Positive electrode active material, lithium-ion secondary battery, electronic device

Abstract

Provided is a positive electrode active material having a crystal structure that does not easily collapse even with repetition of charge and discharge. Provided is a positive electrode active material having a large charge / discharge capacity. A positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, wherein a surface layer of the positive electrode active material has a larger a-axis lattice constant than the inner part, and has a larger c-axis lattice constant than the inner part. The change rate of the a-axis lattice constant between the surface layer and the inner part is preferably more than 0 but not more than 0.12, and the change rate of the c-axis lattice constant between the surface layer and the inner part is preferable more than 0 but not more than 0.18.

Description

Technical Field

[0001] One aspect of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[0002] In this specification, the electronic device refers to all devices having a power storage device, and all electro-optical devices having a power storage device, information terminal devices having a power storage device, etc. are electronic devices.

Background Art

[0003] In recent years, various power storage devices such as lithium ion secondary batteries, lithium ion capacitors, air batteries, and all-solid-state batteries have been actively developed. In particular, lithium ion secondary batteries with high output and high capacity have rapidly expanded their demand along with the development of the semiconductor industry, and have become indispensable in modern information societies as a source of rechargeable energy.

[0004] Among them, for secondary batteries for mobile electronic devices, etc., there is a high demand for secondary batteries with a large discharge capacity per unit weight and excellent cycle characteristics. In order to meet these demands, improvements to the cathode active material of secondary batteries have been actively carried out (for example, Patent Documents 1 to 3). In addition, research on the crystal structure of cathode active materials has also been conducted (Non-Patent Documents 1 to 3).

[0005] Also, X-ray diffraction (XRD) is one of the techniques used for analyzing the crystal structure of cathode active materials. By using the ICSD (Inorganic Crystal Structure Database) introduced in Non-Patent Document 4, XRD data can be analyzed.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 8-236114 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-124262 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-358953 [Non-Patent Document]

[0007] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-Patent Document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO▲2▼(0.0≦x≦1.0)”, Physical Review B, 80(16);165114 [Non-Patent Document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO▲2▼”, Journal of The Electrochemical Society, 2002, 149(12)A1604-A1609 [Non-Patent Document 4] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., (2002) B58 364 - 369.

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, there is still room for improvement in lithium - ion secondary batteries and the cathode active materials used therein in various aspects such as charge - discharge capacity, cycle characteristics, reliability, safety, or cost.

[0009] One aspect of the present invention is to provide a cathode active material that, when used in a lithium - ion secondary battery, suppresses a decrease in charge - discharge capacity during charge - discharge cycles. Or, one aspect is to provide a cathode active material whose crystal structure is difficult to collapse even when charge - discharge is repeated. Or, one aspect is to provide a cathode active material having a large charge - discharge capacity. Or, one aspect is to provide a secondary battery with high safety or reliability.

[0010] Another aspect of the present invention is to provide a cathode active material, an energy storage device, or a method for producing them.

[0011] Note that the description of these problems does not prevent the existence of other problems. Note that one aspect of the present invention does not need to solve all of these problems. Note that it is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0012] One aspect of the present invention is a cathode active material containing lithium, cobalt, nickel, magnesium, and oxygen, and the lattice constant A of the a - axis of the outermost surface layer of the cathode active material surfaceis the lattice constant A of the internal a-axis core is larger than that, and the lattice constant C of the c-axis of the outermost surface layer surface is the lattice constant C of the internal c-axis core is larger than that, and it is a positive electrode active material.

[0013] In the above, the lattice constant A of the a-axis of the outermost surface layer surface and the lattice constant A of the internal a-axis core The difference Δ A divided by the lattice constant A core The change rate R A exceeds 0 and is 0.12 or less, and the lattice constant C of the c-axis of the outermost surface layer surface and the lattice constant C of the internal c-axis core The difference Δ C divided by the lattice constant C core The change rate R C is preferably greater than 0 and 0.18 or less.

[0014] In the above, the change rate R A is 0.05 or more and 0.07 or less, and the change rate R C is preferably 0.09 or more and 0.12 or less.

[0015] In the above, the lattice constant A of the a-axis of the outermost surface layer surface and the lattice constant A of the internal a-axis core The difference Δ A is smaller than the difference between the lattice constant C of the c-axis of the outermost surface layer surface and the lattice constant C of the internal c-axis core The difference Δ C is preferably larger.

[0016] Another aspect of the present invention is a positive electrode active material having lithium, cobalt, nickel, magnesium, and oxygen, wherein at least a part of the outermost surface layer of the positive electrode active material has a layered rock salt-type crystal structure having an alternating transition metal site layer and lithium site layer, and a part of the lithium site layer has a metal element having an atomic number larger than that of lithium.

[0017] In the above, the metal element having an atomic number larger than that of lithium is preferably magnesium, cobalt or aluminum.

[0018] In the above, in the cross-sectional TEM image of the outermost surface layer, the luminance of the lithium site layer is preferably 3% or more and 60% or less of the luminance of the transition metal site layer.

[0019] In the above, the concentration of nickel in the outermost surface layer is 1 atomic% or less, and the concentration of nickel in the entire positive electrode active material is preferably 0.05% or more and 4% or less of the concentration of cobalt.

[0020] In the above, the outermost surface layer has a region where bright spots indicating a rock salt-type crystal structure belonging to the space group Fm-3m or Fd-3m and bright spots indicating a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the ultramicro electron beam diffraction image, and the interior preferably has a region where bright spots indicating a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the ultramicro electron beam diffraction image.

[0021] In the above, the spin density caused by any one or more of divalent nickel ions, trivalent nickel ions, divalent cobalt ions and tetravalent cobalt ions is 2.0×10 17 spins / g or more and 1.0×10 21 spins / g or less is preferable.

[0022] In the above, the positive electrode active material contains aluminum, and the concentration of aluminum in the entire positive electrode active material is preferably 0.05% or more and 4% or less of the concentration of cobalt.

[0023] In the above, in the energy dispersive X-ray analysis of the cross-section of the positive electrode active material, the peak of the aluminum concentration is preferably located at a depth of 5 nm or more and 30 nm or less from the surface toward the center.

[0024] Another aspect of the present invention is a lithium-ion secondary battery having a positive electrode active material, the positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, and the lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material surface is larger than the lattice constant A of the a-axis inside, and the lattice constant C of the c-axis of the outermost surface layer of the positive electrode active material core is larger than the lattice constant C of the c-axis inside. It is a lithium-ion secondary battery. surface is larger than the lattice constant C of the c-axis inside. It is a lithium-ion secondary battery. core is larger than the lattice constant C of the c-axis inside. It is a lithium-ion secondary battery.

[0025] Another aspect of the present invention is an electronic device having the above secondary battery.

Advantages of the Invention

[0026] According to one aspect of the present invention, by using it in a lithium-ion secondary battery, a positive electrode active material can be provided in which a decrease in charge / discharge capacity during charge / discharge cycles is suppressed. Or, a positive electrode active material with a crystal structure that is difficult to collapse even when charge / discharge is repeated can be provided. Or, a positive electrode active material with a large charge / discharge capacity can be provided. Or, a secondary battery with high safety or reliability can be provided.

[0027] Also, according to one aspect of the present invention, a positive electrode active material, a power storage device, or a method for manufacturing them can be provided.

[0028] Note that the description of these effects does not prevent the existence of other effects. Note that one aspect of the present invention does not necessarily have all of these effects. Note that other effects will be naturally apparent from the descriptions in the specification, drawings, claims, etc., and it is possible to extract these other effects from the descriptions in the specification, drawings, claims, etc.

Brief Description of the Drawings

[0029] FIG. 1A is a cross-sectional view of the positive electrode active material, and FIGS. 1B, 1C1, and 1C2 are partial cross-sectional views of the positive electrode active material. FIGS. 2A1 to 2C2 are partial cross-sectional views of the positive electrode active material. Figure 3 is a cross-sectional view of the positive electrode active material. Figure 4 is a diagram for explaining the depth of charge and crystal structure of the positive electrode active material. Figure 5 is a diagram showing the XRD pattern calculated from the crystal structure. Figure 6 is a diagram for explaining the depth of charge and crystal structure of the positive electrode active material of the comparative example. Figure 7 is a diagram showing the XRD pattern calculated from the crystal structure. Figures 8A to 8C are lattice constants calculated from XRD. Figures 9A to 9C are lattice constants calculated from XRD. Figure 10 is a diagram for explaining the manufacturing method of the positive electrode active material. Figure 11 is a diagram for explaining the manufacturing method of the positive electrode active material. Figure 12 is a diagram for explaining the manufacturing method of the positive electrode active material. Figure 13 is a diagram for explaining the manufacturing method of the positive electrode active material. Figure 14 is a diagram for explaining the manufacturing method of the positive electrode active material. Figure 15 is a diagram for explaining the manufacturing method of the positive electrode active material. Figures 16A and 16B are cross-sectional views of the active material layer when a graphene compound is used as the conductive material. Figures 17A and 17B are diagrams for explaining an example of a secondary battery. Figures 18A to 18C are diagrams for explaining an example of a secondary battery. Figures 19A and 19B are diagrams for explaining an example of a secondary battery. Figures 20A to 20C are diagrams for explaining a coin-type secondary battery. Figures 21A to 21D are diagrams for explaining a cylindrical secondary battery. Figures 22A and 22B are diagrams for explaining an example of a secondary battery. Figures 23A to 23D are diagrams for explaining an example of a secondary battery. Figures 24A and 24B are diagrams for explaining an example of a secondary battery. Figure 25 is a diagram for explaining an example of a secondary battery. Figures 26A to 26C are diagrams for explaining a laminate-type secondary battery. Figures 27A and 27B are diagrams for explaining a laminate-type secondary battery. Figure 28 is a view showing the appearance of a secondary battery. Figure 29 is a view showing the appearance of a secondary battery. Figures 30A to 30C are views for explaining a method of manufacturing a secondary battery. Figures 31A to 31H are views for explaining an example of an electronic device. Figures 32A to 32C are views for explaining an example of an electronic device. Figure 33 is a view for explaining an example of an electronic device. Figures 34A to 34D are views for explaining an example of an electronic device. Figures 35A to 35C are views showing an example of an electronic device. Figures 36A to 36C are views for explaining an example of a vehicle. Figures 37A to 37D are SEM images of the surface of a positive electrode active material. Figure 38A is a cross-sectional TEM image of a positive electrode active material. Figures 38B and 38C are selected area electron diffraction images of a part of Figure 38A. Figures 39A and 39B are micro electron diffraction images of a positive electrode active material. Figure 40A is a cross-sectional TEM image of a positive electrode active material. Figures 40B and 40C are micro electron diffraction images of a part of Figure 40A. Figure 41A is a cross-sectional TEM image of a positive electrode active material. Figures 41B and 41C are micro electron diffraction images of a part of Figure 41A. Figures 42A to 42C are cross-sectional STEM images of a positive electrode active material. Figure 43A is a cross-sectional STEM image of a positive electrode active material and is a rotated view of Figure 42B. Figure 43B is the measurement result of the luminance of Figure 43A. Figure 44A is a graph obtained by correcting the background from Figure 43B. Figure 44B is a bright-field image of a cross-sectional STEM of a positive electrode active material. Figure 45A is a cross-sectional HAADF-STEM image of a positive electrode active material. Figures 45B to 45F are the results of EDX surface analysis. Figure 46A is a cross-sectional HAADF-STEM image of a positive electrode active material. Figures 46B to 46D are the results of EDX surface analysis. Figure 47A is a cross-sectional HAADF-STEM image of the positive electrode active material. Figures 47B to 47E are diagrams in which the brightness of the results of EDX surface analysis is inverted. Figure 48 is a cross-sectional HAADF-STEM image of the positive electrode active material. Figures 49A and 49B are the results of EDX line analysis of the positive electrode active material. Figures 50A and 50B are SEM images of the positive electrode active material. Figures 51A and 51B are the grayscale values of the positive electrode active material. Figures 52A and 52B are the luminance histograms of the positive electrode active material. Figure 53 is an XRD pattern of the positive electrode active material. Figures 54A and 54B are enlarged XRD patterns of a part of Figure 53. Figure 55 is an XRD pattern of the positive electrode active material. Figures 56A and 56B are enlarged XRD patterns of a part of Figure 55. Figure 57 is an XRD pattern of the positive electrode active material. Figures 58A and 58B are enlarged XRD patterns of a part of Figure 57. Figure 59 is an XRD pattern of the positive electrode active material. Figures 60A and 60B are enlarged XRD patterns of a part of Figure 59. Figures 61A and 61B are graphs showing the cycle characteristics of the positive electrode active material. Figures 62A and 62B are graphs showing the cycle characteristics of the positive electrode active material. Figures 63A and 63B are graphs showing the cycle characteristics of the positive electrode active material. Figures 64A and 64B are graphs showing the cycle characteristics of the positive electrode active material. Figures 65A and 65B are graphs showing the cycle characteristics of the positive electrode active material. Figures 66A and 66B are graphs showing the cycle characteristics of the positive electrode active material. Figures 67A and 67B are graphs showing the cycle characteristics of the positive electrode active material. Figures 68A and 68B are graphs showing the cycle characteristics of the positive electrode active material.

Embodiments for Carrying Out the Invention

[0030] 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 those skilled in the art can easily understand that its form and details can be variously changed. Also, the present invention is not to be construed as being limited to the description of the embodiments shown below.

[0031] In this specification and the like, Miller indices are used for the notation of crystal planes and directions. Individual planes indicating crystal planes are represented by ( ). In crystallography, notations for crystal planes, directions, and space groups are represented by numbers with a bar on top, but in this specification and the like, due to application notation constraints, instead of putting a bar on top of the numbers, a -(minus sign) may be attached in front of the numbers for expression.

[0032] In this specification and the like, segregation refers to a phenomenon in a solid composed of a plurality of elements (for example, A, B, C) in which a certain element (for example, B) is spatially non-uniformly distributed.

[0033] Also, the surface of the positive electrode active material shall refer to the surface layer portion including the outermost surface layer and the surface of the composite oxide including the inside and the like. Therefore, it is assumed that the positive electrode active material does not contain carbonic acid, hydroxy groups, etc. chemisorbed after production. Also, it is assumed that the positive electrode active material does not contain the electrolyte solution, binder, conductive material, or compounds derived therefrom attached to it. Also, the positive electrode active material does not necessarily have to be a region having lithium sites that all contribute to charge and discharge.

[0034] In this specification and the like, the layered rock salt-type crystal structure of the composite oxide containing lithium and transition metals refers to a crystal structure having a rock salt-type ion arrangement in which cations and anions are alternately arranged, and the transition metals and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as partial deficiency of cations or anions, and it is only necessary that two-dimensional diffusion of lithium ions is possible. Also, strictly speaking, the layered rock salt-type crystal structure may be a structure in which the lattice of the rock salt-type crystal is distorted.

[0035] In this specification and the like, the rock-salt type crystal structure refers to a structure in which cations and anions are alternately arranged. Note that there may be some deficiencies in cations or anions.

[0036] In this specification and the like, a mixture refers to a mixture of a plurality of materials. After the mutual diffusion of the elements contained in the mixture occurs, it may be referred to as a composite. Even if there is some unreacted material, it may be referred to as a composite. Also, the positive electrode active material may be rephrased as a composite, a composite oxide, or a material.

[0037] In this specification and the like, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium contained in the positive electrode active material has been removed. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0038] In this specification and the like, the depth of charge when all the insertable and removable lithium has been inserted is defined as 0, and the depth of charge when all the insertable and removable lithium contained in the positive electrode active material has been removed is defined as 1.

[0039] Generally, in a positive electrode active material having a layered rock-salt type crystal structure, when the lithium between the layered structures composed of transition metals and oxygen decreases, the crystal structure becomes unstable. Therefore, in a secondary battery using common lithium cobaltate, the charging is limited to a charging depth of 0.4, a charging voltage of 4.3 V (in the case of a counter electrode lithium), and a charging capacity of about 160 mAh / g.

[0040] In contrast, a positive electrode active material with a depth of charge of 0.74 or more and 0.9 or less, more specifically, a depth of charge of 0.8 or more and 0.83 or less, shall be referred to as a positive electrode active material charged at a high voltage. Therefore, for example, in the case of LiCoO2, if the charge capacity is charged to 219.2 mAh / g, it is a positive electrode active material charged at a high voltage. Also, in LiCoO2, in a 25°C environment, constant current charging is performed with the charging voltage of 4.525 V or more and 4.7 V or less (in the case of a lithium counter electrode), and then the positive electrode active material after constant voltage charging until the current value becomes 0.01C, or about 1 / 5 to 1 / 100 of the current value during constant current charging, shall also be referred to as a positive electrode active material charged at a high voltage. Note that C is an abbreviation for Capacity rate, and 1C refers to the magnitude of the current that fully charges or fully discharges the charge and discharge capacity of a secondary battery in 1 hour.

[0041] Regarding the positive electrode active material, inserting lithium ions is referred to as discharging. Also, a positive electrode active material with a depth of charge of 0.06 or less, or a positive electrode active material that has discharged 90% or more of its capacity from a state charged at a high voltage, shall be referred to as a fully discharged positive electrode active material. For example, in the case of LiCoO2, if the charge capacity is 219.2 mAh / g, it is in a state charged at a high voltage, and the positive electrode active material after discharging 197.3 mAh / g or more, which is 90% of the charge capacity, is a fully discharged positive electrode active material. Also, in LiCoO2, the positive electrode active material after constant current discharging until the battery voltage becomes 3V or less (in the case of a lithium counter electrode) in a 25°C environment shall also be referred to as a fully discharged positive electrode active material.

[0042] In addition, in this specification and the like, as an example of a secondary battery using the positive electrode and the positive electrode active material of one aspect of the present invention, a case where lithium metal is used as the counter electrode may be shown, but the secondary battery of one aspect of the present invention is not limited thereto. Other materials may be used for the negative electrode, such as graphite and lithium titanate. The properties of the positive electrode and the positive electrode active material of one aspect of the present invention, such as that the crystal structure is not easily broken even when charge and discharge are repeated and good cycle characteristics can be obtained, are not affected by the material of the negative electrode. Also, for the secondary battery of one aspect of the present invention, a case may be shown where charge and discharge are performed at a voltage higher than a general charging voltage of about 4.7 V with lithium as the counter electrode, but charge and discharge may be performed at a lower voltage. When charging and discharging at a lower voltage, it is expected that the cycle characteristics will be even better than those shown in this specification and the like.

[0043] In addition, in this specification and the like, unless otherwise specified, the charging voltage and the discharging voltage refer to the voltage in the case of lithium as the counter electrode. However, even for the same positive electrode, the charge and discharge voltages of the secondary battery vary depending on the material used for the negative electrode. For example, since the potential of graphite is about 0.1 V (vs Li / Li + ), in the case of a negative electrode of graphite, the charge and discharge voltages are about 0.1 V lower than in the case of lithium as the counter electrode.

[0044] (Embodiment 1) In this embodiment, the positive electrode active material of one aspect of the present invention will be described with reference to FIGS. 1 to 9.

[0045] FIG. 1A is a cross-sectional view of a positive electrode active material 100 which is one aspect of the present invention. Enlarged views of the vicinity of A-B in FIG. 1A are shown in FIGS. 1B, 1C1 and 1C2. Enlarged views of the vicinity of C-D in FIG. 1A are shown in FIGS. 2A1, 2A2, 2B1, 2B2, 2C1 and 2C2.

[0046] As shown in FIGS. 1A to 2C2, the positive electrode active material 100 has a surface layer portion 100a and an interior 100b. The boundary between the surface layer portion 100a and the interior 100b is shown by a broken line in these figures. Also, a part of the crystal grain boundary is shown by a one-dot broken line in FIG. 1A. Further, the positive electrode active material 100 has an outermost surface layer 100c in a part of the surface layer portion 100a. The boundary of the outermost surface layer 100c in the surface layer portion 100a is shown by a two-dot broken line in FIG. 1B.

[0047] In this specification and the like, the region from the surface to the inside of the positive electrode active material up to about 10 nm is referred to as the surface layer portion 100a. The surface formed by cracks and the like may also be referred to as the surface. The surface layer portion 100a may also be referred to as the vicinity of the surface, or the vicinity of the surface region or the shell. Further, the region deeper than the surface layer portion 100a of the positive electrode active material is referred to as the inside 100b. The inside 100b may also be referred to as the inside region or the core. Further, among the surface layer portions 100a of the positive electrode active material, the region from the surface to 3 nm toward the inside 100b is referred to as the outermost surface layer 100c.

[0048] <Each region and lattice constant> The positive electrode active material 100 according to one aspect of the present invention preferably has a crystal structure in both the surface layer portion 100a and the inside 100b. Further, the lattice constant of the a-axis of the crystal structure of the surface layer portion 100a is preferably larger than the lattice constant A of the a-axis of the crystal structure of the inside 100b. Also, the lattice constant of the b-axis of the crystal structure of the surface layer portion 100a is preferably larger than the lattice constant B of the b-axis of the crystal structure of the inside 100b. Also, the lattice constant of the c-axis of the crystal structure of the surface layer portion 100a is preferably larger than the lattice constant C of the c-axis of the crystal structure of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b.

[0049] Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. surface Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. surface Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. surface Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b. core Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystal structure. Also, the lattice constant A of the a-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the a-axis of the surface layer portion 100a and the lattice constant A of the a-axis of the inside 100b. Also, the lattice constant B of the b-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the b-axis of the surface layer portion 100a and the lattice constant B of the b-axis of the inside 100b. Also, the lattice constant C of the c-axis of the crystal structure of the outermost surface layer 100c is preferably larger than the lattice constant of the c-axis of the surface layer portion 100a and the lattice constant C of the c-axis of the inside 100b.

[0050] Also, the lattice constant A of the a-axis of the outermost surface layer surface minus the lattice constant A of the a-axis of the interior core is defined as Δ A Similarly, the lattice constant C of the c-axis of the outermost surface layer surface minus the lattice constant C of the c-axis of the interior core is defined as Δ C At this time, it is preferable that Δ A is larger than Δ C

[0051] Also, as shown in the following formulas (1) and (2), the value obtained by dividing Δ A by A core is defined as the change rate R A Also, the value obtained by dividing Δ C by C core is defined as the change rate R C

[0052]

Equation

[0053]

Equation

[0054] At this time, the change rate R A is preferably greater than 0 and less than or equal to 0.12, more preferably greater than or equal to 0.05 and less than or equal to 0.07. Or preferably greater than 0 and less than or equal to 0.07. Or preferably greater than or equal to 0.05 and less than or equal to 0.12.

[0055] Also, the change rate R C is preferably greater than 0 and less than or equal to 0.18, more preferably greater than or equal to 0.09 and less than or equal to 0.12. Or preferably greater than 0 and less than or equal to 0.12. Or preferably greater than or equal to 0.09 and less than or equal to 0.18.

[0056] The lattice constants are calculated as belonging to the same space group in order to facilitate comparison between regions.

[0057] ​​For example, it is preferable to calculate using a model in which all regions have the same crystal structure, the same space group, and the same number of atoms per unit cell. For example, a layered rock salt type of R-3m cannot be described by Fm-3m, but it is possible to represent a rock salt type of Fm-3m by R-3m. Therefore, for example, when the internal 100b has the characteristics of a layered rock salt type of R-3m and the surface layer 100a and the outermost surface layer 100c have the characteristics of a rock salt type of Fm-3m, if the lattice constants are calculated using the crystal structure of the layered rock salt type of space group R-3m as a model for all of them, it becomes easy to compare the lattice constants of each region. In the crystal structure of the layered rock salt type of space group R-3m, the lengths of the a-axis and the b-axis are equal. Therefore, hereinafter, regarding the layered rock salt type of space group R-3m, the a-axis will be described as a representative.

