Positive electrode active material particles and lithium ion secondary battery

Abstract

Provided are novel positive electrode active material particles and a lithium ion secondary battery using the same. These positive electrode active material particles have lithium, a transition metal M, and oxygen. The transition metal M is one or more selected from the group consisting of cobalt, nickel, and manganese. Each of the positive electrode active material particles has, in the stated order from the surface toward the interior, a rock salt-type crystal structure, a spinel'-type crystal structure, and a layered rock salt-type crystal structure. When analyzed by using each of the particles as a whole, the positive electrode active material particle has a Ti / transition metal M ratio (a weight ratio) of 0.0005 or smaller.

Description

Positive electrode active material particles and lithium-ion secondary batteries

[0001] One aspect of the present invention relates to a product, a method, or a method of manufacture; or to a process, a machine, a manufacture, or a composition of matter. Another aspect of the present invention relates to an energy storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a method of manufacturing the same.

[0002] In this specification, "electronic equipment" refers to all devices that have an energy storage device, and all electro-optical devices with an energy storage device, information terminal devices with an energy storage device, etc., are considered electronic equipment.

[0003] In recent years, there has been a great deal of development on various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries. In particular, the demand for lithium-ion secondary batteries, which offer high output and high capacity, has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable as a source of rechargeable energy in today's information society.

[0004] In particular, there is a high demand for secondary batteries for mobile electronic devices that have a large discharge capacity per unit weight and excellent cycle characteristics. To meet these demands, there is a great deal of research being done on improving the positive electrode active material of secondary batteries (for example, Patent Documents 1 and 2). Research is also being conducted on the crystal structure of positive electrode active materials (Non-Patent Documents 1 to 3).

[0005] X-ray diffraction (XRD) is one of the methods used to analyze the crystal structure of positive electrode active materials. By using ICSD (Inorganic Crystal Structure Database), which is introduced in Non-Patent Document 4, XRD data can be analyzed. For example, the lattice constant of lithium cobalt oxide, as described in Non-Patent Document 5, can be referenced from ICSD. For Rietveld method analysis, for example, the analysis program RIETAN-FP (Non-Patent Document 6) can be used. In addition, VESTA (Non-Patent Document 7) can be used as crystal structure plotting software.

[0006] Micro-electron diffraction is also effective in identifying the crystal structure of the positive electrode active material, particularly the crystal structure of the surface layer. For analyzing the electron diffraction pattern, for example, the analysis program ReciPro (Non-Patent Literature 8) can be used.

[0007] Furthermore, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images are also effective for identifying the crystal structure of the surface layer. For calculating HAADF-STEM images, software such as abTEM (Non-Patent Literature 9) can be used.

[0008] Japanese Patent Publication No. 2018-206747 Japanese Patent Publication No. 2022-070247

[0009] M.Mikami et al.,“Controlling lithium cobalt oxide phase transition using molten fluoride salt for improved lithium−ion batteries”,Communications Materials 5:108(2024)E.Rossen,J.N.Reimersand J.R.Dahn,“Synthesis and electrochemistry of spinel LT−LiCoO▲2▼”,Solid State Ionics 62(1993)53−60Thandavarayan Maiyalagan et al.,“Spinel−type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions”,Nature Communications 5:3949(2014)A.Belsky 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.J.Akimoto,Y.Gotoh,Y.Oosawa,“Synthesis and structure refinement of LiCoO▲2▼ single crystals”Journal of Solid State Chemistry(1998)141,p.298−302.F.Izumi and K.Momma,“Three−Dimensional Visualization in Powder Diffraction”Solid State Phenom.130,15−20(2007)K.Momma and F.Izumi,“VESTA 3 for three−dimensional visualization of crystal,volumetric and morphological data” J. Appl. Cryst. (2011). 44, 1272-1276 Seto, Y. & Ohtsuka, M. “ReciPro: free and open-source multipurpose crystallographic software integrating a crystal model database and viewer, diffraction and microscopy simulators, and diffraction data analysis tools" (2022). J. Appl. Cryst. 55. Jacob Madsen and Toma Susi. The abTEM code: transmission electron microscopy from first principles. Open Research Europe 1:24, 2021. doi:10.12688 / openreseurope.

[0010] Lithium-ion secondary batteries still have room for improvement in various aspects, including output characteristics, discharge capacity, cycle characteristics, reliability, safety, and cost. For example, to suppress side reactions with the electrolyte, to suppress changes in the crystal structure of the positive electrode active material particle surface, or to suppress phase changes during charging and discharging, the positive electrode active material may have a core-shell structure. In other words, the inside of the particle (core) may be coated with an oxide (shell) containing elements different from those inside. However, if there is a discontinuous interface between the coating layer and the inside, changes in interatomic distances and other parameters will be large at that interface. That is, the interatomic distance of the coating layer and the interatomic distance of the inside will be different, and the difference will be large. Since the volume of the positive electrode active material particles changes with charging and discharging, discontinuous interfaces can cause defects. In particular, defects are likely to occur if there is a large lattice mismatch at the interface of different crystals. Also, oxides containing elements different from those inside may not allow lithium ions to diffuse sufficiently. If the diffusion of lithium ions in the positive electrode active material is inhibited, it becomes an internal resistance of the secondary battery, and the charge and discharge capacity decreases.

[0011] Therefore, one aspect of the present invention aims to provide positive electrode active material particles or composite oxides that can be used in lithium-ion secondary batteries and in which the decrease in discharge capacity during charge-discharge cycles is suppressed. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides that are less prone to defects and / or crystal structure collapse even after repeated charge-discharge cycles. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides with a large charge-discharge capacity. Alternatively, one aspect aims to provide a secondary battery or vehicle that is safe or highly reliable.

[0012] Furthermore, one aspect of the present invention aims to provide positive electrode active material particles, composite oxides, energy storage devices, or methods for producing the same.

[0013] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims.

[0014] Therefore, one aspect of the present invention proposes positive electrode active material particles in which the interatomic distance and crystal structure gradually change from the surface to the interior. Alternatively, it proposes positive electrode active material particles in which the interatomic distance and crystal structure gradually change from the interior to the surface. Thus, the positive electrode active material particles of one aspect of the present invention have a layered rock salt type crystal structure with a two-dimensional lithium diffusion pathway in the interior, and two different crystal structures in the surface layer. One of the two crystal structures in the surface layer has a lithium diffusion pathway different from that of the layered rock salt type.

[0015] One aspect of one aspect of the present invention is a positive electrode active material particle having lithium, a transition metal M, oxygen, and an additive element, wherein the transition metal M is one or more selected from cobalt, nickel, and manganese, and the positive electrode active material particle has, in order from the surface to the interior, a rock salt type crystal structure, a Spinel' type crystal structure, and a layered rock salt type crystal structure.

[0016] Further, in the above, the positive electrode active material particles have magnesium as an additive element, and the positive electrode active material particles have a layered rock salt-type crystal structure of space group R-3m of 90% or more in the Rietveld analysis of the XRD pattern. The layered rock salt-type crystal structure has alternating transition metal M layers and lithium layers. In the Spinel'-type crystal structure, no atoms are confirmed at the tetrahedral sites in the cross-sectional ABF-STEM image and the HAADF-STEM image, and bright spots with high brightness and bright spots with low brightness are alternately arranged in the depth direction in the transition metal M layer of the HAADF-STEM image. In the ICP-MS analysis of the positive electrode active material particles, it is preferable that Ti / transition metal M (weight ratio) is 0.0005 or less.

[0017] Further, in the above, in the Spinel'-type crystal structure, it is preferable that no atoms are confirmed at the tetrahedral sites in the cross-sectional ABF-STEM image and the HAADF-STEM image, and atoms exist at the octahedral sites.

[0018] Further, in the above, the Spinel'-type crystal structure is preferably assigned to the space group Fd-3m and has a transition metal M at the 16d site.

[0019] Further, in the above, the angle formed by the anion arrangement in the layered rock salt-type crystal structure and the anion arrangement in the Spinel'-type crystal structure is 0° or more and 5° or less, and the angle formed by the anion arrangement in the Spinel'-type crystal structure and the anion arrangement in the rock salt-type crystal structure is preferably 0° or more and 5° or less.

[0020] Further, in the above, when the first atomic layer where cations are observed in the cross-sectional ABF-STEM image and the HAADF-STEM image of the surface where lithium is inserted and removed is defined as the first layer, it is preferable that the first to fourth layers have the characteristics of the rock salt-type crystal structure and the fourth to eighth layers have the characteristics of the Spinel'-type crystal structure.

[0021] Another aspect of the present invention is a positive electrode active material particle comprising lithium, a transition metal M, oxygen, and an additive element, wherein the transition metal M is one or more selected from cobalt, nickel, and manganese, and the positive electrode active material particle sequentially exhibits the characteristics of a layered rock salt type crystal structure, a Spinel' type crystal structure, and a rock salt type crystal structure from the interior to the surface, and the Ti / Co (weight ratio) of the positive electrode active material particle is 0.0005 or less in ICP-MS analysis of the positive electrode active material particle.

[0022] Another aspect of the present invention is a lithium-ion secondary battery having the positive electrode active material particles described above.

[0023] According to one aspect of the present invention, it is possible to provide positive electrode active material particles or composite oxides that can be used in lithium-ion secondary batteries and in which the decrease in discharge capacity during charge-discharge cycles is suppressed. Alternatively, it is possible to provide positive electrode active material particles or composite oxides that are less prone to defects and / or crystal structure collapse even after repeated charge-discharge cycles. Alternatively, it is possible to provide positive electrode active material particles or composite oxides with a large charge-discharge capacity. Alternatively, it is possible to provide a secondary battery or vehicle that is safe or highly reliable.

[0024] Furthermore, according to one aspect of the present invention, positive electrode active material particles, composite oxides, energy storage devices, or methods for producing the same can be provided.

[0025] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims.

