Positive electrode active material particles and method for producing positive electrode active material particles

Abstract

The present invention provides: lithium nickel cobalt manganate which has improved charge / discharge capacity, reliability or safety; and a secondary battery which includes the same. The present invention specifically provides positive electrode active material particles which each have lithium, a transition metal M1 (M1 is one or more selected from among Ni, Co, Mn, and V), oxygen, and magnesium. The positive electrode active material particles each have a core, a first shell that is located outside the core, and a second shell that is located outside the first shell. The first shell and the second shell have more cobalt than the core, and the second shell has more magnesium than the core and the first shell. With respect to the above-described positive electrode active material particles, it is preferable that the orientations of the crystals of the core, the first shell, and the second shell are generally the same.

Description

Positive electrode active material particles and method for producing positive electrode active material particles

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

[0002] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like.

[0003] In recent years, the development of various power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, has been actively pursued. Demand for high-power, high-energy-density lithium-ion secondary batteries has been rapidly expanding in modern society, along with the development of portable information terminals (PDAs) such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, next-generation clean-energy automobiles (CEs) such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), and the semiconductor industry. These batteries have become indispensable to modern society as a rechargeable energy source.

[0004] In lithium-ion secondary batteries, lithium cobalt oxide (LiCoO) with a layered rock salt crystal structure is used as a high-capacity positive electrode active material. ２ ), lithium nickel cobalt manganese oxide (LiNi ａ Co ｂ Mn ｃ O ２ , a+b+c=1) have been put into practical use.

[0005] Lithium nickel-cobalt manganese oxide (Ni-MnO) is one of the cathode active materials used in lithium-ion secondary batteries for electric vehicles. Various attempts have been made to modify the surface layer of Ni-MnO using various elements and techniques to remove residual lithium and suppress side reactions with the electrolyte (see, for example, Patent Documents 1 and 2, and Non-Patent Document 1).

[0006] Furthermore, positive electrode active materials known as lithium-excess materials have attracted attention because they can store far more lithium ions than current lithium cobalt oxide, lithium nickel cobalt manganese oxide, and the like (Non-Patent Documents 2 to 6).

[0007] JP 2020-064858 International Publication WO2020 / 065441

[0008] Near−surface reconstruction in Ni−rich layered cathodes for high−performance lithium−ion batteries.Hoon−Hee Ryu,Hyung−Woo Lim,Sin Gyu Lee & Yang−Kook Sun.Nature Energy 9,47−56(2024)Reversible Oxygen Participation to the Redox Processes Revealed for Li▲1.20▼Mn▲0.54▼Co▲0.13▼Ni▲0.13▼O▲2▼.Hideyuki Koga et al.,Journal of The Electrochemical Society,160(6)A786−A792(2013)Functioning Mechanism of AlF▲3▼ Coating on the Li− and Mn−Rich Cathode Materials.Jianming Zheng et al.,Chemistry of Materials,26,6320−6327(2014)Lithium− and Manganese−Rich Oxide Cathode Materials for High−Energy Lithium Ion Batteries.Jun Wang et al.,Advanced Energy Materials,6,1600906(2016)Challenges and Recent Advances in High Capacity Li−Rich Cathode Materials for High Energy Density Lithium−Ion Batteries.Wei He et al.,Advanced materials,33,2005937(2021)In situ formed partially disordered phases as earth−abundant Mn−rich cathode materials.Zijian Cai et al.,Nature Energy(2023).https: / / doi.org / 10.1038 / s41560−023−01375−9

[0009] However, further improvements are desired in various aspects of positive electrode active materials, including lithium nickel cobalt manganese oxide and lithium-excess systems, and secondary batteries using such materials, such as capacity, cycle characteristics, charge / discharge characteristics, reliability, safety, and cost.

[0010] Therefore, an object of one embodiment of the present invention is to provide a positive electrode active material particle or a composite oxide in which a decrease in voltage or discharge capacity during charge / discharge cycles is suppressed. Another object is to provide a positive electrode active material particle or a composite oxide in which a change in crystal structure during charge is suppressed. Another object is to provide a positive electrode active material particle or a composite oxide in which oxygen release is suppressed. Another object is to provide a positive electrode active material particle or a composite oxide in which a discharge capacity is large. Another object is to provide a secondary battery with high safety or reliability.

[0011] Another object of one embodiment of the present invention is to provide novel positive electrode active material particles, a composite oxide, a power storage device, or a manufacturing method thereof.

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

[0013] In one embodiment of the present invention, the cathode active material particles have a core-shell structure and are configured to have two shells. The first shell is a layer rich in cobalt as a transition metal, and the second shell located outside the first shell is a layer rich in magnesium. Furthermore, a fluoride salt that functions as a flux is used to effectively dope magnesium into the second shell.

[0014] One aspect of the present invention is a positive electrode active material particle comprising lithium, a transition metal M1 (M1 is one or more selected from Ni, Co, Mn, and V), oxygen, and magnesium, wherein the positive electrode active material particle has a core, a first shell on the outside of the core, and a second shell on the outside of the first shell, wherein the first shell and the second shell each contain more cobalt than the core, and the second shell contains more magnesium than the core and the first shell.

[0015] Another embodiment of the present invention provides positive electrode active material particles that include lithium, a transition metal M2 (M is one or more selected from Mn, Cr, Mo, Nb, V, Fe, Ni, Ti, and Ru), oxygen, magnesium, and fluorine, wherein the positive electrode active material particles have an atomic ratio Li / M2 greater than 1, and the positive electrode active material particles have a core, a first shell outside the core, and a second shell outside the first shell, and the first shell and the second shell contain more cobalt than the core, and the second shell contains more magnesium than the core and the first shell.

[0016] In the above, it is preferable that the positive electrode active material particles contain fluorine, and the second shell contains more fluorine than the first shell.

[0017] In the above, the second shell preferably has more fluorine than the core.

[0018] In the above, it is preferable that the crystal orientations of the core, the first shell, and the second shell are approximately the same.

[0019] In the above, it is also preferable that the second shell contains more of one or more elements selected from titanium, aluminum, nickel, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, beryllium, europium, gadolinium, and antimony than the core and the second shell.

[0020] In the above, it is preferable that the first shell is present in at least a part of a region having a depth of 3 nm or more and 50 nm or less from the surface of the positive electrode active material particle, and that the second shell is present in at least a part of a region having a depth of 0.5 nm or more and less than 3 nm from the surface of the positive electrode active material particle.

[0021] In the above, the positive electrode active material particles are preferably secondary particles.

[0022] Another aspect of the present invention is a method for producing positive electrode active material particles, the method comprising: mixing a first composite oxide having lithium, a transition metal M1 (M1 is one or more selected from Ni, Co, Mn, and V), and oxygen, and having a layered rock-salt crystal structure of space group R-3m, with a solution containing cobalt to produce a first mixture; performing a first heating process on the first mixture to produce a second composite oxide; mixing the second composite oxide with a magnesium source and a fluorine source to produce a second mixture; and performing a second heating process on the second mixture to produce positive electrode active material particles.

[0023] Another aspect of the present invention is Li ｘ M2 ２−ｘ O ２ (M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2) with a solution containing cobalt to prepare a first mixture; subjecting the first mixture to a first heating treatment to prepare a second composite oxide; subjecting the second composite oxide to a magnesium source and a fluorine source to prepare a second mixture; and subjecting the second mixture to a second heating treatment to prepare positive electrode active material particles.

[0024] In the above, it is preferable that the cobalt-containing solution contains an aqueous cobalt sulfate solution, the magnesium source contains magnesium fluoride, and the fluorine source contains lithium fluoride.

[0025] In the above, it is preferable that the heating temperature of the first heating is 250°C or higher and 900°C or lower and the heating time is 2 hours or higher and 10 hours or lower, and that the heating temperature of the second heating is 700°C or higher and 900°C or lower and the heating time is 2 hours or higher and 10 hours or lower.

[0026] Another aspect of the present invention is a method for producing positive electrode active material particles, the method comprising: mixing a first composite oxide having lithium, a transition metal M1 (M1 is one or more selected from Ni, Co, Mn, and V), and oxygen, and having a layered rock-salt crystal structure of space group R-3m, with a cobalt source, a magnesium source, and a fluorine source to produce a mixture; and heating the mixture to produce positive electrode active material particles.

[0027] Another aspect of the present invention is Li ｘ M2 ２−ｘ O ２ (M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2), with a cobalt source, a magnesium source, and a fluorine source to prepare a mixture; and heating the mixture to prepare positive electrode active material particles.

[0028] In the above, the heating temperature is preferably 700° C. or more and 900° C. or less, and the heating time is preferably 2 hours or more and 10 hours or less.

[0029] According to one embodiment of the present invention, it is possible to provide a positive electrode active material particle or composite oxide in which a decrease in voltage or discharge capacity during charge / discharge cycles is suppressed. Alternatively, it is possible to provide a positive electrode active material particle or composite oxide in which a change in crystal structure during charging is suppressed. Alternatively, it is possible to provide a positive electrode active material particle or composite oxide in which oxygen desorption is suppressed. Alternatively, it is possible to provide a positive electrode active material particle or composite oxide in which a discharge capacity is large. Alternatively, it is possible to provide a secondary battery with high safety or reliability.

[0030] According to one embodiment of the present invention, novel positive electrode active material particles, a composite oxide, a power storage device, or a manufacturing method thereof can be provided.