[0058] Also, even if it is difficult to describe all regions with the same space group, when the anion packing is almost common, it can be said that models with the same number of anions have equivalent symmetry. In this case, instead of the lattice constant, the distance between anions may be used for comparison between regions. For example, the rock salt type, the layered rock salt type, and the spinel type all have an anion cubic close-packed structure (ccp arrangement), and it can be said that they have a structure with almost common anion packing. In such cases, even if the space groups are different, they can be compared as having similar symmetries. The distance between anions can be calculated, for example, from the result of Rietveld analysis of the XRD pattern.

[0059] Hereinafter, an example of using the crystal structure of the layered rock salt type of space group R-3m as a model for calculating the lattice constants of each region will be described, but it is not limited to this. It is preferable to select an optimal structure according to the material of the positive electrode active material 100. For example, it is preferable to adopt the crystal structure that occupies the largest volume among the crystal structures of the positive electrode active material 100. In addition to the layered rock salt type, crystal structures such as the rock salt type, the spinel type, and the olivine type can be used.

[0060] The determination of whether the surface layer 100a, the interior 100b, and the outermost surface layer 100c have a crystal structure, and the determination of the lattice constant when they have a crystal structure can be performed by, for example, cross-sectional TEM, cross-sectional STEM, and electron beam diffraction such as selected area electron diffraction and nano-beam electron diffraction.

[0061] If a regular atomic arrangement can be observed in a cross-sectional TEM image, a cross-sectional STEM image, etc., it can be said that it has a crystal structure. Also, if a diffraction pattern having regular spots can be observed in an electron beam diffraction image, etc., it can be said that it has a crystal structure.

[0062] Selected area electron diffraction enables analysis of the crystal structure in a region as small as about 20 nm, and nano-beam electron diffraction enables analysis of an even smaller region of about 1 nm, which is suitable for determining the lattice constants of the surface layer 100a and the outermost surface layer 100c.

[0063] However, in these electron beam diffraction methods, measurement errors may occur due to distortion of the camera length, etc. Therefore, it is preferable that the significant figures of the lattice constant obtained by the electron beam diffraction method be two digits. Alternatively, the lattice constant obtained from these electron beam diffraction methods may be corrected with reference to the lattice constant obtained from powder XRD or literature values, etc.

[0064] For example, in the positive electrode active material 100, the interior 100b occupies most of the volume. Therefore, it can be considered that the lattice constant of the entire positive electrode active material 100 obtained by powder XRD is equal to the lattice constant of the interior 100b obtained by electron beam diffraction. Thus, the corrected lattice constants of the surface layer 100a and the outermost surface layer 100c can be obtained from the ratio of the lattice constants of the interior 100b, the surface layer 100a, and the outermost surface layer 100c obtained by electron beam diffraction and the lattice constant obtained from powder XRD.

[0065] It is preferable that the concentration of the additive element described later in the surface layer 100a is higher than that in the interior 100b. Also, it is preferable that the additive has a concentration gradient. Further, when there are a plurality of additive elements, it is preferable that the depth of the concentration peak from the surface differs depending on the additive element.

[0066] For example, an additive element X preferably has a concentration gradient that increases from the interior 100b toward the surface, as shown by the gradation in FIG. 1C1. Examples of the additive element X that preferably has such a concentration gradient include magnesium, fluorine, titanium, silicon, phosphorus, boron, calcium, and the like.

[0067] Another additive element Y preferably has a concentration gradient and a concentration peak in a region deeper than that in FIG. 1C1, as shown by the gradation in FIG. 1C2. The concentration peak may be present in the surface layer portion 100a or may be deeper than the surface layer portion 100a. It is preferable to have a concentration peak in a region other than the outermost surface layer 100c. For example, it is preferable to have a peak in a region from 5 nm to 30 nm from the surface. Examples of the additive element Y that preferably has such a concentration gradient include aluminum and manganese.

[0068] Further, due to the above-described concentration gradient of the additive element, it is preferable that the crystal structure continuously changes from the interior 100b toward the surface layer portion 100a and the outermost surface layer 100c.

[0069] For example, the case where the interior 100b has a layered rock salt-type crystal structure will be described. One of the characteristics of the layered rock salt-type crystal structure is that it has alternating transition metal M layers and lithium layers between the cubic closest-packed structures of anions. Therefore, in the interior 100b, when observed by cross-sectional TEM or the like, the transition metal M layers with a large atomic number observed with strong brightness and the lithium layers observed with weak brightness are alternately observed. Note that oxygen and fluorine of the anions both have a small atomic number, so they are observed with a brightness similar to that of lithium. These elements with a small atomic number may not form distinct bright spots and may only have a slight difference in brightness from the background.

[0070] In this specification and the like, when there are layers observed with strong brightness and layers observed with weak brightness alternately in a cross-sectional TEM image or the like, it is considered to have the characteristics of a layered rock salt-type crystal structure. Note that this characteristic is observed when viewed from a direction perpendicular to the c-axis in the layered rock salt-type crystal structure. Even if it has a layered rock salt-type crystal structure, this characteristic may not be observed when viewed from other directions.

[0071] On the other hand, in the outermost surface layer 100c, since the concentration of the additive element is high, the additive element enters a part of the lithium sites. Since the lithium sites are surrounded by anions such as oxygen, metal elements such as magnesium and aluminum among the additives are likely to enter. Also, a transition metal M, for example, cobalt may enter a part of the lithium sites. Since all of these metals have an atomic number larger than that of lithium, they are observed with stronger brightness than lithium in a cross-sectional TEM or the like.

[0072] Note that an additive element or lithium may also enter a part of the transition metal M sites. In this case, it is observed with weaker brightness than the transition metal M in a cross-sectional TEM or the like.

[0073] When such a large number of cation substitutions occur, it comes to have the characteristics of a rock salt-type crystal structure in which there is no difference between the lithium sites and the transition metal sites. Having the characteristics of a rock salt-type crystal structure can also be said to suggest that the additive element is present at a sufficient concentration. When the additive element is present at a sufficient concentration, elution of the transition metal M and detachment of oxygen that may occur during charging at a high voltage can be suppressed. Therefore, the battery characteristics, especially the continuous charge resistance, can be improved, and a secondary battery with high safety and reliability can be obtained.

[0074] On the other hand, it is preferable that the outermost surface layer 100c also has the characteristics of the same layered rock salt-type crystal structure as the interior 100b. This is because if the surface is covered only with a rock salt-type crystal structure, the diffusion path of lithium is inhibited, and there is a risk that the internal resistance will increase during charge and discharge. For the same reason, it is preferable that the characteristics of the rock salt-type crystal structure are limited to about 3 nm from the surface.

[0075] Therefore, it is preferable that the outermost surface layer 100c has both the characteristics of a layered rock salt crystal structure and the characteristics of a rock salt crystal structure. That is, the outermost surface layer 100c has a layered rock salt crystal structure having layers observed with strong brightness and layers observed with weak brightness alternately in a cross-sectional TEM image or the like, and further preferably has a metal with an atomic number larger than that of lithium at a part of the lithium sites.

[0076] When the additive element is present at a preferable concentration at a part of the lithium sites of the outermost surface layer 100c, the brightness of the lithium site layer becomes 3% or more and 60% or less of the brightness of the transition metal M site layer in the cross-sectional TEM image. More preferably, it becomes 4% or more and 50% or less. Even more preferably, it becomes 6% or more and 40% or less. Or 3% or more and 50% or less is preferable. Or 3% or more and 40% or less is preferable. Or 4% or more and 60% or less is preferable. Or 4% or more and 40% or less is preferable. Or 6% or more and 60% or less is preferable. Or 6% or more and 50% or less is preferable. Note that the lithium site layer and the transition metal M site layer used for comparison preferably have a width of 5 nm or more in parallel with the arrangement of the transition metal M.

[0077] The brightness in cross-sectional TEM or the like can be calculated, for example, by integrating the brightness of the pixels in the dark field image of the cross-sectional TEM. Similarly, the brightness of the transition metal M site layer and the lithium site layer can be calculated by integrating the brightness of the pixels in parallel with these layers. Specifically, the image may be converted into a grayscale with black being brightness 0 and white being brightness 255, and the brightness of each pixel may be integrated one column at a time. Further, in order to facilitate the comparison of the brightness of the metal site layer, correction may be made to exclude the brightness derived from elements with a small atomic number such as oxygen.

[0078] Note that the sample for cross-sectional TEM or the like has a thickness of about 20 nm to 200 nm. Therefore, when there are irregularities on the surface of the positive electrode active material 100, accurate brightness may not be obtained in the shallow part from the surface. Therefore, when comparing the brightness, it is necessary to perform the comparison between parts where the brightness is stably obtained. For example, when the maximum value of the brightness of the transition metal M site layer is set to 1, the transition metal M site layer having a brightness of 0.7 or more is considered to have a stable brightness.

[0079] In the present specification and the like, the surface of the positive electrode active material 100 in a cross-sectional TEM image, a cross-sectional STEM image, etc. is defined as the surface on which a metal element having an atomic number larger than that of lithium is first observed. More specifically, it is defined as the nucleus of a metal element having an atomic number larger than that of lithium, that is, the point where the peak of brightness in a cross-sectional TEM image or the like exists.

[0080] Note that at least a part of the outermost surface layer 100c of the positive electrode active material may have both the characteristics of the layered rock salt type crystal structure and the characteristics of the rock salt type crystal structure as described above. If the crystal plane exposed on the surface of the positive electrode active material is substantially parallel to the (001) plane of R-3m, the above characteristics are likely to be observed. However, depending on the crystal plane, these characteristics may not be clearly observed in some cases. Therefore, the brightness ratio between the transition metal site layer and the lithium site layer does not necessarily have to be within the above range.

[0081] Also, the characteristics of the layered rock salt type crystal structure and the rock salt type crystal structure can be analyzed by electron beam diffraction.

[0082] The rock salt type has one type of cation and high symmetry. On the other hand, the layered rock salt type has two types of cations arranged regularly, so it has lower symmetry than the rock salt type. Therefore, there are twice as many bright spots corresponding to a specific plane orientation as in the rock salt type.

[0083] Also, in the case of a crystal structure having both the characteristics of the rock salt type and the layered rock salt type, in the diffraction image, there is a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are alternately arranged. The bright spots common to the rock salt type and the layered rock salt type have strong brightness, and the bright spots generated only in the layered rock salt type have weak brightness.

[0084] Note that it is preferable that the transition metal M, particularly cobalt and nickel, is uniformly dissolved in the entire positive electrode active material 100. When the concentration of a part of the transition metal M, for example, nickel, is low, it may be below the detection limit in analysis such as XPS.

[0085] For example, if the number of nickel atoms is 2 atomic % or less compared to the number of cobalt atoms, the nickel in the lithium composite oxide will be 0.5 atomic % or less. On the other hand, the detection limits of XPS and EDX are approximately 1 atomic %. Therefore, if nickel is uniformly dissolved in the entire positive electrode active material 100, it can be below the detection limit by analysis methods such as XPS and EDX. In this case, being below the detection limit can also be said to suggest that the concentration of nickel is 1 atomic % or less and that it is dissolved in the entire positive electrode active material 100.

[0086] On the other hand, if ICP-MS or the like is used, it is possible to quantify transition metals even if the concentration is 1 atomic % or less.

[0087] Note that the positive electrode active material 100 may have an additive element that is widely dissolved in the interior 100b thereof and has no concentration gradient. Also, a part of the transition metal M contained in the positive electrode active material 100, for example, manganese, may have a concentration gradient that becomes higher from the interior 100b toward the surface.

[0088] <Contained elements> The positive electrode active material 100 contains lithium, a transition metal M, oxygen, and an additive element. The positive electrode active material 100 may be said to be a composite oxide represented by LiMO2 to which an additive element is added. However, the positive electrode active material according to one aspect of the present invention only needs to have the crystal structure of a lithium composite oxide represented by LiMO2, and its composition is not strictly limited to Li:M:O = 1:1:2.

[0089] As the transition metal M included in the positive electrode active material 100, it is preferable to use a metal capable of forming a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, only cobalt may be used as the transition metal included in the positive electrode active material 100, only nickel may be used, two types of cobalt and manganese, or two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. That is, the positive electrode active material 100 can have a composite oxide containing lithium and the transition metal M, such as lithium cobaltate, lithium nickelate, lithium cobaltate in which part of cobalt is substituted with manganese, lithium cobaltate in which part of cobalt is substituted with nickel, and lithium nickel-manganese-cobaltate.

[0090] In particular, when 75 atomic% or more, preferably 90 atomic% or more, more preferably 95 atomic% or more of cobalt is used as the transition metal M included in the positive electrode active material 100, there are many advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics. Further, when the transition metal M has nickel in addition to cobalt in the above range, it may suppress the deviation of the layered structure composed of octahedrons of cobalt and oxygen. Therefore, it is preferable because the crystal structure may become more stable particularly in the charged state at high temperature.

[0091] Note that the transition metal M does not necessarily have to contain manganese. By using the positive electrode active material 100 that substantially does not contain manganese, the above advantages such as relatively easy synthesis, easy handling, and excellent cycle characteristics may become greater. The weight of manganese contained in the positive electrode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0092] On the other hand, when 33 atomic% or more, preferably 60 atomic% or more, more preferably 80 atomic% or more of nickel is used as the transition metal M included in the positive electrode active material 100, the raw material may be less expensive compared to the case where there is a large amount of cobalt, and the charge and discharge capacity per unit weight may increase, which is preferable.

[0093] Note that the transition metal M does not necessarily contain nickel.

[0094] As the additive element included in the positive electrode active material 100, it is preferable to use at least one of magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. These additive elements may stabilize the crystal structure of the positive electrode active material 100 as described later. That is, the positive electrode active material 100 can have lithium cobaltate added with magnesium and fluorine, lithium cobaltate added with magnesium, fluorine, and titanium, lithium nickel-cobaltate added with magnesium and fluorine, lithium cobalt-aluminate added with magnesium and fluorine, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate added with magnesium and fluorine, lithium nickel-manganese-cobaltate added with magnesium and fluorine, and the like. In the present specification and the like, the additive element may be referred to as a mixture, a part of a raw material, an impurity element, or the like.

[0095] Note that the additive element does not necessarily contain magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, or boron.

[0096] In the positive electrode active material 100 according to one aspect of the present invention, even when lithium is removed from the positive electrode active material 100 by charging, the surface layer portion 100a having a high concentration of the additive, that is, the outer peripheral portion of the particle, reinforces the layered structure composed of octahedrons of cobalt and oxygen so that it does not break.

[0097] Further, the concentration gradient of the additive element is preferably the same gradient throughout the surface layer portion 100a of the positive electrode active material 100. It may also be said that it is preferable that the reinforcement derived from the high impurity concentration is homogeneously present in the surface layer portion 100a. Even if there is reinforcement in a part of the surface layer portion 100a, if there is a portion without reinforcement, stress may concentrate on the portion without reinforcement. When stress concentrates on a part of the particles, defects such as cracks may occur therefrom, leading to cracking of the positive electrode active material and a decrease in charge-discharge capacity.

[0098] In this specification and the like, "homogeneous" refers to a phenomenon in which, in a solid composed of a plurality of elements (for example, A, B, C), a certain element (for example, A) is distributed with similar characteristics in a specific region. It is sufficient that the concentrations of the elements in the specific regions are substantially the same. For example, the difference in the element concentrations between the specific regions may be within 10%. Examples of the specific region include the surface layer portion, the surface, the convex portion, the concave portion, the interior, and the like.

[0099] However, it is not necessarily required that the concentration gradient of all the additive elements be homogeneous throughout the entire surface layer portion 100a of the positive electrode active material 100. Examples of the distribution of the additive element X in the vicinity of C-D in FIG. 1A are shown in FIGS. 2A1, 2B1, and 2C1. Examples of the distribution of the additive element Y in the vicinity of C-D are shown in FIGS. 2A2, 2B2, and 2C2.

[0100] For example, as shown in FIGS. 2A1 and 2A2, there may be a region of the surface layer portion 100a where neither the additive element X nor the additive element Y is present. Also, as shown in FIGS. 2B1 and 2B2, there may be a region where the additive element X is present but the additive element Y is not present. Further, as shown in FIGS. 2C1 and 2C2, there may be a region where the additive element X is not present but the additive element Y is present. The additive element Y in FIG. 2C2 preferably has a peak in a region that is not the outermost surface layer, similar to FIG. 1C2. For example, it preferably has a peak in a region exceeding 3 nm and up to 30 nm from the surface.

[0101] Further, the positive electrode active material 100 may have an embedded portion 102 and a convex portion 103 as shown in FIG. 1A. An additive element may be present in the embedded portion 102 and the convex portion 103 at a higher concentration than in the interior 100b or the surface layer portion 100a.

[0102] The positive electrode active material 100 may have a concave portion, a crack, a depression, a V-shaped cross section, etc. These are one of the defects, and when charging and discharging are repeated, elution of the transition metal M, collapse of the crystal structure, cracking of the main body, detachment of oxygen, etc. may occur. However, if the embedded portion 102 is present so as to embed these, elution of the transition metal M, etc. can be suppressed. Therefore, the positive electrode active material 100 with excellent reliability and cycle characteristics can be obtained.

[0103] Further, the positive electrode active material 100 may have a convex portion 103 as a region where the additive element is unevenly distributed.

[0104] As described above, if the additive element contained in the positive electrode active material 100 is excessive, it may have an adverse effect on the insertion and extraction of lithium. Also, when used as a secondary battery, it may cause an increase in internal resistance, a decrease in charge and discharge capacity, etc. On the other hand, if it is insufficient, it may not be distributed throughout the surface layer portion 100a, and the effect of suppressing the deterioration of the crystal structure may become insufficient. Thus, the impurity element (also referred to as an additive element) needs to be at an appropriate concentration in the positive electrode active material 100, but its adjustment is not easy.

[0105] Therefore, if the positive electrode active material 100 has a region where the impurity element is unevenly distributed, a part of the excessive impurities is removed from the interior 100b of the positive electrode active material 100, and an appropriate impurity concentration can be obtained in the interior 100b. Thereby, an increase in internal resistance, a decrease in charge and discharge capacity, etc. when used as a secondary battery can be suppressed. Suppressing an increase in the internal resistance of the secondary battery is an extremely preferable characteristic particularly in high-rate charging and discharging, for example, charging and discharging at 2C or more.

[0106] In the case of the positive electrode active material 100 having a region where impurity elements are unevenly distributed, it is permissible to mix impurities to some extent in excess in the manufacturing process. Therefore, the margin in production becomes wider, which is preferable.

[0107] In this specification and the like, uneven distribution means that the concentration of a certain element is different from others. It may also be referred to as segregation, precipitation, non-uniformity, bias, high concentration or low concentration.

[0108] Magnesium, which is one of the additive elements X, is divalent and is more stable in the lithium site than in the transition metal site in the layered rock salt-type crystal structure, so it easily enters the lithium site. When magnesium exists in the lithium site of the surface layer portion 100a at an appropriate concentration, it is easy to maintain the layered rock salt-type crystal structure. In addition, the presence of magnesium can suppress the release of oxygen around magnesium during high-voltage charging. Magnesium is preferable as long as it is at an appropriate concentration and does not adversely affect the insertion and extraction of lithium accompanying charge and discharge. However, if it is excessive, there is a risk of adversely affecting the insertion and extraction of lithium. Therefore, as described later, it is preferable that the surface layer portion 100a has a higher concentration of the transition metal M than, for example, magnesium.

[0109] Aluminum, which is one of the additive elements Y, is trivalent and can exist in the transition metal site in the layered rock salt-type crystal structure. Aluminum can suppress the elution of surrounding cobalt. In addition, since aluminum has a strong binding force with oxygen, it can suppress the release of oxygen around aluminum. Therefore, when the positive electrode active material 100 has aluminum as an additive element, the crystal structure is less likely to collapse even when charge and discharge are repeated.

[0110] Fluorine is a monovalent anion. When a part of oxygen is replaced by fluorine in the surface layer portion 100a, the lithium detachment energy becomes smaller. This is because the change in the valence of cobalt ions accompanying lithium detachment is from trivalent to tetravalent when there is no fluorine, and from divalent to trivalent when there is fluorine, due to the different redox potentials. Therefore, when a part of oxygen is replaced by fluorine in the surface layer portion 100a of the positive electrode active material 100, it can be said that the detachment and insertion of lithium ions near fluorine occur smoothly. Therefore, when used in a secondary battery, it is preferable because the charge-discharge characteristics, rate characteristics, etc. are improved.

[0111] Titanium oxide is known to have super hydrophilicity. Therefore, by using the positive electrode active material 100 having titanium oxide in the surface layer portion 100a, the wettability with respect to a highly polar solvent may be improved. When used as a secondary battery, the contact at the interface between the positive electrode active material 100 and the highly polar electrolyte may be improved, and there is a possibility of suppressing an increase in internal resistance.

[0112] As the charging voltage of the secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material according to one aspect of the present invention has a stable crystal structure even at a high voltage. Since the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress a decrease in the charge-discharge capacity accompanying repeated charge and discharge.

[0113] In addition, a short circuit in the secondary battery not only causes problems in the charging operation and discharging operation of the secondary battery, but also may cause heat generation and ignition. In order to realize a safe secondary battery, it is preferable that the short circuit current is suppressed even at a high charging voltage. The positive electrode active material 100 according to one aspect of the present invention suppresses the short circuit current even at a high charging voltage. Therefore, a secondary battery having both a high charge-discharge capacity and safety can be achieved.

[0114] The concentration gradient of the additive element can be evaluated using, for example, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like. Among EDX measurements, the measurement while scanning within a region and the two-dimensional evaluation within the region is called EDX surface analysis. Also, the measurement while linearly scanning and the evaluation of the distribution of atomic concentration within the positive electrode active material particles is called line analysis. Furthermore, in some cases, the data of a linear region extracted from the surface analysis of EDX is also called line analysis. Also, the measurement without scanning a certain region is called point analysis.

[0115] By EDX surface analysis (for example, elemental mapping), the concentration of the additive element can be quantitatively analyzed in the surface layer portion 100a including the outermost surface layer 100c of the positive electrode active material 100, the interior 100b, the vicinity of the crystal grain boundary, and the like. Also, by EDX line analysis, the concentration distribution and the maximum value of the additive element can be analyzed.

[0116] When performing EDX line analysis on the positive electrode active material 100 having magnesium as an additive element, the peak of the magnesium concentration in the surface layer portion 100a is preferably present up to a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, that is, in the outermost surface layer 100c, more preferably present up to a depth of 1 nm, and even more preferably present up to a depth of 0.5 nm.

[0117] Also, in the positive electrode active material 100 having magnesium and fluorine as additive elements, the distribution of fluorine preferably overlaps with the distribution of magnesium. Therefore, when performing EDX line analysis, the peak of the fluorine concentration in the surface layer portion 100a is preferably present up to a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, that is, in the outermost surface layer 100c, more preferably present up to a depth of 1 nm, and even more preferably present up to a depth of 0.5 nm.

[0118] Note that not all additive elements need to have the same concentration distribution. For example, when the positive electrode active material 100 has aluminum as an additive element, it is preferably distributed slightly differently from magnesium and fluorine as described above. For example, when performing EDX line analysis, it is preferable that the peak of the magnesium concentration is closer to the surface than the peak of the aluminum concentration in the surface layer portion 100a. For example, the peak of the aluminum concentration is preferably present at a depth of 0.5 nm or more and 50 nm or less from the surface of the positive electrode active material 100 toward the center, more preferably present at a depth of 5 nm or more and 30 nm or less. Or it is preferably present at a depth of 0.5 nm or more and 30 nm or less. Or it is preferably present at a depth of 5 nm or more and 50 nm or less.