[0026] Figure 1A is a cross-sectional view illustrating the internal structure of a secondary battery, and Figure 1B is a cross-sectional view illustrating the positive electrode and electrolyte of the secondary battery. Figures 2A and 2B are cross-sectional views illustrating a positive electrode active material according to one embodiment of the present invention, and Figure 2C is a model illustrating a Spinel'-type crystal structure. Figure 3A is a model illustrating a Spinel'-type crystal structure, Figure 3B is a schematic diagram of the surface layer of a positive electrode active material according to one embodiment of the present invention, and Figure 3C is the result of a HAADF-STEM simulation for a Spinel'-type crystal structure. Figure 4 is a diagram illustrating the histogram of the grayscale of an ABF-STEM image. Figures 5A, 5B, and 5C are diagrams illustrating a method for producing positive electrode active material particles. Figure 6A is an exploded perspective view of a coin-type secondary battery, Figure 6B is a perspective view of a coin-type secondary battery, and Figure 6C is a cross-sectional perspective view thereof. Figure 7A shows an example of a cylindrical secondary battery. Figure 7B shows an example of a cylindrical secondary battery. Figure 7C shows multiple examples of cylindrical secondary batteries. Figure 7D shows an example of an energy storage system having multiple cylindrical secondary batteries. Figures 8A and 8B are diagrams illustrating examples of secondary batteries, and Figure 8C shows the inside of a secondary battery. Figures 9A, 9B, and 9C are diagrams illustrating examples of secondary batteries. Figures 10A and 10B show the external appearance of a secondary battery. Figures 11A, 11B, and 11C illustrate a method for manufacturing a secondary battery. Figure 12A shows an example of a battery pack configuration, Figure 12B shows an example of a battery pack configuration, and Figure 12C shows an example of a battery pack configuration. Figure 13A is a perspective view of a battery pack showing one aspect of the present invention, Figure 13B is a block diagram of the battery pack, and Figure 13C is a block diagram of a vehicle having a battery pack. Figures 14A, 14B, 14C, and 14D illustrate an example of a transport vehicle. Figure 14E illustrates an example of an artificial satellite. Figures 15A and 15B illustrate an energy storage device according to one aspect of the present invention. Figure 16A shows an electric bicycle, Figure 16B shows a secondary battery for an electric bicycle, and Figure 16C illustrates a scooter. Figures 17A, 17B, 17C, and 17D illustrate examples of electronic devices. Figure 18A shows an example of a wearable device, Figure 18B shows a perspective view of a wristwatch-type device, and Figure 18C illustrates a side view of a wristwatch-type device.Figure 19 is a cross-sectional HAADF-STEM image of the positive electrode active material particles. Figure 20A is a cross-sectional ABF-STEM image of the positive electrode active material particles, and Figure 20B is a HAADF-STEM image. Figure 21A is a diagram showing the cross-sectional ABF-STEM image of the positive electrode active material particles with the grayscale of the HAADF-STEM image subtracted. Figure 21B is a diagram explaining the crystal structure of each region in the ABF-STEM image. Figure 22A is a cross-sectional HAADF-STEM image of the positive electrode active material particles. Figures 22B, 22C, and 22D are measured electron diffraction patterns. Figure 23A is a cross-sectional HAADF-STEM image of the positive electrode active material particles. Figures 23B and 23C are EELS plane analysis results. Figure 23D is the EELS spectrum at the measurement point shown in Figure 23A. Figures 24A and 24B are graphs showing the results of cross-sectional STEM-EDX radiation analysis of positive electrode active material particles. Figure 25 is a graph showing some elements extracted from Figure 24B. Figures 26A and 26B are graphs showing the results of cross-sectional STEM-EDX radiation analysis of positive electrode active material particles.

[0027] The following describes embodiments for carrying out the present invention with reference to drawings and other illustrations. However, the present invention is not limited to the following embodiments. It is possible to modify the embodiments for carrying out the invention without departing from the spirit of the present invention.

[0028] Furthermore, in drawings, size, layer thickness, or area may be exaggerated for clarity. Therefore, the scale is not necessarily limited.

[0029] Furthermore, ordinal numbers such as "first," "second," etc., in this specification are added to avoid confusion of constituent elements and do not indicate any order or rank, such as process order or layering order. Even if an ordinal number is not used for a term in this specification, an ordinal number may be used in the claims to avoid confusion of constituent elements. Even if an ordinal number is used for a term in this specification, a different ordinal number may be used in the claims. Even if an ordinal number is used for a term in this specification, the ordinal number may be omitted in the claims.

[0030] In this specification, space groups are expressed using international notation (or Hermann-Mauguin notation) in short notation. Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by superscripting numbers, but in this specification, due to formatting constraints, a minus sign (-) may be placed before the number instead of a superscript. Individual orientations indicating directions within a crystal are represented by [ ], collective orientations indicating all equivalent directions are represented by < >, individual crystal planes are represented by ( ), and collective planes with equivalent symmetry are represented by {}. Furthermore, for ease of understanding the structure, trigonal crystals represented by space group R-3m are generally represented as a composite hexagonal lattice, and in this specification, unless otherwise specified, space group R-3m will be represented as a composite hexagonal lattice. In addition, (hkl) as well as (hkil) may be used as Miller indices. Here, i is -(h+k).

[0031] In this specification, the term "particle" is not limited to spherical shapes (circular cross-sections), but may also refer to individual particles with elliptical, rectangular, trapezoidal, triangular, rounded quadrilateral, or asymmetrical cross-sections, and individual particles may also have irregular shapes.

[0032] Furthermore, the space group of positive electrode active material particles, etc., is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, "belonging to a certain space group," "being part of a certain space group," or "being a certain space group" can be rephrased as "being identified to a certain space group."

[0033] Furthermore, if the anion has a structure in which three layers are stacked with a slight offset from each other, such as ABCABC, it will be called a cubic close-packed structure. Therefore, the anion does not have to be strictly a cubic lattice. At the same time, since real crystals always have defects, the analysis results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) patterns such as electron diffraction patterns or TEM (Transmission Electron Microscope) images, spots may appear at positions slightly different from the theoretical positions. For example, if the deviation in orientation from the theoretical position is between 0° and 5°, it can be said that it has a cubic close-packed structure.

[0034] Furthermore, the distribution of an element refers to the region in which that element is continuously detected within a non-noise range using a certain continuous analytical method. A region in which an element is continuously detected within a non-noise range can also be defined as a region in which the element is always detected when the analysis is performed multiple times.

[0035] In this specification and other documents, the positive electrode active material may be referred to as a composite oxide, positive electrode material, positive electrode material, positive electrode material for secondary batteries, positive electrode material for lithium-ion secondary batteries, etc.

[0036] Furthermore, when describing the characteristics of individual particles of the positive electrode active material in the following embodiments, it is not necessarily required that all particles possess those characteristics. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected positive electrode active material particles possess those characteristics, it can be said that this is sufficient to improve the characteristics of the positive electrode active material particles and the secondary battery having them.

[0037] Unless otherwise specified, the materials of a secondary battery (positive electrode active material particles, negative electrode active material, electrolyte, electrolyte solution, separator, etc.) will be described in their state before degradation. Note that a decrease in discharge capacity due to aging and burn-in treatments during the secondary battery manufacturing process is not considered degradation. For example, a secondary battery consisting of a single cell or a battery pack can be considered to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. The rated capacity for secondary batteries for portable devices conforms to JIS C 8711:2019. For other secondary batteries, the specifications may conform to various JIS and IEC standards, including those for electric vehicle propulsion and industrial use, in addition to the above JIS standard.

[0038] In this specification, the state of a secondary battery before material degradation is referred to as the initial product or initial state, and the state after degradation (the state in which the secondary battery has a discharge capacity of less than 97% of its rated capacity) may be referred to as a used product or in use, or a used product or a used state.

[0039] In this specification, the (001) plane and the (003) plane, etc., may be collectively referred to as the (00l) plane. In this specification, the (00l) plane in space group R-3m may be referred to as the C plane, basal plane, etc. Furthermore, in layered composite oxides of transition metal M and lithium, including lithium cobalt oxide, lithium has a two-dimensional diffusion pathway. That is, the diffusion pathway of lithium can be said to exist along the plane. In this specification, the plane where the diffusion pathway of lithium is exposed, that is, the plane where lithium is inserted and removed (specifically, the plane other than the (00l) plane), may be referred to as the edge plane.

[0040] In this specification, the phrase "A and / or B" may be used, but this is just one example of how A alone, B alone, or A and B may be included.

[0041] (Embodiment 1) In this embodiment, a secondary battery and positive electrode active material particles according to one aspect of the present invention will be described using Figures 1A to 3C.

[0042] [Battery] A lithium-ion secondary battery according to one aspect of the present invention comprises a positive electrode, a negative electrode, and an electrolyte. If the electrolyte contains an electrolyte solution, a separator is provided between the positive electrode and the negative electrode. Furthermore, an outer casing may be provided that covers at least a portion of the area around the positive electrode, the negative electrode, and the electrolyte.

[0043] This embodiment will primarily describe the positive electrode and positive electrode active material particles of a battery according to one aspect of the present invention. The method for producing the positive electrode active material particles according to one aspect of the present invention will be described in Embodiment 2, and the details of the remaining components of the lithium-ion secondary battery according to one aspect of the present invention will be described in Embodiment 3 and subsequent embodiments.

[0044] Figure 1A is a schematic cross-sectional view illustrating the internal structure of a lithium-ion secondary battery 10. The lithium-ion secondary battery 10 has a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22 on the positive electrode current collector 21, and the negative electrode 12 has a negative electrode current collector 31 and a negative electrode active material layer 32. As shown in the figure, the positive electrode active material layer 22 and the negative electrode active material layer 32 face each other with the separator 13 in between. Although not shown in Figure 1A, the electrolyte is contained in the voids of the positive electrode active material layer 22, the voids of the separator 13, and the voids of the negative electrode active material layer 32.

[0045] Although Figure 1A shows one positive electrode 11, one negative electrode 12, and one separator 13, the lithium-ion secondary battery according to one embodiment of the present invention is not limited to this structure. It may also have a structure with two positive electrodes 11, two negative electrodes 12, and two separators 13, or even more electrodes stacked. Furthermore, instead of the stacked structure shown in Figure 1A, a wound structure may also be used.

[0046] Figure 1B is an enlarged view of the area A enclosed by the dashed line in Figure 1A.

[0047] The positive electrode active material layer 22 comprises positive electrode active material particles 100 (also called the first positive electrode active material), a second positive electrode active material 200, and a conductive material 41. Although not shown in the figures, in addition to the positive electrode active material particles 100, the second positive electrode active material 200, and the conductive material 41, it may also have a binder.

[0048] Furthermore, the voids in the positive electrode active material layer 22 are preferably filled with electrolyte 51, as shown in the figure. For example, it is preferable that 60% or more of the voids in the positive electrode active material layer 22 are filled with electrolyte 51, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, and most preferably 99% or more. Note that the voids in the positive electrode active material layer 22 refer to the regions in the positive electrode active material layer 22 other than the solid components (positive electrode active material, conductive material, etc.).

[0049] [Positive electrode] The positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 has positive electrode active material particles 100, and the positive electrode active material particles 100 are a group of particles consisting of multiple particles.

[0050] <Positive electrode active material particles 100> The positive electrode active material particles 100 have the function of taking in lithium ions and releasing them during charging and discharging. The positive electrode active material used in one aspect of the present invention can be a material that does not degrade easily during charging and discharging. Specifically, it is preferable to use positive electrode active material particles (composite oxide) having the characteristics described in this embodiment and a particle size (median diameter (D50)) of 10 μm or more and 50 μm or less, preferably 9 μm or more and 25 μm or less.

[0051] The positive electrode active material particles 100 are the main constituent material of the positive electrode active material layer 22. The weight of the positive electrode active material particles 100 is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more of the weight of the solid components of the positive electrode active material layer 22. If the particle size of the positive electrode active material particles 100 is too small, the surface area will become too large, which may lead to excessive reaction between the positive electrode active material surface and the electrolyte. For this reason, the particle size (median diameter (D50)) of the positive electrode active material is preferably 10 μm or more. Furthermore, if the particle size of the positive electrode active material is larger than the thickness of the active material layer, as described later, the particle density of the active material layer cannot be increased. Therefore, it is preferable that the largest particle size be 50 μm or less.

[0052] The second positive electrode active material 200 is a positive electrode active material with a smaller particle size than the positive electrode active material particles 100. Other than particle size, the description of the positive electrode active material particles 100 can be used as a reference. By mixing positive electrode active materials with different particle sizes, the particle density of the active material layer can be increased.

[0053] Particle size can be measured using a particle size analyzer (laser diffraction particle size distribution analyzer) that employs laser diffraction and scattering methods. D50 is the particle size at which the cumulative amount accounts for 50% of the cumulative curve of the particle size distribution measurement results. Particle size measurement is not limited to laser diffraction particle size distribution measurement; the major axis of the particle cross-section may also be measured by analysis using SEM (Scanning Electron Microscope) or TEM. As a method for measuring D50 from analysis using SEM or TEM, for example, 20 or more particles can be measured, a cumulative curve can be created, and the particle size at which the cumulative amount accounts for 50% can be defined as D50.