[0031] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0032] FIG. 1A is a cross-sectional view of a positive electrode active material particle. FIG. 1B is a surface view of a positive electrode active material particle. FIG. 1C is a cross-sectional view of a positive electrode active material particle. FIG. 2A is a cross-sectional view of a positive electrode active material particle. FIG. 2B is a diagram illustrating each region of a positive electrode active material particle in a cross-sectional analysis. FIG. 3 is a flowchart illustrating an example of a method for producing positive electrode active material particles. FIGS. 4A and 4B are flowcharts illustrating an example of a method for producing positive electrode active material particles. FIGS. 5A to 5D are diagrams illustrating a positive electrode. FIGS. 6A and 6B are diagrams illustrating a lithium ion battery. FIGS. 7A to 7C are diagrams illustrating a lithium ion battery. FIGS. 8A to 8D are diagrams illustrating a lithium ion battery and an energy storage system. FIGS. 9A to 9C are diagrams illustrating a lithium ion battery. FIGS. 10A to 10C are diagrams illustrating a lithium ion battery. FIGS. 11A to 11C are diagrams illustrating an electric vehicle. FIGS. 12A to 12D are diagrams illustrating a transportation vehicle. Figures 13A to 13C are diagrams illustrating a two-wheeled vehicle, etc. Figures 14A to 14D are diagrams illustrating electronic equipment, etc. Figures 15A to 15D are diagrams illustrating an example of space equipment.

[0033] Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention should not be construed as being limited to the following examples. The embodiments of the present invention can be modified within the scope of the spirit of the present invention.

[0034] In this specification, space groups are expressed using short notation in international notation (or Hermann-Mauguin notation). Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by adding a superscript bar to the numbers. However, due to formatting constraints, in this specification, instead of adding a bar above the numbers, a minus sign (-) may be added before the numbers. Individual orientations indicating directions within a crystal are expressed using [ ], collective orientations indicating all equivalent directions are expressed using < >, individual planes indicating crystal planes are expressed using ( ), and collective planes with equivalent symmetry are expressed using {}. Trigonal crystals expressed in the space group R-3m are generally expressed as a hexagonal composite hexagonal lattice to facilitate understanding of the structure. Miller indices may also be expressed using (hkil) instead of (hkl). Here, i is -(h+k). In this specification and the like, for the space group R-3m, unless otherwise specified, crystal planes and the like are expressed as a composite hexagonal lattice.

[0035] In this specification and the like, when simply referring to a positive electrode active material, there are cases where the description refers to multiple positive electrode active material particles and cases where the description refers to a single positive electrode active material particle, depending on the analytical method, etc. For example, in the case of descriptions relating to scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX) line analysis, STEM-electron energy loss spectroscopy (STEM-EELS), and electron diffraction, the description refers to a single positive electrode active material particle unless otherwise specified. On the other hand, in the case of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), various mass analyses, etc., the description refers to multiple positive electrode active material particles unless otherwise specified.

[0036] In this specification and the like, the term "particle" is not limited to referring only to spherical particles (having a circular cross-sectional shape), but may also refer to cross-sectional shapes of individual particles such as ellipsoids, rectangles, trapezoids, triangles, squares with rounded corners, asymmetric shapes, etc. Furthermore, individual particles may have irregular shapes. Furthermore, when simply referring to particles, this term includes primary particles and secondary particles.

[0037] Furthermore, when describing the characteristics of the positive electrode active material particles, it is not necessary for all particles to have 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 have the preferred characteristics described below, it can be said that the positive electrode active material and the secondary battery having the same are sufficiently effective in improving their properties.

[0038] The distribution of a certain element refers to a region in which the element is continuously detected within a range that is not a noise by a certain continuous analytical method. A region in which the element is continuously detected within a range that is not a noise can also be referred to as a region in which the element is always detected when the analysis is performed multiple times.

[0039] The space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification and the like, "belonging to a certain space group," "belonging to a certain space group," or "being a certain space group" can be rephrased as "identified with a certain space group."

[0040] In this specification, a rock salt crystal structure refers to a cubic crystal structure in which cations and anions are arranged alternately. It can also be said to be a crystal structure in which anions are arranged in a cubic close-packed manner, with cations occupying all octahedral positions. There may be one type of cation and one type of anion, or multiple types of cations and anions. There may be deficiencies of cations or anions.

[0041] In this specification, the layered rock salt crystal structure refers to a crystal structure that is similar to the rock salt structure in that cations and anions at octahedral positions are arranged alternately, and in which it is clear that multiple types of cations are present, and the arrangement of at least one type of cation forms a two-dimensional plane. If lithium ions form a two-dimensional plane, two-dimensional diffusion of lithium is possible. Note that defects such as vacancies of cations or anions may also be present.

[0042] In this specification, the term "disordered rock salt" refers to a crystal structure that has a cubic crystal structure, and is similar to the rock salt structure in that cations and anions at octahedral positions are arranged alternately, and in addition, it is clear that multiple types of cations are present, and the arrangement of these cations is irregular. In a lithium-rich composite oxide, the irregular arrangement of cations means that the ratio of the frequency of occurrence of each cation type at each cation site is approximately fixed, and no significant difference is observed between cation sites. For example, in a HAADF-STEM (High-angle Annular Dark Field Scanning TEM) image, this means that there is no significant difference in the contrast of the cation sites. Note that defects such as deficiencies of cations or anions may exist.

[0043] In this specification and the like, the term "spinel type" refers to a material having a cubic crystal structure and represented by the general formula AB ２ O ４ The spinel crystal structure is represented by the formula: where anions are arranged in a cubic close-packed manner and cations are present at octahedral and tetrahedral positions. The atomic ratio of cations present at octahedral and tetrahedral positions is 2:1, but this atomic ratio does not need to be exact and can be, for example, a:1 (a is 1.9 or more and 2.1 or less). The spinel crystal structure is preferably determined from, for example, an electron diffraction pattern, an FFT pattern of a TEM image or an FFT pattern of a STEM image, STEM-EELS, or the like.

[0044] In all rock salt, layered rock salt, irregular rock salt, and spinel structures, anions are arranged in a cubic close-packed pattern. If the anion arrangement is roughly close to cubic close-packed, it can be considered cubic close-packed. A cubic close-packed anion arrangement refers to a state in which the second layer of anions is arranged above the voids of the first layer of anions, and the third layer of anions is arranged directly above the voids of the second layer of anions, but not directly above the first layer of anions. Therefore, the anions do not necessarily have to be arranged in a cubic lattice. Furthermore, because real crystals always have defects, analytical results do not necessarily conform to theory. For example, in FFT (fast Fourier transform) patterns such as electron diffraction patterns or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, a cubic close-packed structure can be considered to exist if the orientation from the theoretical positions is 5 degrees or less, or 2.5 degrees or less.

[0045] Furthermore, cathode active material particles to which an additive element that improves conductivity and / or an additive element that stabilizes the crystal structure has been added may be referred to as a composite oxide, a cathode material, a cathode ingredient, a cathode material for secondary batteries, or the like. Furthermore, in this specification and the like, the cathode active material particles of one embodiment of the present invention preferably contain a compound. Furthermore, in this specification and the like, the cathode active material particles of one embodiment of the present invention preferably contain a composition. Furthermore, in this specification and the like, the cathode active material particles of one embodiment of the present invention preferably contain a composite. Furthermore, in this specification and the like, the term "composite oxide" refers to an oxide having multiple types of cations. The composite oxide has oxygen as an anion, but is not limited to oxygen, and may also contain anions such as fluorine and chlorine in addition to oxygen.

[0046] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material particles of one embodiment of the present invention have a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material particles in a charged state can suppress a decrease in charge / discharge capacity due to repeated charge / discharge.

[0047] Unless otherwise specified, the materials (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) contained in secondary batteries are described in their pre-degradation state. Note that a decrease in discharge capacity due to aging and burn-in treatments during secondary battery manufacturing is not considered to be degradation. For example, a lithium-ion secondary cell or lithium-ion secondary battery pack (hereinafter referred to as a lithium-ion secondary battery) can be said to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. For lithium-ion secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to not only the above JIS standard but also various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0048] Embodiment 1 In this embodiment, features of a positive electrode active material particle of one embodiment of the present invention will be described with reference to FIGS. 1A to 2B.

[0049] Positive electrode active material particle 101 of one embodiment of the present invention includes lithium, a transition metal M1 or a transition metal M2 (M1 is one or more selected from Ni, Co, Mn, and V, and M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru), oxygen, and an additive element.

[0050] The positive electrode active material particles 101 are preferably a composite oxide in which an additive element is added to a layered rock salt type lithium nickel cobalt manganese oxide belonging to the space group R-3m, or a compound in which an additive element is added to a lithium-excess composite oxide.

[0051] [Lithium nickel cobalt manganese oxide] Lithium nickel cobalt manganese oxide that is not an excess lithium system has a composition of LiMO ２ (M1 is one or more selected from Ni, Co, Mn and V), and refers to a composite oxide having a layered rock salt type crystal structure belonging to the space group R-3m.

[0052] [Lithium-excess composite oxide] A lithium-excess composite oxide is a composite oxide having a composition of Li ｘ M2 ２−ｘ O ２(M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2.) Note that part of O may be substituted with other anions such as F and / or Cl.

[0053] Li ｘ M2 ２−ｘ O ２ As is clear from the expression (1<x<2), the Li / M2 (atomic ratio) of the lithium-excess composite oxide is greater than 1. It is also preferable that the Li / M2 ratio is greater than 1 in the positive electrode active material particle 101 of one embodiment of the present invention, in which an additive element is added to a lithium-excess composite oxide.

[0054] Examples of lithium-excess composite oxides include layered rock-salt type composite oxides and disordered rock-salt type composite oxides.