[0119] When performing line analysis or surface analysis on the positive electrode active material 100, the ratio (I / M) of the number of atoms of the impurity element I to the transition metal M in the surface layer portion 100a is preferably 0.05 or more and 1.00 or less. Further, when the impurity element is titanium, the ratio (Ti / M) of the number of atoms of titanium to the transition metal M is preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less. When the impurity element is magnesium, the ratio (Mg / M) of the number of atoms of magnesium to the transition metal M is preferably 0.4 or more and 1.5 or less, more preferably 0.45 or more and 1.00 or less. When the impurity element is fluorine, the ratio (F / M) of the number of atoms of fluorine to the transition metal M is preferably 0.05 or more and 1.5 or less, more preferably 0.3 or more and 1.00 or less.

[0120] The surface of the positive electrode active material 100 in the EDX line analysis result can be estimated, for example, as follows. For an element uniformly present in the interior 100b of the positive electrode active material 100, such as a transition metal M such as oxygen or cobalt, the point at which the detected amount in the interior 100b becomes half is defined as the surface.

[0121] Since the positive electrode active material 100 is a composite oxide, it is preferable to estimate the surface using the detected amount of oxygen. Specifically, first, the average value O of the oxygen concentration is obtained from a region where the detected amount of oxygen in the interior 100b is stable. aveDetermine this. At this time, if oxygen O considered to be due to chemisorption or background is detected outside the surface, background when it is detected, subtract O background from the measured value to obtain the average value O ave of the oxygen concentration. This average value O ave of 1 / 2, that is, 1 / 2O ave The measurement point showing the measured value closest to can be estimated to be the surface of the positive electrode active material.

[0122] Also, the surface can be estimated using the transition metal M included in the positive electrode active material 100. For example, when 95% or more of the transition metal M is cobalt, the surface can be estimated in the same manner as above using the detected amount of cobalt. Or it can be estimated in the same manner using the sum of the detected amounts of a plurality of transition metals M. The detected amount of the transition metal M is suitable for estimating the surface in that it is hardly affected by chemisorption.

[0123] When performing line analysis or surface analysis on the positive electrode active material 100, the ratio (I / M) of the additive element I to the transition metal M in the vicinity of the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less. Or preferably 0.20 or more and 0.30 or less. Or preferably 0.20 or more and 0.20 or less. Or preferably 0.25 or more and 0.50 or less. Or preferably 0.25 or more and 0.20 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.

[0124] For example, when the additive element is magnesium and the transition metal M is cobalt, the atomic ratio (Mg / Co) of magnesium to cobalt is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less. Or preferably 0.020 or more and 0.30 or less. Or preferably 0.020 or more and 0.20 or less. Or preferably 0.025 or more and 0.50 or less. Or preferably 0.025 or more and 0.20 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.

[0125] Further, the positive electrode active material 100 may have a film on at least a part of its surface. An example of the positive electrode active material 100 having a film 104 is shown in FIG. 3.

[0126] The film 104 is preferably formed, for example, by deposition of decomposition products of the electrolytic solution accompanying charge and discharge. Particularly when high-voltage charging is repeated, it is expected that the charge-discharge cycle characteristics will be improved by having a film derived from the electrolytic solution on the surface of the positive electrode active material 100. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing elution of the transition metal M. The film 104 preferably has, for example, carbon, oxygen, and fluorine. Further, when LiBOB and / or SUN (succinonitrile) is used in a part of the electrolytic solution, a high-quality film is easily obtained. Therefore, it is more preferable that the film 104 has boron and / or nitrogen because it is likely to form a high-quality film. Also, the film 104 does not have to cover all of the positive electrode active material 100.

[0127] <Crystal structure> Materials having a layered rock salt-type crystal structure such as lithium cobalt oxide (LiCoO2) are known to have a high discharge capacity and be excellent as the positive electrode active material of a secondary battery. Examples of materials having a layered rock salt-type crystal structure include composite oxides represented by LiMO2.

[0128] In transition metal compounds, it is known that the strength of the Jahn-Teller effect varies depending on the number of electrons in the d orbitals of the transition metal.

[0129] In compounds having nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charge and discharge are performed at a high voltage in LiNiO2, there is a concern that the crystal structure may collapse due to distortion. It is suggested that the influence of the Jahn-Teller effect is small in LiCoO2, and it may be more excellent in resistance when charged at a high voltage, which is preferable.

[0130] The cathode active material will be described with reference to FIGS. 4 to 7. FIGS. 4 to 7 describe the case where cobalt is used as the transition metal M included in the cathode active material.

[0131] <Conventional cathode active material> The cathode active material shown in FIG. 6 is lithium cobalt oxide (LiCoO2) to which fluorine and magnesium are not added by the manufacturing method described later. As described in Non-Patent Document 1, Non-Patent Document 2, etc., the crystal structure of the lithium cobalt oxide shown in FIG. 6 changes depending on the depth of charge.

[0132] As shown in FIG. 6, lithium cobalt oxide at a charge depth of 0 (discharged state) has a region having a crystal structure of space group R-3m, lithium occupies an octahedral site, and there are three CoO2 layers in the unit cell. Therefore, this crystal structure may be referred to as an O3-type crystal structure. Note that the CoO2 layer refers to a structure in which octahedral structures in which oxygen is six-coordinated to cobalt are continuously arranged in a plane in a state of sharing edges.

[0133] When the charge depth is 1, it has a crystal structure of space group P-3m1, and there is one CoO2 layer in the unit cell. Therefore, this crystal structure may be referred to as an O1-type crystal structure.

[0134] Lithium cobalt oxide when the charge depth is about 0.8 has a crystal structure of space group R-3m. This structure can also be said to be a structure in which structures of CoO2 such as P-3m1 (O1) and structures of LiCoO2 such as R-3m (O3) are alternately stacked. Therefore, this crystal structure may be referred to as an H1-3 type crystal structure. In reality, in the H1-3 type crystal structure, the number of cobalt atoms per unit cell is twice that of other structures. However, in this specification including FIG. 6, for easy comparison with other crystal structures, the H1-3 type crystal structure will be shown in a figure in which the c-axis is halved with respect to the unit cell.

[0135] 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 oxygen atoms respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, as will be described later, the O3’ type crystal structure of one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen is different in the case of the O3’ structure and the H1-3 type structure, and the change from the O3 structure in the O3’ structure is smaller than that in the H1-3 type structure. The selection of which unit cell is more preferable for representing the crystal structure of the positive electrode active material can be made, for example, by selecting so that the value of GOF (goodness of fit) is smaller in the Rietveld analysis of XRD.

[0136] When high-voltage charging such that the charging voltage becomes 4.6 V or more based on the redox potential of lithium metal, or deep charging such that the depth of charge becomes 0.8 or more, and discharging are repeated, lithium cobaltate repeats a change in crystal structure (that is, a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m (O3) structure in the discharged state.

[0137] However, the shift of the CoO2 layer is large between these two crystal structures. As shown by the dotted line and arrow in Fig. 6, in the H1-3 type crystal structure, the CoO2 layer is largely shifted from R-3m (O3). Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0138] Furthermore, the volume difference is also large. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.0% or more.

[0139] In addition, a structure in which CoO2 layers such as P-3m1(O1) having an H1-3 type crystal structure are continuous is likely to be unstable.

[0140] Therefore, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is because when the crystal structure collapses, the sites where lithium can exist stably decrease, and it becomes difficult for lithium to be inserted and removed.

[0141] <The positive electrode active material of one embodiment of the present invention> ≪Crystal structure≫ The positive electrode active material 100 of one embodiment of the present invention can reduce the shift of the CoO2 layer during repeated high-voltage charge and discharge. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. In addition, 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, when the positive electrode active material of one embodiment of the present invention holds a high-voltage charged state, a short circuit may be less likely to occur. In such a case, the safety is further improved, which is preferable.

[0142] In the positive electrode active material of one embodiment of the present invention, the change in the crystal structure and the volume difference per the same number of transition metal M atoms in a fully discharged state and a state charged at a high voltage are small.

[0143] The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown in FIG. 4. The positive electrode active material 100 is a composite oxide having lithium, cobalt as the transition metal M, and oxygen. In addition to the above, it is preferable to have magnesium as an additive. It is also preferable to have fluorine as an additive.

[0144] The crystal structure at a charge depth of 0 (discharge state) in Fig. 4 is the same R-3m (O3) as in Fig. 6. On the other hand, the positive electrode active material 100 has crystals with a structure different from the H1-3 type crystal structure when fully charged. This structure belongs to the space group R-3m and is not a spinel-type crystal structure, but ions such as cobalt and magnesium occupy the oxygen six-coordination positions, and the arrangement of cations has symmetry similar to that of the spinel type. Also, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, in this specification, etc., this structure is referred to as an O3'-type crystal structure or a pseudo-spinel-type crystal structure. Thus, the O3'-type crystal structure may be rephrased as a pseudo-spinel-type crystal structure. Also, in both the case of the O3-type crystal structure and the O3'-type crystal structure, it is preferable that magnesium is thinly present between the CoO2 layers, that is, in the lithium sites. Also, it is preferable that fluorine is randomly and thinly present in the oxygen sites.

[0145] Note that in the O3'-type crystal structure, light elements such as lithium may occupy the oxygen four-coordination positions, and in this case as well, the arrangement of ions has symmetry similar to that of the spinel type.

[0146] Also, in Fig. 4, it is shown that lithium exists at all lithium sites with the same probability, but the positive electrode active material 100 of one aspect of the present invention is not limited to this. It may be present biasedly at some lithium sites. For example, like Li 0.5 CoO2 belonging to the space group P2 / m, it may be present at some aligned lithium sites. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0147] Also, it can be said that the O3'-type crystal structure is a crystal structure similar to the CdCl2-type crystal structure although it has Li randomly between the layers. This crystal structure similar to the CdCl2 type is close to the crystal structure when lithium nickelate is charged to a charge depth of 0.94 (Li 0.06 NiO2), but it is known that pure lithium cobaltate or a layered rock salt-type positive electrode active material containing a large amount of cobalt usually does not take this crystal structure.

[0148] In the positive electrode active material 100 according to one aspect of the present invention, changes in the crystal structure when charging at a high voltage and a large amount of lithium is released are suppressed more than in conventional positive electrode active materials. For example, as shown by the dotted line in FIG. 4, in these crystal structures, there is almost no shift in the CoO2 layer.

[0149] More specifically, the positive electrode active material 100 according to one aspect of the present invention has high crystal structure stability even when the charging voltage is high. For example, in a conventional positive electrode active material, there is a region of a charging voltage that forms an H1-3 type crystal structure, for example, a region of a charging voltage that can maintain the crystal structure of R-3m (O3) even at a voltage of about 4.6 V with reference to the potential of lithium metal, and further, in a region where the charging voltage is increased, for example, there is a region where an O3' type crystal structure can be taken even at a voltage of about 4.65 V to 4.7 V with reference to the potential of lithium metal. Further increasing the charging voltage may finally result in the observation of an H1-3 type crystal. Also, even when the charging voltage is lower (for example, when the charging voltage is 4.5 V or more and less than 4.6 V with reference to the potential of lithium metal), the positive electrode active material 100 according to one aspect of the present invention may take an O3' type crystal structure.

[0150] Therefore, in the positive electrode active material 100 according to one aspect of the present invention, the crystal structure is less likely to collapse even when charging and discharging are repeated at a high voltage.

[0151] In addition, when using graphite as the negative electrode active material in a secondary battery, for example, the voltage of the secondary battery decreases by the potential of graphite compared to the above. The potential of graphite is about 0.05 V to 0.2 V with reference to the potential of lithium metal. Therefore, for example, even when the voltage of a secondary battery using graphite as the negative electrode active material is 4.3 V or more and 4.5 V or less, the positive electrode active material 100 according to one aspect of the present invention can maintain the crystal structure of R-3m (O3), and in a region where the charging voltage is further increased, for example, when the voltage of the secondary battery exceeds 4.5 V and is 4.6 V or less, it can take an O3' type crystal structure. Furthermore, even when the charging voltage is lower, for example, when the voltage of the secondary battery is 4.2 V or more and less than 4.3 V, the positive electrode active material 100 according to one aspect of the present invention may take an O3' type crystal structure.

[0152] The crystal structure of the O3’ type can be shown by the coordinates of cobalt and oxygen in the unit cell as Co(0,0,0.5), O(0,0,x), where 0.20 ≤ x ≤ 0.25.

[0153] Additives such as magnesium, which are randomly and thinly present in the CoO2 layer, that is, the lithium site, have the effect of suppressing the displacement of the CoO2 layer when charged at a high voltage. Therefore, when magnesium is present between the CoO2 layers, it is likely to form an O3’ type crystal structure. Therefore, it is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100 of one aspect of the present invention. Further, in order to distribute magnesium throughout the particles, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 100 of one aspect of the present invention.

[0154] However, if the temperature of the heat treatment is too high, cation mixing occurs and the possibility of additives such as magnesium entering the cobalt site increases. Magnesium present in the cobalt site has no effect of maintaining the R-3m structure during high-voltage charging. Furthermore, if the temperature of the heat treatment is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0155] Therefore, it is preferable to add a fluorine compound to lithium cobaltate before the heat treatment for distributing magnesium throughout the particles. Adding a fluorine compound causes a decrease in the melting point of lithium cobaltate. By lowering the melting point, it becomes easier to distribute magnesium throughout the particles at a temperature at which cation mixing is less likely to occur. Furthermore, the presence of the fluorine compound is expected to improve the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolyte.

[0156] Note that if the magnesium concentration is increased to a value equal to or higher than the desired value, the effect on the stabilization of the crystal structure may be reduced. This is presumably because magnesium enters not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the cathode active material according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less, more preferably more than 0.01 and less than 0.04, and even more preferably about 0.02 times the number of atoms of the transition metal M. Alternatively, it is preferably 0.001 times or more and less than 0.04. Alternatively, it is preferably 0.01 or more and 0.1 or less. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the cathode active material using ICP-MS or the like, or may be based on the value of the raw material formulation in the process of producing the cathode active material.

[0157] One or more metals selected from, for example, nickel, aluminum, manganese, titanium, vanadium, and chromium may be added to lithium cobaltate as a metal other than cobalt (hereinafter referred to as metal Z). In particular, it is preferable to add one or more of nickel and aluminum. Manganese, titanium, vanadium, and chromium may tend to stably take a tetravalent state, and may contribute highly to structural stability. By adding metal Z, in the cathode active material according to one embodiment of the present invention, for example, the crystal structure may become more stable in the charged state at a high voltage. Here, in the cathode active material according to one embodiment of the present invention, metal Z is preferably added at a concentration that does not significantly change the crystallinity of lithium cobaltate. For example, it is preferably an amount that does not exhibit the Jahn-Teller effect or the like described above.

[0158] As shown in the legend in FIG. 4, transition metals such as nickel and manganese and aluminum are preferably present at the cobalt sites, but a part thereof may be present at the lithium sites. Magnesium is preferably present at the lithium sites. A part of oxygen may be substituted with fluorine.

[0159] As the magnesium concentration of the positive electrode active material of one embodiment of the present invention increases, the charge-discharge capacity of the positive electrode active material may decrease. As a factor, for example, when magnesium enters the lithium site, the amount of lithium contributing to charge-discharge decreases. In addition, excessive magnesium may generate a magnesium compound that does not contribute to charge-discharge. When the positive electrode active material of one embodiment of the present invention has nickel as metal Z in addition to magnesium, the charge-discharge capacity per unit weight and per unit volume may be increased. When the positive electrode active material of one embodiment of the present invention has aluminum as metal Z in addition to magnesium, the charge-discharge capacity per unit weight and per unit volume may be increased. When the positive electrode active material of one embodiment of the present invention has nickel and aluminum in addition to magnesium, the charge-discharge capacity per unit weight and per unit volume may be increased.

[0160] Hereinafter, the concentrations of elements such as magnesium and metal Z contained in the positive electrode active material of one embodiment of the present invention are represented by the number of atoms.

[0161] The number of atoms of nickel contained in 100 of the positive electrode active material of one embodiment of the present invention is preferably more than 0% and 7.5% or less, preferably 0.05% or more and 4% or less, preferably 0.1% or more and 2% or less, more preferably 0.2% or more and 1% or less of the number of atoms of cobalt. Or preferably more than 0% and 4% or less. Or preferably more than 0% and 2% or less. Or preferably 0.05% or more and 7.5% or less. Or preferably 0.05% or more and 2% or less. Or preferably 0.1% or more and 7.5% or less. Or preferably 0.1% or more and 4% or less. 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 GD-MS, ICP-MS, etc., or may be based on the value of the raw material formulation in the process of producing the positive electrode active material.

[0162] The nickel contained in the above concentration is likely to be uniformly dissolved in the entire positive electrode active material 100, and thus particularly contributes to the stabilization of the crystal structure of the interior 100b. Further, when divalent nickel is present in the interior 100b, divalent additive elements such as magnesium, which are randomly and thinly present in the lithium sites in the vicinity thereof, may be more stably present. Therefore, elution of magnesium can be suppressed even after charge and discharge at a high voltage. Therefore, the charge-discharge cycle characteristics can be improved. Thus, having both the effect of nickel in the interior 100b and the effects of magnesium, aluminum, titanium, fluorine, etc. in the surface layer portion 100a is extremely effective for stabilizing the crystal structure during high-voltage charging.

[0163] The number of aluminum atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.05% or more and 4% or less, preferably 0.1% or more and 2% or less, more preferably 0.3% or more and 1.5% or less of the number of cobalt atoms. Or preferably 0.05% or more and 2% or less. Or preferably 0.1% or more and 4% or less. The concentration of aluminum shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using GD-MS, ICP-MS, etc., or may be based on the value of the blending of raw materials in the process of producing the positive electrode active material.

[0164] The positive electrode active material according to one embodiment of the present invention preferably has element W, and preferably uses phosphorus as element W. Further, the positive electrode active material according to one embodiment of the present invention more preferably has a compound containing phosphorus and oxygen.

[0165] When the positive electrode active material according to one embodiment of the present invention has a compound containing element W, short circuits may be suppressed when maintaining a charged state at a high voltage.

[0166] When the positive electrode active material according to one embodiment of the present invention has phosphorus as element X, hydrogen fluoride generated by the decomposition of the electrolytic solution may react with phosphorus, and the hydrogen fluoride concentration in the electrolytic solution may decrease.

[0167] When the electrolyte contains LiPF6, hydrogen fluoride may be generated by hydrolysis. In addition, hydrogen fluoride may also be generated by the reaction between PVDF used as a component of the positive electrode and an alkali. By reducing the hydrogen fluoride concentration in the charge liquid, corrosion of the current collector and peeling of the film may be suppressed in some cases. In addition, a decrease in adhesiveness due to gelation or insolubilization of PVDF may be suppressed in some cases.

[0168] When the positive electrode active material of one aspect of the present invention has magnesium in addition to element X, the stability in a high-voltage charged state is extremely high. When element X is phosphorus, the number of phosphorus atoms is preferably 1% or more and 20% or less, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less of the number of cobalt atoms. Or preferably 1% or more and 10% or less. Or preferably 1% or more and 8% or less. Or preferably 2% or more and 20% or less. Or preferably 2% or more and 8% or less. Or preferably 3% or more and 20% or less. Or preferably 3% or more and 10% or less. In addition, the number of magnesium atoms is preferably 0.1% or more and 10% or less, more preferably 0.5% or more and 5% or less, and even more preferably 0.7% or more and 4% or less of the number of cobalt atoms. Or preferably 0.1% or more and 5% or less. Or preferably 0.1% or more and 4% or less. Or preferably 0.5% or more and 10% or less. Or preferably 0.5% or more and 4% or less. Or preferably 0.7% or more and 10% or less. Or preferably 0.7% or more and 5% or less. The concentrations of phosphorus and magnesium shown here may be values obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS, or may be based on the values of the raw material formulation in the process of producing the positive electrode active material.

[0169] The positive electrode active material may have cracks. When phosphorus, more specifically, a compound containing, for example, phosphorus and oxygen, is present inside the positive electrode active material having the crack as the surface, the progress of the crack may be suppressed in some cases.

[0170] ≪Surface layer part≫ Magnesium is preferably distributed throughout the particles of the positive electrode active material 100 of one embodiment of the present invention. In addition to this, it is preferable that the magnesium concentration in the surface layer portion 100a is higher than the average of the whole particles. Or, it is preferable that the magnesium concentration in the surface layer portion 100a is higher than the concentration in the interior 100b. For example, it is preferable that the magnesium concentration in the surface layer portion 100a measured by XPS or the like is higher than the average magnesium concentration of the whole particles measured by ICP-MS or the like. Or, it is preferable that the magnesium concentration in the surface layer portion 100a measured by EDX surface analysis or the like is higher than the magnesium concentration in the interior 100b.

[0171] Further, when the positive electrode active material 100 of one embodiment of the present invention contains one or more metals selected from elements other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal in the surface layer portion 100a is higher than the average of the whole particles. Or, it is preferable that the concentration of the metal in the surface layer portion 100a is higher than that in the interior 100b. For example, it is preferable that the concentration of the element other than cobalt in the surface layer portion 100a measured by XPS or the like is higher than the concentration of the element in the average of the whole particles measured by ICP-MS or the like. Or, it is preferable that the concentration of the element other than cobalt in the surface layer portion 100a measured by EDX surface analysis or the like is higher than the concentration of the element other than cobalt in the interior 100b.

[0172] Unlike the inside of the crystal, the surface layer portion is in a state where the bonds are broken, and during charging, lithium escapes from the surface, so it is a portion where the lithium concentration is likely to be lower than that in the interior. Therefore, it is a portion that is likely to become unstable and the crystal structure is likely to collapse. If the magnesium concentration in the surface layer portion 100a is high, the change in the crystal structure can be more effectively suppressed. Also, when the magnesium concentration in the surface layer portion 100a is high, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution will be improved.

[0173] Also, it is preferable that the concentration of fluorine in the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention is higher than the average of the whole particle. Or, it is preferable that the fluorine concentration in the surface layer portion 100a is higher than the concentration in the interior 100b. By the presence of fluorine in the surface layer portion 100a which is the region in contact with the electrolytic solution, the corrosion resistance against hydrofluoric acid can be effectively improved.

[0174] Thus, it is preferable that the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention has a composition different from that of the interior 100b, with a higher concentration of additive elements such as magnesium and fluorine than the interior 100b. Also, it is preferable that the composition has a crystal structure stable at room temperature (25°C). Therefore, the surface layer portion 100a may have a crystal structure different from that of the interior 100b. For example, at least a part of the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention may have a rock salt-type crystal structure. Also, when the surface layer portion 100a and the interior 100b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 100a and the interior 100b are substantially the same.

[0175] The anions of the layered rock salt-type crystal and the rock salt-type crystal take a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions of the O3'-type crystal take a cubic close-packed structure. When these are in contact, there are crystal planes where the orientations of the cubic close-packed structures composed of anions are aligned. However, since the space groups of the layered rock salt-type crystal and the O3'-type crystal are R-3m, different from the space groups of the rock salt-type crystal Fm-3m (the space group of a general rock salt-type crystal) and Fd-3m (the space group of the rock salt-type crystal having the simplest symmetry), the Miller indices of the crystal planes satisfying the above conditions are different between the layered rock salt-type crystal and the O3'-type crystal and the rock salt-type crystal. In this specification, in the case of a layered rock salt-type crystal, an O3'-type crystal, and a rock salt-type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are substantially the same.

