sample 2, except that the weight was weighed out so as to have the composition shown below.

[0469] Sample 6 was prepared in the same manner as Sample 2, except that the first heating temperature was set to 950° C. and oxygen gas was flowed at 10 L / min during the second heating.

[0470] The manufacturing conditions for Samples 1 to 6 are shown in Table 1.

[0471] [Table 1]

[0472] <xps> The above-prepared Sample 1 and Sample 2 were subjected to elemental analysis using XPS under the following conditions for XPS analysis. Measurement equipment: PHI Quantera II X-ray source: Monochromatic Al Kα (1486.6eV) Detection area: 100 μmφ Detection depth: Approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: Wide, Li1s, Co2p, Ti2p, O1s, C1s, F1s, S2p, Ca2p, Mg1s, Na1s, Zr3d

[0473] The XPS results are shown in Table 2, and the relative values ​​when the number of cobalt atoms is taken as 1 are shown in Table 3.

[0474] [Table 2]

[0475] [Table 3]

[0476] As shown in Table 2, the magnesium concentration was less than 4.5 atomic % in sample 1 and greater than 4.5 atomic % in sample 2.

[0477] <Cycle characteristics> Next, secondary batteries were fabricated using Samples 1 to 6, and the cycle characteristics were evaluated.

[0478] First, the positive electrode active material, AB, and PVDF were mixed in a weight ratio of 95:2.5:2.5 to prepare a slurry, which was then applied to an aluminum current collector using NMP as the solvent.

[0479] After the slurry was applied to the current collector, the solvent was evaporated. A positive electrode was obtained by the above process. The amount of active material carried on the positive electrode was approximately 7.1 mg / cm. 2 It was decided.

[0480] Using the prepared positive electrode, a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated.

[0481] The counter electrode was made of lithium metal.

[0482] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, to which 2 wt% vinylene carbonate (VC) was added as an additive.

[0483] The separator was made of polypropylene with a thickness of 25 μm.

[0484] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0485] The cycle test was carried out under the following conditions: the charging voltage was 4.6 V; the measurement temperature was 25°C; charging was CC / CV (0.5 C, 0.05 C cut), discharging was CC (0.5 C, 2.5 V cut), and a 10-minute rest period was provided before the next charge. In this example, 1 C was 137 mA / g.

[0486] 28A shows the results of the cycle test of the discharge capacity of Samples 1 to 6. Compared with Sample 1 and Sample 3, which were not subjected to the second heating, Samples 2, 4, 5, and 6, which were subjected to the second heating, showed extremely good cycle characteristics. Among those subjected to the second heating, Sample 6, which was fired at a temperature of 950°C, showed the best performance.

[0487] 28B shows the results of the cycle test on the average discharge voltage of Samples 1 to 6. Samples 5 and 6 showed little decrease in average discharge voltage even after 50 cycles, with the average discharge voltage at the 50th cycle being 0.06 V for Sample 6 and 4.02 V for Sample 5. A high average discharge voltage is preferable because it allows for the supply of high electrical energy.

[0488] On the other hand, the average discharge voltage at the 50th cycle for Sample 1 was 3.32 V, for Sample 2 it was 3.58 V, for Sample 3 it was 3.17 V, and for Sample 4 it was 3.47 V. Samples 1 and 3, which did not undergo the second heating, showed a significant decrease in average discharge voltage. This was presumably due to an increase in the internal resistance of the battery.

[0489] From the above, it can be said that Sample 6 exhibits very good cycle characteristics in terms of both discharge capacity and average discharge voltage. Although Sample 5 does not reach the discharge capacity of Samples 2, 4, and 6, it has good cycle characteristics in terms of average discharge voltage, demonstrating that it is a positive electrode active material that can supply high electrical energy even after undergoing charge-discharge cycles.

[0490] It was also confirmed that the magnesium concentration in the surface layer increased through the second heating process, reaching 4.5 atomic % or more and the ratio of magnesium to cobalt concentrations (Mg / Co) reaching 0.30 or more. It was also revealed that the cycle characteristics were significantly improved through the second heating process.

[0491] <Crystal structure after charging> Next, secondary batteries were fabricated using Samples 1 to 6 fabricated through the second heating, and the crystal structures after charging were analyzed using XRD.

[0492] First, coin cells were fabricated using the positive electrode active materials of Samples 1 to 6 in the same manner as in the cycle test.

[0493] The coin cells for analyzing the crystal structure after the first charge were CCCV charged at 4.6 V. More specifically, they were charged at a constant current of 0.5 C (68.5 mA / g), and then at a constant voltage until the current reached 0.01 C (1.37 mA / g).

[0494] The coin cell used to analyze the crystal structure after the second charge (2nd charge) was charged and discharged once under the same conditions as the cycle test, and then CCCV charged at 4.6 V. More specifically, it was charged at a constant current of 0.5 C (68.5 mA / g), and then charged at a constant voltage until the current value reached 0.01 C (1.37 mA / g).