[0055] <Layered rock salt type> The layered rock salt type lithium-excess layered oxide contains Li ２ MnO ３ And LiM1O ２ (M1 is one or more selected from Ni, Co, Mn, and V) in a certain ratio. ２ For example, LiCoO ２ , LiNiO ２ , LiNi ａ Co ｂ Mn ｃ O ２ (a+b+c=1), etc.

[0056] Li ２ MnO ３ has a crystal structure with space group C2 / m symmetry, and LiMO ２ has a crystal structure with space group R-3m symmetry. ２ MnO ３ and LiM1O ２A material synthesized by mixing these in a certain ratio will be a solid solution having a P2 / m crystal structure, a C2 / m crystal structure, or an R-3m crystal structure. Alternatively, it will be a composite structure having a region of the C2 / m crystal structure and a region of the R-3m crystal structure. Furthermore, the composite structure can have a region of the P2 / m crystal structure instead of, or in addition to, either the region of the C2 / m crystal structure or the region of the R-3m crystal structure.

[0057] Li in space group C2 / m ２ MnO ３ and LiMO of space group R-3m ２ In all of these, the cations and anions are adjacent to each other, each occupying an octahedral position. Even when these solid solutions have a crystal structure of space group P2 / m, the cations and anions can each occupy an octahedral position. These structures are edge-sharing octahedra with anions at the vertices and a cation at the center, and can be called distorted rock salt structures. Furthermore, when the cations are regularly arranged, these composite oxides having a crystal structure of space group P2 / m, C2 / m, and / or R-3m can all have a layered rock salt type crystal structure.

[0058] As the layered rock salt type lithium-excess composite oxide, for example, 0.3Li ２ MnO ３ -0.7Li (Ni １／３ Co １／３ Mn １／３ ) O ２ Also written as Li １．１４ Mn ０．４６ Ni ０．２ Co ０．２ O ２ , 0.5Li ２ MnO ３ -0.5Li(Ni １／３ Mn １／３ Co １／３ O ２ ) also written as Li １．２ Mn ０．５４ Co ０．１３ Ni ０．１３ O ２ , 0.5Li ２ MnO ３ -0.5Li(Ni １／２ Mn１／２ O ２ ) also written as Li １．２ Mn ０．６ Ni ０．２ O ２ etc. can be used.

[0059] <Irregular rock salt type> Irregular rock salt type lithium-rich composite oxides are those with a composition of Li ｘ M2 ２−ｘ O ２ (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2), has a rock-salt type crystal structure belonging to the space group Fm-3m, and refers to a composite oxide in which the arrangement of cations is irregular. Note that a portion of O may be substituted with other anions such as F and / or Cl.

[0060] Examples of the combination of elements contained in the disordered rock-salt type lithium-excess composite oxide include Li—Cr—Mo—O, Li—Ti—Mn—O, Li—Ni—Mn—O, Li—Nb—Mn—O, Li—Nb—Fe—O, Li—Ti—Fe—O, Li—Ti—Ni—O, Li—V—O, Li—Nb—V—O, Li—V—O—F, Li—Mn—O—F, Li—Mn—O—F, Li—Mo—O—F, and the like.

[0061] [Additive Element] The positive electrode active material particles 101 preferably contain, as an additive element, one or more selected from magnesium, fluorine, titanium, aluminum, nickel, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, beryllium, europium, gadolinium, and antimony.

[0062] [Core-Shell Structure] As shown in FIG. 1A, the positive electrode active material particle 101 has a core 200, a first shell 201 on the outside of the core, and a second shell 202 on the outside of the first shell.

[0063] The core 200 has the characteristics of lithium nickel cobalt manganese oxide or a lithium-rich composite oxide. When the core 200 has the characteristics of lithium nickel cobalt manganese oxide, it preferably has a layered rock salt crystal structure belonging to the space group R-3m. When the core 200 has the characteristics of a lithium-rich layered oxide, it preferably has the crystal structure of the layered rock salt type lithium-rich layered oxide and / or the disordered rock salt type lithium-rich layered oxide described above.

[0064] The first shell 201 and the second shell 202 have more cobalt than the core 200. That is, the first shell 201 has a higher concentration and / or detectable amount of cobalt than the core 200. The first shell 201 preferably has the same or similar crystal structure as the core 200. For example, the first shell 201 preferably has a layered rock-salt crystal structure belonging to the space group R-3m, or a layered rock-salt or disordered rock-salt crystal structure belonging to the space group C2 / m.

[0065] Furthermore, the second shell 202 has a larger amount of the additive element than the core 200 and the first shell 201. That is, the second shell 202 has a higher concentration and / or detectable amount of the additive element than the core 200 and the first shell 201. When an element not contained in the core 200 is used as the additive element, it is preferable that the element be detected in the second shell 202. When an element also contained in the core 200 is used as the additive element, it is preferable that the element be detected in the core 200 as well, and that the concentration and / or detectable amount in the second shell 202 be higher than in the core 200.

[0066] The second shell 202 contains more additive elements than the core 200 and the first shell 201, and therefore has a different composition from the core 200 and the first shell 201. Therefore, the crystal structure of the second shell 202 is preferably different from the crystal structure of the core 200. Similarly, the crystal structure of the second shell 202 is preferably different from the crystal structure of the first shell 201. For example, the second shell 202 preferably has a rock salt crystal structure.

[0067] The second shell 202, which is a region including the surface of the positive electrode active material particle 101 or a region close to the surface, contains a large amount of added elements and has a rock salt type crystal structure, which can suppress side reactions with the electrolyte and / or phase changes of the positive electrode active material particle that occur during charging and discharging.

[0068] Furthermore, the presence of the first shell 201 rich in cobalt enables the formation of the second shell 202. For example, as disclosed in Patent Document 2, even if an additive element such as magnesium is added to lithium nickel-cobalt manganese oxide without the first shell 201 and heated, the additive element may not be unevenly distributed on the surface. This is thought to be because magnesium is easily dissolved in lithium nickel-cobalt manganese oxide. However, in the case of lithium cobalt oxide, magnesium is difficult to dissolve in lithium cobalt oxide. Therefore, adding magnesium and heating the mixture allows the additive element to be unevenly distributed in a region near the surface. Therefore, in one embodiment of the present invention, a first shell 201 rich in cobalt is provided on the outside of lithium nickel-cobalt manganese oxide or a lithium-excess composite oxide. This allows the formation of a second shell 202 rich in additive elements such as magnesium.

[0069] Incidentally, being unevenly distributed in a certain region means that it is present at a higher concentration than in other regions, or that a higher detectable amount is obtained than in other regions.

[0070] <Approximate Matching of Orientations> When the second shell 202 has a different crystal structure from the first shell 201 and the core 200, it is preferable that the orientations of the two crystal structures are approximately the same.

[0071] In this specification, when the orientations of the cubic close-packed structures formed by anions in rock salt, layered rock salt, irregular rock salt, and spinel types are aligned, it may be said that the crystal orientations are roughly the same. Also, the three-dimensional structural similarity in which the crystal orientations are roughly aligned, or the same crystallographic orientation, is called topotaxis.

[0072] The fact that the crystal orientations of the two regions roughly coincide 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 FFT patterns of TEM images and FFT patterns of STEM images, etc. Furthermore, XRD (X-ray Diffraction), neutron diffraction, etc. can also be used as materials for determination.

[0073] TEM images, STEM images, etc. provide images that reflect the crystal structure. Electron diffraction patterns also provide information on the crystal orientation of each location. Nanobeam electron diffraction is particularly useful for obtaining information on the crystal orientation of a small area.

[0074] When the crystal planes of the layered rock salt and the rock salt structure coincide with each other, the coincidence of the crystal planes can be observed by a high-resolution STEM image, an electron diffraction pattern, etc. It is preferable to use different electron diffraction methods, such as selected area diffraction and nanobeam diffraction, depending on the particle size and / or the range of the rock salt structure of the first shell 201.

[0075] For example, in a HAADF-STEM image, contrast proportional to the atomic number is obtained, and elements with larger atomic numbers are observed brighter. ２ In the case of (M1 is one or more selected from Ni, Co, Mn, and V), the transition metal M1 has the largest atomic number, so the electron beam is strongly scattered at the position of the transition metal M1, and if there is an arrangement of transition metals M1, it is observed as an arrangement of dots with strong brightness.

[0076] Therefore, in a HAADF-STEM image, when an electron beam is incident perpendicular to the c-axis of the layered rock-salt composite hexagonal lattice, an arrangement of highly bright dots originating from the transition metal M1 on the (003) plane is obtained as a bright band (bright strip). Also, when an electron beam is incident perpendicular to the rock-salt (111) plane, an arrangement of dots originating from the metal elements on the (111) plane is obtained as a bright band. Thus, when repetition of bright bands is observed in both regions of the STEM image, and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, or when the difference in spacing between the bright bands is within 15%, it can be determined that the crystal planes are roughly aligned, i.e., the crystal orientations are roughly aligned.

[0077] Therefore, in a HAADF-STEM image, if an array of highly bright dots is observed in two regions with different crystal structures and the angle between the arrays is 5 degrees or less or 2.5 degrees or less, or if the difference in spacing between the arrays is within 15%, it can be determined that the crystal orientations are roughly consistent.

[0078] In ABF-STEM, elements with smaller atomic numbers are observed brighter, but like HAADF-STEM, contrast according to the atomic number is obtained, so the crystal orientation can be determined in the same way as with HAADF-STEM images.