[0176] The approximate alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc. can also be used as materials for determination. In TEM images, etc., the arrangement of cations and anions can be observed as a repetition of bright and dark lines. When the orientations of the cubic close-packed structures in the layered rock salt-type crystal and the rock salt-type crystal are aligned, it can be observed that the angle formed by the repetition of bright and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that in TEM images, etc., light elements such as oxygen and fluorine may not be clearly observable, but in that case, the alignment can be determined by the arrangement of metal elements.

[0177] However, if the surface layer portion 100a consists only of MgO or has only a structure in which MgO and CoO(II) are solid-solved, the insertion and extraction of lithium become difficult. Therefore, the surface layer portion 100a should have at least cobalt and also have lithium in the discharged state, and it is necessary to have a path for the insertion and extraction of lithium. Also, it is preferable that the concentration of cobalt is higher than that of magnesium.

[0178] Also, the additive element X is preferably located in the surface layer portion 100a of the particles of the positive electrode active material 100 according to one aspect of the present invention. For example, the positive electrode active material 100 according to one aspect of the present invention may be covered with a film having the additive element X.

[0179] ≪Grain boundary≫ In addition to the distribution described above, it is more preferable that a part of the additive element included in the positive electrode active material 100 according to one aspect of the present invention is segregated at the grain boundaries 101 as shown in FIG. 1A.

[0180] More specifically, it is preferable that the magnesium concentration at the grain boundaries 101 of the positive electrode active material 100 and in the vicinity thereof is higher than that in other regions of the interior 100b. Also, it is preferable that the fluorine concentration at the grain boundaries 101 and in the vicinity thereof is higher than that in other regions of the interior 100b.

[0181] The grain boundary 101 is one of the surface defects. Therefore, it is as unstable as the particle surface and is likely to initiate a change in the crystal structure. Thus, if the magnesium concentration at the grain boundary 101 and in its vicinity is high, the change in the crystal structure can be more effectively suppressed.

[0182] Also, when the magnesium and fluorine concentrations at the grain boundary and in its vicinity are high, even if cracks occur along the grain boundary 101 of the particles of the positive electrode active material 100 of one aspect of the present invention, the magnesium and fluorine concentrations increase near the surface generated by the cracks. Therefore, the corrosion resistance against hydrofluoric acid can be enhanced even in the positive electrode active material after cracks occur.

[0183] In this specification and the like, the vicinity of the grain boundary 101 shall refer to the region up to about 10 nm from the grain boundary. Also, the grain boundary refers to a plane with a change in the atomic arrangement and can be observed in an electron microscope image. Specifically, it shall refer to a location where the angle formed by the repetition of bright and dark lines in the electron microscope image exceeds 5 degrees.

[0184] <<Particle size>> If the particle size of the positive electrode active material 100 of one aspect of the present invention is too large, there are problems such as difficulty in lithium diffusion and the surface of the active material layer becoming too rough when coated on the current collector. On the other hand, if it is too small, there are also problems such as difficulty in supporting the active material layer during coating on the current collector and an excessive reaction with the electrolytic solution. Therefore, the median diameter (D50) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Or preferably 1 μm or more and 40 μm or less. Or preferably 1 μm or more and 30 μm or less. Or preferably 2 μm or more and 100 μm or less. Or preferably 2 μm or more and 30 μm or less. Or preferably 5 μm or more and 100 μm or less. Or preferably 5 μm or more and 40 μm or less.

[0185] <Analysis method> Whether the positive electrode active material is the positive electrode active material 100 of one embodiment of the present invention that exhibits an O3'-type crystal structure when charged at a high voltage can be determined by analyzing the positively charged electrode using XRD, electron beam diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, compare the high crystallinity and crystal orientation, analyze the periodic lattice strain and crystallite size, and sufficient accuracy can be obtained by measuring the positive electrode obtained by disassembling the secondary battery as it is. etc., is preferable.

[0186] The positive electrode active material 100 of one embodiment of the present invention is characterized in that there is little change in the crystal structure between the charged state and the discharged state at a high voltage as described above. A material in which a crystal structure with a large change from the discharged state occupies 50 wt% or more in the charged state at a high voltage is not preferable because it cannot withstand the charge and discharge at a high voltage. And it should be noted that the target crystal structure may not be obtained only by adding an additive element. For example, even though they have something in common in that they are lithium cobaltate having magnesium and fluorine, there are cases where the O3'-type crystal structure is 60 wt% or more and the H1-3 type crystal structure occupies 50 wt% or more in the charged state at a high voltage. Also, at a predetermined voltage, the O3'-type crystal structure may become almost 100 wt%, and when the predetermined voltage is further increased, the H1-3 type crystal structure may occur. Therefore, in order to determine whether it is the positive electrode active material 100 of one embodiment of the present invention, analysis of the crystal structure including XRD is necessary.

[0187] However, the positive electrode active material in the charged state or the discharged state at a high voltage may change its crystal structure when exposed to the atmosphere. For example, it may change from the O3'-type crystal structure to the H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0188] <<Charging method>> To determine whether a certain composite oxide is the cathode active material 100 of an aspect of the present invention, high-voltage charging can be carried out, for example, by fabricating a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and then charging it.

[0189] More specifically, for the cathode, a slurry obtained by mixing a cathode active material, a conductive additive, and a binder can be used, which is coated on an aluminum foil cathode current collector.

[0190] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery is different from that of the cathode. Unless otherwise specified, the voltage and potential in this specification and the like refer to the potential of the cathode.

[0191] As the electrolyte in the electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) can be used. For the electrolyte solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of EC:DEC = 3:7 and 2 wt% vinylene carbonate (VC) can be used.

[0192] A 25-μm-thick polypropylene can be used for the separator.

[0193] For the cathode can and the anode can, those made of stainless steel (SUS) can be used.

[0194] The coin cell fabricated under the above conditions is charged at a constant current of 0.5C at an arbitrary voltage (for example, 4.6V, 4.65V, or 4.7V), and then charged at a constant voltage until the current value reaches 0.01C. Note that 1C can be set to 137 mA / g or 200 mA / g. The temperature is 25°C. After charging in this way, if the coin cell is disassembled in a glove box under an argon atmosphere to take out the cathode, a cathode active material charged at a high voltage can be obtained. When performing various analyses thereafter, it is preferable to seal it in an argon atmosphere to suppress the reaction with external components. For example, XRD can be performed by enclosing it in a sealed container under an argon atmosphere.

[0195] ≪XRD≫ The apparatus and conditions for XRD measurement are not particularly limited. For example, measurement can be carried out under the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: CuKα ray Output: 40KV, 40mA Slit system: Div. Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scan Measurement range (2θ): 15° (degree) or more and 90° or less Step width (2θ): Set to 0.01° Counting time: 1 second / step Sample stage rotation: 15 rpm

[0196] When the measurement sample is powder, it can be set by methods such as putting it in a glass sample folder or sprinkling the sample on a silicon non-reflecting plate coated with grease. When the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape and set according to the measurement surface required by the apparatus.

[0197] The ideal powder XRD patterns calculated from the models of the O3’-type crystal structure and the H1-3 type crystal structure by CuKα1 ray are shown in FIGS. 5 and 7. Also shown for comparison are the ideal XRD patterns calculated from the crystal structures of LiCoO2 (O3) with a charge depth of 0 and CoO2 (O1) with a charge depth of 1. The patterns of LiCoO2 (O3) and CoO2 (O1) were created using Reflex Powder Diffraction, which is one of the modules of Materials Studio (BIOVIA), from the crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 4). The range of 2θ was set from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562×10 -10m and λ2 were not set, and the 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 estimated from the XRD pattern of the positive electrode active material of one aspect of the present invention, fitted using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0198] As shown in Fig. 5, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° or more and 19.50° or less) and 2θ = 45.55 ± 0.10° (45.45° or more and 45.65° or less). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° or more and 19.40° or less) and 2θ = 45.55 ± 0.05° (45.50° or more and 45.60° or less). However, as shown in Fig. 7, peaks do not appear at these positions in the H1-3 type crystal structure and CoO2 (P-3m1, O1). Therefore, it can be said that the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in the state charged at a high voltage is a characteristic of the positive electrode active material 100 of one aspect of the present invention.

[0199] This can also mean that the positions where the XRD diffraction peaks appear are close in the crystal structure at a charge depth of 0 and the crystal structure when charged at a high voltage. More specifically, it can be said that the difference in the positions where peaks appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less, in two or more, more preferably three or more, of the main diffraction peaks of both.

[0200] Note that the cathode active material 100 according to one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage, but not all of the particles need to have an O3'-type crystal structure. It may contain other crystal structures or a part thereof may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a cathode active material with excellent cycle characteristics can be obtained sufficiently.

[0201] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when Rietveld analysis is performed, the O3'-type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0202] In addition, the crystallite size of the O3'-type crystal structure of the particles of the cathode active material only decreases to about 1 / 10 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as those of the cathode before charge and discharge, a clear peak of the O3'-type crystal structure can be confirmed after high-voltage charging. On the other hand, in simple LiCoO2, even if a part has a structure similar to the O3'-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0203] In the cathode active material according to one embodiment of the present invention, as described above, it is preferable that the influence of the Jahn-Teller effect is small. The cathode active material according to one embodiment of the present invention preferably has a layered rock salt-type crystal structure and mainly contains cobalt as a transition metal. Further, in the cathode active material according to one embodiment of the present invention, within a range where the influence of the Jahn-Teller effect is small, in addition to cobalt, the above-described metal Z may be contained.

[0204] In the cathode active material, using XRD analysis, the range of lattice constants where the influence of the Jahn-Teller effect is presumed to be small is considered.

[0205] Figure 8 shows the results of calculating the lattice constants of the a-axis and c-axis using XRD when the cathode active material of one embodiment of the present invention has a layered rock salt-type crystal structure and contains cobalt and nickel. Figure 8A shows the results for the a-axis, and Figure 8B shows the results for the c-axis. The XRD patterns used for these calculations are powders after the synthesis of the cathode active material and before being incorporated into the cathode. The nickel concentration on the horizontal axis indicates the concentration of nickel when the sum of the atomic numbers of cobalt and nickel is 100%. The cathode active material was prepared in the same manner as the preparation method of Figure 11 described later, except that no aluminum source was used. The nickel concentration indicates the concentration of nickel when the sum of the atomic numbers of cobalt and nickel in the cathode active material is 100%.

[0206] Figure 9 shows the results of estimating the lattice constants of the a-axis and c-axis using XRD when the cathode active material of one embodiment of the present invention has a layered rock salt-type crystal structure and contains cobalt and manganese. Figure 9A shows the results for the a-axis, and Figure 9B shows the results for the c-axis. The lattice constants shown in Figure 9 are powders after the synthesis of the cathode active material and are based on XRD measurements before being incorporated into the cathode. The manganese concentration on the horizontal axis indicates the concentration of manganese when the sum of the atomic numbers of cobalt and manganese is 100%. The cathode active material was prepared according to the preparation method of Figure 11 described later, except that a manganese source was used instead of a nickel source and no aluminum source was used. The manganese concentration indicates the concentration of manganese when the sum of the atomic numbers of cobalt and manganese in step S21 is 100%.

[0207] Figure 8C shows the value (a-axis / c-axis) obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis for the cathode active material whose lattice constant results are shown in Figures 8A and 8B. Figure 9C shows the value (a-axis / c-axis) obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis for the cathode active material whose lattice constant results are shown in Figures 9A and 9B.

[0208] As shown in Fig. 8C, when the nickel concentration is 5% and 7.5%, the a-axis / c-axis shows a tendency to change significantly, and the strain of the a-axis is increasing. This strain may be the Jahn-Teller strain. It is suggested that an excellent positive electrode active material with small Jahn-Teller strain can be obtained when the nickel concentration is less than 7.5%.

[0209] Next, as shown in Fig. 9A, when the manganese concentration is 5% or more, the behavior of the change in lattice constant is different, suggesting that it does not follow Vegard's law. Therefore, it is suggested that the crystal structure is different when the manganese concentration is 5% or more. Thus, the manganese concentration is preferably, for example, 4% or less.

[0210] Note that the above ranges of nickel concentration and manganese concentration do not necessarily apply to the surface layer portion 100a. That is, in the surface layer portion 100a, it may be higher than the above concentrations.

[0211] From the above, when considering the preferable range of the lattice constant, in the positive electrode active material of one aspect of the present invention, in the layered rock salt type crystal structure of the particles of the positive electrode active material in a state where charge and discharge are not performed or in a discharged state, which can be estimated from the XRD pattern, the lattice constant of the a-axis is larger than 2.814×10 -10 m and smaller than 2.817×10 -10 m, and the lattice constant of the c-axis is larger than 14.05×10 -10 m and smaller than 14.07×10 -10 m. The state where charge and discharge are not performed may be, for example, the powder state before producing the positive electrode of the secondary battery.

[0212] Alternatively, in the layered rock salt type crystal structure of the particles of the positive electrode active material in a state where charge and discharge are not performed or in a discharged state, the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is preferably larger than 0.20000 and smaller than 0.20049.

[0213] Alternatively, when XRD analysis is performed on the layered rock salt-type crystal structure of the particles of the positive electrode active material in a state where charging and discharging are not performed or in a discharged state, a first peak may be observed at 2θ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2θ of 38.00° or more and 38.80° or less.

[0214] Note that the peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100. The crystal structures of the surface layer portion 100a, the outermost surface layer 100c, etc. can be analyzed by electron beam diffraction or the like of the cross section of the positive electrode active material 100.

[0215] ≪XPS≫ In X-ray photoelectron spectroscopy (XPS), since analysis of a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less) is possible, the concentration of each element can be quantitatively analyzed for about half of the region of the surface layer portion 100a. Also, if narrow scan analysis is performed, the bonding state of the elements can be analyzed. Note that the quantitative accuracy of XPS is often about ±1 atomic %, and the detection limit is about 1 atomic % depending on the element.

[0216] When XPS analysis is performed on the positive electrode active material 100 of one aspect of the present invention, the number of atoms of the additive element is preferably 1.6 times or more and 6.0 times or less the number of atoms of the transition metal M, and more preferably 1.8 times or more and less than 4.0 times. When the additive is magnesium and the transition metal M is cobalt, the number of atoms of magnesium is preferably 1.6 times or more and 6.0 times or less the number of atoms of cobalt, and more preferably 1.8 times or more and less than 4.0 times. Also, the number of atoms of a halogen such as fluorine is preferably 0.2 times or more and 6.0 times or less the number of atoms of the transition metal M, and more preferably 1.2 times or more and 4.0 times or less.

[0217] When performing XPS analysis, for example, monochromatized aluminum can be used as the X-ray source. Also, the take-off angle can be, for example, 45°. For example, measurement can be performed with the following apparatus and conditions. Measuring apparatus: QuanteraII manufactured by PHI X-ray source: Monochromatic Al (1486.6 eV) Detection area: 100 μmφ Detection depth: Approximately 4 - 5 nm (extraction angle 45°) Measurement spectrum: Wide scan, narrow scan for each detected element

[0218] When XPS analysis is performed on the positive electrode active material 100 of one aspect of the present invention, the peak indicating the binding energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This is a value different from both 685 eV, which is the binding energy of lithium fluoride, and 686 eV, which is the binding energy of magnesium fluoride. That is, when the positive electrode active material 100 of one aspect of the present invention contains fluorine, it is preferably a bond other than lithium fluoride and magnesium fluoride.

[0219] Furthermore, when XPS analysis is performed on the positive electrode active material 100 of one aspect of the present invention, the peak indicating the binding energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably about 1303 eV. This is a value different from 1305 eV, which is the binding energy of magnesium fluoride, and is a value close to the binding energy of magnesium oxide. That is, when the positive electrode active material 100 of one aspect of the present invention contains magnesium, it is preferably a bond other than magnesium fluoride.

[0220] Additive elements that are preferably present in a large amount in the surface layer portion 100a, such as magnesium and aluminum, preferably have a higher concentration measured by XPS or the like than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry), GD-MS (glow discharge mass spectrometry), or the like.

[0221] When magnesium and aluminum are processed to expose their cross-sections and the cross-sections are analyzed using TEM-EDX, it is preferable that the concentration of the surface layer portion 100a is higher than the concentration of the interior 100b. The processing can be performed, for example, by FIB (Focused Ion Beam).

[0222] In the analysis by XPS (X-ray photoelectron spectroscopy), the number of magnesium atoms is preferably 0.4 times or more and 1.5 times or less the number of cobalt atoms. On the other hand, the ratio of the number of magnesium atoms Mg / Co by the analysis of ICP-MS is preferably 0.001 or more and 0.06 or less.

[0223] On the other hand, it is preferable that nickel contained in the transition metal M is not unevenly distributed in the surface layer portion 100a but is distributed throughout the entire positive electrode active material 100. However, this is not the case when there is a region where the above-described additive elements are unevenly distributed.

[0224] ≪ESR≫ As described above, in the positive electrode active material of one embodiment of the present invention, it is preferable to have cobalt and nickel as transition metals and magnesium as an additive element. As a result, a part of Co 3+ is replaced by Ni 2+ and a part of Li + is preferably replaced by Mg 2+ . As Li + is replaced by Mg 2+ , the Ni 2+ may be reduced to Ni 3+ . Also, a part of Li + is replaced by Mg 2+ , and accordingly, the nearby Co 3+ may be reduced to Co 2+ . Further, a part of Co 3+ is replaced by Mg 2+ , and accordingly, the nearby Co 3+ may be oxidized to Co 4+ .

[0225] Therefore, the positive electrode active material which is one embodiment of the present invention is Ni 2+, Ni 3+ , Co 2+ and Co 4+ It is preferable to have any one or more of them. Also, Ni per unit weight of the positive electrode active material 2+ , Ni 3+ , Co 2+ and Co 4+ The spin density caused by any one or more of them is preferably 2.0×10 17 spins / g or more and 1.0×10 21 spins / g or less. By using the positive electrode active material having the above-mentioned spin density, the crystal structure in the charged state is particularly preferably stabilized. Note that if the magnesium concentration is too high, Ni 2+ , Ni 3+ , Co 2+ and Co 4+ The spin density caused by any one or more of them may be lowered.

[0226] The spin density in the positive electrode active material can be analyzed, for example, by using the electron spin resonance method (ESR: Electron Spin Resonance).

[0227] ≪EPMA≫ EPMA (electron probe microanalysis) enables quantification of elements. In the case of surface analysis, the distribution of each element can be analyzed.

[0228] In EPMA, a region from the surface to a depth of about 1 μm is analyzed. Therefore, the concentration of each element may be different from the measurement results using other analytical methods. For example, when the surface analysis of the positive electrode active material 100 is performed, the concentration of the additive present in the surface layer may be lower than the result of XPS. Also, the concentration of the additive present in the surface layer may be higher than the result of ICP-MS or the value of the raw material formulation in the process of manufacturing the positive electrode active material.

[0229] When performing EPMA surface analysis on the cross-section of the positive electrode active material 100 according to one embodiment of the present invention, it is preferable that the additive elements have a concentration gradient in which the concentration increases from the inside to the surface layer portion. More specifically, as shown in FIG. 1C1, magnesium, fluorine, titanium, and silicon preferably have a concentration gradient that increases from the inside to the surface. Also, as shown in FIG. 2C2, aluminum preferably has a concentration peak in a region deeper than the peak of the concentration of the above elements. The peak of the aluminum concentration may be present in the surface layer portion or may be deeper than the surface layer portion.

[0230] It is assumed that the surface and surface layer portion of the positive electrode active material according to one embodiment of the present invention do not contain carbonic acid, hydroxy groups, etc. chemisorbed after the production of the positive electrode active material. It is also assumed that it does not contain the electrolytic solution, binder, conductive material, or compounds derived therefrom attached to the surface of the positive electrode active material. Therefore, when quantifying the elements contained in the positive electrode active material, correction may be made to exclude carbon, hydrogen, excessive oxygen, excessive fluorine, etc. that can be detected by surface analysis such as XPS and EPMA.

[0231] ≪Surface roughness and specific surface area≫ The surface of the positive electrode active material 100 according to one embodiment of the present invention is preferably smooth and has few irregularities. The fact that the surface is smooth and has few irregularities is one factor indicating that the distribution of additive elements in the surface layer portion 100a is good.

[0232] The fact that the surface is smooth and has few irregularities can be determined, for example, from the 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, etc.

[0233] For example, as follows, the smoothness of the surface can be quantified from the cross-sectional SEM image of the positive electrode active material 100.

[0234] First, the positive electrode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, a protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image using image processing software. For example, after performing Gaussian blur (σ = 2), binarization is performed. Further, interface extraction is performed using image processing software. Furthermore, the interface line between the protective film or the like and the positive electrode active material 100 is selected using an automatic selection tool or the like, and the data is extracted into spreadsheet software or the like. Using the functions of spreadsheet software or the like, correction is performed from the regression curve (quadratic regression), a parameter for calculating roughness is obtained from the data after slope correction, and the root mean square surface roughness (RMS) with the standard deviation calculated is obtained. Also, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm on the outer periphery of the particles.

[0235] On the particle surface of the positive electrode active material 100 of the present 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 of the root mean square surface roughness (RMS).

[0236] Note that the image processing software for performing noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. Also, the spreadsheet software or the like is not particularly limited, but for example, Microsoft Office Excel can be used.

[0237] Also, for example, the actual specific surface area A measured by the gas adsorption method by 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 between them.

[0238] The ideal specific surface area A i is calculated and obtained assuming that the diameter of all particles is the same as D50, the weight is the same, and the shape is an ideal sphere.

[0239] The median diameter D50 can be measured by a particle size distribution meter using the laser diffraction / scattering method or the like. The specific surface area can be measured by, for example, a specific surface area measuring device using the gas adsorption method by the constant volume method or the like.

[0240] The positive electrode active material 100 according to one aspect of the present invention has an ideal specific surface area A obtained from the median diameter D50 i and an actual specific surface area A R with a ratio A R / A i of 2.1 or less, which is preferable.

[0241] This embodiment can be used in combination with other embodiments.

[0242] (Embodiment 2) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described with reference to FIGS. 10 to 14.

[0243] <Step S11> As step S11 in FIG. 10, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) having lithium, transition metal M, and oxygen.

[0244] As the lithium source, for example, lithium carbonate, lithium fluoride, lithium hydroxide, lithium oxide, or the like can be used.

[0245] As the transition metal M, 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. For example, at least one of manganese, cobalt, and nickel can be used. That is, only cobalt may be used as the transition metal M source, only nickel may be used, two types of cobalt and manganese, or two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used.

[0246] When using a metal capable of forming a layered rock salt type composite oxide, it is preferable to use a mixing ratio of cobalt, manganese, and nickel within a range capable of adopting a layered rock salt type crystal structure. Further, within a range capable of adopting a layered rock salt type crystal structure, aluminum may be added to these transition metals.

[0247] As the transition metal M source, oxides, hydroxides, etc. of the above-mentioned metals exemplified as the transition metal M can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. As the manganese source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0248] <Step S12> Next, as step S12, the above lithium source and transition metal M source are mixed. The mixing can be carried out dry or wet. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the grinding media, for example.