[0054] The positive electrode active material particles 100 will be described using Figures 2A to 3C. Figure 2A is a schematic cross-sectional view of positive electrode active material particles 100 according to one embodiment of the present invention. As shown in Figure 2A, the positive electrode active material particles 100 have a surface layer 100a and an interior 100b. The boundary between the surface layer 100a and the interior 100b is indicated by a dashed line in the figure.

[0055] The surface layer 100a of the positive electrode active material particles 100 refers to, for example, a region within 10 nm perpendicular or nearly perpendicular to the surface, extending inward from the surface. Nearly perpendicular means an angle of 80° to 100°. Surfaces formed by cracks and / or fissures may also be considered the surface. The surface layer 100a is synonymous with the vicinity of the surface, the vicinity of the surface region, or the shell.

[0056] Furthermore, the region deeper than the surface layer 100a of the positive electrode active material particle 100 is called the interior 100b. Interior 100b is synonymous with the interior region or core. The interior 100b of the positive electrode active material particle 100 has a layered rock salt type crystalline structure belonging to space group R-3m.

[0057] The interior 100b occupies almost the entire volume of the positive electrode active material particles 100. Therefore, when the positive electrode active material particles 100 or the positive electrode containing them are measured by XRD and the XRD pattern is subjected to Rietveld analysis, it is preferable that 90% or more of the crystal structure is a layered rock salt type crystal structure with space group R-3m, and more preferably 95% or more. The same is preferable when diffraction methods other than XRD are used.

[0058] Figure 2B is an enlarged schematic diagram of the surface layer 100a of the area indicated by the rectangle in Figure 2A. The surface layer 100a of the positive electrode active material particle 100 has region I and region II. Region I is located on the outermost part of the positive electrode active material particle 100, includes the surface, and has a rock salt type crystal structure. Region II is adjacent to region I and is located closer to the interior 100b than region I, and has a Spinel' type crystal structure. The surface layer 100a may also have region III. Region III is adjacent to region II and is located closer to the interior 100b than region II, and, like the interior 100b, has a layered rock salt type crystal structure belonging to space group R-3m.

[0059] In other words, the positive electrode active material particles 100 have, in order from the surface toward the interior, a rock salt type crystal structure, a Spinel' type crystal structure, and a layered rock salt type crystal structure. To put it another way, the positive electrode active material particles 100 have, in order from the interior toward the surface, the characteristics of a layered rock salt type crystal structure, a Spinel' type crystal structure, and a rock salt type crystal structure.

[0060] In this specification, a rock salt-type crystal structure refers to a structure belonging to the cubic space group Fm-3m, in which cations (positive ions) and anions (negative ions) are arranged alternately. It can also be described as a crystal structure in which anions are arranged in cubic close-packing, with cations occupying all octahedral positions. There may be one type of cation and one type of anion, or multiple types. There may be vacancies in the cations or anions.

[0061] Furthermore, the layered rock salt type crystal structure belonging to space group R-3m is similar to the rock salt type in that cations and anions are arranged alternately at octahedral positions, and in addition, it is clear that multiple types of cations exist, and the arrangement of at least two of these cations forms a two-dimensional plane. If one of these two types of cations is a lithium ion, the lithium ion forms a two-dimensional plane, allowing for two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present.

[0062] Furthermore, the Spinel' type crystal structure belongs to the cubic space group Fd-3m and has a first type of cation at the 16c site, a second type of cation at the 16d site, and an anion at the 32e site in the Wyckoff positions. Figure 2C shows a model diagram of a unit cell of the Spinel' type crystal structure. Figure 3A shows a model diagram of the Spinel' type crystal structure viewed from a different orientation with an increased number of atoms compared to Figure 2C. The Spinel' type crystal structure is LiTiO ２ It is also called a type crystal structure, modified spinel structure, or spinel-related structure. On the other hand, it does not have a cation at the 8a site, hence the name MgAl ２ O ４ This differs from the spinel structure in the narrow sense.

[0063] Figure 3B shows a model diagram of the crystal structure of the surface layer 100a. As shown in Figure 3B, it is preferable that the crystal orientation of the rock salt type crystal structure in region I and the Spinel' type crystal structure in region II are roughly the same. It is also preferable that the crystal orientation of the Spinel' type crystal structure in region II and the layered rock salt type crystal structure in region III and the interior 100b are roughly the same.

[0064] In this specification, when the orientations of the cubic close-packed structure composed of anions are aligned in rock salt type, layered rock salt type, and Spinel' type, it is sometimes said that the crystal orientations are roughly the same. Furthermore, having a three-dimensional structural similarity such that the crystal orientations are roughly the same, or having the same crystallographic orientation, is called topotaxy.

[0065] The approximate agreement of crystal orientation in two regions can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron diffraction patterns, etc. It can also be determined from the FFT patterns of TEM images and STEM images, etc. Furthermore, XRD (X-ray Diffraction) and neutron diffraction can also be used as indicators.

[0066] TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc., can provide images that reflect the crystal structure. Furthermore, electron diffraction patterns can provide information on the crystal orientation at specific locations. In particular, nanobeam electron diffraction is useful for obtaining information on the crystal orientation in narrow regions.

[0067] In particular, ABF-STEM allows observation of the arrangement of anions such as oxygen, making it a suitable analytical method for determining the approximate agreement of crystal orientation. If the angle between the oxygen arrangements in two regions with different crystal structures in an ABF-STEM image is 5 degrees or less, it can be determined that the crystal orientations are approximately consistent. For example, the oxygen arrangement in region I, indicated by the arrow in Figure 3B, is O Ｉ And the oxygen sequence in region II O ＩＩ If the angle between them is between 0° and 5°, then the crystal orientations of region I and region II are said to be roughly the same. Similarly, O ＩＩ And, the oxygen sequence in region III ＩＩＩ If the angle between them is between 0° and 5°, then the crystal orientations of region II and region III are said to be roughly the same.

[0068] <Elements contained> The positive electrode active material particles 100 contain lithium, a transition metal M (where M is one or more selected from cobalt, nickel, and manganese), oxygen, and additive elements. Alternatively, the positive electrode active material particles 100 may be a composite oxide of the transition metal M and lithium (LiMO). ２ ) may have additive elements added to it. However, the positive electrode active material particles 100 in one embodiment of the present invention may have the crystal structure described later. Therefore, the composition is not strictly limited to Li:M:O = 1:1:2.

[0069] The positive electrode active material particles of a lithium-ion secondary battery need to contain a redox-capable transition metal in order to maintain charge neutrality even when lithium ions are inserted and removed. In one embodiment of the present invention, it is preferable to use cobalt as the transition metal M responsible for the redox reaction in the positive electrode active material particles 100. In addition to cobalt, at least one or more selected from nickel and manganese may be used. It is preferable that the cobalt content of the transition metals in the positive electrode active material particles 100 is 75 atomic percent or more, preferably 90 atomic percent or more, and more preferably 95 atomic percent or more, as this offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics.

[0070] It is preferable to use one or more additive elements selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, calcium, barium, bromine, and beryllium. Furthermore, the sum of transition metals among the additive elements is preferably less than 25 atomic percent, more preferably less than 10 atomic percent, and even more preferably less than 5 atomic percent.

[0071] It is preferable that the additive elements are solid-dissolved in the positive electrode active material particles 100. For example, when line analysis is performed using STEM-EDX (energy-dispersive X-ray spectrometer), it is preferable that the position where the additive elements are detected in the depth direction is deeper than the position where the transition metal M is detected, i.e., located inside the positive electrode active material particles 100.

[0072] These additive elements further stabilize the crystalline structure of the positive electrode active material particles 100. They also suppress the phase change of the positive electrode active material particles 100 during charging and discharging.

[0073] In order to ensure a stable composition and crystal structure, particularly in the surface layer 100a of the positive electrode active material particles 100, it is preferable that the surface layer 100a has a higher concentration of one or more selected additive elements than the interior 100b. Furthermore, it is preferable that the one or more selected additive elements in the positive electrode active material particles 100 have a concentration gradient. In addition, it is preferable that the detected amount of additive elements is high in regions I and II within the surface layer 100a.

[0074] For example, by having magnesium as an additive element in the surface layer 100a, side reactions between the surface of the positive electrode active material particles 100 and the electrolyte can be suppressed. Also, magnesium ions are divalent and readily enter the lithium sites in the layered rock salt type crystal structure. Magnesium present in the lithium sites has the effect of suppressing the phase change of the positive electrode active material particles 100, making it particularly suitable as an additive element. Furthermore, if the magnesium concentration in the surface layer 100a is high, it can be expected that the corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte will improve.

[0075] Furthermore, since fluorine is a monovalent anion, if some of the oxygen in the surface layer 100a is replaced by fluorine, the lithium ion desorption energy may be reduced. Therefore, if some of the oxygen in the surface layer 100a of the positive electrode active material particles 100 is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. As a result, when the positive electrode active material particles 100 are used in a secondary battery, the charge-discharge characteristics, high-current characteristics, etc., can be improved. In addition, the presence of fluorine in the surface layer 100a, which is the part that comes into contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid. Furthermore, as will be described in detail in other embodiments, if the melting point of fluorides, including lithium fluoride, is lower than the melting point of other additive element sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of other additive element sources.

[0076] The transition metal M present in the positive electrode active material particles 100 is mainly divalent in the rock salt type crystal structure and mainly trivalent in the layered rock salt type crystal structure. Since the ionic radius of the transition metal M is larger in the divalent state than in the trivalent state, a discontinuity in the anion arrangement occurs when the rock salt type and layered rock salt type crystal structures are in direct contact. However, as shown in Figure 3B, the crystal orientation is roughly consistent from the surface rock salt type crystal structure to the internal layered rock salt type crystal structure 100b, and by having a Spinel' type crystal structure between the rock salt type crystal structure and the layered rock salt crystal structure, the change in interionic distance and the valency of the transition metal M can be slowed down. In other words, the Spinel' type crystal structure can function as a buffer layer between the rock salt type and layered rock salt type crystal structures.

[0077] In the rock salt-type crystal structure of region I of the positive electrode active material particle 100, lithium, transition metal M, and additive elements that act as cations can be assumed as cations, and oxygen and fluorine can be assumed as anions.

[0078] In the layered rock salt-type crystal structure of region III and interior 100b of the positive electrode active material particle 100, lithium can be assumed as the first type of cation, transition metal M as the second type of cation, and oxygen as the anion.

[0079] In the case of the Spinel' type crystal structure of the positive electrode active material particles 100, lithium or an additive element that becomes a cation can be assumed as the first type of cation at the 16c site, a transition metal M or an additive element that becomes a cation can be assumed as the second type of cation at the 16d site, and oxygen can be assumed as the anion at the 32e site. When lithium is present at the 16c site in the Spinel' type crystal structure, the surrounding transition metal M becomes trivalent. On the other hand, when an additive element that becomes a divalent cation, such as magnesium, is present, the surrounding transition metal M becomes divalent. In the Spinel' type crystal structure of region II, it is preferable that there are more additive elements that become divalent cations, such as magnesium, at the 16c site on the side closer to region I than on the side closer to region III. Similarly, it is more preferable that there is more lithium at the 16c site on the side closer to region III than on the side closer to region III. In region II, the presence of more divalent transition metal M on the side closer to region I than on the side closer to region III mitigates the mismatch at the interface between region I and region II. Furthermore, the presence of more trivalent transition metal M closer to region III than closer to region I mitigates the mismatch at the interface between region III and region II. In other words, region II can function more effectively as a buffer layer.