[0079] Furthermore, information on the crystal orientation of each region can be obtained from FFT patterns of TEM images, FFT patterns of STEM images, etc., or electron diffraction patterns. For example, information on whether the <001> direction in the layered rock salt structure region and the <111> direction in the rock salt structure region roughly coincide can be obtained. When the crystal orientations coincide within 5 degrees or less or 2.5 degrees or less, it can be determined that the crystal planes roughly coincide, i.e., the crystal orientations roughly coincide.

[0080] In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not contiguous with other reciprocal lattice points to form concentric rings. Spot-like reciprocal lattice points that are not contiguous with other reciprocal lattice points indicate high crystallinity.

[0081] Similarly, when the orientations of the irregular rock salt type and the rock salt type are roughly the same, the <111> directions of both may roughly coincide. When the orientations of the irregular rock salt type and the spinel type are roughly the same, the <111> directions of both may roughly coincide. When the orientations of the layered rock salt type and the spinel type are roughly the same, the <111> directions of both may roughly coincide.

[0082] It is known that layered rock salt type positive electrode active material particles of space group R-3m are likely to have the (001) plane and its equivalent plane, as well as the (104) plane and its equivalent plane, as crystal planes. Therefore, for example, when observing the (001) plane using a TEM or the like, it is preferable to first select positive electrode active material particles in which a crystal plane expected to be the (001) plane is observed using a SEM or the like, and then thin-section the positive electrode active material particles using a focused ion beam (FIB) or the like so that the (001) plane can be observed in a TEM or the like with an electron beam

[120] incident. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock salt type positive electrode active material particles so that the (001) plane can be easily observed. Similarly, in the case of positive electrode active material particles of other crystal structures, it is preferable to thin-section the particles so that the arrangement of the transition metal M1 can be easily observed.

[0083] The second shell 202 has a substantially identical crystal structure to the first shell 201 and the core 200, so that the second shell 202, which contains a large amount of the additive element, functions as a pillar supporting the crystal structure of the positive electrode active material particle 101. Among the additive elements, magnesium is particularly preferable because it has a strong bond with oxygen and is expected to function well as a pillar of the positive electrode active material particle 101. In other words, the presence of the additive element stabilizes the crystal structure of the surface and bulk of the positive electrode active material particle 101. Therefore, it is possible to suppress changes in the crystal structure and / or oxygen desorption during charging of the positive electrode active material particle 101.

[0084] Therefore, the positive electrode active material particles 101 can be positive electrode active material particles 101 in which the decrease in the initial discharge capacity relative to the initial charge capacity is suppressed, or positive electrode active material particles 101 with good rate characteristics, or positive electrode active material particles 101 in which the decrease in voltage or discharge capacity during charge / discharge cycles is suppressed.

[0085] <Example of roughly matching orientation> For the second shell 202 and the first shell 201 and core 200 to have different crystal structures and roughly matching orientations, it is necessary that they share a common anion packing structure and that there is no significant mismatch in their lattice constants. More precisely, taking into account different space groups, it is necessary that there is no significant mismatch in the metal-metal distance and the interlayer distance. The metal-metal distance here refers to the average distance between the nearest metal atoms in the same layer. The interlayer distance refers to the average distance between two metal layers. The metal layer refers to the plane on which metal atoms are arranged, and in the case of a rock salt structure and an irregular rock salt structure (Fm-3m), it refers to the (111) plane. In the case of a layered rock salt structure, it refers to the (001) plane for R-3m and the (001) plane for C / 2m. In the case of a spinel structure (Fd-3m), it refers to the (111) plane. In cases where there are multiple types of metals and there is regularity, it may refer to the plane on which the same type of metal is most abundantly arranged.

[0086] With regard to the metal-metal distance and interlayer distance, when the ratio of first shell 201 / second shell 202 is 0.94 or more and 1.06 or less, the crystal structures of first shell 201 and second shell 202 can be approximately the same. Furthermore, when the ratio of core 200 / second shell 202 is 0.94 or more and 1.06 or less, the crystal structures of second shell 202 can be approximately the same as those of first shell 201 and core 200.

[0087] [Shell Thickness] If the first shell 201 is too thin, the effect of forming the second shell 202 may not be fully achieved, so the thickness of the first shell 201 is preferably 3 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. On the other hand, if the first shell 201 is too thick, the amount of cobalt required increases, resulting in increased costs. Therefore, the thickness of the first shell 201 is preferably 50 nm or less, and more preferably 40 nm or less.

[0088] Furthermore, if the second shell 202 is too thin, there is a risk that the surface and bulk of the positive electrode active material particle 101 may not be sufficiently stabilized, so the thickness of the second shell 202 is preferably 0.5 nm or more, more preferably 1 nm or more. It can also be 2 nm or more. On the other hand, a thinner second shell 202 makes it easier to increase the charge / discharge capacity. Therefore, the thickness of the second shell 202 is preferably less than 3 nm.

[0089] It is preferable that second shell 202 has a rock salt type crystal structure, but the rock salt type crystal structure does not necessarily have to be only present in second shell 202. For example, core 200 and a part of first shell 201 may have a rock salt type crystal structure.

[0090] Furthermore, the second shell 202 does not necessarily need to cover the entire surface of the positive electrode active material particle 101. However, in order to function as a pillar, the second shell 202 preferably exists on 50% or more, preferably 70% or more, and more preferably 90% or more of the surface of the positive electrode active material particle 101.

[0091] Furthermore, the second shell 202 does not have to have a rock-salt type crystal structure entirely. For example, a portion of the second shell 202 may be amorphous, or may have another crystal structure. Similarly, the core 200 and the first shell 201 do not have to have a layered rock-salt type crystal structure entirely. For example, a portion of the second shell 202 may be amorphous, or may have another crystal structure.

[0092] 1A , the positive electrode active material particle 101 may have a secondary particle formed by aggregation, adhesion, and / or sintering of a plurality of primary particles. The presence of secondary particles is preferable because it can increase the particle size and facilitates coating onto a current collector, for example.

[0093] 1B and 1C , a positive electrode active material particle 102, which is a secondary particle according to one embodiment of the present invention, will be described. Fig. 1B is a schematic surface diagram of the positive electrode active material particle 102, and Fig. 1C is a schematic cross-sectional diagram of the positive electrode active material particle 102. As shown in Fig. 1B , the positive electrode active material particle 102 includes a plurality of positive electrode active material particles 101, which are primary particles.

[0094] As shown in cathode active material particle 101A in Fig. 1C, core 200 is preferably covered with first shell 201 and second shell 202. However, as shown in cathode active material particles 101B to 101F in Fig. 1C, the entire cathode active material particle 101 does not necessarily have to be covered with first shell 201 and second shell 202.

[0095] For example, as in the case of cathode active material particle 101B and cathode active material particle 101C, the portions in contact with other primary particles may not be covered with first shell 201 and second shell 202 because they are less susceptible to side reactions with the electrolyte. Furthermore, as in cathode active material particle 101D, some of the primary particles may not have first shell 201. Furthermore, as in cathode active material particle 101E, some of the primary particles may not have second shell 202. Furthermore, as in cathode active material particle 101F, some of the primary particles may have a portion of core 200 extending to the surface. Furthermore, as in cathode active material particle 101G, some of the primary particles may not have first shell 201 and second shell 202.

[0096] An additional element may also be used as a sintering aid when granulating the primary particles into secondary particles.

[0097] [Particle size] When the core 200 has the characteristics of a lithium-excess composite oxide, the particle size of the positive electrode active material particles 101, which are primary particles, is preferably 500 nm or less, more preferably 250 nm or less, in order to suppress the diffusion resistance of lithium within the particles. On the other hand, if the particle size is too small, disadvantages such as a tendency for aggregation to occur may occur. Therefore, the median diameter is more preferably 75 nm or more.

[0098] When core 200 has the characteristics of lithium nickel cobalt manganese oxide, the diameter of positive electrode active material particle 101, which is a primary particle, is preferably 75 nm or more and 1 μm or less, since the diffusion resistance is lower than that of a lithium-excess composite oxide.

[0099] Furthermore, the positive electrode active material particles 101, which are primary particles, are preferably single crystals.

[0100] The particle diameter of the positive electrode active material particles 102, which are secondary particles, is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Alternatively, 1 μm or more and 40 μm or less is preferable. Alternatively, 1 μm or more and 30 μm or less is preferable. Alternatively, 2 μm or more and 100 μm or less is preferable. Alternatively, 2 μm or more and 30 μm or less is preferable. Alternatively, 5 μm or more and 100 μm or less is preferable. Alternatively, 5 μm or more and 40 μm or less is preferable.

[0101] [Analysis] <Composition> The composition of the positive electrode active material particles according to one embodiment of the present invention is preferably evaluated by combining multiple analyses. For example, among the elements contained in the positive electrode active material particles, the proportions of the main components lithium, transition metal M1 and transition metal M2, and oxygen are preferably determined by ICP-MS (inductively coupled plasma mass spectrometry) or the like. The proportions of the additive elements are preferably determined by an analysis sensitive to trace elements such as GD-MS (glow discharge mass spectrometry).

[0102] <Distribution of Added Element> The distribution of the added element in the positive electrode active material particles according to one embodiment of the present invention is preferably evaluated by, for example, cross-sectional analysis of the positive electrode active material particles. For example, cross-sectional STEM-EDX is preferred because of its high spatial resolution. To further increase the spatial resolution in STEM-EDX ray analysis, it is preferable that the beam diameter of the electron beam (also referred to as beam diameter, probe diameter, or probe diameter) is small. The beam diameter in STEM-EDX ray analysis is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less.

[0103] Cross-sectional EPMA (electron probe microanalyzer) is also preferred because it has a low detection limit for elements.