[0249] <Step S13> Next, as step S13, the material mixed above is heated. This step may be referred to as firing or first heating for the purpose of distinguishing it from the subsequent heating step. The heating is preferably carried out at 800°C or higher and less than 1100°C, more preferably at 900°C or higher and 1000°C or lower, and even more preferably about 950°C. Or 800°C or higher and 1000°C or lower is preferable. Or 900°C or higher and 1100°C or lower is preferable. If the temperature is too low, there is a risk that the decomposition and melting of the lithium source and the transition metal M source will be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal responsible for the oxidation-reduction reaction used as the transition metal M, evaporation of lithium, etc. For example, when cobalt is used as the transition metal M, defects where cobalt becomes divalent may occur.

[0250] The heating time can be, for example, 1 hour or more and 100 hours or less, preferably 2 hours or more and 20 hours or less. Or preferably 1 hour or more and 20 hours or less. Or preferably 2 hours or more and 100 hours or less. A shorter heating time is more productive and preferred. The firing is preferably carried out in an atmosphere with little water such as dry air (for example, dew point -50°C or lower, more preferably -100°C or lower). For example, heating is carried out at 1000°C for 10 hours, the temperature rise is preferably 200°C / h, and the flow rate of the dry atmosphere is preferably 10 L / min. Thereafter, the heated material can be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably 10 hours or more and 50 hours or less.

[0251] However, the cooling to room temperature in step S13 is not essential. If there is no problem in performing the subsequent steps S41 to S44, the cooling may be to a temperature higher than room temperature.

[0252] <Step S14> Next, as step S14, the material fired above is recovered to obtain a composite oxide (LiMO2) having lithium, transition metal M, and oxygen. Specifically, lithium cobaltate, lithium manganate, lithium nickelate, lithium cobaltate in which part of cobalt is substituted with manganese, lithium cobaltate in which part of cobalt is substituted with nickel, or lithium nickel-manganese-cobaltate, etc. are obtained.

[0253] Also, as step S14, a composite oxide having lithium, transition metal M, and oxygen synthesized in advance may be used. In this case, steps S11 to S13 can be omitted.

[0254] For example, as a pre-synthesized composite oxide, lithium cobaltate particles (trade name: Celseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used. This is lithium cobaltate with a median diameter (D50) of approximately 12 μm, and in impurity analysis by glow discharge mass spectrometry (GD-MS), the magnesium concentration and fluorine concentration are 50 ppm wt or less, the calcium concentration, aluminum concentration, and silicon concentration are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentration of elements other than lithium, cobalt, and oxygen is 150 ppm wt or less.

[0255] Alternatively, lithium cobaltate particles (trade name: Celseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This is lithium cobaltate with a median diameter (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentration of elements other than lithium, cobalt, and oxygen is about the same as or less than that of C-10N.

[0256] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobaltate particles (Celseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0257] <Step S21> Next, as step S21, as materials for the mixture 902, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared. It is also preferable to prepare a lithium source.

[0258] As the fluorine source, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), sodium hexafluoroaluminate (Na3AlF6), etc. can be used. Further, the fluorine source is not limited to a solid. For example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. can be used and mixed into the atmosphere in the heating process described later. Also, a plurality of fluorine sources may be mixed and used. Among them, lithium fluoride is preferable because it has a relatively low melting point of 848 °C among solid fluorine sources and is easily melted in the annealing process described later.

[0259] As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used.

[0260] As the lithium source, for example, lithium fluoride, lithium carbonate can be used. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Also, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0261] In this embodiment, lithium fluoride LiF is prepared as a fluorine source, and magnesium fluoride MgF₂ is prepared as a fluorine source and a magnesium source. When lithium fluoride LiF and magnesium fluoride MgF₂ are mixed at about LiF:MgF₂ = 65:35 (molar ratio), the effect of lowering the melting point is the highest. On the other hand, if the amount of lithium fluoride increases, there is a concern that lithium becomes excessive and the cycle characteristics deteriorate. Therefore, the molar ratio of lithium fluoride LiF to magnesium fluoride MgF₂ is preferably LiF:MgF₂ = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF₂ = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF₂ = x:1 (x is in the vicinity of 0.33). In this specification and the like, the vicinity means a value greater than 0.9 times and less than 1.1 times that value.

[0262] Further, when performing the following mixing and pulverization steps wet, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, acetone is used.

[0263] <Step S22> Next, in step S22, the materials of the above mixture 902 are mixed and pulverized. The mixing can be performed dry or wet, but wet is preferred because it can be pulverized into smaller particles. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the pulverization media, for example. It is preferable to perform this mixing and pulverization step sufficiently to pulverize the mixture 902 into fine powder.

[0264] <Step S23> Next, in step S23, the materials mixed and pulverized above are recovered to obtain a mixture 902. The mixture 902 preferably has, for example, a D50 (median diameter) of 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. Or 600 nm or more and 10 μm or less is preferable. Or 1 μm or more and 20 μm or less is preferable. If the mixture 902 is micronized in this way, when it is mixed with a composite oxide having lithium, transition metal M, and oxygen in a later step, the mixture 902 can be easily and uniformly adhered to the surface of the composite oxide particles. If the mixture 902 is uniformly adhered to the surface of the composite oxide particles, it is preferable because halogen and magnesium can be easily and uniformly distributed in the surface layer part of the composite oxide particles after heating. If there is a region in the surface layer part that does not contain halogen and magnesium, there is a possibility that it is difficult to form the O3'-type crystal structure described later in the charged state.

[0265] <Step S41> Next, in step S41, the LiMO2 obtained in step S14 and the mixture 902 are mixed. The ratio of the number of atoms M of the transition metal in the composite oxide having lithium, transition metal, and oxygen to the number of atoms Mg of magnesium in the mixture 902 is preferably M:Mg = 100:y (0.1 ≦ y ≦ 6), more preferably M:Mg = 100:y (0.3 ≦ y ≦ 3).

[0266] The mixing in step S31 is preferably under milder conditions than the mixing in step S12 so as not to break the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, it can be said that the dry method is less likely to break particles than the wet method. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the pulverization media, for example.

[0267] <Step S42> Next, in step S42, the materials mixed above are recovered to obtain a mixture 903.

[0268] In the present embodiment, a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobaltate with few impurities is described. However, one aspect of the present invention is not limited to this. Instead of the mixture 903 in step S42, a material obtained by adding a magnesium source, a fluorine source, etc. to a starting material of lithium cobaltate and firing it may be used. In this case, since it is not necessary to separate the steps of steps S11 to S14 and the steps of steps S21 to S23, it is simple and highly productive.

[0269] Alternatively, lithium cobaltate to which magnesium and fluorine have been added in advance may be used. If lithium cobaltate to which magnesium and fluorine have been added is used, the steps up to step S42 can be omitted, which is simpler.

[0270] Furthermore, a magnesium source and a fluorine source may be further added to lithium cobaltate to which magnesium and fluorine have been added in advance.

[0271] <Step S43> Next, in step S43, the mixture 903 is heated in an atmosphere containing oxygen. The heating is preferably heating with an effect of suppressing adhesion so that the particles of the mixture 903 do not adhere to each other. This step may be referred to as annealing for the purpose of distinguishing it from the previous heating step.

[0272] Examples of heating with an effect of suppressing adhesion include heating while stirring the mixture 903, heating while vibrating the container containing the mixture 903, and the like.

[0273] The heating temperature in step S43 needs to be equal to or higher than the temperature at which the reaction between LiMO2 and the mixture 902 proceeds. The temperature at which the reaction proceeds here may be any temperature at which mutual diffusion of the elements possessed by LiMO2 and the mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in the case of an oxide, 0.757 times the melting temperature T m of (Tammann temperature T dSolid-phase diffusion occurs from . Therefore, for example, when LiMO2 is LiCoO2, since the melting point of LiCoO2 is 1130 °C, the temperature in step S43 may be 500 °C or higher.

[0274] However, it is more preferable that the temperature is equal to or higher than the temperature at which at least a part of the mixture 903 melts, so that the reaction proceeds more easily. Therefore, the annealing temperature is preferably equal to or higher than the eutectic point of the mixture 902. When the mixture 902 contains LiF and MgF2, since the eutectic point of LiF and MgF2 is around 742 °C, it is preferable to set the temperature in step S43 to 742 °C or higher.

[0275] In addition, for the mixture 903 mixed so that LiCoO2:LiF:MgF2 = 100:0.33:1 (molar ratio), an endothermic peak is observed at around 830 °C in differential scanning calorimetry (DSC measurement). Therefore, the annealing temperature is more preferably 830 °C or higher.

[0276] A higher annealing temperature is preferable because the reaction proceeds more easily, the annealing time can be shortened, and the productivity is high.

[0277] However, the annealing temperature needs to be equal to or lower than the decomposition temperature of LiMO2 (1130 °C in the case of LiCoO2). Also, at a temperature near the decomposition temperature, although in trace amounts, decomposition of LiMO2 is a concern. Therefore, the annealing temperature is preferably 1130 °C or lower, more preferably 1000 °C or lower, even more preferably 950 °C or lower, and even more preferably 900 °C or lower.

[0278] Therefore, as the annealing temperature, 500°C or higher and 1130°C or lower is preferable, 500°C or higher and 1000°C or lower is more preferable, 500°C or higher and 950°C or lower is still more preferable, and 500°C or higher and 900°C or lower is still more preferable. Also, 742°C or higher and 1130°C or lower is preferable, 742°C or higher and 1000°C or lower is more preferable, 742°C or higher and 950°C or lower is still more preferable, and 742°C or higher and 900°C or lower is still more preferable. Also, 830°C or higher and 1130°C or lower is preferable, 830°C or higher and 1000°C or lower is more preferable, 830°C or higher and 950°C or lower is still more preferable, and 830°C or higher and 900°C or lower is still more preferable.

[0279] Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range.

[0280] In the production method described in this embodiment, some materials, for example, lithium fluoride which is a fluorine source, function as a flux. Due to this function, the annealing temperature can be lowered to below the decomposition temperature of LiMO2, for example, 742°C or higher and 950°C or lower, additives such as magnesium can be distributed in the surface layer portion, and a positive electrode active material with good characteristics can be produced.

[0281] However, since gaseous lithium fluoride is lighter than oxygen, when lithium fluoride volatilizes due to heating, the lithium fluoride in the mixture 903 decreases. Then the function as a flux becomes weak. Therefore, it is necessary to heat while suppressing the volatilization of lithium fluoride. Even if lithium fluoride is not used as the fluorine source or the like, Li and F on the surface of LiMO2 may react to generate lithium fluoride and volatilize. Therefore, even if a fluoride having a melting point higher than that of lithium fluoride is used, it is similarly necessary to suppress volatilization.

[0282] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing lithium fluoride, that is, to heat the mixture 903 in a state where the partial pressure of lithium fluoride in the heating furnace is high. By such heating, the volatilization of lithium fluoride in the mixture 903 can be suppressed.

[0283] Annealing is preferably carried out at an appropriate time. The appropriate annealing time varies depending on conditions such as the annealing temperature, the particle size and composition of the LiMO2 particles in step S14. When the particles are small, a lower temperature or a shorter time may be more preferable than when they are large.

[0284] For example, when the median diameter (D50) of the particles in step S14 is about 12 μm, the annealing temperature is preferably, for example, 600 °C or higher and 950 °C or lower. The annealing time is preferably, for example, 3 hours or longer, more preferably 10 hours or longer, and even more preferably 60 hours or longer.

[0285] On the other hand, when the median diameter (D50) of the particles in step S24 is about 5 μm, the annealing temperature is preferably, for example, 600 °C or higher and 950 °C or lower. The annealing time is preferably, for example, 1 hour or longer and 10 hours or shorter, and more preferably about 2 hours.

[0286] The temperature reduction time after annealing is preferably, for example, 10 hours or longer and 50 hours or shorter.

[0287] <Step S44> Next, in step S44, the material annealed above can be recovered to produce the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. By sieving, if the positive electrode active materials 100 are stuck together, this can be eliminated.

[0288] Next, a manufacturing method different from that of FIG. 10 will be described with reference to FIGS. 11 to 14. Since there are many parts common to FIG. 10, mainly the different parts will be described. For the common parts, the description of FIG. 10 can be referred to.

[0289] In FIG. 10, the manufacturing method of mixing the LiMO2 obtained in step S14 and the mixture 902 in step S41 was described, but one aspect of the present invention is not limited to this. As shown in steps S31 and S32 of FIGS. 11 to 14, other additive elements may be further mixed.

[0290] As the additive elements, for example, one or more selected from nickel, aluminum, manganese, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. FIGS. 11 to 14 show examples in which two types, a nickel source as step S31 and an aluminum source as step S32, are used as the additive elements.

[0291] These additive elements are preferably used after being micronized into oxides, hydroxides, fluorides, etc. of each element. The micronization can be performed, for example, wetly.

[0292] As shown in FIG. 11, the nickel source and the aluminum source can be mixed in step S42 simultaneously with the mixture 902. This method is preferable because the number of annealing times is small and the productivity is high.

[0293] Also, as shown in FIG. 12, a plurality of additive sources may be mixed in different steps. For example, the nickel source can be mixed in step S61-1, and the aluminum source can be mixed in step S61-2. When mixing the additive sources in a plurality of steps in this way, the mixing method can be changed. For example, nickel hydroxide can be used as the nickel source and mixed by the solid-phase method in step S61-1, and aluminum alkoxide can be used as the aluminum source and mixed by the sol-gel method in step S61-2. By going through such steps, the distribution of the additive elements may be made better in some cases.

[0294] The sol-gel method can be performed, for example, as follows.

[0295] First, the alkoxide of the additive element is dissolved in alcohol. The alkoxy group of the alkoxide of the additive element preferably has 1 to 18 carbon atoms, and the carbon may be substituted or unsubstituted.

[0296] For example, as the aluminum alkoxide, aluminum isopropoxide, aluminum butoxide, aluminum ethoxide, etc. can be used.

[0297] As the alcohol of the solvent, for example, methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol can be used. It is preferable to use the same kind of alcohol as the alkoxy group of the additive element. The water contained in the solvent is preferably 3% by volume or less, and more preferably 0.3% by volume or less. By using alcohol as the solvent, the deterioration of LiMO2 in the production process can be suppressed compared to the case of using water.

[0298] Next, the object to be treated is mixed with the alcohol solution of the alkoxide of the additive element and stirred in an atmosphere containing water vapor.

[0299] By placing it in an atmosphere containing H2O, hydrolysis of the alkoxide of the additive element occurs. Subsequently, dehydration condensation occurs between the products. By repeating this hydrolysis and condensation reaction, a sol of the oxide of the additive element is generated. This reaction also occurs on the object to be treated, and a layer containing the additive element is formed on the surface. Then, the object to be treated is recovered, and the alcohol is vaporized to obtain the mixture 903.

[0300] Also, as shown in FIG. 13, annealing may be performed multiple times as step S53 and step S55, and a fixing suppression operation step S54 may be performed therebetween. The annealing conditions for step S53 and step S55 can refer to the description of step S43. Examples of the fixing suppression operation include crushing with a pestle, mixing using a ball mill, mixing using a rotating and revolving mixer, sieving, vibrating a container containing the composite oxide, etc.

[0301] Also, as shown in FIG. 14, after mixing LiMO2 and the mixture 902 in step S41 and annealing, the nickel source and the aluminum source may be mixed in step S61. This is taken as the mixture 904. As step S63, the mixture 904 is annealed again. The annealing conditions can refer to the description in step S43.

[0302] Also, the steps of introducing the additive elements may be interchanged. For example, as shown in FIG. 15, first, the mixture 901 having a nickel source and an aluminum source and LiMO2 are mixed, annealed in step S43, and then may be mixed with the mixture 902 having a magnesium source and a fluorine source.

[0303] Thus, by separating the steps of introducing the transition metal M and the additive, it may be possible to change the depth-direction profile of each element. For example, the concentration of the additive element can be increased in the surface layer portion compared to the inside of the particle. Also, based on the number of atoms of the transition metal M, the ratio of the number of atoms of the additive element to the reference can be made higher in the surface layer portion than in the inside.

[0304] This embodiment can be used in combination with other embodiments.

[0305] (Embodiment 3) In this embodiment, an example of a secondary battery according to an aspect of the present invention will be described with reference to FIGS. 16 to 19.

[0306] <Configuration Example 1 of Secondary Battery> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example.

[0307] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material and may have a conductive material and a binder. As the positive electrode active material, the positive electrode active material produced by using the production method described in the previous embodiment is used.

[0308] Further, the positive electrode active material described in the previous embodiment may be mixed with another positive electrode active material and used.

[0309] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0310] Further, 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.

[0311] Further, as another positive electrode active material, a composition formula Li a Mn b M c O dIt is possible to use a lithium manganese composite oxide that can be represented by [the given formula]. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particles of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≤ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particles of the lithium manganese composite oxide can be measured, for example, using ICP-MS (Inductively Coupled Plasma Mass Spectrometer). Also, the oxygen composition of the entire particles of the lithium manganese composite oxide can be measured, for example, using EDX (Energy Dispersive X-ray Analysis). Further, it can be determined by using the valence evaluation of melting gas analysis and XAFS (X-ray Absorption Fine Structure) analysis in combination with ICPMS analysis. Note that the lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0312] Hereinafter, as an example, a cross-sectional configuration example when graphene or a graphene compound is used as the conductive material in the active material layer 200 will be described.

[0313] FIG. 16A shows a longitudinal sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 100, graphene or a graphene compound 201 as the conductive material, and a binder (not shown).

[0314] In this specification and the like, the graphene compound 201 includes multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-oxidized graphene, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-oxidized graphene, graphene quantum dots, and the like. The graphene compound refers to a substance that contains carbon, has a flat or sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may be referred to as a carbon sheet. The graphene compound may have a functional group. Further, the graphene compound preferably has a bent shape. Also, the graphene compound may be curled to be like a carbon nanofiber.

[0315] In this specification and the like, graphene oxide refers to a substance that contains carbon and oxygen, has a sheet-like shape, and has a functional group, particularly an epoxy group, a carboxy group, or a hydroxy group.

[0316] In this specification and the like, reduced graphene oxide refers to a substance that contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. It may be referred to as a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting such carbon and oxygen concentrations, it can function as a highly conductive material even in small amounts. Also, reduced graphene oxide preferably has an intensity ratio G / D of the G band and the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0317] Graphene compounds may have excellent electrical properties such as high conductivity, and excellent physical properties such as high flexibility and high mechanical strength. Also, graphene compounds have a sheet-like shape. Graphene compounds may have a curved surface, enabling surface contact with low contact resistance. Also, they may be very conductive even when thin, and can efficiently form conductive paths in the active material layer in a small amount. Therefore, by using a graphene compound as a conductive material, the contact area between the active material and the conductive material can be increased. Preferably, the graphene compound adheres to at least a part of the active material particles. Also, preferably, the graphene compound overlaps at least a part of the active material particles. Also, preferably, the shape of the graphene compound coincides with at least a part of the shape of the active material particles. The shape of the active material particles refers to, for example, the unevenness of a single active material particle or the unevenness formed by a plurality of active material particles. Also, preferably, the graphene compound surrounds at least a part of the active material particles. Also, the graphene compound may have holes.

[0318] When using active material particles with a small particle size, for example, active material particles of 1 μm or less, the specific surface area of the active material particles is large, and more conductive paths connecting the active material particles are required. In such a case, it is preferable to use a graphene compound that can efficiently form conductive paths even in a small amount.

[0319] Due to having the above-mentioned properties, it is particularly effective to use a graphene compound as a conductive material in secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles, secondary batteries for drones, etc. may require rapid charging and rapid discharging characteristics. Also, in mobile electronic devices, etc., rapid charging characteristics may be required. Rapid charging and rapid discharging may also be referred to as high-rate charging and high-rate discharging. For example, it refers to charging and discharging at 1C, 2C, or 5C or more.

[0320] In the longitudinal section of the active material layer 200, as shown in FIG. 16B, sheet-like graphene or graphene compound 201 is roughly uniformly dispersed inside the active material layer 200. In FIG. 16B, graphene or graphene compound 201 is schematically represented by a thick line, but actually it is a thin film having a single or multiple layer thickness of carbon molecules. Since a plurality of graphene or graphene compound 201 are formed so as to partially cover a plurality of granular positive electrode active materials 100 or stick on the surfaces of a plurality of granular positive electrode active materials 100, they are in surface contact with each other.

[0321] Here, by bonding a plurality of graphene or graphene compounds to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is covered with the graphene net, the graphene net can also function as a binder that binds the active materials to each other. Therefore, the amount of the binder can be reduced or it can be not used, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the charge and discharge capacity of the secondary battery can be increased.

[0322] Here, it is preferable to use graphene oxide as the graphene or graphene compound 201, mix it with the active material to form a layer that becomes the active material layer 200, and then reduce it. That is, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide having extremely high dispersibility in a polar solvent for the formation of the graphene or graphene compound 201, the graphene or graphene compound 201 can be roughly uniformly dispersed inside the active material layer 200. Since the solvent is volatilized and removed from the dispersion medium containing uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene or graphene compound 201 remaining in the active material layer 200 partially overlaps and is dispersed to the extent of being in surface contact with each other, so that a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or using a reducing agent.

[0323] Therefore, unlike granular conductive materials such as acetylene black that make point contact with the active material, graphene or a graphene compound 201 enables surface contact with low contact resistance. Thus, the electrical conductivity between the granular positive electrode active material 100 and graphene or the graphene compound 201 can be improved with a smaller amount than that of a normal conductive material. Therefore, the ratio in the active material layer 200 of the positive electrode active material 100 can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

[0324] Also, by previously using a spray dryer, a graphene compound, which is a conductive material, can be formed as a film covering the entire surface of the active material, and a conductive path can be formed between the active materials with the graphene compound.

[0325] Also, materials used for forming the graphene compound may be mixed with the graphene compound and used for the active material layer 200. For example, particles used as a catalyst for forming the graphene compound may be mixed with the graphene compound. Examples of the catalyst for forming the graphene compound include particles containing 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.

[0326] [Binder] As the binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Also, fluororubber can be used as the binder.

[0327] Also, as the binder, it is preferable to use, for example, a water-soluble polymer. As the water-soluble polymer, for example, polysaccharides can be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch can be used. Further, it is more preferable to use these water-soluble polymers in combination with the above-described rubber material.

[0328] Alternatively, as the binder, it is preferable to use materials such as polystyrene, methyl polyacrylate, 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.

[0329] A plurality of the above binders may be used in combination.

[0330] For example, a material having an especially excellent viscosity adjustment effect and other materials may be used in combination. For example, although rubber materials and the like are excellent in adhesive force and elastic force, it may be difficult to adjust the viscosity when mixed with a solvent. In such a case, for example, it is preferable to mix with a material having an especially excellent viscosity adjustment effect. As the material having an especially excellent viscosity adjustment effect, for example, a water-soluble polymer may be used. Further, as the water-soluble polymer having an especially excellent viscosity adjustment effect, the above-described polysaccharides, for example, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch can be used.

[0331] Note that cellulose derivatives such as carboxymethyl cellulose have increased solubility by forming salts such as sodium salts and ammonium salts of carboxymethyl cellulose, making it easier to exhibit the effect as a viscosity modifier. By increasing the solubility, the dispersibility with the active material and other components can also be enhanced when preparing the electrode slurry. In this specification, the cellulose and cellulose derivatives used as the electrode binder shall include their salts.

[0332] Water-soluble polymers can stabilize the viscosity by dissolving in water and can stably disperse the active material and other materials combined as binders, such as styrene-butadiene rubber, in an aqueous solution. In addition, due to having functional groups, it is expected to be easily adsorbed stably on the surface of the active material. Also, cellulose derivatives such as carboxymethyl cellulose have many materials having functional groups such as hydroxyl groups and carboxyl groups. Due to having functional groups, it is expected that the polymers interact with each other and exist covering the surface of the active material widely.