[0080] Furthermore, since the 16c site and the 16d site are equivalent in terms of symmetry, it is also possible to assume cobalt at the 16c site and lithium at the 16d site.

[0081] In a Spinel-type crystal structure, the 16c sites located in the three-dimensional direction serve as lithium diffusion pathways. Therefore, even if a portion of the surface of the positive electrode active material particles 100 is covered with a material with low lithium ion conductivity, lithium can still diffuse three-dimensionally to the uncovered regions, and the lithium ion diffusion resistance of the positive electrode active material particles 100 does not decrease easily. Thus, having this crystal structure offers advantages in terms of suppressing the internal resistance of secondary batteries and improving charge and discharge capacity.

[0082] In the present specification and the like, when the crystal orientations of regions I to III are substantially the same as shown in FIG. 3B, for the cation layers in regions I and II, when they are on the extension line of the Li layer in the layered rock salt-type crystal structure, they may be referred to as the Li layer. Similarly, when they are on the extension line of the transition metal M layer, they may be referred to as the transition metal M layer.

[0083] <Cross-sectional STEM image, etc.> In the cross-sectional ABF-STEM image and the HAADF-STEM image, it may be observed that there is no distinct contrast difference between cation sites in region I having a rock salt-type crystal structure.

[0084] On the other hand, in region III and interior 100b having a layered rock salt-type crystal structure, there is a distinct contrast difference between the transition metal M layer and the lithium layer, and it may be observed that these two types of layers are stacked alternately.

[0085] In the case of the Spinel’-type crystal structure, all of the cations such as lithium, the additive element serving as a cation, and the transition metal M are present at octahedral sites and not at tetrahedral sites. Therefore, in region II having a Spinel’-type crystal structure, it may be observed that atoms are confirmed at octahedral sites and not at tetrahedral sites in the cross-sectional ABF-STEM image.

[0086] The HAADF-STEM simulation result of MgCoO having a Spinel’-type crystal structure obtained by calculation is shown in FIG. 3C. As shown in FIG. 3C, in the HAADF-STEM simulation result, it may be observed that bright spots with high luminance and bright spots with low luminance are arranged alternately in the transition metal M layer in the horizontal direction of the figure. The conditions for this calculation are as follows. Software: abTEM version 1.0.0beta22 Number of atoms: Mg 288, Co 288, O 576 Incident beam: Accelerating voltage 80 kV Convergence angle 20 mrad Defocus 40 Å Detector: Acquisition angle 70 - 200 mrad Grid points: 1024×1024 Slice thickness: 0.5 Å

[0087] ​​≪Method for determining whether or not a Spinel'-type crystal structure is present≫ An example of a method for determining whether or not the surface layer 100a has region II, that is, whether or not it has a Spinel'-type crystal structure, from cross-sectional ABF-STEM images and HAADF-STEM images will be described.

[0088] <Data and Assumptions> First, prepare cross-sectional ABF-STEM images and HAADF-STEM images of the same region in the surface layer. For the ABF-STEM image, it is preferable that the incident electron beam position is appropriately adjusted so that the atomic positions of both light elements and transition metal M are imaged in black (low gradation). For the HAADF-STEM image, it is preferable that the atomic positions of the transition metal M are imaged in white (high gradation).

[0089] Let N be the number of transition metals M present in the octahedral sites of the prepared ABF-STEM and HAADF-STEM images (where N is an integer greater than or equal to 1). By adding two possible relative positions to these N transition metals M in the octahedral sites, 2N tetrahedral sites can be identified. The relative positions of the tetrahedral sites can be determined from the electron beam incidence angle and a narrow-sense spinel crystal structure model. Tetrahedral sites may contain lithium, transition metals M, and additive elements that form cations, such as magnesium.

[0090] Similarly, the relative positions of octahedral sites in the Li layer can be determined from the electron beam incidence angle and the Spinel'-type crystal structure model.

[0091] ≪Parameters≫ Next, based on the above assumptions, determine the parameters listed in Table 1.

[0092]

[0093] Of the parameters shown in Table 1, the range of tonal values ​​that atoms at tetrahedral and octahedral sites can occupy in the ABF-STEM image can be determined as follows.

[0094] First, a histogram of tonal gradation is created using the ABF-STEM image. It is preferable to create the histogram by extracting a highly crystalline portion of the ABF-STEM image, such as region III or an image within that region. Multiple peaks can be seen in this histogram. Specifically, there are peaks with low gradation due to the presence of atoms and peaks with high gradation due to the vacuum.

[0095] These multiple peaks are separated by peak separation calculation as shown in Figure 4. For the separated peaks, the peak with low gradation originating from the presence of atoms is called Apeak, and the peak with high gradation originating from the vacuum is called Bpeak. Note that in ABF-STEM, differences in contrast can occur depending on the atomic number, so multiple peaks originating from the presence of atoms may be observed. In this case, they will be called A1peak, A2peak, and so on, in descending order of gradation, as shown in Figure 4.

[0096] In this case, the midpoints of A1peak and Bpeak can be defined as V_high and O_V_high in Table 1.

[0097] V_low and O_V_low can be the lowest grayscale levels among all grayscale levels.

[0098] Next, the following steps are taken to identify the position of the transition metal M: 1. For each pixel position in the ABF-STEM image and the HAADF-STEM image, the difference in tonal range is calculated by subtracting the tonal range of the HAADF-STEM image from the tonal range of the ABF-STEM image, and difference data is obtained. 2. A binarized image is created from the difference data. Areas with small tonal differences are designated as black, and areas with large differences as white. 3. Continuous connected components, i.e., continuous white areas, are obtained from the binarized image. 4. From all connected components, those whose size is reasonable considering the ionic radius of the transition metal M and whose shape is close to a circle are selected and considered to be the transition metal M. 5. The centroid of each transition metal M atom is determined and considered to be the position of the transition metal M atom.

[0099] Next, perform the following process A for each transition metal M atom. 6. Add (Mg_rel_X1, Mg_rel_Y1) to the position of the transition metal M atom to find the position of the tetrahedral site corresponding to the transition metal M (Mg_X1, Mg_Y1). 7. Calculate the average V1 of the tonal range within radius R centered on Mg_X1, Mg_Y1 from the ABF-STEM image. 8. If V_low < V1 < V_high, assume that an atom exists at the tetrahedral site near that transition metal M atom, and terminate the process. 9. Add (Mg_rel_X2, Mg_rel_Y2) to the position of the transition metal M atom to find the tetrahedral site corresponding to the transition metal M (Mg_X2, Mg_Y2). 10. Calculate the average V2 of the tonal range within radius R centered on Mg_X2, Mg_Y2 from the ABF-STEM image. 11. If V_low < V2 < V_high, it is assumed that an atom exists at the tetrahedral site near the transition metal M atom, and the process is terminated. 12. If no atom is found to exist at the tetrahedral site near the transition metal M atom in any region of the ABF-STEM image, it can be determined that there is no atom at the tetrahedral site in that region.

[0100] Next, the following process B is performed on each transition metal M atom. 13. Add (O_rel_X, O_rel_Y) to the position of the transition metal M atom to find the coordinates (O_X, O_Y) of the octahedral site corresponding to the transition metal M. 14. Calculate the average of the grayscale levels O_V in the range of radius O_R centered on O_X, O_Y from the ABF-STEM image. 15. If O_V_low < O_V < O_V_high, it is assumed that an atom exists in the octahedral site near that transition metal M atom. 16. If O_V_low ≥ O_V or O_V ≤ O_V_high, it is assumed that no atom exists in the octahedral site near that transition metal M atom, and the process is terminated. 17. If an atom exists in the octahedral site of the Li layer in any region of the ABF-STEM image, it can be determined that an atom exists in the octahedral site in that region.

[0101] Based on the above processes A and B, regions where atoms are found to be present at octahedral sites and absent at tetrahedral sites can be determined to have a Spinel'-type crystal structure.

[0102] Although cross-sectional STEM is a method for analyzing thin section samples, the thin section may have multiple crystal structures in the depth direction. Therefore, even if atoms are determined to be present at tetrahedral sites, if atoms are present at octahedral sites in the Li layer, it can be determined that the sample has region II with a Spinel'-type crystal structure.

[0103] The Spinel'-type crystal structure of the positive electrode active material particle 100 shares similarities with the rock salt-type crystal structure in that it has atoms in octahedral sites, but differs in symmetry. For example, the largest interplanar spacing (d value) determined from electron diffraction is similar for the Spinel'-type crystal structure and the layered rock salt-type crystal structure, and these are about twice as large as those of the rock salt-type crystal structure. Similarly, the distance from the zero-order diffraction spot to the nearest primary-order diffraction spot in the electron diffraction pattern is similar for the Spinel'-type crystal structure and the rock salt-type crystal structure, with the rock salt-type crystal structure being about twice as large. Here, A and B being similar means that when A is set to 1, B is between 0.94 and 1.06, and A being about twice as large as B means that when A is set to 1, B is between 1.88 and 2.12.

[0104] Furthermore, the positive electrode active material particles 100 do not necessarily have to contain magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, or beryllium as additive elements.

[0105] For example, if the positive electrode active material particles 100 do not contain titanium, the above-mentioned advantages, such as having excellent cycle characteristics, become even greater. The weight ratio of titanium to transition metal M (Ti / transition metal M) contained in the entire positive electrode active material particles 100 is preferably 0.0005 or less, and more preferably 0.0001 or less. For the analysis of the entire positive electrode active material particles 100, for example, inductively coupled plasma mass (ICP-MS) analysis can be used. Furthermore, when the surface layer 100a of the positive electrode active material particles 100 is analyzed by STEM-EDX, it is preferable that characteristic X-rays caused by titanium are not detected, that is, they are below the detection limit (for example, less than 0.3 atomic%).

[0106] Similarly, using silicon-free positive electrode active material particles 100 is preferable because it is easier to improve the stability of the crystal structure. For example, in STEM-EDX analysis of the surface layer 100a of the positive electrode active material particles 100, it is preferable that the maximum silicon concentration when the denominator is the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, gallium, and molybdenum is 3 atomic percent or less.

[0107] Furthermore, the positive electrode active material particles 100 are free from electrolytes, electrolyte decomposition products, organic solvents, binders, conductive materials, or compounds derived therefrom that are attached to the positive electrode active material particles 100.

[0108] Since the positive electrode active material particles 100 are compounds containing a transition metal and oxygen that can be inserted into and removed from lithium, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) and oxygen, which undergo oxidation-reduction during lithium insertion and removal, are present and the region where they are absent is considered the surface of the positive electrode active material particles. Surfaces created by slip, cracks, and / or fissures may also be considered the surface of the positive electrode active material particles. When the positive electrode active material particles are subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material particles. As a protective film, single-layer or multi-layer films of carbon, metal, oxide, resin, etc. may be used.

[0109] Furthermore, while region I has a rock salt-type crystalline structure, not all of region I has to have a rock salt-type crystalline structure. It may contain other crystalline structures, or part of it may be amorphous. Similarly, not all of region II has to have a Spinel'-type crystalline structure; it may contain other crystalline structures, or part of it may be amorphous. Similarly, not all of region III has to have a layered rock salt-type crystalline structure; it may contain other crystalline structures, or part of it may be amorphous.