[0104] Multiple analyses can be combined for evaluation as needed.

[0105] 2A and 2B , a case where the surface and interface of each region of a positive electrode active material particle according to one embodiment of the present invention are evaluated using cross-sectional STEM-EDX analysis is described. Fig. 2A is a schematic cross-sectional view of a positive electrode active material particle 101 similar to Fig. 1A , with arrows X and Y indicating the direction of analysis from the surface to the interior. Fig. 2B is a schematic view of a depth profile analysis of one of the added elements (A) and cobalt (Co) in the cross-sectional STEM-EDX analysis results.

[0106] As shown in FIG. 2B , the interface between the core 200 and the first shell 201 is the same as the detected amount of cobalt Co ＣＯＲＥ and the detected amount Co of the part most frequently detected near the surface of the positive electrode active material particle 101. ＭＡＸ The detection amount Co is 1 / 2 of the sum of ５０％ Therefore, the first shell 201 has a maximum cobalt detection amount going from the surface to the inside, and then a maximum value going from the surface to the inside. ５０％ This refers to the region extending from the core 200 to the measurement point closest to the first shell 202, which does not overlap with the second shell 202. If the cobalt content of the core 200 is below the lower detection limit, the detected amount is considered to be 0, and the above definition is followed. If the detected amount of cobalt is a gradual gradation, the interface with the core 200 may be unclear, or the interface may not form a smooth curve.

[0107] 2B, the interface between the first shell 201 and the second shell 202 is the same as the detected amount A of the additive element at the center of the positive electrode active material particle 101. ＣＯＲＥ and the detected amount A of the part most frequently detected near the surface of the positive electrode active material particle 101 ＭＡＸ A detection amount A is 1 / 2 of the sum of ５０％ Therefore, the second shell 202 includes the surface, and the detected amount of the additive element increases toward the inside. ５０％This refers to the region up to where the X-ray spectrum reaches a value of 0.01. When there are multiple additive elements, the element that is easiest to detect and / or quantify is adopted, taking into account the composition of the positive electrode active material particle 101. For example, when there is an additive element that is not contained in the core 200, it is preferable to adopt this additive element. It is also preferable to adopt an element whose characteristic X-ray spectrum overlaps little with the element contained in the core 200. It is also preferable to adopt an element that is more easily detected near the surface.

[0108] Furthermore, depending on the particle size of the positive electrode active material particles, each region may not necessarily fit within a single field of view in the STEM-EDX analysis. Therefore, the results of point analysis of different fields measured under the same conditions can also be used. For example, the results of point analysis performed every few nanometers from the center of the particle toward the surface can be used.

[0109] <Surface> The positive electrode active material particles of one embodiment of the present invention are compounds containing a transition metal M1 or M2 and oxygen, which are capable of lithium insertion / extraction. Therefore, in this specification and the like, the interface between a region where the transition metal M1 or M2, which is oxidized / reduced upon lithium insertion / extraction, and oxygen are present and a region where they are not present is defined as the surface of the positive electrode active material particles. Surfaces formed by slips, cracks, and / or fissures may also be considered the surface of the positive electrode active material particles. When analyzing positive electrode active material particles, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material particles. The protective film may be a single-layer or multilayer film of carbon, metal, oxide, resin, or the like.

[0110] For the same reason, the positive electrode active material particles of one embodiment of the present invention are made of aluminum oxide (Al ２ O ３ This does not include metal oxides with no lithium sites that can contribute to charge and discharge, such as those attached to the positive electrode active material particles, carbonates chemically adsorbed after the production of the positive electrode active material particles, or hydroxyl groups. Note that the attached metal oxides refer to metal oxides whose crystal structure does not generally match that of the lithium-excess composite oxides, for example.

[0111] Furthermore, the positive electrode active material particles do not include electrolytes, organic solvents, binders, conductive materials, or compounds derived from these materials that are attached to the positive electrode active material particles.

[0112] In STEM-EDX-ray analysis and the like, in principle or due to measurement errors, the graph of the detected amount of characteristic X-rays of an element does not change sharply, and it may be difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX-ray analysis and the like, a reference point may be used. The reference point is the point where the detected amount of characteristic X-rays of a transition metal M (hereinafter, transition metals M1 and M2 are collectively referred to as transition metals M) is equal to the average value M of the detected amount of characteristic X-rays of the internal transition metal M. ＡＶＥ and the average M of the detected amount of characteristic X-rays of the transition metal M in the background. ＢＧ The point where the detected amount of oxygen characteristic X-rays is 50% of the sum of the detected amount of oxygen characteristic X-rays and the average value O ＡＶＥ and the average value O of the detected amount of characteristic X-rays of oxygen in the background ＢＧ The reference point determined from the transition metal M is set to a point where the sum of the X-rays detected from the transition metal M and the oxygen is 50% of the sum of the X-rays detected from the transition metal M and the oxygen. If the reference point determined from the transition metal M differs from the reference point determined from the oxygen, this is considered to be due to the influence of a metal oxide, carbonate, or the like containing oxygen adhering to the surface, and therefore the reference point determined from the transition metal M can be adopted. In addition, in the case of a positive electrode active material particle 100 having a plurality of transition metals M, the M of the transition metal element with the largest amount of characteristic X-rays detected inside is set to a point where the sum of the X-rays detected from the transition metal M and the oxygen is 50% of the sum of the X-rays detected from the transition metal M and the oxygen. ＡＶＥ and M ＢＧ The reference point can be determined using the following formula:

[0113] The average value M of the detected amount of characteristic X-rays of the transition metal M in the background ＢＧ can be obtained by averaging, for example, a range of 2 nm or more, preferably 3 nm or more, from the outside of the positive electrode active material particle 100, avoiding the vicinity where the detected amount of characteristic X-rays of the transition metal M starts to increase. ＡＶＥ can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, at a depth of 30 nm or more, preferably more than 50 nm, from the region where the detected amount of characteristic X-rays of the transition metal M and oxygen becomes saturated and stable, for example, the region where the detected amount of characteristic X-rays of the transition metal M starts to increase. ＢＧ and the average value O of the detected amount of characteristic X-rays of oxygen inside ＡＶＥ can also be found in the same way.

[0114] Furthermore, the surface of a positive electrode active material particle in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between an area where an image derived from the crystalline structure of the positive electrode active material particle is observed and an area where it is not observed, and is the outermost area where atomic columns derived from the atomic nuclei of metal elements having atomic numbers larger than that of lithium among the metal elements constituting the positive electrode active material particle are observed. Alternatively, it is the intersection of a tangent drawn to the brightness profile from the surface toward the bulk in the STEM image and the axis in the depth direction. The surface in an STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.

[0115] Furthermore, the spatial resolution of STEM-EDX is approximately 1 nm. Therefore, the maximum value of the additive element profile may deviate by approximately 1 nm. For example, even if the maximum value of the additive element profile of magnesium or the like is outside the surface obtained above, the difference between the maximum value and the surface can be considered an error if it is less than 1 nm.

[0116] In addition, a peak in STEM-EDX-ray analysis refers to the detected intensity in each element profile or the maximum value of the characteristic X-rays for each element. Note that noise in STEM-EDX-ray analysis may be a measured value with a half-width less than the spatial resolution (R), for example, R / 2 or less.

[0117] The influence of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated values ​​measured over six scans can be used as the profile of each element. The number of scans is not limited to six; more scans can be performed and the average can be used as the profile of each element.

[0118] Elemental quantification in STEM-EDX analysis can be achieved using a standardless quantification method that utilizes the k-factor built into the analytical instrument and / or analytical software. Furthermore, when determining elemental concentrations from quantitative results, the target elements (also referred to as denominator elements) preferably include elements used in the target material, raw materials, the mesh on which the thin section sample is placed, the instrument components, and thin section processing, such as the following 14 elements: carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, and gallium. Furthermore, when simply referring to the detected amount of a certain element, the number of characteristic X-ray counts and the concentration are also included.

[0119] The STEM-EDX analysis can be performed, for example, as follows: First, a protective film is vapor-deposited on the surface of the positive electrode active material particles. For example, carbon can be vapor-deposited using an ion sputtering device (MC1000 manufactured by Hitachi High-Technologies).

[0120] Next, the positive electrode active material particles are thinned to prepare STEM cross-section samples. For example, the thinning process can be performed using an FIB-SEM device (Hitachi High-Tech XVision 200TBS). Pickup is performed using an MPS (microprobing system), and the finishing process can be performed under conditions such as an acceleration voltage of 10 kV.

[0121] STEM-EDX ray analysis can be performed using, for example, a STEM device (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W (two-pronged) EDX detector. During EDX ray analysis, the emission current of the STEM device is set to 6 μA or more and 10 μA or less, and a portion of the thinned sample with minimal depth and unevenness is measured. The magnification is, for example, approximately 150,000 times. The conditions for EDX ray analysis can be drift correction, a line width of 42 nm, a pitch of 0.2 nm, and six or more frames.

[0122] <Analysis of particle size and particle size distribution using cross-sectional SEM image of positive electrode> The particle size and particle size distribution of the positive electrode active material particles 101 can be calculated from a cross-sectional SEM image of the positive electrode active material particles 101 by, for example, the following method.

[0123] First, an analysis region is cut out from the acquired cross-sectional SEM image so as to obtain a cross section of the positive electrode active material particles 101 sufficient for image analysis. For example, it is preferable to cut out a range in which 100 or more cross sections of the positive electrode active material particles 101 can be obtained.

[0124] The cross-sectional SEM image may be cut out using a function of image processing software, for example, ImageJ, which may be used as the image processing software, and cut out using its crop function.