[0333] When the binder covering or in contact with the surface of the active material forms a film, it is also expected to play a role as a passivation film and suppress the decomposition of the electrolyte. Here, the passivation film is a film having no electrical conductivity or having extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Further, it is more desirable that the passivation film suppresses the electrical conductivity while allowing lithium ions to conduct.

[0334] [Positive current collector] As the current collector, materials with high conductivity such as metals like stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used. Also, the material used for the positive electrode current collector preferably does not elute at the potential of the positive electrode. Further, an aluminum alloy added with elements such as silicon, titanium, neodymium, scandium, molybdenum to improve heat resistance can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as foil, plate, sheet, net, punching metal, expanded metal, etc. The current collector preferably has a thickness of 5 μm or more and 30 μm or less.

[0335] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Also, the negative electrode active material layer may have a conductive material and a binder.

[0336] [Negative electrode active material] As the negative electrode active material, for example, alloy-based materials, carbon-based materials, etc. can be used.

[0337] As the negative electrode active material, an element capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger charge and discharge capacity compared to carbon, and in particular, silicon has a large theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, there are SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, elements capable of performing charge and discharge reactions through alloying and dealloying reactions with lithium, and compounds containing such elements, etc. may be referred to as alloy-based materials.

[0338] In this specification, etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can also be expressed as SiO x where x preferably has a value near 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less. Alternatively, 0.2 or more and 1.2 or less is preferable. Alternatively, 0.3 or more and 1.5 or less is preferable.

[0339] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0340] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which may be preferable. Examples of natural graphite include flake graphite, spheroidized natural graphite, etc.

[0341] Graphite exhibits a potential as low as that of lithium metal (0.05 V or more and 0.3 V or less vs. Li / Li + ) when lithium ions are inserted into the graphite (when a lithium-graphite intercalation compound is formed). As a result, a lithium-ion secondary battery can exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as a relatively high charge-discharge capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal.

[0342] In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0343] In addition, as the negative electrode active material, Li 3-x M x N (M = Co, Ni, Cu) having an Li3N-type structure, which is a complex nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable.

[0344] When using a complex nitride of lithium and a transition metal, since the negative electrode active material contains lithium ions, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, a complex nitride of lithium and a transition metal can be used as the negative electrode active material by previously desorbing the lithium ions contained in the positive electrode active material.

[0345] In addition, a material in which a conversion reaction occurs can also be used as the negative electrode active material. For example, transition metal oxides that do not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Materials in which a conversion reaction occurs further include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, CoS 0.89 , 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.

[0346] As the conductive material and binder that the negative electrode active material layer can have, the same materials as the conductive material and binder that the positive electrode active material layer can have can be used.

[0347] [Negative electrode current collector] For the negative electrode current collector, the same materials as the positive electrode current collector can be used. It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0348] [Electrolyte solution] The electrolyte has a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., one kind, or two or more of these can be used in any combination and ratio.

[0349] In addition, by using one or more ionic liquids (room temperature molten salts) that are flame retardant and hardly volatile as the solvent of the electrolyte, even if the internal temperature of the secondary battery rises due to internal short circuit, overcharge, etc., rupture and ignition of the secondary battery can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions, etc.

[0350] In addition, as the electrolyte dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B12 Cl 12 One kind of lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc., or two or more of these can be used in any combination and ratio.

[0351] For the electrolytic solution used in the secondary battery, it is preferable to use a highly purified electrolytic solution with a low content of granular dust and elements other than the constituent elements of the electrolytic solution (hereinafter, also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolytic solution is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0352] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolytic solution. The concentration of the added material may be, for example, 0.1 wt% or more and 5 wt% or less based on the entire solvent. VC or LiBOB is particularly preferable because it easily forms a good film.

[0353] In addition, a polymer gel electrolyte obtained by swelling a polymer with an electrolytic solution may be used.

[0354] By using the polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. In addition, the secondary battery can be made thinner and lighter.

[0355] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, gel of fluorine-based polymer, etc. can be used.

[0356] As the polymer, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the formed polymer may have a porous shape.

[0357] Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide)-based material can be used. When using a solid electrolyte, it is not necessary to install a separator or a spacer. Further, since the entire battery can be solidified, there is no risk of liquid leakage and the safety is dramatically improved.

[0358] 〔Separator〕 Moreover, the secondary battery preferably has a separator. As the separator, for example, those formed of paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into an envelope shape and arranged to wrap either the positive electrode or the negative electrode.

[0359] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0360] Coating with a ceramic-based material improves oxidation resistance, suppresses deterioration of the separator during high-voltage charge and discharge, and can improve the reliability of the secondary battery. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere, and can improve the output characteristics. Coating with a polyamide-based material, particularly aramid, improves heat resistance and can improve the safety of the secondary battery.

[0361] For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Also, a mixed material of aluminum oxide and aramid may be coated on the surface of the polypropylene film that contacts the positive electrode, and a fluorine-based material may be coated on the surface that contacts the negative electrode.

[0362] Using a separator with a multilayer structure can maintain the safety of the secondary battery even when the overall thickness of the separator is thin, so the charge and discharge capacity per unit volume of the secondary battery can be increased.

[0363] 〔Outer package〕 As the outer package of the secondary battery, for example, a metal material such as aluminum or a resin material can be used. Also, a film-shaped outer package can be used. As the film, for example, a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide is provided with a metal thin film excellent in flexibility such as aluminum, stainless steel, copper, or nickel, and further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided on the metal thin film as the outer surface of the outer package. A three-layer structure film can be used.

[0364] <Configuration example 2 of secondary battery> Hereinafter, as an example of the configuration of the secondary battery, the configuration of the secondary battery using a solid electrolyte layer will be described.

[0365] As shown in FIG. 17A, a secondary battery 400 according to an aspect of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0366] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. As the positive electrode active material 411, the positive electrode active material produced using the production method described in the previous embodiment is used. Further, the positive electrode active material layer 414 may have a conductive assistant and a binder.

[0367] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that has neither the positive electrode active material 411 nor the negative electrode active material 431.

[0368] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. Further, the negative electrode active material layer 434 may have a conductive assistant and a binder. When metallic lithium is used for the negative electrode 430, as shown in Fig. 17B, the negative electrode 430 that does not have the solid electrolyte 421 can be used. When metallic lithium is used for the negative electrode 430, it is preferable because the energy density of the secondary battery 400 can be improved.

[0369] As the solid electrolyte 421 included in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0370] Examples of the sulfide-based solid electrolyte include thiophosphosilicate-based (Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 、Li 3.25 P 0.95It includes sulfide-based solid electrolytes (such as S4, etc.). Sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft, so the conductive path is easily maintained even after charge and discharge.

[0371] Oxide-based solid electrolytes include materials having a perovskite crystal structure (such as La 2 / 3-x Li 3x TiO3, etc.), materials having a NASICON crystal structure (such as Li 1-X Al X Ti 2-X (PO4)3, etc.), materials having a garnet crystal structure (such as Li7La3Zr2O 12 etc.), materials having a LISICON crystal structure (such as Li 14 ZnGe4O 16 etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (such as Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), and oxide crystallized glasses (such as Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.). Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0372] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can be used as solid electrolytes.

[0373] Also, different solid electrolytes may be mixed and used.

[0374] Among them, Li having a NASICON crystal structure 1+x Al x Ti 2-x(PO4)3(0 < x < 1) (hereinafter referred to as LATP) contains elements such as aluminum and titanium 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.

[0375] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it preferably has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0376] For example, FIG. 18 shows an example of a cell for evaluating the materials of an all-solid-state battery.

[0377] FIG. 18A is a schematic 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, both of which are made of stainless steel. Also, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0378] The evaluation material is placed on the electrode plate 751, surrounded by an insulating tube 752 around it, and is in a state of being pressed by the electrode plate 753 from above. A perspective view of the periphery of this evaluation material enlarged is shown in FIG. 18B.

[0379] As an example of the evaluation material, a stack of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in FIG. 18C. Note that the same reference numerals are used for the same parts in FIGS. 18A, 18B, and 18C.

[0380] The electrode plate 751 and the lower member 761 that are electrically connected to the positive electrode 750a can be regarded as corresponding to the positive electrode terminal. The electrode plate 753 and the upper member 762 that are electrically connected to the negative electrode 750c can be regarded as corresponding to the negative electrode terminal. Electrical resistance and the like can be measured while applying pressure to the evaluation material through the electrode plate 751 and the electrode plate 753.

[0381] Also, for the exterior body of the secondary battery according to one aspect of the present invention, it is preferable to use a package having excellent airtightness. For example, a ceramic package or a resin package can be used. Further, when sealing the exterior body, it is preferable to perform the sealing under a closed atmosphere that blocks outside air, for example, inside a glove box.

[0382] FIG. 19A shows a perspective view of a secondary battery according to one aspect of the present invention having an exterior body and shape different from those in FIG. 18. The secondary battery in FIG. 19A has external electrodes 771 and 772 and is sealed with an exterior body having a plurality of package members.

[0383] An example of a cross-section cut along the dashed line in FIG. 19A is shown in FIG. 19B. The laminate having the positive electrode 750a, the solid electrolyte layer 750b, and the negative electrode 750c is surrounded and sealed by a package member 770a provided with an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c provided with an electrode layer 773b on a flat plate. For the package members 770a, 770b, and 770c, an insulating material, for example, a resin material or a ceramic, can be used.

[0384] The external electrode 771 is electrically connected to the positive electrode 750a through the electrode layer 773a and functions as a positive electrode terminal. Also, the external electrode 772 is electrically connected to the negative electrode 750c through the electrode layer 773b and functions as a negative electrode terminal.

[0385] This embodiment can be used in appropriate combination with other embodiments.

[0386] (Embodiment 4) In this embodiment, an example of the shape of a secondary battery having a positive electrode described in the previous embodiment will be described. The materials used for the secondary battery described in this embodiment can refer to the description of the previous embodiment.

[0387] <Coin-type secondary battery> First, an example of a coin-type secondary battery will be described. FIG. 20A is an external view of a coin-type (single-layer flat-type) secondary battery, and FIG. 20B is a cross-sectional view thereof.

[0388] The coin-type secondary battery 300 has a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal, which 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 therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0389] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, the active material layer may be formed only on one side.

[0390] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys thereof or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolyte, it is preferable to coat with nickel or aluminum. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0391] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with the electrolyte. As shown in FIG. 20B, with the positive electrode can 301 at the bottom, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are pressure-bonded via the gasket 303 to manufacture the coin-shaped secondary battery 300.

[0392] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0393] Here, the flow of current during charging of the secondary battery will be described with reference to FIG. 20C. When a secondary battery using lithium is regarded as a single closed circuit, the movement of lithium ions and the flow of current are in the same direction. In a secondary battery using lithium, the anode and cathode are reversed during charging and discharging, and the oxidation reaction and reduction reaction are also reversed. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Accordingly, in this specification, whether during charging, discharging, when a reverse pulse current is flowing, or when a charging current is flowing, the positive electrode is referred to as the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode is referred to as the "negative electrode" or the "- electrode (minus electrode)". Using terms such as anode and cathode related to oxidation and reduction reactions would result in them being reversed during charging and discharging, which may cause confusion. Therefore, the terms anode and cathode will not be used in this specification. If the terms anode and cathode are used, it is necessary to specify whether it is during charging or discharging and also indicate which one corresponds to the positive electrode (plus electrode) and the negative electrode (minus electrode).

[0394] A charger is connected to the two terminals shown in FIG. 20C, and the secondary battery 300 is charged. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0395] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to FIG. 21. An external view of the cylindrical secondary battery 600 is shown in FIG. 21A. FIG. 21B is a diagram schematically showing a cross section of the cylindrical secondary battery 600. As shown in FIG. 21B, the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0396] Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with nickel, aluminum, or the like. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. As the non-aqueous electrolytic solution, the same one as that used for the coin-type secondary battery can be used.

[0397] Since the positive and negative electrodes used in a cylindrical battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 603 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold value. Also, the PTC element 611 is a thermal sensing resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used.

[0398] Also, as shown in FIG. 21C, a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between a conductive plate 613 and a conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then further in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0399] Figure 21D is a top view of module 615. The conductive plate 613 is shown by a dotted line for clarity. As shown in Figure 21D, module 615 may have conductive wires 616 that electrically connect a plurality of secondary batteries 600. A conductive plate can be superimposed and provided on the conductive wires 616. Also, a temperature control device 617 may be provided between the plurality of secondary batteries 600. When the secondary battery 600 overheats, it can be cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of module 615 is less likely to be affected by the outside air temperature. The heat medium of the temperature control device 617 preferably has insulation and non-flammability.

[0400] By using the positive electrode active material described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with a high charge and discharge capacity and excellent cycle characteristics can be obtained.

[0401] <Structural Example of Secondary Battery> Another structural example of the secondary battery will be described with reference to FIGS. 22 to 26.

[0402] FIGS. 22A and 22B are views showing the external appearance of a battery pack. The battery pack has a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to an antenna 914 via the circuit board 900. Also, a label 910 is attached to the secondary battery 913. Further, as shown in FIG. 22B, the secondary battery 913 is connected to a terminal 951 and a terminal 952. The circuit board 900 is fixed with a seal 915.

[0403] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 951, the terminal 952, the antenna 914, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, etc.

[0404] The circuit 912 may be provided on the back surface of the circuit board 900. Note that the antenna 914 is not limited to a coil shape, and may be, for example, linear or plate-shaped. Also, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 914 may be a flat plate conductor. This flat plate conductor can function as one of the conductors for electric field coupling. That is, the antenna 914 may function as one of the two conductors of the capacitor. Thereby, power exchange can be performed not only by electromagnetic fields and magnetic fields but also by electric fields.

[0405] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of, for example, shielding the electromagnetic field generated by the secondary battery 913. As the layer 916, for example, a magnetic material can be used.

[0406] Note that the structure of the battery pack is not limited to that shown in FIG. 22.

[0407] For example, as shown in FIGS. 23A and 23B, antennas may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 22A and 22B. FIG. 23A is an external view showing one of the pair of surfaces, and FIG. 23B is an external view showing the other of the pair of surfaces. Note that, for the same parts as those of the secondary battery shown in FIGS. 22A and 22B, the description of the secondary battery shown in FIGS. 22A and 22B can be appropriately incorporated.

[0408] As shown in FIG. 23A, the antenna 914 is provided with the layer 916 interposed therebetween on one of the pair of surfaces of the secondary battery 913, and as shown in FIG. 23B, the antenna 918 is provided with the layer 917 interposed therebetween on the other of the pair of surfaces of the secondary battery 913. The layer 917 has a function of, for example, shielding the electromagnetic field generated by the secondary battery 913. As the layer 917, for example, a magnetic material can be used.

[0409] By adopting the above structure, the sizes of both the antenna 914 and the antenna 918 can be increased. The antenna 918 has a function of, for example, performing data communication with an external device. For the antenna 918, an antenna having a shape applicable to the antenna 914 can be applied, for example. As a communication method between the secondary battery and other devices via the antenna 918, a response method that can be used between the secondary battery and other devices, such as NFC (Near Field Communication), can be applied.

[0410] Alternatively, as shown in FIG. 23C, a display device 920 may be provided on the secondary battery 913 shown in FIGS. 22A and 22B. The display device 920 is electrically connected to the terminal 911. Note that a label 910 may not be provided at the portion where the display device 920 is provided. For the same portions as the secondary battery shown in FIGS. 22A and 22B, the description of the secondary battery shown in FIGS. 22A and 22B can be appropriately incorporated.

[0411] The display device 920 may display, for example, an image indicating whether charging is in progress, an image indicating the power storage amount, or the like. As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used. For example, by using an electronic paper, the power consumption of the display device 920 can be reduced.

[0412] Alternatively, as shown in FIG. 23D, a sensor 921 may be provided on the secondary battery 913 shown in FIGS. 22A and 22B. The sensor 921 is electrically connected to the terminal 911 via the terminal 922. For the same portions as the secondary battery shown in FIGS. 22A and 22B, the description of the secondary battery shown in FIGS. 22A and 22B can be appropriately incorporated.

[0413] As the sensor 921, for example, it may have a function capable of measuring displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. By providing the sensor 921, for example, data (such as temperature) indicating the environment where the secondary battery is placed can be detected and stored in the memory within the circuit 912.

[0414] Furthermore, a structural example of the secondary battery 913 will be described with reference to FIGS. 24 and 25.

[0415] The secondary battery 913 shown in FIG. 24A has a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 24A, for the sake of convenience, the housing 930 is shown separated, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0416] Note that, as shown in FIG. 24B, the housing 930 shown in FIG. 24A may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 24B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the region surrounded by the housing 930a and the housing 930b.

[0417] As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna such as the antenna 914 may be provided inside the housing 930a. As the housing 930b, for example, a metal material can be used.

[0418] Furthermore, the structure of the wound body 950 is shown in FIG. 25. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0419] The negative electrode 931 is connected to the terminal 911 shown in FIG. 22 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG. 22 via the other of the terminals 951 and 952.

[0420] By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0421] <Laminated secondary battery> Next, an example of a laminated secondary battery will be described with reference to FIGS. 26 to 36. If the laminated secondary battery has a flexible configuration and is mounted on an electronic device having at least a part of a flexible portion, the secondary battery can also be bent in accordance with the deformation of the electronic device.

[0422] The laminated secondary battery 980 will be described with reference to FIG. 26. The laminated secondary battery 980 has a wound body 993 shown in FIG. 26A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950 described in FIG. 25, the wound body 993 is formed by laminating the negative electrode 994 and the positive electrode 995 with the separator 996 interposed therebetween and winding the laminated sheet.

[0423] Note that the number of layers of the laminate composed of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required charge-discharge capacity and the element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0424] As shown in FIG. 26B, the wound body 993 described above is housed in a space formed by thermocompression bonding or the like a film 981 serving as an exterior body and a film 982 having a recess, whereby a secondary battery 980 as shown in FIG. 26C can be manufactured. The wound body 993 has lead electrodes 997 and 998 and is impregnated with an electrolytic solution inside the film 981 and the film 982 having a recess.

[0425] For the film 981 and the film 982 having a recess, a metal material such as aluminum or a resin material can be used. If a resin material is used as the material of the film 981 and the film 982 having a recess, the film 981 and the film 982 having a recess can be deformed when a force is applied from the outside, and a flexible storage battery can be manufactured.

[0426] Also, although FIGS. 26B and 26C show an example using two films, a space may be formed by bending one film, and the wound body 993 described above may be housed in the space.

[0427] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 having a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0428] Also, in FIG. 26, an example of the secondary battery 980 having a wound body in a space formed by a film serving as an exterior body has been described. However, for example, as shown in FIG. 27, a secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film serving as an exterior body may be used.

[0429] The laminated secondary battery 500 shown in Fig. 27A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolytic solution 508, and an exterior body 509. A separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. Further, the interior of the exterior body 509 is filled with the electrolytic solution 508. As the electrolytic solution 508, the electrolytic solution shown in Embodiment 3 can be used.

[0430] In the laminated secondary battery 500 shown in Fig. 27A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, a part of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged to be exposed outside the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed outside the exterior body 509, and a lead electrode may be ultrasonically bonded to the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 so that the lead electrode is exposed outside.

[0431] In the laminated secondary battery 500, the exterior body 509 may be formed of a three-layer laminated film in which a metal thin film with excellent flexibility such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film.

[0432] An example of the cross-sectional structure of the laminated secondary battery 500 is shown in Fig. 27B. In Fig. 27A, for simplicity, an example composed of two current collectors is shown, but actually, as shown in Fig. 27B, it is composed of a plurality of electrode layers.

[0433] In FIG. 27B, as an example, the number of electrode layers is 16. Even when the number of electrode layers is 16, the secondary battery 500 has flexibility. FIG. 27B shows a structure with a total of 16 layers, where the negative electrode current collector 504 has 8 layers and the positive electrode current collector 501 has 8 layers. Note that FIG. 27B shows a cross-section of the extraction portion of the negative electrode, and the 8-layer negative electrode current collector 504 is ultrasonically bonded. Of course, the number of electrode layers is not limited to 16, and it may be more or less. When the number of electrode layers is large, a secondary battery with a larger charge and discharge capacity can be obtained. When the number of electrode layers is small, the battery can be made thinner and have excellent flexibility.

[0434] Here, an example of the external view of the laminate-type secondary battery 500 is shown in FIGS. 28 and 29. FIGS. 28 and 29 include a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0435] FIG. 30A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. 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 the 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, that is, a tab region. The area and shape of the tab regions of the positive electrode and the negative electrode are not limited to the examples shown in FIG. 30A.

[0436] <Manufacturing method of laminate-type secondary battery> Here, an example of the manufacturing method of the laminate-type secondary battery whose external view is shown in FIG. 28 will be described with reference to FIGS. 30B and 30C.

[0437] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 30B shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown where five sets of negative electrodes and four sets of positive electrodes are used. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like may be used. Similarly, the tabs of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0438] Next, the negative electrode 506, the separator 507, and the positive electrode 503 are arranged on the exterior body 509.

[0439] Next, as shown in FIG. 30C, the exterior body 509 is bent at the portion indicated by the broken line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided in a part (or one side) of the exterior body 509 so that the electrolytic solution 508 can be introduced later.

[0440] Next, the electrolytic solution 508 (not shown) is introduced into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolytic solution 508 is preferably performed under a reduced-pressure atmosphere or an inert atmosphere. And finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

[0441] By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery 500 with a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0442] In the all-solid-state battery, by applying a predetermined pressure in the stacking direction of the stacked positive and negative electrodes, the contact state of the interfaces inside can be kept good. By applying a predetermined pressure in the stacking direction of the positive and negative electrodes, it is possible to suppress the expansion in the stacking direction due to the charge and discharge of the all-solid-state battery, and the reliability of the all-solid-state battery can be improved.

[0443] This embodiment can be used in appropriate combination with other embodiments.

[0444] (Embodiment 5) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described.

[0445] First, an example of mounting the bendable secondary battery described in the previous embodiment on an electronic device is shown in FIGS. 31A to 31G. Examples of electronic devices to which the bendable secondary battery is applied include, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or a mobile phone device), a portable game machine, a portable information terminal, an audio playback device, and a large game machine such as a pachinko machine.

[0446] In addition, it is also possible to incorporate a secondary battery having a flexible shape along the inner wall or outer wall of a house or building, or the curved surface of the interior or exterior of an automobile.

[0447] FIG. 31A shows an example of a mobile phone. The mobile phone 7400 includes, in addition to a display unit 7402 incorporated in a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 has a secondary battery 7407. By using the secondary battery of one aspect of the present invention as the secondary battery 7407, a lightweight and long-life mobile phone can be provided.

[0448] FIG. 31B shows the state in which the mobile phone 7400 is bent. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided inside it is also bent. At that time, the state of the bent secondary battery 7407 is shown in FIG. 31C. The secondary battery 7407 is a thin rechargeable battery. The secondary battery 7407 is fixed in the bent state. Note that the secondary battery 7407 has a lead electrode electrically connected to a current collector. For example, the current collector is a copper foil, which is alloyed with a part of gallium to improve the adhesion to the active material layer in contact with the current collector, and has a configuration with high reliability in the state where the secondary battery 7407 is bent.

[0449] FIG. 31D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Also, FIG. 31E shows the state of the bent secondary battery 7104. When the secondary battery 7104 is bent and worn on the user's arm, the housing deforms and the curvature of part or all of the secondary battery 7104 changes. Note that the degree of bending at an arbitrary point on a curve represented by the value of the radius of a corresponding circle is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or the secondary battery 7104 changes within a range where the radius of curvature is 40 mm or more and 150 mm or less. If the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm or more and 150 mm or less, high reliability can be maintained. By using the secondary battery according to one aspect of the present invention for the secondary battery 7104 described above, a lightweight and long-life portable display device can be provided.