[0495] Table 4 shows the charge capacities for the first and second charges.

[0496] [Table 4]

[0497] The charged coin cell was then disassembled in an argon-filled glove box to remove the positive electrode, which was then washed with DMC (dimethyl carbonate) to remove the electrolyte. The positive electrode was then placed in a sealed container for XRD measurement in an argon atmosphere. Analysis was then performed using powder XRD (Bruker D8 ADVANCE) with CuKα1 radiation. The XRD instrument was set up for powder samples, with the sample height adjusted to fit the required measurement surface. The sample was also set flat, without any curvature.

[0498] Figure 29 shows the XRD patterns of the positive electrodes of coin cells using the positive electrode active materials of Samples 1 to 6 after the first charge. For comparison, the patterns of the O3' type, as in Figure 4, and the H1-3 type and LiCoO2, as in Figure 6, are also shown. Figure 30A shows an enlarged view of the region where 2θ is between 18° and 20°. This region contains peaks corresponding to the (003) plane of the O3 and O3' type crystal structures and the (006) plane of the H1-3 type. Figure 30B also shows an enlarged view of the region where 2θ is between 43° and 46°. This region contains peaks corresponding to the (104) plane of the O3 and O3' type crystal structures and the (107) plane of the H1-3 type.

[0499] The maximum value, half-width, and area intensity ratio were calculated for the peaks with 2θ between 18° and 20° and between 43° and 46° after the initial charge. TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker) was used for the calculations, with single profile fitting, PV (position value) peak type, and a background Chebychev order of 20. The results are shown in Table 5.

[0500] [Table 5]

[0501] Figure 31 shows the XRD patterns of the positive electrodes of coin cells using the positive electrode active materials of Samples 2, 4, and 6 after the second charge. Similarly, Figure 32A shows an enlarged view of the region where 2θ is between 18° and 20°, and Figure 32B shows an enlarged view of the region where 2θ is between 43° and 46°.

[0502] Furthermore, the maximum value, half-width, and area intensity ratio were calculated in the same manner for the peak with 2θ of 18° or more and 20° or less and the peak with 2θ of 43° or more and 46° or less after the second charge. The results are shown in Table 6.

[0503] [Table 6]

[0504] As shown in Table 5, in the analysis after the first charge, the area intensity I of Sample 1 without the second heating H1-3(006) / I O3’+O3(003) On the other hand, Sample 2, Sample 4 to Sample 6, which had undergone the second heating, all had an area intensity I H1-3(006) / I O3’+O3(003) was 37% or less and 40% or less.

[0505] As shown in Table 6, the area intensity I H1-3(006) / I O3’+O3(003) Although there is a tendency for the area intensity I H1-3(006) / I O3’+O3(003) was less than 40%.

[0506] From the above, it was confirmed that the positive electrode active material that underwent the second heating has the O3' structure after charging. Furthermore, it was revealed that the area intensity ratio of the peak corresponding to the (006) plane of the H1-3 type to the peak corresponding to the (003) plane of the O3' type and O3 type was 60% or less, more specifically, 40% or less, in the analysis after the first charge.

[0507] Even without the second heating step, the addition of magnesium and other additive elements to the lithium sites could partially suppress the deformation along the c-axis after charging, but the effect was insufficient. This was thought to be because the additive elements were only well distributed in a part of the surface layer. [Explanation of symbols]

[0508] 100: Positive electrode active material, 100a: Surface layer, 100b: Interior, 101: Grain boundary, 102: Crack< / xps>

Claims

1. A method for producing a secondary battery, comprising: the secondary battery has a positive electrode, the positive electrode has a positive electrode active material, The positive electrode active material is produced through a first production step to a third production step, the first preparation step is a step of mixing lithium carbonate, cobalt carbonate, magnesium oxide, and lithium fluoride to prepare a mixture; the second preparation step is a step of preparing a composite oxide by heating the mixture at 900° C. or higher and 1100° C. or lower for 5 hours or higher and 20 hours or lower; The third preparation step is a step of heating the composite oxide at 742°C or higher and 920°C or lower for 1 hour or higher and 10 hours or lower. Method for making secondary batteries.

2. A method for producing a secondary battery, comprising: the secondary battery has a positive electrode, the positive electrode has a positive electrode active material, The positive electrode active material is produced through a first production step to a third production step, the first preparation step is a step of mixing lithium carbonate, cobalt carbonate, magnesium oxide, and lithium fluoride to prepare a mixture; the second preparation step is a step of putting the mixture into a container, then closing a lid and heating at 900° C. or higher and 1100° C. or lower for 5 hours or longer and 20 hours or shorter to prepare a composite oxide; The third preparation step is a step of placing the composite oxide in a container, then closing a lid and heating at 742°C or higher and 920°C or lower for 1 hour or higher and 10 hours or lower. Method for making secondary batteries.

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