[0125] Next, the cut-out first image is binarized using image processing software, and particle analysis is performed.

[0126] ImageJ, for example, can be used as the image processing software. The binarization process will be described below. A first image displayed on a 256-value grayscale is used as a frequency graph excluding black (value 0) and white (value 255), and the low-value side (HWHM_L) and high-value side (HWHM_H) are determined as the half-width at half maximum (HWHM) of the maximum peak in the frequency graph. Next, a minimum value a in a range twice the width of HWHM_L on the low-value side from the value corresponding to the peak top (maximum frequency) of the maximum peak, and a maximum value b in a range twice the width of HWHM_H on the high-value side are determined.

[0127] Next, binarization is performed so that values ​​less than a are white, values ​​greater than a and less than b are black, and values ​​greater than b are white. Specifically, the threshold function of ImageJ is used to perform binarization as Threshold (a, b). After that, random bright spots thought to be caused by the conductive material are removed using the Gray Morphology (radius = 3, operator = open, type = circle) and Gray Morphology (radius = 1, operator = close, type = circle) conditions, and a second image can be obtained.

[0128] Next, using the second image, the particle size (projected area) was determined to be 0.5 μm using the Analyze Particles function of ImageJ. ２ 700 μm or more ２The following particles are detected, and the area S of each particle is obtained. Next, the diameter r of each particle is calculated based on the area S of each particle (Equation 1).

[0129]

[0130] In this way, the particle size and particle size distribution of each particle can be calculated from the cross-sectional SEM image. Performing the above analysis is called performing particle size distribution analysis using a cross-sectional SEM image of the positive electrode.

[0131] <Crystallinity of Primary Particles> Whether or not the primary particles are single crystals can be determined by measuring the crystal orientation using, for example, electron backscatter diffraction (EBSD) of a cross section of the positive electrode active material particle. More specifically, if the surface or grain boundary of the primary particle observable by cross section SEM coincides with the area of ​​the mapping of the crystal orientation captured by EBSD, the primary particle can be said to be single crystal.

[0132] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0133] Embodiment 2 In this embodiment, an example of a method for manufacturing positive electrode active material particles of one embodiment of the present invention will be described with reference to FIGS. 3A to 4B.

[0134] [Production Method 1] First, in step S14 of FIG. ２ (M1 is one or more selected from Ni, Co, Mn and V) or Li ｘ M2 ２−ｘ O ２ (M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2) is prepared.

[0135] LiM1O ２ and Li ｘ M2 ２−ｘ O ２ The method for producing the above is not particularly limited, but it can be performed by, for example, a solid phase method. When the solid phase method is used, for example, lithium carbonate (Li ２ CO ３), lithium hydroxide (LiOH) and / or lithium oxide (Li ２ O) or the like can be used. As the M1 source and M2 source, oxides of the transition metals M1 and M2 can be used, for example, nickel cobalt manganese hydroxide (Ni ａ Co ｂ Mn ｃ (OH) ２ , a+b+c=1), manganese oxide (Mn ２ O ３ , MnO ２ and / or MnO), manganese carbonate (MnCO ３ ), nickel hydroxide (Ni(OH) ２ ), nickel oxide (NiO ２ ), cobalt hydroxide (Co(OH) ２ ), cobalt oxide (Co ２ O ３ ), ruthenium oxide (RuO ２ ), iron oxide (Fe ２ O ３ ), titanium oxide (TiO ２ ), vanadium oxide (V ２ O ３ ), molybdenum dioxide (MoO ２ ) etc. can be used.

[0136] Next, the lithium source and the M1 source or M2 source are mixed. A pulverization step during mixing is useful for reducing the particle size. A bead mill and / or a ball mill is preferably used for the pulverization step. A planetary ball mill can be used as the ball mill. Either a dry or wet ball mill can be used.

[0137] Next, the first mixture prepared above is heated. The heating temperature can be, for example, 900° C. or higher and 1200° C. or lower. The heating time can be, for example, 15 minutes or higher and 10 hours or lower. ２ or Li ｘ M2 ２−ｘ O ２ When preparing the irregular rock salt Li ｘ M2 ２−ｘ O ２When preparing the film, it is preferable to heat the film in an inert atmosphere such as argon or nitrogen.

[0138] After the heating step, a crushing step is preferably carried out to further reduce the particle size, and the crushing step preferably employs a bead mill, a ball mill and / or a mixer.

[0139] Next, in step S20 of Fig. 3, a cobalt source is prepared. The cobalt source may be a solid, but is preferably a solution containing cobalt. For example, an aqueous solution of cobalt sulfate, cobalt nitrate, cobalt chloride, or cobalt alkoxide may be used.

[0140] Next, in step S21, LiM1O ２ or Li ｘ M2 ２−ｘ O ２ When a solution containing cobalt is used as the cobalt source, LiMO is obtained in the mixing step. ２ or Li ｘ M2 ２−ｘ O ２ This method has good productivity because it can also serve as a cleaning step for the cobalt source. In this case, a vortex mixer, a stirrer and agitator, and / or various other agitators can be used for mixing. When the cobalt source is solid, a dry or wet bead mill and / or ball mill can be used for mixing. After mixing, it is preferable to provide a drying step as needed.

[0141] A first mixture 899 is prepared by the above process (step S22).

[0142] Next, in step S23, the first mixture 899 is heated. To distinguish it from other heating steps, this step may be referred to as the first heating. In this step, the shell and a part of the transition metal M1 or transition metal M2 around it are substituted with cobalt. If the heating temperature is too low, there is a risk that the cobalt will not be sufficiently solid-dissolved. Therefore, the heating temperature is preferably 250°C or higher, more preferably 500°C or higher, and even more preferably 700°C or higher. On the other hand, if the temperature is too high, LiM1O ２ or Li ｘ M2 ２−ｘ O２ Since there is a risk of thermal decomposition, the heating temperature is preferably 1050° C. or less.

[0143] The shorter the heating time, the higher the productivity, but if the heating time is too short, there is a risk that the cobalt will not be sufficiently dissolved. The heating time is preferably, for example, from 2 hours to 10 hours.

[0144] After heating, it is preferable to sieve the mixture as necessary. Through the above steps, a composite oxide 900 having a large amount of cobalt in the shell and its surrounding area is produced (step S24).

[0145] Next, in step S30, an additive element source (A source) is prepared. In this specification, the additive element is synonymous with a mixture or a part of a raw material. As the additive element source, a simple additive element or a compound of the additive element can be used.

[0146] When magnesium is used as an additive element, magnesium oxide (MgO) and / or magnesium fluoride (MgF ２ When fluorine is used as an additive element, the fluorine source is preferably a fluoride of a typical metal element, such as lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF) and / or magnesium fluoride (MgF ２ In consideration of use in a lithium ion battery, it is particularly preferable to use lithium fluoride as the fluorine source.

[0147] The fluorides of these typical metal elements function as a flux that lowers the melting point of the additive element source in the subsequent heating step, and can promote the diffusion and doping of the additive element in the second shell 202. The mixture containing the fluoride has a melting point of Li ｘ M2 ２−ｘ O ２ This is preferable because it is lower than the decomposition temperature of ethylenediaminetetraacetic acid and is therefore safer.

[0148] Therefore, it is preferable that fluorine is contained in the second shell 202. Furthermore, it is preferable that the fluorine contained in the second shell 202 has a bonding state different from that of the fluoride used as the fluorine source. For example, MgF ２It is preferable that the second shell 202 contains fluorine and has a bonding state different from both MgF and LiF. More specifically, it is preferable that the second shell 202 has an O-Mg-F bond in XPS. XPS analysis will be described later. ２ The fact that the fluoride has a bond different from that of LiF is one factor that indicates that the fluoride functioned as a flux in the heating process.

[0149] However, after functioning as a flux, fluorine may be lost due to volatilization or the like, and therefore even if fluorine is added as an additive element, there may be cases where fluorine is not detected in the second shell 202 of the positive electrode active material particle 101 after production.

[0150] Next, the composite oxide 900 is mixed with an additive element source to prepare a second mixture 901 .

[0151] Next, the second mixture 901 is heated. To distinguish it from other heating steps, this step may be referred to as the second heating. If the heating temperature is too low, the doping of the additive element may become non-uniform and / or insufficient. Therefore, the heating temperature is preferably 500°C or higher, and more preferably 700°C or higher. On the other hand, if the temperature is too high, the composite oxide 900 may be thermally decomposed, so the heating temperature is preferably 1050°C or lower. Furthermore, in order to suppress the volatilization of fluorides such as LiF, 900°C or lower is more preferable.

[0152] The shorter the heating time, the higher the productivity, but if the heating time is too short, there is a risk that the diffusion and doping of the additive element will be insufficient. The heating time is preferably, for example, from 2 hours to 10 hours.

[0153] During this heating step, the composite oxide 900 and the additive element source are partially melted, allowing the additive elements, including magnesium, to be effectively diffused and doped. Because of this partial melting, the crystal structure of the second shell 202 is influenced by the crystal structures of the first shell 201 and the core 200, and the orientation of the crystal structures of the second shell 202 and the first shell 201 and the core 200 generally coincides. The second shell 202 thus formed stabilizes the crystal structures of the surface and bulk of the positive electrode active material particle 101. This makes it possible to suppress changes in the crystal structure and / or oxygen desorption during charging of the positive electrode active material particle 101.

[0154] The optimum ranges for the heating temperature and heating time may differ depending on the particle size of the composite oxide 900 .

[0155] Through the above steps, the positive electrode active material particles 101 can be produced (step S34).