[0110] Furthermore, even in methods for analyzing thin section samples such as cross-sectional STEM, it is possible that the thin section may have multiple crystal structures in the depth direction. Also, if the crystal orientations of regions I to III are roughly consistent, the crystal structure can change continuously. Therefore, regions I to III may overlap, and the boundaries may not always be clear.

[0111] Furthermore, the entire surface layer 100a of the positive electrode active material particles 100 does not necessarily have regions I and II. In particular, region II can exert a sufficient effect if it is present on the edge surface, which is the surface where the lithium diffusion pathway is exposed. Among the edge surfaces, it is preferable that region II having a Spinel' type crystal structure is present on surfaces that are nearly parallel to the c axis, such as the (012) plane in the layered rock salt type crystal structure of space group R-3m. On the other hand, region II does not necessarily have to be present on the basal surface, the (00l) plane.

[0112] <Grain Boundaries> In addition to the distribution described above, it is more preferable that the additive elements in the positive electrode active material particles 100 of one embodiment of the present invention are concentrated at or near the grain boundaries. In other words, it is more preferable that the additive elements are present at higher concentrations in defects such as grain boundaries, cracks, and voids than in other regions.

[0113] In this specification, "non-uniformity" refers to a situation where the concentration of an element in one region differs from that in other regions. It is synonymous with segregation, precipitation, heterogeneity, bias, or a mixture of areas with high and low concentrations.

[0114] For example, it is preferable that the magnesium concentration at and near the grain boundaries of the positive electrode active material particles 100 is higher than that of the interior 100b outside the grain boundaries. It is also preferable that the fluorine concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries. Furthermore, it is preferable that the nickel concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries. Furthermore, it is preferable that the aluminum concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries.

[0115] Grain boundaries are a type of surface defect. Therefore, like surfaces, they tend to be unstable and prone to initiating changes in crystal structure. For this reason, increasing the concentration of additive element A at and near the grain boundaries can more effectively suppress changes in crystal structure.

[0116] Furthermore, if the magnesium and fluorine concentrations are high at and near the grain boundaries, even if cracks occur along the grain boundaries of the positive electrode active material particles 100 according to one embodiment of the present invention, the magnesium and fluorine concentrations will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material particles after cracks have occurred.

[0117] <EDX> It is preferable that one or more of the additive elements in the positive electrode active material particles 100 have a concentration gradient. It is even more preferable that the depth of the concentration peaks from the surface differs depending on the additive element. The concentration gradient of the additive elements can be evaluated, for example, by exposing the cross-section of the positive electrode active material particles 100 using FIB (Focused Ion Beam) and analyzing the cross-section using EDX, EPMA (Electron Probe Microanalysis), etc.

[0118] In EDX measurements, the method of scanning within a region to evaluate that region in two dimensions is called EDX surface analysis. The method of scanning linearly to evaluate the distribution of atomic concentration within positive electrode active material particles is called line analysis. Furthermore, sometimes the extraction of linear region data from EDX surface analysis is also called line analysis. Finally, measuring a region without scanning is called point analysis.

[0119] EDX surface analysis (e.g., elemental mapping) allows for quantitative analysis of the concentration of additive elements in the surface layer 100a, interior 100b, and near grain boundaries of the positive electrode active material particles 100. EDX radiation analysis allows for analysis of the concentration distribution and maximum value of the additive elements. Furthermore, analysis using thinned samples, such as STEM-EDX, is preferable because it allows for analysis of the concentration distribution in the depth direction from the surface to the center of the positive electrode active material particles in a specific region, without being affected by the distribution in the depth direction.

[0120] Since the positive electrode active material particles 100 are compounds containing a transition metal and oxygen that can insert and remove lithium, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) and oxygen, which undergo oxidation and reduction during lithium insertion and removal, are present and the region where they are absent, is defined as the surface of the positive electrode active material particles. When the positive electrode active material particles are subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material particles. As the protective film, single-layer or multi-layer films of carbon, metal, oxide, resin, etc., may be used.

[0121] In STEM-EDX ray analysis, due to the principle or measurement errors, the graph of the detected characteristic X-rays of an element does not change sharply, making it difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX ray analysis, the detected amount of characteristic X-rays of the transition metal M is considered to be the average value M of the detected characteristic X-rays of the transition metal M inside the surface. ＡＶＥ And the average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ The point where the sum of the two is 50%, or where the amount of oxygen characteristic X-rays detected is equal to the average value of the amount of oxygen characteristic X-rays detected inside. ＡＶＥ And the average value of the detected characteristic X-rays of background oxygen O ＢＧ The reference point is the point at which the sum of the two values ​​becomes 50%. Note that if the point at which the detected amount of characteristic X-rays of the transition metal M becomes 50% of the sum of the average detected amount of characteristic X-rays of the internal transition metal M and the average detected amount of characteristic X-rays of the background transition metal M is different from the point at which the detected amount of characteristic X-rays of oxygen becomes 50% of the sum of the average detected amount of characteristic X-rays of internal oxygen and the average detected amount of characteristic X-rays of background oxygen, it is thought to be due to the influence of oxygen-containing metal oxides, carbonates, etc. adhering to the surface, and therefore the point at which the detected amount of characteristic X-rays of the transition metal M becomes 50% of the average detected amount of characteristic X-rays of internal transition metal M ＡＶＥ And the average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ The point at 50% of the sum of these can be adopted as the reference point. Also, in the case of positive electrode active material particles having multiple transition metals M, the transition metal element M that has the highest amount of characteristic X-rays detected inside is selected. ＡＶＥ and M ＢＧ The above reference points can be determined using this method.

[0122] The average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ For example, the average value M of the detected characteristic X-rays of the transition metal M can be determined by averaging the range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material particles, while avoiding the vicinity where the detection amount of characteristic X-rays of the transition metal M begins to increase. ＡＶＥ The average value of the background characteristic X-ray O is obtained by averaging a range of 2 nm or more, preferably 3 nm or more, from a depth of 30 nm or more, preferably more than 50 nm, in the region where the detection amount of characteristic X-rays of transition metal M and oxygen saturates and stabilizes, for example, from the region where the detection amount of characteristic X-rays of transition metal M begins to increase. ＢＧ and the average value of the detected amount of characteristic X-rays of the internal oxygen O ＡＶＥ This can be calculated in a similar manner.

[0123] Furthermore, the surface of the positive electrode active material particles 100 in cross-sectional STEM images, etc., is defined as the boundary between the region where an image originating from the crystal structure of the positive electrode active material particles is observed and the region where it is not observed, and is the outermost region where atomic columns originating from the nuclei of metal elements with atomic numbers greater than lithium among the metal elements constituting the positive electrode active material particles are confirmed.

[0124] Furthermore, in STEM-EDX analysis, a peak refers to the maximum value of a convex shape appearing on the graph of characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. Noise in STEM-EDX analysis can include measurements with a width at half maximum (FWHM) below the spatial resolution (R), for example, R / 2 or less.

[0125] Furthermore, in STEM-EDX analysis, a peak refers to the maximum value of a convex shape appearing on the graph of characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. Noise in STEM-EDX analysis can include measurements with a width at half maximum (FWHM) below the spatial resolution (R), for example, R / 2 or less.

[0126] Scanning the same location multiple times under the same conditions can reduce the effects of noise. For example, the cumulative value measured by two scans can be used as the detected value for each element. The number of scans is not limited to two; more scans can be performed, and the cumulative value can be used as the detected value for each element.

[0127] STEM-EDX radiation analysis can be performed, for example, as follows: First, a protective film is deposited on the surface of the positive electrode active material particles. For example, carbon can be deposited using an ion sputtering apparatus (Hitachi High-Tech MC1000).

[0128] Next, the positive electrode active material particles are thinned to prepare a STEM cross-sectional sample. For example, thinning can be performed using a FIB-SEM device (Hitachi High-Tech XVision 200TBS). In this case, pickup is performed using an MPS (microprobing system), and the finishing conditions can be set to, for example, an acceleration voltage of 10kV.

[0129] STEM-EDX ray analysis can be performed using, for example, a STEM instrument (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W EDX detector. An example of the conditions for EDX ray analysis using the Hitachi High-Tech HD-2700 is to set the emission current of the STEM instrument to 6 μA to 10 μA and measure areas of the thinned sample with little depth and unevenness. The magnification can be, for example, around 150,000x. The conditions for EDX ray analysis can be drift-corrected, with a line width of 42 nm, a pitch of 0.2 nm, and 6 or more frames.

[0130] To achieve high spatial resolution in STEM-EDX ray analysis, it is preferable to have a small electron beam diameter (also called beam diameter, probe diameter, or probe diameter). In STEM-EDX ray analysis, the beam diameter is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. Furthermore, to increase the analytical sensitivity in STEM-EDX ray analysis, it is preferable to increase the electron beam current (also called probe current). Therefore, it is preferable that the apparatus used for STEM-EDX ray analysis be equipped with a spherical aberration correction device (Cs collector) that can reduce the beam diameter and increase the beam current.

[0131] Furthermore, in positive electrode active material particles 100 having magnesium and fluorine as additive elements, it is preferable that the distribution of fluorine has a region that overlaps with the distribution of magnesium. For example, it is preferable that the difference in depth direction between the peak of fluorine concentration or detected amount and the peak of magnesium concentration or detected amount is within 10 nm, more preferably within 3 nm, even more preferably within 1 nm, and still more preferably within 0.5 nm.

[0132] In positive electrode active material particles 100 having magnesium as an additive element, when STEM-EDX radiation analysis is performed on the surface layer 100a, it is preferable that there is a region where the maximum concentration of magnesium, when the denominator is the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, gallium, and molybdenum, is 10 at% or more, more preferably 15 at% or more, and even more preferably 20 at% or more. Having a sufficient amount of magnesium in the surface layer 100a makes it easier to form a more stable Spinel'-type crystal structure.

[0133] Furthermore, it is preferable that the peak of magnesium concentration or detected amount is located inside the reference point. Having a sufficient concentration of magnesium in the region inside the reference point facilitates the formation of a Spinel'-type crystal structure.

[0134] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0135] (Embodiment 2) In this embodiment, an example of a method for producing positive electrode active material particles 100 according to one aspect of the present invention will be described using Figures 5A to 5C.

[0136] The heating conditions are crucial for producing the positive electrode active material particles 100. The lower limit of the heating temperature is the temperature at which the reaction proceeds from the starting material. The temperature at which the reaction proceeds is any temperature at which mutual diffusion of the elements present in the starting material occurs, and it may be lower than the melting temperature of the starting material. To explain using oxides as an example, the melting temperature T ｍ 0.757 times (Tammann temperature T) ｄ It is known that solid-phase diffusion occurs from this point. Therefore, a heating temperature of, for example, 650°C or higher is preferable.

[0137] Furthermore, to achieve the distribution of additive elements as described above, it is preferable to provide a sufficient heating time. The heating time is preferably more than 100 hours, and more preferably between 100 hours and 150 hours. Heating may be carried out in multiple stages, in which case it is preferable that the total heating time to reach 650°C is within the above range. For example, it is preferable that the total time the furnace heating temperature is set to 650°C or higher is within the above range. The cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.

[0138] Method 1 for producing positive electrode active material particles 100 will be explained using Figure 5A. Here, magnesium and fluorine will be used as additive elements.

[0139] <Step S11> In step S11 shown in Figure 5A, a lithium source (Li source), a transition metal M source (M source), a magnesium source (Mg source), and a fluorine source (F source) are prepared as starting materials.

[0140] As a lithium source, it is preferable to use a lithium-containing compound, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. The lithium source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0141] As the source of the transition metal M, it is preferable to use a compound containing the transition metal M, for example, an oxide of the transition metal M, a hydroxide of the transition metal M, etc.