[0450] FIG. 31F shows an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0451] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mails, text viewing and creation, music playback, Internet communication, and computer games.

[0452] The display unit 7202 is provided with a curved display surface and can perform display along the curved display surface. Further, the display unit 7202 is provided with a touch sensor and can be operated by touching the screen with a finger, a stylus, or the like. For example, by touching the icon 7207 displayed on the display unit 7202, an application can be launched.

[0453] In addition to time setting, the operation button 7205 can have various functions such as turning on and off the power, turning on and off wireless communication, executing and canceling the silent mode, and executing and canceling the power saving mode. For example, the functions of the operation button 7205 can be freely set by the operating system incorporated in the portable information terminal 7200.

[0454] Further, the portable information terminal 7200 can execute short-range wireless communication conforming to a communication standard. For example, it can also make a hands-free call by communicating with a wireless communication-enabled headset.

[0455] The portable information terminal 7200 is also provided with an input / output terminal 7206 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal 7206. Note that the charging operation may be performed by wireless power supply without passing through the input / output terminal 7206.

[0456] The display unit 7202 of the portable information terminal 7200 has a secondary battery according to one aspect of the present invention. By using the secondary battery according to one aspect of the present invention, a lightweight and long-life portable information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 31E can be incorporated inside the housing 7201 in a curved state or in a state where it can be curved inside the band 7203.

[0457] The portable information terminal 7200 preferably has a sensor. As the sensor, for example, it is preferable to mount a human body sensor such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0458] Figure 31G shows an example of a bracelet-type display device. The display device 7300 has a display unit 7304 and includes a secondary battery according to one aspect of the present invention. Further, the display device 7300 may be provided with a touch sensor on the display unit 7304 and may also function as a portable information terminal.

[0459] The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. Further, the display device 7300 can change the display status by means of communication-standardized short-range wireless communication or the like.

[0460] Further, the display device 7300 is provided with input / output terminals and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminals. Note that the charging operation may be performed by wireless power supply without using the input / output terminals.

[0461] By using the secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0462] An example of mounting the secondary battery with good cycle characteristics shown in the previous embodiment on an electronic device will be described with reference to FIGS. 31H, 32, and 33.

[0463] By using the secondary battery according to one aspect of the present invention as the secondary battery of a consumer electronic device, a lightweight and long-life product can be provided. For example, consumer electronic devices include an electric toothbrush, an electric shaver, an electric beauty device, etc. As the secondary battery for these products, considering the ease of use by the user, a secondary battery having a stick shape, being small, lightweight, and having a large charge / discharge capacity is desired.

[0464] FIG. 31H is a perspective view of an apparatus also called a tobacco-containing smoking device (electronic cigarette). In FIG. 31H, the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and overdischarging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 31H has external terminals so that it can be connected to a charging device. Since the secondary battery 7504 becomes the tip portion when held, it is desirable that the total length is short and the weight is light. The secondary battery according to one aspect of the present invention has a high charge-discharge capacity and good cycle characteristics, so that it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period.

[0465] Next, FIGS. 32A and 32B show an example of a foldable tablet terminal. The tablet terminal 9600 shown in FIGS. 32A and 32B includes a housing 9630a, a housing 9630b, a movable part 9640 that connects the housing 9630a and the housing 9630b, a display unit 9631 including a display unit 9631a and a display unit 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, a tablet terminal having a wider display unit can be obtained. FIG. 32A shows the tablet terminal 9600 in an open state, and FIG. 32B shows the tablet terminal 9600 in a closed state.

[0466] Further, the tablet terminal 9600 has a power storage body 9635 inside the housing 9630a and the housing 9630b. The power storage body 9635 is provided across the housing 9630a and the housing 9630b through the movable part 9640.

[0467] The display unit 9631 can have all or part of its area as the touch panel area, and data can be input by touching an icon, character, input form, etc. displayed in the area. For example, keyboard buttons can be displayed on the entire surface of the display unit 9631a on the housing 9630a side, and information such as characters and images can be displayed and used on the display unit 9631b on the housing 9630b side.

[0468] Alternatively, a keyboard can be displayed on the display unit 9631b on the housing 9630b side, and information such as characters and images can be displayed and used on the display unit 9631a on the housing 9630a side. Also, a keyboard display switch button for the touch panel can be displayed on the display unit 9631, and the keyboard can be displayed on the display unit 9631 by touching the button with a finger or a stylus.

[0469] Also, touch input can be simultaneously performed on the touch panel areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side.

[0470] Also, the switches 9625 to 9627 can be interfaces not only for operating the tablet terminal 9600 but also for switching various functions. For example, at least one of the switches 9625 to 9627 may function as a switch for turning the power of the tablet terminal 9600 on and off. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display orientation such as vertical or horizontal display, or a function of switching between black and white display and color display. Also, for example, at least one of the switches 9625 to 9627 may have a function of adjusting the brightness of the display unit 9631. Also, the brightness of the display unit 9631 can be optimized according to the amount of external light detected by the optical sensor built into the tablet terminal 9600 during use. Note that the tablet terminal may incorporate other detection devices such as a gyro and an acceleration sensor for detecting inclination in addition to the optical sensor.

[0471] Also, in FIG. 32A, an example is shown in which the display areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side are substantially the same. However, the respective display areas of the display unit 9631a and the display unit 9631b are not particularly limited, and the size of one may be different from that of the other, and the display quality may also be different. For example, one may be a display panel capable of performing a higher-definition display than the other.

[0472] FIG. 32B shows a state in which the tablet terminal 9600 is closed in a two-fold manner. The tablet terminal 9600 has a charging / discharging control circuit 9634 including a housing 9, a solar cell 9633, and a DCDC converter 9636. Further, as the power storage body 9635, a power storage body according to one aspect of the present invention is used.

[0473] As described above, since the tablet terminal 9600 can be folded in two, the housing 9630a and the housing 9630b can be folded so as to overlap each other when not in use. By folding, the display unit 9631 can be protected, so that the durability of the tablet terminal 9600 can be improved. In addition, since the power storage body 9635 using the secondary battery according to one aspect of the present invention has a high charge / discharge capacity and good cycle characteristics, a tablet terminal 9600 that can be used for a long time over a long period can be provided.

[0474] In addition to this, the tablet terminal 9600 shown in FIGS. 32A and 32B can also have functions such as a function of displaying various information (still images, moving images, text images, etc.), a function of displaying a calendar, a date, or a time on the display unit, a touch input function of touch-inputting or editing the information displayed on the display unit, and a function of controlling processing by various software (programs).

[0475] The solar cell 9633 mounted on the surface of the tablet terminal 9600 can supply power to the touch panel, the display unit, the video signal processing unit, etc. Note that the solar cell 9633 can be provided on one side or both sides of the housing 9630, and can be configured to efficiently charge the power storage body 9635. As the power storage body 9635, using a lithium ion battery has advantages such as downsizing.

[0476] Also, the configuration and operation of the charge / discharge control circuit 9634 shown in FIG. 32B will be described with reference to the block diagram in FIG. 32C. FIG. 32C shows the solar cell 9633, the power storage body 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631. The power storage body 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the parts of the charge / discharge control circuit 9634 shown in FIG. 32B.

[0477] First, an example of the operation when power is generated by the solar cell 9633 due to external light will be described. The power generated by the solar cell is stepped up or down by the DCDC converter 9636 so as to be a voltage for charging the power storage body 9635. When the power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the voltage required for the display unit 9631. When the display unit 9631 is not displaying, SW1 may be turned off and SW2 may be turned on to charge the power storage body 9635.

[0478] Note that the solar cell 9633 is shown as an example of a power generation means, but is not particularly limited, and may be configured to charge the power storage body 9635 by other power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that wirelessly (non-contact) transmits and receives power for charging, or a configuration that combines other charging means may be used.

[0479] FIG. 33 shows an example of another electronic device. In FIG. 33, a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, and the like. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8004. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, the secondary battery 8004 according to one aspect of the present invention can be used as an uninterruptible power supply, making it possible to use the display device 8000.

[0480] The display unit 8002 can use a semiconductor display device such as a liquid crystal display device, a light emitting device having a light emitting element such as an organic EL element in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0481] Note that the display device includes all display devices for information display, such as those for personal computers and advertising displays, in addition to those for receiving TV broadcasts.

[0482] In FIG. 33, a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. In FIG. 33, a case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed is illustrated, but the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power supply from a commercial power source, or can use the power stored in the secondary battery 8103. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, the secondary battery 8103 according to one aspect of the present invention can be used as an uninterruptible power supply, making it possible to use the lighting device 8100.

[0483] In FIG. 33, the installed lighting device 8100 provided on the ceiling 8104 is illustrated. However, the secondary battery according to one aspect of the present invention can be used not only for the installed lighting device provided on the ceiling 8104 but also for the installed lighting devices provided on, for example, the side wall 8105, the floor 8106, the window 8107, etc., and can also be used for a desktop lighting device or the like.

[0484] Moreover, as the light source 8102, an artificial light source that artificially obtains light using electric power can be used. Specifically, an incandescent bulb, a discharge lamp such as a fluorescent lamp, and a light-emitting element such as an LED or an organic EL element can be cited as an example of the above artificial light source.

[0485] In FIG. 33, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using the secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, etc. In FIG. 33, the case where the secondary battery 8203 is provided in the indoor unit 8200 is illustrated. However, the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power supply from a commercial power source or can use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8203 according to one aspect of the present invention as an uninterruptible power supply, the air conditioner can be used.

[0486] In FIG. 33, a separate-type air conditioner composed of an indoor unit and an outdoor unit is illustrated. However, the secondary battery according to one aspect of the present invention can also be used for an integrated-type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0487] In FIG. 33, the electric refrigerator 8300 is an example of an electronic device using the secondary battery 8304 according to one aspect of the present invention. Specifically, the electric refrigerator 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 33, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator 8300 can receive power supply from a commercial power source or use the power stored in the secondary battery 8304. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8304 according to one aspect of the present invention as an uninterruptible power supply, the electric refrigerator 8300 can be used.

[0488] Among the above-described electronic devices, high-frequency heating devices such as microwave ovens and electronic devices such as electric rice cookers require high power in a short time. Therefore, by using the secondary battery according to one aspect of the present invention as an auxiliary power supply to supplement the power that cannot be covered by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0489] Also, during the time when the electronic device is not in use, particularly during the time when the ratio of the actually used power amount to the total power amount that can be supplied by the commercial power source supplier (referred to as the power usage rate) is low, by storing power in the secondary battery, it is possible to suppress an increase in the power usage rate outside the above time period. For example, in the case of the electric refrigerator 8300, power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed. Then, during the day when the temperature rises and the refrigerator door 8302 and the freezer door 8303 are opened and closed, by using the secondary battery 8304 as an auxiliary power supply, the power usage rate during the day can be kept low.

[0490] According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be enhanced. Further, according to one aspect of the present invention, a secondary battery with a high charge-discharge capacity can be obtained. Thus, the characteristics of the secondary battery can be improved, and therefore, the secondary battery itself can be made smaller and lighter. Therefore, by mounting the secondary battery, which is one aspect of the present invention, on the electronic device described in this embodiment, an electronic device with a longer lifespan and a lighter weight can be obtained.

[0491] This embodiment can be implemented in appropriate combination with other embodiments.

[0492] (Embodiment 6) In this embodiment, an example of an electronic device using the secondary battery described in the previous embodiment will be described with reference to FIGS. 34A to 35C.

[0493] FIG. 34A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Further, when the user uses it in daily life or outdoors, a wearable device that can perform not only wired charging with an exposed connector part to enhance the anti-splash performance, water resistance performance, or dustproof performance but also wireless charging is desired.

[0494] For example, a secondary battery, which is one aspect of the present invention, can be mounted on the glasses-type device 4000 as shown in FIG. 34A. The glasses-type device 4000 has a frame 4000a and a display part 4000b. By mounting the secondary battery on the temple part of the frame 4000a having a curvature, a glasses-type device 4000 that is lightweight, has a good weight balance, and has a long continuous use time can be obtained. By providing a secondary battery, which is one aspect of the present invention, a configuration that can cope with space saving due to the miniaturization of the housing can be realized.

[0495] In addition, a secondary battery according to one aspect of the present invention can be mounted on the headset-type device 4001. The headset-type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A secondary battery can be provided inside the flexible pipe 4001b or inside the earphone unit 4001c. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0496] In addition, a secondary battery according to one aspect of the present invention can be mounted on the device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0497] In addition, a secondary battery according to one aspect of the present invention can be mounted on the device 4003 that can be attached to clothing. A secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0498] In addition, a secondary battery according to one aspect 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 supply / reception unit 4006b, and a secondary battery can be mounted inside the belt portion 4006a. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0499] In addition, a secondary battery, which is one aspect of the present invention, can be mounted on the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and a secondary battery can be provided in the display unit 4005a or the belt unit 4005b. By providing the secondary battery, which is one aspect of the present invention, it is possible to realize a configuration that can cope with space saving accompanying the miniaturization of the housing.

[0500] The display unit 4005a can display not only the time but also various information such as incoming mails and phone calls.

[0501] In addition, since the wristwatch-type device 4005 is a wearable device of a type that is directly wound around the wrist, it may be equipped with sensors for measuring the user's pulse, blood pressure, etc. Data regarding the user's exercise amount and health can be accumulated to manage the health.

[0502] FIG. 34B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0503] In addition, a side view is shown in FIG. 34C. FIG. 34C shows a state in which the secondary battery 913 is built in. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is provided at a position overlapping the display unit 4005a and is small and lightweight.

[0504] FIG. 34D shows an example of wireless earphones. Here, wireless earphones having a pair of main bodies 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0505] The main bodies 4100a and 41,00b have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may have a display unit 4104. It is also preferable to have a substrate on which circuits such as wireless ICs are mounted, charging terminals, etc. They may also have a microphone.

[0506] Case 4110 has a secondary battery 4111. It preferably has a substrate on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, etc.

[0507] Bodies 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. Thereby, audio data etc. sent from other electronic devices can be played back by bodies 4100a and 4100b. Also, if bodies 4100a and 4100b have microphones, the sound acquired by the microphones can be sent to other electronic devices, and the audio data after being processed by the electronic devices can be sent back to bodies 4100a and 4100b for playback. Thereby, it can also be used as, for example, a translator.

[0508] Also, charging can be performed from the secondary battery 4111 of case 4100 to the secondary battery 4103 of body 4100a. As the secondary battery 4111 and the secondary battery 4103, the coin-type secondary battery, the cylindrical secondary battery, etc. of the previous embodiment can be used. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode has a high energy density, and by using it for the secondary battery 4103 and the secondary battery 4111, a configuration that can cope with space saving accompanying the miniaturization of the wireless earphone can be realized.

[0509] FIG. 35A shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the 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, etc. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, etc. The cleaning robot 6300 can move automatically, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0510] For example, the cleaning robot 6300 can analyze the image captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Also, when an object that is likely to get caught in the brush 6304, such as wiring, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one aspect of the present invention and semiconductor devices or electronic components inside it. By using the secondary battery 6306 according to one aspect of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be made into an electronic device with a long operating time and high reliability.

[0511] FIG. 35B shows an example of a robot. The robot 6400 shown in FIG. 35B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, an arithmetic unit, etc.

[0512] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user by using the microphone 6402 and the speaker 6404.

[0513] The display unit 6405 has a function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer can be enabled.

[0514] The upper camera 6403 and the lower camera 6406 have the function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0515] The robot 6400 includes a secondary battery 6409 according to an aspect of the present invention and semiconductor devices or electronic components inside thereof. By using the secondary battery according to an aspect of the present invention in the robot 6400, the robot 6400 can be made into an electronic device with a long operating time and high reliability.

[0516] FIG. 35C shows an example of an aircraft. The aircraft 6500 shown in FIG. 35C has a propeller 6501, a camera 6502, a secondary battery 6503, etc., and has the function of autonomous flight.

[0517] For example, the image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of obstacles when moving. Also, the remaining battery level can be estimated from the change in the storage capacity of the secondary battery 6503 by the electronic component 6504. The aircraft 6500 includes a secondary battery 6503 according to an aspect of the present invention inside thereof. By using the secondary battery according to an aspect of the present invention in the aircraft 6500, the aircraft 6500 can be made into an electronic device with a long operating time and high reliability.

[0518] This embodiment can be implemented in appropriate combination with other embodiments.

[0519] (Embodiment 7) In this embodiment, an example of mounting a secondary battery, which is an aspect of the present invention, on a vehicle is shown.

[0520] When a secondary battery is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized.

[0521] In FIG. 36, a vehicle using a secondary battery, which is one aspect of the present invention, is illustrated. The automobile 8400 shown in FIG. 36A is an electric vehicle that uses an electric motor as a power source for running. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. Further, the automobile 8400 has a secondary battery. As the secondary battery, the modules of the secondary battery shown in FIGS. 21C and 21D may be arranged with respect to the floor portion inside the vehicle. Alternatively, a battery pack in which a plurality of secondary batteries shown in FIG. 24 are combined may be installed with respect to the floor portion inside the vehicle. The secondary battery can not only drive the electric motor 8406 but also supply power to a light-emitting device such as a headlight 8401 and a room light (not shown).

[0522] Further, the secondary battery can supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has. Further, the secondary battery can supply power to semiconductor devices such as a navigation system that the automobile 8400 has.

[0523] The automobile 8500 shown in Fig. 36B can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, or the like to the secondary battery of the automobile 8500. Fig. 36B shows a state in which charging is being performed from a ground-mounted charging device 8021 to a secondary battery 8024 mounted on the automobile 8500 via a cable 8022. When charging, the charging method, the connector standard, etc. may be appropriately performed in a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility or may be a household power supply. For example, by plug-in technology, the secondary battery 8024 mounted on the automobile 8500 can be charged by external power supply. Charging can be performed by converting AC power into DC power via a conversion device such as an AC-DC converter.

[0524] Also, although not shown, a power receiving device can be mounted on the vehicle, and power can be supplied non-contact from a power transmitting device on the ground for charging. In the case of this non-contact power supply method, by incorporating a power transmitting device in a road or an outer wall, charging can be performed not only while the vehicle is stopped but also while it is running. Also, using this non-contact power supply method, power may be transmitted and received between vehicles. Furthermore, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or running. For such non-contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0525] Also, Fig. 36C is an example of a two-wheeled vehicle using a secondary battery according to an aspect of the present invention. The scooter 8600 shown in Fig. 36C includes a secondary battery 8602, a side mirror 8601, and a direction indicator light 8603. The secondary battery 8602 can supply electricity to the direction indicator light 86_{03}.

[0526] Also, the scooter 8600 shown in Fig. 36C can store the secondary battery 8602 in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small. The secondary battery 8602 is removable, and during charging, the secondary battery 8602 can be carried indoors, charged, and stored before driving.

[0527] According to one aspect of the present invention, the cycle characteristics of a secondary battery are improved, and the charge-discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it contributes to reducing the weight of the vehicle, so the cruising range can be improved. In addition, the secondary battery mounted on the vehicle can also be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using a commercial power supply during the peak of power demand. If it is possible to avoid using a commercial power supply during the peak of power demand, it can contribute to energy saving and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long time, so the amount of use of rare metals such as cobalt can be reduced.

[0528] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0529] In this example, the positive electrode active material 100 of one aspect of the present invention was prepared and its characteristics were analyzed.

[0530] <Preparation of positive electrode active material> The sample prepared in this example will be described with reference to the manufacturing method shown in FIG. 14.

[0531] As LiMO2 in step S14, commercially available lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Celsid C-10N) having cobalt as a transition metal M and having no additive element in particular was prepared. Lithium fluoride and magnesium fluoride were mixed by a solid-phase method in the same manner as in steps S21 to S23, step S41, and step S42. When the number of cobalt atoms was 100, the number of lithium fluoride molecules was added to be 0.33, and the number of magnesium fluoride molecules was added to be 1. This was designated as mixture 903.

[0532] Next, annealing was performed in the same manner as in step S43. 30 g of the mixture 903 was placed in a rectangular alumina container, covered, and heated in a muffle furnace. The inside of the furnace was purged and oxygen gas was introduced, and it was not flowed during heating. The annealing temperature was 900 °C and the annealing time was 20 hours.

[0533] Nickel hydroxide and aluminum hydroxide were added and mixed to the composite oxide after heating in the same manner as in steps S31, S32, S61, and S62. When the number of cobalt atoms was set to 100, the number of nickel atoms was added to be 0.5 and the number of aluminum atoms was added to be 0.5. This was designated as mixture 904.

[0534] Next, annealing was performed in the same manner as in step S63. 100 g of the mixture 904 was placed in a rectangular alumina container, covered, and heated in a muffle furnace. The flow rate of oxygen gas during heating was set to 10 L / min. The annealing temperature was 850 °C and the annealing time was 10 hours. The positive electrode active material thus prepared was designated as sample 1-1 (step S66).

[0535] Next, a sample prepared in the same manner as sample 1-1 except that the annealing in step S43 was at 850 °C for 60 hours and the flow rate of oxygen gas during heating was 10 L / min, and the annealing in step S63 was at 850 °C for 2 hours, was designated as sample 1-2.

[0536] Next, a nickel source and an aluminum source were mixed together with a magnesium source and a fluorine source in the same manner as the manufacturing method shown in FIG. 11, and a sample prepared in the same manner as sample 1-1 except that the annealing in step S43 was at 850 °C for 60 hours and the flow rate of oxygen gas during heating was 10 L / min, was designated as sample 1-3.

[0537] Next, as in the manufacturing method shown in Fig. 15, a nickel source and an aluminum source were first mixed with lithium cobaltate, and after passing through the annealing in step S43 (850 °C, 2 hours, oxygen gas flow rate of 10 L / min during heating), a magnesium source and a fluorine source were then mixed. A sample prepared in the same manner as sample 1-1 except that the annealing in step S63 (850 °C, 2 hours) was performed was designated as sample 1-4.

[0538] Next, as in the manufacturing method shown in Fig. 12, a sample prepared by using aluminum isopropoxide (Al(O-i-Pr)3) as an aluminum source and mixing it in a process different from that of the nickel source was designated as sample 1-5. At this time, isopropanol was used as the solvent for Al isopropoxide. The mixture obtained by the mixing in S61-1 and Al isopropoxide were reacted with water contained in the air for 17 hours while stirring, and then dried in a ventilation drying oven at 80 °C for 3 hours to be dried and solidified. Further, the annealing in step S63 (850 °C, 2 hours) was performed. Other conditions were the same as those of sample 1-2.

[0539] Next, when the number of cobalt atoms was set to 100, a sample prepared by adding so that the number of molecules of lithium fluoride was 0.66 and the number of molecules of magnesium fluoride was 2 and otherwise the same as sample 1-5 was designated as sample 1-6.

[0540] Next, as in the manufacturing method shown in Fig. 13, a sample prepared by repeating the annealing and the adhesion suppression operation a plurality of times was designated as sample 1-7. At this time, the first and second annealings were at 900 °C for 10 hours, and the third annealing was at 920 °C for 10 hours. As an adhesion suppression operation during the annealing, the composite oxide was put into a mortar and crushed with a pestle. Other conditions were the same as those of sample 1-3.

[0541] Next, a sample prepared in the same manner as sample 1-7 except that the temperature of the third annealing was 900 °C was designated as sample 1-8.