[0156] <XPS Measurement> When XPS measurement is performed on the positive electrode active material particles 101, the excitation X-rays can be monochromated Al and the detection area can be 100 μmφ. The take-off angle (the angle between the tilt of the sample stage and the detection direction of the detector) can be, for example, 45° or 15°. The detection depth at a take-off angle of 45° is approximately 4 to 5 nm, and the detection depth at a take-off angle of 15° is approximately 2 nm. The correction standards can be Mg1s and C1s.

[0157] In the obtained XPS spectrum of Mg1s, if an O-Mg-F bond is present, the bond energy of the Mg is ２ The lower limit of detection for O-Mg-F bonds is about 10%, and the error in the waveform analysis results is about ±2%.

[0158] [Preparation Method 2] In Preparation Method 1, only the cobalt source is added in step S20, but the method for preparing positive electrode active material particles according to one embodiment of the present invention is not limited to this. The lithium source may be added simultaneously with the cobalt source.

[0159] In Preparation Method 2, an example will be described in which a cobalt source and a lithium source are added simultaneously, unlike Preparation Method 1. This preparation method can suppress lattice defects in the crystal due to lithium deficiency.

[0160] First, in step S14 of FIG. 4A, LiMO was added to the ２ or Li ｘ M2 ２−ｘ O ２ A composite oxide represented by the following formula is prepared.

[0161] Next, in step S20a, a cobalt source and a lithium source are prepared. When the atomic ratio of cobalt to lithium is Li:Co=z:1, z is preferably 0.5 to 1.5, more preferably 0.8 to 1.2, and most preferably about 1.

[0162] Thereafter, similarly to the manufacturing method 1, steps S21 to S34 are carried out to manufacture the positive electrode active material particles 101.

[0163] [Preparation Method 3] In Preparation Method 1 and Preparation Method 2, the cobalt source and the additive element source were added in different steps and then heated, but the method for preparing positive electrode active material particles according to one embodiment of the present invention is not limited thereto. The cobalt source and the additive element source may be added simultaneously and the heating step may be performed once, or the cobalt source and the additive element source may be added in separate steps and then the heating step may be performed once. Furthermore, when multiple additive elements are used, the number of mixing steps and heating steps may be further increased.

[0164] In Fabrication Method 3, an example will be described in which the cobalt source and the additive element source are added simultaneously and the heating step is performed only once, unlike Fabrication Method 1. This fabrication method has fewer heating steps, which allows production costs to be reduced.

[0165] First, in step S14 of FIG. 4B, LiMO ２ or Li ｘ M2 ２−ｘ O ２ A composite oxide represented by the following formula is prepared.

[0166] Next, in step S40, a cobalt source and an additive element source are prepared. The cobalt source may be liquid or solid. In addition to the cobalt source described in Preparation Method 1, cobalt oxide (Co ３ O ４ ), cobalt hydroxide (Co(OH) ２ ), cobalt carbonate (CoCO ３ ) etc. can be used.

[0167] The source of the additive element can be determined by referring to Preparation Method 1.

[0168] Next, in step S41, LiM1O ２ or Li ｘ M2 ２−ｘ O ２ The cobalt source and the additive element source are mixed to prepare a mixture 902. Next, the mixture 902 is heated to prepare the positive electrode active material particles 101. These steps can be performed by referring to steps S31 to S34 of the preparation method 1.

[0169] In addition, in the production methods 1 to 3, LiMO ２ or Li ｘ M2 ２−ｘ O ２ and a cobalt source by a solution method or a solid-phase method, but one embodiment of the present invention is not limited thereto. For example, a composite oxide represented by the formula (I) is mixed with a cobalt source by a sputtering method using a target containing cobalt. ２ or Li ｘ M2 ２−ｘ O ２ Alternatively, a cobalt-containing layer may be formed on a composite oxide represented by the following formula: Alternatively, a cobalt-containing layer may be formed by a CVD (Chemical Vapor Deposition) method or an ALD (Atomic Layer Deposition) method using a cobalt-containing precursor.

[0170] In addition, using a compound containing cobalt, LiMO was synthesized by a mechanochemical method. ２ or Li ｘ M2 ２−ｘ O ２ Alternatively, a layer containing cobalt may be formed on the composite oxide represented by the formula:

[0171] The manufacturing methods exemplified in this embodiment mode can be combined as appropriate. This embodiment mode can also be combined as appropriate with other embodiment modes.

[0172] Embodiment 3 In this embodiment, a structure of a lithium ion battery will be described.

[0173] [Positive Electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes positive electrode active material particles, and may further include at least one of a conductive additive and a binder. The positive electrode active material particles may be those described in the previous embodiment.

[0174] The positive electrode active material particles described in the above embodiment may be mixed with other positive electrode active material particles.

[0175] Other examples of positive electrode active material particles include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, LiFePO ４ , LiFeO ２ , LiNiO ２ , LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ , MnO ２ The following compounds are exemplified:

[0176] Other positive electrode active material particles include LiMn ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0177] FIG. 5A shows an example of a schematic cross-sectional view of a positive electrode.

[0178] The current collector 550 can be, for example, a metal foil. The positive electrode can be formed by applying a slurry to a metal foil and drying it. Note that pressing may be performed after drying. The positive electrode is formed by forming an active material layer on the current collector 550.

[0179] The slurry is a material liquid used to form an active material layer on the current collector 550, and refers to a material containing an active material, a binder, and a solvent, and preferably further mixed with a conductive additive. The slurry is also called an electrode slurry or an active material slurry, and is sometimes called a positive electrode slurry when forming a positive electrode active material layer, and a negative electrode slurry when forming a negative electrode active material layer.

[0180] The positive electrode active material particles 561 have a function of taking in and / or releasing lithium ions during charging and discharging. The positive electrode active material particles 561 used in one embodiment of the present invention can be made of a material that is less susceptible to deterioration during charging and discharging even at a high charging voltage.

[0181] The positive electrode active material particles 561 used in one embodiment of the present invention can be any material that shows little deterioration due to charging and discharging even at a high charging voltage, and can be the material described in Embodiment 1. Note that the positive electrode active material particles 561 can be made of two or more materials with different particle sizes as long as the material shows little deterioration due to charging and discharging even at a high charging voltage.

[0182] The conductive additive is also called a conductivity-imparting agent or a conductive material, and a carbon material can be used. By attaching the conductive additive between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. In this specification, the term "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covers part of the surface of the active material, the conductive additive is embedded in the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0183] Specific examples of carbon materials that can be used as the conductive additive include carbon black (furnace black, acetylene black, graphite, etc.).

[0184] FIG. 5A illustrates carbon black 553 as a conductive additive.

[0185] A binder (resin) may be mixed to bond the active material to the current collector 550, such as a metal foil, in the positive electrode of a lithium-ion battery. The binder is also called a binding agent. The binder is a polymeric material, and adding a large amount of binder reduces the proportion of active material in the positive electrode, thereby reducing the discharge capacity of the lithium-ion battery. Therefore, it is preferable to mix the binder in a minimum amount. In FIG. 5A , the areas not filled with the positive electrode active material particles 561, the second active material 562, and the carbon black 553 represent voids or binder.

[0186] 5A shows an example in which the positive electrode active material particles 561 are spherical, but this is not particularly limited. For example, the cross-sectional shape of the positive electrode active material particles 561 may be elliptical, rectangular, trapezoidal, conical, polygonal with rounded corners, or asymmetrical. For example, FIG. 5B shows an example in which the positive electrode active material particles 561 have a polygonal shape with rounded corners.

[0187] 5B includes graphene 554 as a carbon material used as a conductive additive in the positive electrode. In FIG. 5B, a positive electrode active material layer including positive electrode active material particles 561, graphene 554, and carbon black 553 is formed over a current collector 550.

[0188] In the step of mixing the graphene 554 and the carbon black 553 to obtain electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of the graphene.

[0189] Furthermore, when the mixture of graphene 554 and carbon black 553 is within the above range, the dispersion stability of carbon black 553 is excellent and agglomerations are less likely to occur during slurry preparation. Furthermore, when the mixture of graphene 554 and carbon black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only carbon black 553 as a conductive additive. Increasing the electrode density can increase the capacity per unit weight. Specifically, the density of the positive electrode active material layer measured gravimetrically can be 3.5 g / cc or more.

[0190] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive additive, by mixing the first carbon material (graphene) and the second carbon material (acetylene black) within the above range, it is possible to accommodate rapid charging, and therefore it is particularly effective when used as an in-vehicle lithium-ion battery.

[0191] 5C illustrates an example of a positive electrode in which carbon fibers 555 are used instead of graphene. Fig. 5C shows an example different from Fig. 5B. The use of carbon fibers 555 can prevent aggregation of carbon black 553 and improve dispersibility.

[0192] In FIG. 5C, the regions not filled with the positive electrode active material particles 561, the carbon fibers 555, and the carbon black 553 indicate voids or binders.

[0193] Another example of a positive electrode is shown in Fig. 5D. Fig. 5C shows an example in which carbon fiber 555 is used in addition to graphene 554. Using both graphene 554 and carbon fiber 555 can prevent aggregation of carbon black such as carbon black 553 and further improve dispersibility.

[0194] In FIG. 5D , regions that are not filled with positive electrode active material particles 561 , carbon fibers 555 , graphene 554 , and carbon black 553 indicate voids or binders.

[0195] A lithium ion battery can be produced by using any one of the positive electrodes shown in FIGS. 5A to 5D , placing a separator on the positive electrode, and placing the laminate obtained by placing the negative electrode on the separator in a container (such as an exterior body or a metal can) and filling the container with a liquid electrolyte.