[0142] Magnesium sources such as magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate can be used. Multiple magnesium sources may also be used.

[0143] Examples of fluorine sources include lithium fluoride (LiF) and magnesium fluoride (MgF). ２ ), aluminum fluoride (AlF ３ ), cobalt fluoride (CoF ２ CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF) ２ ), cerium fluoride (CeF ３ CeF ４ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６ ) and the like can be used. Among them, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later.

[0144] <Steps S12 and S13> Next, the lithium source, cobalt source, magnesium source, and fluorine source are crushed and mixed (Step S12) to produce a mixture 903 (Step S13). Crushing and mixing can be done dry or wet. Wet crushing and mixing can produce finer particles. If wet crushing is used, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the first lithium source and cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then crush and mix. By using dehydrated acetone of the above purity, the amount of impurities that may be mixed in can be reduced.

[0145] For grinding and mixing, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they produce less impurity. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0146] <Step S14> Next, in step S14, the mixture 903 is heated. The heating conditions are preferably such that the total heating time at which the temperature reaches 650°C or higher exceeds 100 hours.

[0147] <Step S15> In step S15, the heated material is recovered to obtain positive electrode active material particles 100. At this time, the recovered particles can be crushed by sieving as needed. By the above steps, positive electrode active material particles 100 according to one embodiment of the present invention can be produced.

[0148] Method 2 for producing positive electrode active material particles 100 will be explained using Figures 5B and 5C. Unlike Method 1, lithium cobalt oxide will be used as the starting material, serving as both a lithium source and a transition metal M source.

[0149] <Step S21> In step S21 shown in Figure 5B, lithium cobalt oxide, a magnesium source, and a fluorine source are prepared. The magnesium source and fluorine source are collectively referred to as source A. The magnesium source and fluorine source can be described in step S11.

[0150] The magnesium source and fluorine source may be added to lithium cobalt oxide separately, or they may be mixed together before being added to the lithium cobalt oxide, as shown in steps S21a to S21c of Figure 5C.

[0151] <Steps S22 and S23> Next, the lithium cobalt oxide, magnesium source and fluorine source are crushed and mixed (Step S22) to prepare mixture 903 (Step S23). For crushing and mixing, refer to the description in Step S12.

[0152] <Step S24> Next, in step S24, the mixture 903 is heated. The heating conditions are preferably such that the total heating time at which the temperature reaches 650°C or higher exceeds 100 hours.

[0153] In addition, the reaction proceeds more readily if the temperature is above the melting point of one or more of the materials selected from the mixture 903. For example, LiF and MgF are used as source A. ２ If LiF and MgF are present, ２ Since the eutectic point is around 742°C, it is preferable that the lower limit of the heating temperature in step S33 be 742°C or higher.

[0154] Also, LiCoO ２ :LiF:MgF ２ The mixture obtained by mixing in a molar ratio of 100:0.33:1 has an initial melting temperature T ｉｍThe temperature is 779°C, and the melting peak temperature is T. ｐｍ The temperature is 815°C, and the melting end temperature is T. ｅｍ The temperature is 826°C. Therefore, a lower limit of 826°C or higher is more preferable for the heating temperature.

[0155] A higher heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0156] The upper limit of the heating temperature should be below the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures near the decomposition temperature, there is a concern that lithium cobalt oxide may decompose, albeit in small amounts. Furthermore, when heating mixture 903, it is preferable to control the partial pressure of fluorine or fluoride, which may be due to a fluorine source, within an appropriate range. If the temperature is too high, the fluoride will decrease due to evaporation. For example, the vapor pressure of lithium fluoride rises sharply from 900°C. Therefore, the heating temperature is more preferably 1000°C or lower, even more preferably 950°C or lower, and still more preferably 900°C or lower.

[0157] Based on these considerations, the heating temperature in step S24 is preferably 650°C to 1130°C, more preferably 650°C to 1000°C, even more preferably 650°C to 950°C, and even more preferably 650°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Furthermore, 826°C to 1130°C, 826°C to 1100°C is preferred, more preferably 826°C to 1000°C, even more preferably 826°C to 950°C, and even more preferably 826°C to 920°C.

[0158] <Step S25> In step S25, the heated material is recovered to obtain positive electrode active material particles 100. At this time, the recovered particles can be crushed by sieving as needed. By the above steps, positive electrode active material particles 100 according to one embodiment of the present invention can be produced.

[0159] The manufacturing method of this embodiment can be freely combined with other manufacturing methods of this embodiment. Furthermore, the contents of this embodiment can be freely combined with the contents of other embodiments.

[0160] (Embodiment 3) In this embodiment, an example of the shape of a secondary battery having a positive electrode manufactured by the manufacturing method described in the previous embodiment will be explained.

[0161] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 6A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 6B is an external view, and Figure 6C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

[0162] Note that Figure 6A is a schematic diagram to show the overlapping (up / down and positional) of the components for clarity. Therefore, Figures 6A and 6B are not perfectly identical corresponding diagrams.

[0163] In Figure 6A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with a gasket between the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 6A. The spacer 322 and washer 312 are used to protect the inside or fix the position within the can when the positive electrode can 301 and the negative electrode can 302 are pressed together. The spacer 322 and washer 312 are made of stainless steel or an insulating material.

[0164] Figure 6B is a perspective view of the completed coin-type rechargeable battery.

[0165] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure. The negative electrode 307 may use lithium metal foil or a lithium-aluminum alloy foil.

[0166] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0167] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel or aluminum to prevent corrosion caused by the electrolyte. 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.

[0168] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in Figure 6C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are pressed together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0169] By having the above configuration, a coin-type secondary battery 300 can be made that has high capacity, high discharge capacity, and excellent cycle characteristics.

[0170] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be explained with reference to Figure 7A. As shown in Figure 7A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated by a gasket (insulating packing) 610.

[0171] Figure 7B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 7B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0172] 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 in between. Although not shown, the battery element is wound around a central axis. The battery can 602 is closed at one end and open at the other. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium, or an alloy thereof, or an alloy of these with other metals (for example, stainless steel), which is corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel and aluminum, etc., to prevent corrosion by the electrolyte. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and insulating plate 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0173] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector.

[0174] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0175] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Metal materials such as aluminum can be used for the positive electrode terminal 603, and copper can be used for the negative electrode terminal 607. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the rise in the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. PTC elements include barium titanate (BaTiO ３ ) semiconductor ceramics and the like can be used.

[0176] Figure 7C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging and / or over-discharging.

[0177] Figure 7D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to the conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0178] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0179] Furthermore, a temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0180] Furthermore, in Figure 7D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0181] [Other structural examples of secondary batteries] Structural examples of secondary batteries will be explained using Figures 8 and 9.

[0182] The secondary battery 913 shown in Figure 8A has a wound body 950 with terminals 951 and 952 provided inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 8A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum), a composite material of metal and resin, etc.

[0183] Furthermore, as shown in Figure 8B, the housing 930 shown in Figure 8A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 8B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0184] An insulating material can be used for the housing 930a. In particular, by using a material such as 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, the antenna may be provided inside the housing 930a. For the housing 930b, for example, a metal material can be used.

[0185] Furthermore, the structure of the wound body 950 is shown in Figure 8C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0186] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 9. The wound body 950a shown in Figure 9A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0187] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 932, a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0188] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0189] As shown in Figure 9B, the negative electrode 931 is electrically connected to terminal 951 by ultrasonic bonding, welding, or crimping. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952 by ultrasonic bonding, welding, or crimping. Terminal 952 is electrically connected to terminal 911b.

[0190] As shown in Figure 9C, the coiled body 950a and the electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure in order to prevent the battery from rupturing.

[0191] As shown in Figure 9B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 9A and 9B can be referenced from the description of the secondary battery 913 shown in Figures 8A to 8C.

[0192] <Laminated Secondary Battery> Next, an example of an external view of a laminated secondary battery is shown in Figures 10A and 10B. Figures 10A and 10B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0193] Figure 11A shows the external view 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 the 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, i.e., the tab region. Note that the area or shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 11A.

[0194] <Method for Manufacturing Laminated Secondary Batteries> An example of a method for manufacturing laminated secondary batteries, whose external appearance is shown in Figure 10A, will be explained using Figures 11B and 11C.

[0195] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 11B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions 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 joining, for example, ultrasonic welding may be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0196] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0197] Next, as shown in Figure 11C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat sealing can be used. At this time, a region that is not joined (hereinafter referred to as an inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0198] Next, the electrolyte is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. The introduction of the electrolyte is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0199] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 503, a secondary battery 500 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0200] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be explained with reference to Figure 12.

[0201] Figure 12A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 12B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 includes a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0202] The interior of the secondary battery 513 may have a structure with a wound body or a structure with a laminated body.

[0203] In the secondary battery pack 531, for example as shown in Figure 12B, a control circuit 590 is located on a circuit board 540. The circuit board 540 is electrically connected to terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0204] Alternatively, as shown in Figure 12C, the system may include a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0205] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0206] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0207] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0208] (Embodiment 4) This embodiment shows an example of a vehicle having a secondary battery according to one aspect of the present invention.

[0209] As for vehicles, secondary batteries can typically be applied to automobiles. Examples of automobiles include next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHEVs or PHVs), and secondary batteries can be applied as one of the power sources installed in these vehicles. Vehicles are not limited to automobiles. For example, examples of vehicles include trains, monorails, ships, submersibles (deep-sea exploration vessels, unmanned submersibles), flying objects (helicopters, unmanned aerial vehicles (drones), airplanes, rockets, artificial satellites), electric bicycles, electric motorcycles, etc., and secondary batteries according to one aspect of the present invention can be applied to these vehicles.

[0210] As shown in Figure 13C, electric vehicles are equipped with a first battery 1301a, 1301b as the main secondary battery for driving, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called a cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a, 1301b.

[0211] The internal structure of the first battery 1301a may be a wound type as shown in Figure 7A or Figure 8C, or a stacked type as shown in Figure 10A or Figure 10B.

[0212] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0213] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and is provided on the first battery 1301a.

[0214] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC / DC circuit 1306. Even when there is a rear motor 1317 on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0215] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio system 1313, power windows 1314, lights 1315, etc.) via the DC / DC circuit 1310.

[0216] Next, the first battery 1301a will be explained using Figure 13A.

[0217] Figure 13A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, the nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0218] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as BTOS (Battery operating system or Battery oxide semiconductor).

[0219] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the metal oxide, it is preferable to use a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium). In particular, it is preferable that the In-M-Zn oxide applicable as the metal oxide is CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In oxide, In-Ga oxide, or In-Zn oxide may also be used as the metal oxide.

[0220] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from -40°C to 150°C, and even if the secondary battery overheats, the change in characteristics is smaller compared to single crystals. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode. The secondary battery and control circuit unit 1320 using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0221] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. Functions to eliminate the 10 causes of instability include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0222] Furthermore, "micro-short" refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short time and small location can cause a large voltage change, the abnormal voltage value may affect subsequent estimations.

[0223] One of the causes of micro-short circuits is said to be that, due to the uneven distribution of positive electrode active material particles after multiple charge-discharge cycles, localized current concentration occurs in parts of the positive and negative electrodes, causing parts of the separator to malfunction, or micro-short circuits to occur due to the generation of by-reactants from side reactions.

[0224] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0225] Next, Figure 13B shows an example of a block diagram of the battery pack 1415 shown in Figure 13A.