[0542] As a comparative example, lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Celsid C-10N) having cobalt as a transition metal and particularly having no additive element was used as Sample 2.

[0543] Sample 3 was prepared in the same manner as Samples 1-3 except that no nickel source and aluminum source were used.

[0544] Sample 4 was prepared in the same manner as Samples 1-5 except that no nickel source and aluminum source were used.

[0545] Sample 5 was prepared in the same manner as Samples 1-5 except that no aluminum source was used.

[0546] Sample 6 was prepared in the same manner as Samples 1-5 except that no nickel source was used.

[0547] Sample 7 was prepared in the same manner as Sample 3 except that when the number of cobalt atoms was 100, 0.17 molecules of lithium fluoride and 0.5 molecules of magnesium fluoride were added.

[0548] Sample 8 was prepared in the same manner as Sample 6 except that when the number of cobalt atoms was 100, 0.17 molecules of lithium fluoride and 0.5 molecules of magnesium fluoride were added, the annealing temperature in Step S43 was 900 °C for 20 hours, and a titanium source was used instead of the aluminum source, and titanium isopropoxide (TTIP) was used as the titanium source.

[0549] The preparation conditions of Samples 1-1 to 8 are shown in Table 1. As is clear from Table 1, Samples 1-1 to 1-8 are all annealed after adding a magnesium source, a fluorine source, a nickel source, and an aluminum source to LiCoO2 having no additive element in particular. Therefore, in order to distinguish them from samples having no common points, all of these may be called Sample 1.

[0550]

Table 1

[0551] <sem> Figure 37A shows the surface SEM image of Sample 1-2, Figure 37B shows that of Sample 1-3, Figure 37C shows that of Sample 1-4, and Figure 37D shows that of Sample 2. It was observed that all of Samples 1-2 to 1-4, to which additives were added and annealed, had rounded corners, few irregularities, and smooth surfaces. On the other hand, Sample 2 without annealing was observed to have relatively sharp corners, many irregularities, and a rough surface.

[0552] <Electron beam diffraction> The results of analyzing the positive electrode active material of Sample 1-1 prepared above by cross-sectional TEM and electron beam diffraction are shown in Figures 38 to 41.

[0553] Figure 38A is a cross-sectional TEM image from the surface of the positive electrode active material to a depth of about 3 μm. The selected area electron beam diffraction image of area1 indicated by the white circle in Figure 38A is shown in Figure 38B. Some of the bright spots in Figure 38B are designated as 1, 2, 3, and O as shown in Figure 38C. O is transmitted light, and 1, 2, and 3 are diffraction spots.

[0554] area1 is at a depth of 50 nm or more from the surface and is inside the positive electrode active material. The measured values of the selected area diffraction image inside were d = 0.144 nm for 1, d = 0.138 nm for 2, and d = 0.479 nm for 3. The plane angles were ∠1O2 = 17°, ∠1O3 = 90°, and ∠2O3 = 74°.

[0555] From these results, it was confirmed that the inside of the positive electrode active material has a layered rock salt-type crystal structure. The lattice constant of the a-axis was 2.88 Å, and the lattice constant of the c-axis was 14.37 Å. Note that 1 Å is 10 -10 m.

[0556] The literature values of layered rock salt-type LiCoO2 are d = 0.141 nm for 1, d = 0.135 nm for 2, d = 0.468 nm for 3, and the plane angles are ∠1O2 = 17°, ∠1O3 = 90°, and ∠2O3 = 73°. The difference from the literature values is considered to be measurement error.

[0557] Figure 39A shows the micro electron beam diffraction image inside the positive electrode active material. Some of the bright spots in Figure 39A are labeled as 1, 2, 3, and O as shown in Figure 39B.

[0558] The measured values of the internal micro electron beam diffraction image were d = 0.142 nm for 1, d = 0.122 nm for 2, and d = 0.240 nm for 3. The plane angles were ∠1O2 = 30°, ∠1O3 = 90°, and ∠2O3 = 59°.

[0559] From these results, it was also confirmed that the inside of the positive electrode active material has a layered rock salt type crystal structure. The lattice constant A of the a-axis core was 2.84 Å, and the lattice constant of the c-axis was C core 14.4 Å.

[0560] Figure 40A is a cross-sectional TEM image from the surface of the positive electrode active material to a depth of about 40 nm. The micro electron beam diffraction image of point2 indicated by * in Figure 40A is shown in Figure 40B. Some of the bright spots in Figure 40B are labeled as 1, 2, 3, and O as shown in Figure 40C.

[0561] Point2 is at a depth of about 13 nm from the surface and is a part of the inside of the positive electrode active material where the aluminum concentration is high in the linear EDX line analysis described later. The measured values of the micro electron beam diffraction image of this part were d = 0.143 nm for 1, d = 0.122 nm for 2, and d = 0.240 nm for 3. The plane angles were ∠1O2 = 31°, ∠1O3 = 89°, and ∠2O3 = 59°.

[0562] From this result as well, it was confirmed that the inside of the positive electrode active material has a layered rock salt type crystal structure. The lattice constant of the a-axis was 2.86 Å, and the lattice constant of the c-axis was 14.4 Å. The values were close to those calculated from Figures 39A and 39B, indicating that there is no significant difference in the lattice constant even in the region with a high aluminum concentration inside.

[0563] Figure 41A is a cross-sectional TEM image from the surface to a depth of about 30 nm of the positive electrode active material. The nanoelectron diffraction image of point 1 indicated by * in Figure 41A is shown in Figure 41B. Some of the bright spots in Figure 41B are designated as 1, 2, 3, and O as shown in Figure 41C.

[0564] Point 1 is the outermost surface layer among the surface layer portions of the positive electrode active material. The measured values of the nanoelectron diffraction image of the outermost surface layer were d = 0.151 nm for 1, d = 0.128 nm for 2, and d = 0.266 nm for 3. The plane angles were ∠1O2 = 31°, ∠1O3 = 90°, and ∠2O3 = 59°.

[0565] As shown in Figure 41B, in the nanoelectron diffraction image of the outermost surface layer, bright spots with strong brightness and bright spots with weak brightness like arrows were alternately arranged. When paying attention to the arrangement of the bright spots including the weak brightness, the crystal structure identified from such a diffraction image of the arrangement is a layered rock salt type. However, when only the bright spots with strong brightness are extracted, it can be judged that the crystal structure is close to the rock salt type. Therefore, it can be said that the outermost surface layer from which this diffraction image was obtained has the characteristics of the layered rock salt type crystal structure, but also has some characteristics of the rock salt type crystal structure. The difference in brightness in such a diffraction image corresponds to the difference in brightness in the TEM image shown in Figure 43B etc.

[0566] Lattice constant A of the a-axis surface was 3.02 Å, and the lattice constant C of the c-axis surface was 15.96 Å.

[0567] The lattice constants of the interior and the outermost surface layer obtained above are shown in Table 2. The literature values are also shown for comparison.

[0568]

Table 2

[0569] As shown in Table 2, in the positive electrode active material of one aspect of the present invention, the lattice constant A of the a-axis of the outermost surface layer, which is a part of the surface layer portion calculated by nanoelectron diffraction surface is 3.02 Å, and the lattice constant A of the a-axis of the interior calculated by nanoelectron diffraction core was larger than 2.84 Å. Similarly, the lattice constant C of the c-axis of the outermost surface layer surface was 15.96 Å, which was larger than the lattice constant C of the internal c-axis calculated by nanoelectron diffraction core of 14.4 Å.

[0570] Table 3 shows the differences and rates of change in the lattice constants of the internal and outermost surface layers obtained by nanoelectron diffraction.

[0571]

Table 3

[0572] As shown in Table 3, the difference Δ surface between the lattice constant A of the a-axis of the outermost surface layer and the lattice constant A of the internal a-axis core was smaller than 0.18 Å, while the difference Δ A between the lattice constant C of the c-axis of the outermost surface layer and the lattice constant C of the internal c-axis surface was 1.56 Å, which was larger. core C

[0573] Also, the rate of change R surface between the lattice constant A of the a-axis of the outermost surface layer and the lattice constant A of the internal a-axis core was 0.063. The rate of change R A between the lattice constant C of the c-axis of the outermost surface layer and the lattice constant C of the internal c-axis surface was 0.108. core C

[0574] From these results, it was revealed that the change in the lattice constant between the internal and outermost surface layers was larger in the c-axis direction than in the a-axis direction.

[0575] <Cross-sectional STEM and luminance> ​​​​Cross-sectional STEM images of the positive electrode active material of Sample 1-1 prepared above are shown in FIGS. 42A to 42C. FIG. 42A is a cross-sectional STEM image from the surface of the positive electrode active material to a depth of about 15 nm. FIG. 42B is a cross-sectional STEM image in the range of about 6 nm in depth and about 8 nm in width from the surface of the positive electrode active material. FIG. 42C is a cross-sectional STEM image to a depth of about 3.5 nm from the surface. These are dark field images.

[0576] As shown in FIG. 42A, inside the positive electrode active material, a layer of transition metal M was observed as a row of strong white bright spots, having a layered rock salt-type crystal structure and showing high crystallinity. Also, the surface of the positive electrode active material was approximately parallel to the (001) plane of the layered rock salt-type crystal structure. Further, the lithium layer present between the transition metal M layers was only slightly gray, and almost no bright spots were observed. The same was true for oxygen that forms an octahedron around the transition metal M. It became clear that in this cross-sectional STEM image, elements with small atomic numbers such as lithium and oxygen do not become distinct bright spots.

[0577] On the other hand, as shown in FIGS. 42B and 42C, weak bright spots were observed at the lithium sites in the outermost surface layer. Since the brightness is higher than that of lithium and oxygen, it is considered to be an element with a larger atomic number than lithium. Also, since the element is present at the lithium site and can be a cation, this is a metal element with a larger atomic number than lithium. That is, it is a transition metal M or a metal element among the additive elements. Among the additive elements possessed by Sample 1-1, the metals are magnesium and aluminum. Therefore, the weak bright spots present at the lithium sites in the outermost surface layer are considered to be cobalt, magnesium, or aluminum.

[0578] Results of comparing the brightness of the transition metal M site layer and the lithium site layer using the cross-sectional STEM image of FIG. 42B are shown in FIGS. 43A to 44B. FIG. 43A is a figure obtained by rotating FIG. 42B by 90°. For the image of FIG. 43A, the brightness was integrated parallel to the transition metal M site layer. FIG. 43B shows the brightness of each pixel row in a graph.

[0579] Next, in order to facilitate comparison of the brightness of the metal elements, the brightness derived from anions such as oxygen atoms was corrected as the background. Specifically, the vertices of the valleys of each peak were approximated by a straight line for correction. The background is shown by a dotted line in Fig. 43B.

[0580] Fig. 44A shows the corrected graph. The horizontal axis is the depth from the surface. The peak of the brightness of the first metal element was taken as the surface. Also, the vertical axis is the intensity, which was normalized with the maximum value of the number of white pixels up to a depth of 6 nm being 1. Fig. 44B shows the figure of Fig. 43A with the brightness reversed for better visibility.

[0581] As shown in Fig. 44A, in the region where the depth from the surface was deeper than 3 nm, the transition metal M site layer existed with strong brightness. There was no peak in the lithium site layer between the transition metal M site layers.

[0582] On the other hand, at a depth of less than about 0.8 nm from the surface, both the transition metal M site layer and the lithium site layer had low peaks and sufficient intensity could not be obtained. There may be an error due to the unevenness of the positive electrode active material. However, at a depth of 0.8 nm or more from the surface, the brightness of the transition metal M site layer was 0.7 or more of the maximum value and sufficient intensity was obtained.

[0583] In the region from a depth of about 0.8 nm from the surface to a depth of 3 nm, a lower peak than the transition metal M site layer was observed in the lithium site layer (arrow of the dotted line in Fig. 44A). This low peak is considered to indicate the presence of the additive metal element or transition metal M in the lithium site layer. The peak of this lithium site layer was 3% or more and 60% or less of the maximum value, more specifically 4% or more and 50% or less, and even more specifically 6% or more and 40% or less. Also, when compared with the intensity of the first sufficient-intensity transition metal site layer, it was 5% or more and 65% or less, more specifically 8% or more and 50% or less.

[0584] <EDX line analysis> The results of EDX line analysis of the surface layer part of the cross-section of the positive electrode active material of Sample 1-1 prepared above are shown in Figs. 45A to 47E.

[0585] For easy comparison, FIGS. 45A, 46A, and 47A show the same cross-sectional HAADF-STEM images including the surface and interior of the positive electrode active material. FIG. 45B is a mapping image of fluorine in the same part as the HAADF-STEM image, FIG. 45C is carbon, FIG. 45D is magnesium, FIG. 45E is oxygen, and FIG. 45F is aluminum. FIG. 46B is a mapping image of nickel in the same part as the HAADF-STEM image, FIG. 46C is silicon, and FIG. 46D is cobalt. To enhance visibility, FIGS. 47B to 47E show the mapping images of some elements with inverted brightness. FIG. 47B is a mapping image of fluorine with inverted brightness, FIG. 47C is magnesium, FIG. 47D is aluminum, and FIG. 47E is nickel.

[0586] From FIGS. 45 to 47, it became clear that oxygen and cobalt were distributed throughout the positive electrode active material. Also, the concentrations of magnesium and fluorine were high in the surface layer, especially in the outermost surface layer. Aluminum was observed to be broadly distributed up to about 30 nm from the surface. Nickel was considered to have a concentration below the background.

[0587] <EDX Line Analysis> Next, EDX line analysis was performed on the surface layer of the positive electrode active material of Sample 1-1. FIG. 48 is a cross-sectional STEM image including the surface and interior of the positive electrode active material. The region surrounded by the white line in FIG. 48 is the measurement region. Analysis was performed from the outside to the inside of the positive electrode active material 100 as indicated by the white arrow in the figure. The results are shown in FIGS. 49A and 49B. The horizontal axis represents the distance from the measurement start point (Distance), and the vertical axis represents atomic% (Atomic%). Note that the detection limit of EDX line analysis is approximately 1 atomic% depending on the element.

[0588] FIG. 49B is an enlarged view of a part of FIG. 49A. From FIGS. 49A and 49B, it was confirmed that magnesium and fluorine were present in the outermost surface layer and had a concentration gradient with the concentration increasing from the inside to the surface. The surface concentration was the highest and was a sharp peak. The distribution of silicon also showed a similar trend.

[0589] The peak of magnesium concentration was at the measurement point with a distance of 4.6 nm and a magnesium concentration of 4.0 atomic %. The peak of fluorine concentration was at the measurement point with a distance of 4.4 nm and a fluorine concentration of 4.0 atomic %.

[0590] The peak of aluminum concentration was at a deeper position than the peaks of magnesium and fluorine, and was broadly distributed over a distance of 20 nm or more. The peak of aluminum concentration was at the measurement point with a distance of 16.1 nm and an aluminum concentration of 3.9 atomic %.

[0591] Nickel was below the detection limit at all measurement points, that is, less than 1 atomic %.

[0592] Oxygen was detected even outside the surface of the positive electrode active material. This is considered to be due to the influence of carbonic acid, hydroxy groups, etc. chemisorbed on the surface after the production of the positive electrode active material, or background.

[0593] When preparing the cross-sectional STEM sample by FIB, a carbon protective film was formed, so a large amount of carbon was detected outside the surface of the positive electrode active material. Carbon inside the surface is considered to be background.

[0594] The surface was estimated as follows from the detected amount of oxygen. First, the range of 20 - 40 nm indicated by the arrow in Fig. 49A was defined as the region where the atomic % of oxygen was stable. The average atomic % of oxygen in this region was 54.4%. Also, the range of 0 - 3 nm in distance was defined as the region where the atomic % of background or chemisorbed oxygen was stable. The average O background in this region was 11.8%. The corrected average O ave of oxygen was taken as 42.6% which is the result of subtracting O background from O ave . Therefore, 1 / 2O ave was 21.3%. The measurement point of oxygen closest to this value was at a distance of 4.4 nm. Therefore, in this example, etc., the surface was estimated to be at a distance of 4.4 nm. This was the same measurement point as the peak of fluorine concentration.

[0595] When estimating the surface from the detected amount of cobalt, it is as follows. The range of 20 - 40 nm in distance was defined as the region where the atomic percentage of cobalt is stable. The average Co of cobalt in this region ave was 37.8 atomic %. Therefore, 1 / 2 Co ave was 18.9 atomic %. The cobalt measurement point closest to this was at a distance of 4.6 nm.

[0596] Thus, regardless of whether oxygen or cobalt is used, the measurement points at almost the same distance are estimated to be the surface. From these results, it can be said that any of the above methods is a reasonable method for estimating the surface.

[0597] Thus, from the EDX surface analysis and line analysis, it was confirmed that the positive electrode active material of one embodiment of the present invention has magnesium and fluorine in the surface layer part, especially in the outermost surface layer, and is the positive electrode active material 100 having a concentration gradient from the inside to the surface. Also, it was confirmed that the concentration peak of aluminum exists at a position deeper than the concentrations of magnesium and fluorine.

[0598] When the distance estimated from the detected amount of oxygen for the surface was 4.4 nm, the peak of the magnesium concentration was at a depth of 0.2 nm. The peak of the fluorine concentration was at a depth of 0 nm. The peak of the aluminum concentration was at a depth of 11.7 nm.

[0599] <Irregularities on the surface of the active material> Next, regarding the smoothness of the surface of the positive electrode active material prepared above, the surface irregularities of Sample 1 - 1 and Sample 2 were measured and evaluated by the following method.

[0600] First, SEM images of Sample 1-1 and Sample 2 were obtained. At this time, the SEM measurement conditions for Sample 1-1 and Sample 2 were made the same. Examples of the measurement conditions include acceleration voltage or magnification. In this example, conductive coatings were applied to Sample 1-1 and Sample 2 as pretreatment before observation. Specifically, platinum sputtering was performed for 20 seconds. Observation was carried out using a scanning electron microscope SU8030 manufactured by Hitachi High-Tech Corporation. The measurement conditions were an acceleration voltage of 5 kV and a magnification of 5000 times. As other measurement conditions, the working distance was 5.0 mm, the emission current was 9 to 10.5 μA, the extraction voltage was 5.8 V, the SEU mode (Upper secondary-electron detector), and the ABC mode (Auto Brightness Contrast Control) were also made the same, and observation was performed with autofocus.

[0601] The SEM images of Sample 1-1 are shown in Fig. 50A, and those of Sample 2 are shown in Fig. 50B. It was observed that the surface of Sample 1-1 heated after adding the additive element was smoother than that of Sample 2. In each figure, the target areas for the next image analysis were indicated by squares. The area of the target area was 4 μm × 4 μm, and the same area was used for all samples. The inside of the target area was made horizontal as the SEM observation surface.

[0602] Here, the inventors focused on the fact that in the images shown in Figs. 50A and 50B, the surfa...

Claims

1. A positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, The lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material ｓｕｒｆａｃｅ is larger than the lattice constant A of the a-axis inside ｃｏｒｅ and The lattice constant C of the c-axis of the outermost layer ｓｕｒｆａｃｅ is larger than the lattice constant C of the c-axis of the interior ｃｏｒｅ and The lattice constant A of the a-axis of the outermost surface layer ｓｕｒｆａｃｅ and the lattice constant A of the a-axis of the interior ｃｏｒｅ The difference Δ Ａ is divided by the lattice constant A ｃｏｒｅ The change rate R Ａ is 0.05 or more and 0.07 or less, The lattice constant C of the c-axis of the outermost surface layer ｓｕｒｆａｃｅ and the lattice constant C of the c-axis of the interior ｃｏｒｅ The difference Δ Ｃ divided by the lattice constant C ｃｏｒｅ The change rate R Ｃ is 0.09 or more and 0.12 or less. The positive electrode active material

2. In Claim 1, The lattice constant A of the a-axis of the outermost surface layer ｓｕｒｆａｃｅ and the lattice constant A of the a-axis of the interior ｃｏｒｅ with a difference Δ Ａ is greater than The lattice constant C of the c-axis of the outermost surface layer ｓｕｒｆａｃｅ and the lattice constant C of the c-axis of the interior ｃｏｒｅ and the difference Δ Ｃ is large, a positive electrode active material.

3. In Claim 1 or Claim 2, the concentration of nickel in the outermost surface layer is 1 atomic % or less, and the concentration of nickel in the entire positive electrode active material is 0.05% or more and 4% or less of the concentration of cobalt. Positive electrode active material.

4. A positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, The lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material ｓｕｒｆａｃｅ is larger than the lattice constant A of the a-axis inside ｃｏｒｅ and The lattice constant C of the c-axis of the outermost layer ｓｕｒｆａｃｅ is larger than the lattice constant C of the c-axis of the interior ｃｏｒｅ and wherein the outermost surface layer has a region where bright spots showing a rock salt-type crystal structure belonging to the space group Fm-3m and bright spots showing a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the convergent electron beam diffraction image, and the interior has a region where bright spots showing a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the convergent electron beam diffraction image. Positive electrode active material.

5. In any one of Claims 1 to 3, the outermost surface layer has a region where bright spots showing a rock salt-type crystal structure belonging to the space group Fm-3m and bright spots showing a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the convergent electron beam diffraction image, and the interior has a region where bright spots showing a layered rock salt-type crystal structure belonging to the space group R-3m are observed in the convergent electron beam diffraction image. Positive electrode active material.

6. A positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, The lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material ｓｕｒｆａｃｅ is larger than the lattice constant A of the a-axis inside ｃｏｒｅ and The lattice constant C of the c-axis of the outermost layer ｓｕｒｆａｃｅ is larger than the lattice constant C of the c-axis of the interior ｃｏｒｅ and A positive electrode active material having a spin density caused by any one or more of divalent nickel ions, trivalent nickel ions, divalent cobalt ions, and tetravalent cobalt ions of 2.0×10 １７ spins / g or more and 1.0×10 ２１ spins / g or less.

7. In any one of Claims 1 to 5, The spin density caused by any one or more of divalent nickel ions, trivalent nickel ions, divalent cobalt ions, and tetravalent cobalt ions is 2.0×10 １７ spins / g or more and 1.0×10 ２１ spins / g or less as a positive electrode active material.

8. In any one of Claims 1 to 7, the positive electrode active material contains aluminum, and the concentration of aluminum in the entire positive electrode active material is 0.05% or more and 4% or less of the concentration of cobalt. Positive electrode active material.

9. A positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, The lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material ｓｕｒｆａｃｅ is larger than the lattice constant A of the a-axis inside ｃｏｒｅ and The lattice constant C of the c-axis of the outermost layer ｓｕｒｆａｃｅ is larger than the lattice constant C of the c-axis of the interior ｃｏｒｅ and the positive electrode active material contains aluminum, the concentration of aluminum in the entire positive electrode active material is 0.05% or more and 4% or less of the concentration of cobalt, and in the energy dispersive X-ray analysis of the cross section of the positive electrode active material, the peak of the concentration of aluminum is located at a depth of 5 nm or more and 30 nm or less from the surface of the positive electrode active material toward the center. Positive electrode active material.

10. In any one of Claims 1 to 7, the positive electrode active material contains aluminum, The concentration of aluminum in the entire positive electrode active material is 0.05% or more and 4% or less of the concentration of cobalt, In the energy dispersive X-ray analysis of the cross section of the positive electrode active material, the peak of the concentration of aluminum is located at a depth of 5 nm or more and 30 nm or less from the surface of the positive electrode active material toward the center, the positive electrode active material.

11. A lithium ion secondary battery having the positive electrode active material according to any one of Claims 1 to 10.

12. An electronic device having the lithium ion secondary battery according to Claim 11.

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