[0226] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current or the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and / or overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch of the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0227] The switch section 1324 can be constructed by combining n-channel or p-channel transistors. The switch section 1324 is not limited to a switch having a Si transistor using single-crystal silicon, but may also be formed using power transistors such as Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0). Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, a control circuit section 1320 using OS transistors can be stacked on the switch section 1324 and integrated into a single chip. Since the volume occupied by the control circuit unit 1320 can be reduced, miniaturization becomes possible.

[0228] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage HV) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage LV) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to cost advantages. Lead-acid batteries have the disadvantage of higher self-discharge and are prone to degradation due to a phenomenon called sulfation compared to lithium-ion secondary batteries. Using a lithium-ion secondary battery for the second battery 1311 offers the advantage of being maintenance-free, but after long-term use, for example more than three years, there is a risk of malfunctions occurring that are difficult to detect at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, it will be impossible to start the motor even if the first batteries 1301a and 1301b have remaining capacity. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery to keep it constantly charged to a full charge state.

[0229] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor.

[0230] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0231] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0232] Although not shown in the diagram, when an electric vehicle is connected to an external charger, the charger's plug or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. In some cases, a control circuit is provided in the charger, and the functions of the battery controller 1302 are not used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the control circuit is also provided in the charger's plug or connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. Furthermore, the ECU uses either a CPU or a GPU.

[0233] External chargers installed at charging stations and other locations may have a 100V-200V outlet, or a 3-phase 200V and 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0234] For rapid charging, a rechargeable battery capable of withstanding high-voltage charging is desired to achieve short charging times.

[0235] Furthermore, by using graphene as a conductive material, it is possible to suppress capacity degradation even when the electrode layer is thickened and the load is increased, and maintain high capacity. As a synergistic effect, a secondary battery with significantly improved electrical characteristics can be realized. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide vehicles with a long driving range, specifically a driving range of 500 km or more on a single charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0236] In particular, the secondary battery of this embodiment described above can achieve a higher operating voltage by using the positive electrode active material particles 100 described in Embodiments 1 and 2, and can increase its usable capacity as the charging voltage increases. Furthermore, by using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, it is possible to provide a secondary battery for vehicles with excellent cycle characteristics.

[0237] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0238] By mounting a secondary battery as shown in any one of Figures 7D, 9C, or 13A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs) can be realized. Furthermore, secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, satellites, space probes, planetary probes, or spacecraft. A secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, a secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0239] Figures 14A to 14D illustrate a transport vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 14A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on the vehicle, one or more examples of the secondary battery shown in Embodiment 4 are installed in one location. The automobile 2001 shown in Figure 14A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device that is electrically connected to the secondary battery module.

[0240] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the secondary battery of the automobile 2001. When charging, the charging method or connector specifications may be carried out as appropriate in accordance with the prescribed methods of CHAdeMO (registered trademark) or Combo. The charging facility may be a charging station installed in a commercial facility or a household power supply. For example, the energy storage device mounted on the automobile 2001 can be charged by supplying power from an external source using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0241] Although not shown in the diagram, a power receiving device can also be mounted on the vehicle, and power can be supplied contactlessly from a ground-based power transmission device for charging. In this contactless power supply method, by incorporating the power transmission device into the road or exterior wall, charging can be performed not only when the vehicle is stopped but also while it is in motion. Furthermore, this contactless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or in motion. For such contactless power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0242] Figure 14B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a nominal voltage of 3.0V to 5.0V. The battery pack 2201 has the same functions as Figure 14A, except for differences in the number of secondary batteries constituting the secondary battery module, so the explanation is omitted.

[0243] Figure 14C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V in series. Therefore, secondary batteries with small variation in characteristics are required. By using secondary batteries that use the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, it is possible to manufacture secondary batteries with stable battery characteristics, enabling low-cost mass production from a yield standpoint. Furthermore, since it has the same functions as Figure 17A except for differences in the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the explanation is omitted.

[0244] Figure 14D shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Figure 14D can be considered a type of transport vehicle because it has wheels for takeoff and landing, and has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0245] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functions as Figure 14A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0246] Figure 14E shows an example of a satellite 2005 equipped with a secondary battery 2204. It is preferable that the secondary battery 2204 is mounted inside the satellite 2005, covered with a heat-insulating material.

[0247] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0248] (Embodiment 5) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in a building will be described with reference to Figures 15A and 15B.

[0249] The house shown in Figure 15A has a power storage device 2612 having a secondary battery, which is one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611, etc. Alternatively, the power storage device 2612 may be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0250] The electricity stored in the energy storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

[0251] Figure 15B shows an example of an energy storage device according to one aspect of the present invention. As shown in Figure 15B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Furthermore, by using a secondary battery with the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode in the energy storage device 791, a synergistic effect on safety can be obtained. The secondary battery with the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by the energy storage device 791 having a secondary battery.

[0252] A control device 790 is installed in the energy storage device 791, and the control device 790 is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0253] Power is supplied from the commercial power supply 701 to the distribution board 703 via the service drop connection section 710. Power is also supplied to the distribution board 703 from the energy storage device 791 and the commercial power supply 701, and the distribution board 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0254] The general load 707 is, for example, an electronic device such as a television or a personal computer, and the energy storage load 708 is, for example, an electronic device such as a microwave oven, refrigerator, or air conditioner.

[0255] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during one day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during one day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0256] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked via the router 709 on electronic devices such as televisions or personal computers. Furthermore, it can be checked via the router 709 on portable electronic devices such as smartphones or tablets. Additionally, the amount of electricity demand predicted by the prediction unit 712 for each time period (or hourly) can be checked on the display unit 706, electronic devices, and portable electronic devices.

[0257] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0258] (Embodiment 6) In this embodiment, as an example of mounting a secondary battery in a vehicle, an example is shown in which a lithium-ion secondary battery according to one aspect of the present invention is mounted in a motorcycle and a bicycle.

[0259] Figure 16A shows an example of an electric bicycle using a power storage device according to one aspect of the present invention. The power storage device according to one aspect of the present invention can be applied to the electric bicycle 8700 shown in Figure 16A. The power storage device according to one aspect of the present invention includes, for example, a plurality of batteries and a protection circuit.

[0260] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 is also portable, and Figure 16B shows it detached from the bicycle. The power storage device 8702 also has multiple storage batteries 8701, which are part of a power storage device according to one embodiment of the present invention, and the remaining battery level can be displayed on a display unit 8703. The power storage device 8702 also has a control circuit 8704 that can control the charging of the secondary battery or detect abnormalities. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. Furthermore, by combining it with a secondary battery that uses the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, a synergistic effect on safety can be obtained. The secondary battery and control circuit 8704 that use the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0261] Figure 16C shows an example of a two-wheeled vehicle using a power storage device according to one embodiment of the present invention. The scooter 8600 shown in Figure 16C is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply electricity to the turn signals 8603. Furthermore, the power storage device 8602, which houses multiple secondary batteries using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, can have a high capacity and contribute to miniaturization.

[0262] Furthermore, the scooter 8600 shown in Figure 16C can accommodate the power storage device 8602 in the under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0263] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0264] (Embodiment 7) This embodiment describes an example in which a secondary battery, which is one aspect of the present invention, is mounted on an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0265] Figure 17A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By providing a secondary battery 2107 that uses the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0266] The mobile phone 2100 can run various applications such as making mobile phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0267] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0268] Furthermore, the mobile phone 2100 is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless communication-enabled headset to enable hands-free calling.

[0269] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows it to directly exchange data with other information terminals via a connector. It can also be charged via the external connection port 2104. However, charging may be performed wirelessly without using the external connection port 2104.

[0270] Furthermore, it is preferable that the mobile phone 2100 has sensors. Preferably, the sensors include, for example, a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0271] Figure 17B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery to be mounted on an unmanned aerial vehicle 2300.

[0272] Figure 17C shows an example of a robot. The robot 6400 shown in Figure 17C is equipped with 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 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0273] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0274] The display unit 6405 has the function of displaying various types of 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. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0275] The upper camera 6403 and the lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407.

[0276] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0277] Figure 17D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0278] The cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that may become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal region. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6306 to be mounted on the cleaning robot 6300.

[0279] Figure 18A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0280] For example, a secondary battery according to one embodiment of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 18A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 can be made with good weight balance and a long continuous usage time. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0281] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. The secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0282] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0283] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0284] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply and receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0285] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and the secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0286] The display unit 4005a can display not only the time, but also various other information such as incoming emails or phone calls.

[0287] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0288] Figure 18B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0289] A side view is also shown in Figure 18C. Figure 18C shows how the secondary battery 913 is built into the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, and can be made high-density and high-capacity, as well as small and lightweight.

[0290] Since the wristwatch-type device 4005 is required to be small and lightweight, by using the positive electrode active material particles 100 described in Embodiments 1 and 2, etc., as the positive electrode of the secondary battery 913, a secondary battery 913 with high energy density and small size can be made.

[0291] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0292] In this embodiment, a positive electrode active material according to one aspect of the present invention was prepared, and its characteristics were analyzed.

[0293] <Preparation of positive electrode active material> The positive electrode active material prepared in this embodiment will be described with reference to the preparation method shown in Figures 5B and 5C.

[0294] [Sample 1] LiCoO in step S21 of Figure 5B ２ For this purpose, we prepared commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.).

[0295] In this embodiment, an A source containing the additive elements Mg and F was prepared according to steps S21a to S21c shown in Figure 5C. First, lithium fluoride (LiF) was prepared as the F source according to step S21a shown in Figure 5C, and magnesium fluoride (MgF) was prepared as the Mg source. ２ ) was prepared. LiF:MgF ２ The two components were weighed in a molar ratio of 1:3. Next, lithium fluoride and magnesium fluoride were mixed in dehydrated acetone and stirred at a rotational speed of 500 rpm for 20 hours. A ball mill was used for mixing, and zirconium oxide balls were used as the media. After mixing, the mixture was sieved through a sieve with a mesh size of 300 μm to obtain source A.

[0296] Next, in step S22, when the number of moles of lithium cobalt oxide was set to 100, the amount of magnesium fluoride contained in source A was weighed so that the number of moles of magnesium fluoride was 1 (1 mol%), and it was mixed with lithium cobalt oxide in a dry manner. At this time, the mixture was stirred at a rotational speed of 150 rpm for 1 hour. This is a gentler stirring condition than that used to obtain source A. Finally, the mixture was sieved through a sieve with a mesh size of 300 μm to obtain a mixture 903 with uniform particle size (step S23).

[0297] Next, in step S24, the mixture 903 was heated. The heating conditions were a heating temperature of 900°C and a heating time of 120 hours. During heating, a lid was placed on the scabbard containing the mixture 903. The furnace was purged to create an oxygen-containing atmosphere, and the entry and exit of the oxygen was blocked. By heating, a positive electrode active material, which is a composite oxide containing Mg and F, was obtained (step S25). The positive electrode active material obtained in this way was designated as Sample 1.

[0298] <STEM Analysis> Sample 1 was sectioned using the FIB method (μ-sampling method), and cross-sectional HAADF-STEM, ABF-STEM, and STEM-EELS analyses were performed.

[0299] The following equipment and conditions were used for STEM: Scanning transmission electron microscope: JEOL JEM-ARM200F NEOARM Observation conditions: Acceleration voltage: 200kV Magnification accuracy: ±10%

[0300] Figure 19 shows a cross-sectional HAADF-STEM image of the positive electrode active material. Figure 20A shows a magnified HAADF-STEM image of a portion of the area indicated by the white dashed line in Figure 19, which corresponds to the edge surface. Figure 20B shows an ABF-STEM image of the same region.

[0301] In HAADF-STEM, transition metals M (cobalt in the case of sample 1), which have a large atomic number among the elements present in the positive electrode active material, are observed as high-gradation elements close to white. In Figure 20A, the horizontal presence of a layer of transition metal M was observed in the interior side, which has a layered rock salt crystal structure.

[0302] In ABF-STEM, both light elements and transition metals are observed as low-gradation, almost black. In Figure 20B, not only the transition metal M but also oxygen and lithium present between the layers of transition metal M could be observed in the layered rock salt crystal structure.

[0303] To facilitate the determination of the crystal structure, the grayscale levels of the HAADF-STEM image in Figure 20A were subtracted from the ABF-STEM image in Figure 20B, following the procedure shown in Embodiment 1, and then converted to absolute values. This difference image is shown in Figure 21A. In the difference image, the transition metal M was observed as a high-grayscale close to white, while the added elements, including oxygen, lithium, and magnesium, were observed as a low-grayscale close to black.

[0304] Figure 21B is the same ABF-STEM image as Figure 20B, with auxiliary lines added. The first atomic layer in which cations are observed is indicated by the arrow 1, and arrows are added sequentially inward up to the 12th cation layer. The first to fourth cation layers constitute region I, which has a rock salt type crystal structure; the fourth to eighth layers constitute region II, which has a Spinel' type crystal structure; and the area inside the eighth layer constitutes region III, which has a layered rock salt type crystal structure. The boundaries of each region are indicated by white dashed lines.

[0305] The arrangement of oxygen in regions I to III Ｉ 〜OＩＩＩ This is indicated by an arrow in Figure 21B. Ｉ and O ＩＩ and O ＩＩ and O ＩＩＩ The angles were all between 0° and 5°, and the crystal orientations in regions I to III were roughly consistent.

[0306] The locations of the octahedral and tetrahedral sites are shown in Figure 21B by solid and dashed circles. In all of regions I through III, atoms were observed at the octahedral sites in the ABF-STEM image in Figure 21B, but no atoms were observed at the tetrahedral sites.

[0307] Figure 22A is the same HAADF-STEM image as Figure 20A. The electron diffraction pattern at the location indicated by point 1 in Figure 22A is shown in Figure 22B, the electron diffraction pattern at the location indicated by point 2 is shown in Figure 22C, and the electron diffraction pattern at the location indicated by point 3 is shown in Figure 22D.

[0308] The electron diffraction pattern of point 1, which includes region I in Figure 22B, generally showed characteristics of a rock salt type crystal structure. The electron diffraction pattern of point 3, which includes region III in Figure 22D, showed characteristics of a layered rock salt type crystal structure with large interplanar spacing in one direction.

[0309] The electron diffraction pattern of point 2, including region II in Figure 22C, showed a closer distance between the zero-order diffraction spot and the nearest primary-order diffraction spot than the rock salt type, exhibiting characteristics of a Spinel'-type crystal structure. In the rock salt type of region I shown in Figure 22B, the distance between the zero-order diffraction spot and the nearest primary-order diffraction spot was approximately twice as far as in the Spinel'-type crystal structure shown in Figure 22C.

[0310] Figure 23A is a HAADF-STEM image of the edge surface of sample 1 shown in Figure 19, Figure 23B is a cobalt mapping image obtained by STEM-EELS analysis of the same region as Figure 23A, and Figure 23C is a magnesium mapping image.

[0311] The measurement regions a to d included in region II of Figure 21B are shown in Figure 23A. The graph of the EELS spectra extracted from a to d in Figure 23A is shown in Figure 23D. The peaks indicated by arrows in Figure 23D originate from magnesium. As shown in Figure 23D, magnesium was detected in a, b, and c among a to d in Figure 23A.

[0312] As shown by A to D in Figure 3A, the Spinel' type crystal structure has, when the cation sites are observed from a certain direction, cation sites A where only the first cation is arranged in the depth direction, cation sites B and C where the first and second cations are arranged alternately, and cation site D where only the second cation is arranged. For example, when the first cation is a magnesium ion, magnesium is present at cation sites A, B, and C but not at D. Therefore, the detection of magnesium at a, b, and c in Figure 23A, and the absence of magnesium at d, is consistent with the characteristics of the Spinel' type crystal structure. Similarly, as shown in Figure 23B, the detection of cobalt at d, and the almost complete absence of cobalt at a, b, and c, is consistent with the characteristics of the Spinel' type crystal structure.

[0313] Figures 24A to 26B show the results of STEM-EDX radiation analysis of the edge surface of sample 1. Figure 24A is a graph with the detected amount on the vertical axis, and Figure 26A is a graph with at% on the vertical axis. In this case, the denominator was the sum of carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, gallium, and molybdenum. Figure 24B is an enlarged graph of Figure 24A. Figure 25 is a graph extracted from Figure 24B showing magnesium and fluorine. Figure 26B is an enlarged graph of Figure 26A.

[0314] As shown in Figures 26A and 26B, magnesium was present at a high concentration in the surface layer of sample 1, with a maximum concentration of 21.4 at%. The maximum detected amount of magnesium was measured at a distance of 11.2 nm, which is inward from the reference point of 10.9 nm. The reference point in Figures 24A to 26B was determined from the average detected amount of the transition metal M at a distance of 0 nm to 5 nm and the average detected amount at a distance of 25 nm to 35 nm.

[0315] 10: Lithium-ion secondary battery, 11: Positive electrode, 12: Negative electrode, 13: Separator, 21: Positive electrode current collector, 22: Positive electrode active material layer, 31: Negative electrode current collector, 32: Negative electrode active material layer, 41: Conductive material, 51: Electrolyte, 100: Positive electrode active material particles, 100a: Surface layer, 100b: Interior, 200: Secondary positive electrode active material, 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 312: Washer, 322: Spacer, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active Material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 509: outer casing, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 513: secondary battery, 514: terminal, 515: seal, 517: antenna, 519: layer, 529: label, 531: secondary battery pack, 540: circuit board, 552: other side, 590: control circuit, 590a: circuit system, 590b: circuit system, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element Element, 613: Safety valve mechanism, 614: Conductive plate, 615: Energy storage system, 616: Secondary battery, 620: Control circuit, 621: Wiring, 622: Wiring, 623: Wiring, 624: Conductor, 625: Insulator, 626: Wiring, 627: Wiring, 628: Conductive plate, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display unit, 707: General load, 708: Energy storage system load, 709: Router, 710: Service drop mounting section, 711: Measurement section, 712: Prediction section, 713: Planning section, 790: Control device , 791: Energy storage device, 796: Underfloor space, 799: Building, 903: Mixture, 911a: Terminal, 911b: Terminal, 913: Secondary battery, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer, 933: Separator, 950: Winding body, 950a: Winding body, 951: Terminal, 952: Terminal, 1300: Rectangular secondary battery, 1301a: First battery, 1301b: First battery, 1302: Battery controller,1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defogger, 1310: DC circuit, 1311: Second battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tires, 1317: Rear motor, 1320: Control circuit section, 1321: Control circuit section, 1322: Control circuit, 1324: Switch section, 1413: Fixing section, 1414: Fixing section, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2005: Artificial satellite, 2100: Mobile phone, 2101: Housing, 2102: Display unit, 2103: Operation buttons, 2104: External connection port, 2105: Speaker, 2106: Microphone, 2107: Rechargeable battery, 2200: Battery pack, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2204: Rechargeable battery, 2300: Unmanned aerial vehicle, 2301: Rechargeable battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 2604: Charging device, 2610: Saw 4000: Glasses-type device, 2611: Wiring, 2612: Power storage device, 4000: Glasses-type device, 4000a: Frame, 4000b: Display unit, 4001: Headset-type device, 4001a: Microphone unit, 4001b: Flexible pipe, 4001c: Earphone unit, 4002: Device, 4002a: Housing, 4002b: Secondary battery, 4003: Device, 4003a: Housing, 4003b: Secondary battery, 4005: Wristwatch-type device, 4005a: Display unit, 4005b: Belt unit, 4006: Belt-type device, 4006a: Belt unit, 4006b: Wireless power supply and reception Part, 6300: Cleaning robot, 6301: Housing, 6302: Display unit, 6303: Camera, 6304: Brush, 6305: Operation button, 6306: Rechargeable battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: Speaker, 6405: Display unit, 6406: Lower camera, 6407: Obstacle sensor, 6408: Movement mechanism, 6409: Rechargeable battery, 8600: Scooter, 8601: Side mirror, 8602: Energy storage device, 8603: Turn signal light, 8604: Under-seat storage, 8700: Electric bicycle,8701: Storage battery, 8702: Energy storage device, 8703: Display unit, 8704: Control circuit,

Claims

Positive electrode active material particles having lithium, a transition metal M, oxygen, and an additive element, The transition metal M is one or more selected from cobalt, nickel, and manganese. The positive electrode active material particles have, in order from the surface toward the interior, a rock salt type crystal structure, a Spinel' type crystal structure, and a layered rock salt type crystal structure. 　 In claim 1, The positive electrode active material particles have magnesium as the additive element. The aforementioned positive electrode active material particles have a layered rock salt type crystal structure of space group R-3m in Rietveld analysis of the XRD pattern, with more than 90% of them. The aforementioned layered rock salt crystal structure consists of alternating layers of transition metal M and lithium. In the aforementioned Spinel'-type crystal structure, no atoms were observed at the tetrahedral sites in the cross-sectional ABF-STEM and HAADF-STEM images, and in the transition metal M layer of the HAADF-STEM image, bright spots of high and low luminosity were alternately arranged in the depth direction. The positive electrode active material particles wherein, in ICP-MS analysis of the positive electrode active material particles, the Ti / transition metal M (weight ratio) is 0.0005 or less. 　 In claim 2, The aforementioned Spinel' type crystal structure is A positive electrode active material particle in which atoms are not observed at tetrahedral sites but are present at octahedral sites in cross-sectional ABF-STEM and HAADF-STEM images. 　 In claim 3, The aforementioned Spinel'-type crystal structure belongs to the space group Fd-3m and has a transition metal M at the 16d site, and is a positive electrode active material particle. 　 In claim 4, The angle between the anion arrangement in the layered rock salt type crystal structure and the anion arrangement in the Spinel' type crystal structure is 0° or more and 5° or less. Positive electrode active material particles in which the angle between the anion arrangement in the Spinel' type crystal structure and the anion arrangement in the rock salt type crystal structure is 0° or more and 5° or less. 　 In claim 5, When the first atomic layer in which cations are observed in the cross-sectional ABF-STEM and HAADF-STEM images of the surface where lithium is inserted and deinserted is defined as the first layer, The first to fourth layers have the characteristics of a rock salt type crystal structure. The fourth to eighth layers are cathode active material particles having the characteristics of a Spinel'-type crystal structure. 　 Positive electrode active material particles having lithium, a transition metal M, oxygen, and an additive element, The transition metal M is one or more selected from cobalt, nickel, and manganese. The positive electrode active material particles have, in order from the inside outwards, characteristics of a layered rock salt type crystal structure, characteristics of a Spinel type crystal structure, and characteristics of a rock salt type crystal structure. The positive electrode active material particles wherein, in ICP-MS analysis of the positive electrode active material particles, the Ti / Co (weight ratio) is 0.0005 or less. 　 A lithium-ion secondary battery having positive electrode active material particles according to any one of claims 1 to 7.

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