[0196] <Binder> As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluorocarbon rubber can also be used as the binder. The above rubber material can be dispersed in a dispersion medium and used. As the dispersion medium, for example, one or more of water, N-methylpyrrolidone (NMP), methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) can be used.

[0197] Furthermore, a water-soluble polymer can be used as the binder. Examples of the water-soluble polymer include polysaccharides. Examples of the polysaccharide include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is also preferable to use these water-soluble polymers in combination with the rubber material described above.

[0198] Alternatively, the binder may be made of a material such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose.

[0199] The binder may be used in combination with two or more of the above.

[0200] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and have the effect of suppressing decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0201] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0202] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material, and may further have a conductive additive and a binder.

[0203] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy material and / or a carbon material can be used.

[0204] The carbon material used for the negative electrode active material may be one or more selected from graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, carbon black, and the like.

[0205] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is therefore preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0206] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋ This allows lithium-ion batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety compared to lithium metal.

[0207] The negative electrode active material may be an element capable of undergoing a charge-discharge reaction through alloying and dealloying reactions with lithium. For example, one or more materials selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. may be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. Compounds containing these elements may also be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0208] In this specification, "SiO" refers to, for example, silicon monoxide. ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0209] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ ) and the like can be used.

[0210] In addition, as the negative electrode active material, a nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N has a large discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0211] When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so that the positive electrode active material particles do not contain lithium ions. ２ O ５ , Cr ３ O ８It is preferable that the material can be combined with a material such as the above. Even when a material containing lithium ions is used as the positive electrode active material, it is possible to use a nitride of lithium and a transition metal as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0212] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0213] Furthermore, a combination of the above-mentioned negative electrode active materials may be used; for example, a negative electrode active material containing a mixture of graphite and silicon particles may be used. Silicon particles are silicon powders used as negative electrode active materials for lithium-ion secondary batteries. These particles have an average particle size distribution, i.e., an average particle size of approximately 100 nm, and are sometimes referred to as nanosilicon particles. The silicon particles used are preferably prepared by pulverizing silicon raw materials to a uniform particle size. The silicon particles may include at least one of silicon, silicon oxide, and silicon alloy. While laser diffraction particle size distribution measurement is typically used to measure particle size, the 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 a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0214] Furthermore, as the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0215] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0216] [Electrolyte Solution] The electrolyte solution contains an organic solvent, but the organic solvent of the electrolyte according to one embodiment of the present invention is not limited to being liquid at 25°C, and may be solid at 25°C or semi-solid at room temperature. The organic solvent of the electrolyte according to one embodiment of the present invention is preferably liquid over a wide temperature range, including temperatures from below freezing to high temperatures, but is not limited thereto. The organic solvent may be liquid, solid, or semi-solid over a wide temperature range, including temperatures from below freezing to high temperatures.

[0217] The organic solvent is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), methyl 3,3,3-trifluoropropionate (MTFP), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultones, and any combination and ratio of two or more of these may be used.

[0218] Because PS has HOMO and LUMO levels equivalent to those of EC and DEC, it is resistant to oxidation and reduction even at high cutoff voltages, and when decomposed on the surface of the positive electrode active material particles, it tends to form polymers. Therefore, it has the advantage of being less likely to gasify into small molecular weight decomposition products. Therefore, the electrolyte preferably contains 0.1 wt% to 10 wt%, more preferably 0.25 wt% to 7.5 wt% of PS.

[0219] FEC is a cyclic carbonate with a high dielectric constant, and when used in an organic solvent, it promotes the dissociation of lithium salts. On the other hand, because FEC has electron-withdrawing substituents, it is more likely to desolvate with lithium ions than EC. Specifically, the solvation energy of lithium ions in FEC is lower than that of EC without electron-withdrawing substituents. Therefore, FEC easily releases lithium ions from the surfaces of the positive electrode active material particles and the negative electrode active material, thereby reducing the internal resistance of the secondary battery. Furthermore, because FEC has a deep highest occupied molecular orbital (HOMO) level, it is less susceptible to oxidation and has improved oxidation resistance. However, there are concerns about the high viscosity of FEC. Therefore, it is recommended to use a mixed organic solvent containing MTFP in addition to FEC alone in the electrolyte. MTFP is a type of chain carbonate, and can reduce the viscosity of the electrolyte solution or maintain the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C). Furthermore, although MTFP has a lower solvation energy than methyl propionate (abbreviated as "MP"), which does not have an electron-withdrawing substituent, it may form a solvation with lithium ions when used in an electrolyte solution. When a mixed organic solvent containing both FEC and MTFP is used, when the volume ratio is FEC:MTFP=1:y, y is preferably 2 or more and 20 or less, more preferably 4 or more and 9 or less.

[0220] The organic solvent described above is free from granular dust or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities"), and oxygen (O ２ ), water (H ２ 0) or water. ) content is preferably low and highly purified. Furthermore, it is preferable that reaction by-products during synthesis are suppressed through appropriate purification. Specifically, the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm. The concentration of water among the impurities can be detected by Karl Fischer titration.

[0221] Furthermore, it is preferable that the above-mentioned organic solvent has almost no peaks due to impurities that can be confirmed by NMR measurement or the like. "Almost no peaks can be confirmed" means that the ratio of the integrated area of ​​the peak due to the impurity to the integrated area of ​​the peak due to the main component (simply referred to as "integral ratio") is 0.005 or less, preferably 0.002 or less. The device used for NMR measurement is not particularly limited, but for example, Bruker's "AVANCE III 400" can be used. Furthermore, among the five peaks of acetonitrile derived from acetonitrile-d3 used as a solvent in 1H-NMR measurement, the central peak can be located at 1.94 ppm.

[0222] For example, in the case of MTFP, it is known that when 1H-NMR is measured using acetonitrile-d3 solvent, four peaks appear at δ between 3.29 ppm and 3.43 ppm. However, if other peaks appear in this vicinity, for example, if a peak appears at δ between 3.24 ppm and 3.29 ppm, the peak is considered to be derived from impurities. Therefore, if the ratio (integral ratio) of the peak area between 3.24 ppm and 3.29 ppm to the peak area between 3.29 ppm and 3.43 ppm is 0.005 or less, preferably 0.002 or less, it can be said that peaks due to impurities are almost impossible to confirm.

[0223] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the electricity storage device. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0224] The electrolyte to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0225] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0226] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0227] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0228] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0229] In addition, the electrolyte can be a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a polymer material such as a polyethylene oxide (PEO)-based solid electrolyte. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0230] [Separator] When the electrolyte contains a liquid electrolyte (also called an electrolyte solution), a separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polypropylene (referred to as PP), polyimide (referred to as PI), polyester, acrylic, polyolefin, and polyurethane. The porosity of the separator can be 35% to 90%, preferably 60% to 85%. Separators using polypropylene can have a porosity of 35% to 45%. Separators using polyimide can have a porosity of 75% to 85%. The separator thickness is preferably 10 μm to 80 μm, more preferably 20 μm to 60 μm. A separator using polyimide is preferable because it can have a high porosity and can be made thick (typically, the thickness is 50 μm or more and 60 μm or less).

[0231] The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0232] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0233] By using a multilayer separator, the safety of the lithium-ion battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the lithium-ion battery can be increased.

[0234] [Exterior Body] The exterior body of a lithium-ion battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0235] This embodiment can be used in combination with other embodiments.

[0236] Embodiment 4 In this embodiment, an example of a lithium ion battery will be described.

[0237] [Laminated Lithium-ion Battery] An example of a laminated lithium-ion battery 500 is shown in Figures 6A and 6B. Figures 6A and 6B are external views, and the lithium-ion battery 500 includes the electrolyte and separator (not shown in Figure 6) described in the above embodiment, a negative electrode 506, and a positive electrode 507. In the lithium-ion battery 500, the negative electrode 506 preferably has a larger area than the positive electrode 507. The lithium-ion battery 500 further includes a negative electrode lead electrode 510 electrically connected to the negative electrode 506 and a positive electrode lead electrode 511 electrically connected to the positive electrode 507. The electrolyte layer, the negative electrode 506, and the positive electrode 507 are housed in an outer casing 509, and a portion of the negative electrode lead electrode 510 and a portion of the positive electrode lead electrode 511 protrude from the outer casing 509. An adhesive region 508 is provided on a portion of the outer periphery of the outer casing 509. Fig. 6A shows an example in which the negative lead electrode 510 and the positive lead electrode 511 protrude from the same side of the exterior body 509, and the adhesive region 508 is located at least on the side from which each lead electrode protrudes and two sides adjacent to that side. Fig. 6B shows an example in which the side from which the negative lead electrode 510 protrudes from the exterior body 509 and the side from which the positive lead electrode 511 protrudes from the exterior body 509 face each other, and the adhesive region 508 is located at least on the two sides from which each lead electrode protrudes and one side sandwiched between those two sides. In Figs. 6A and 6B, the sides on which the adhesive region 508 is not located preferably correspond to the sides along which the exterior body 509 is folded.

[0238] By using the positive electrode active material particles of the present invention in the laminated lithium ion battery 500, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0239] [Coin-type lithium-ion battery] An example of a coin-type lithium-ion battery will be described. Fig. 7A is an exploded perspective view of a coin-type (single-layer flat) lithium-ion battery, Fig. 7B is an external view, and Fig. 7C is a cross-sectional view thereof. Coin-type lithium-ion batteries are mainly used in small electronic devices. In this specification, coin-type lithium-ion batteries include button-type lithium-ion batteries.

[0240] 7A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 7A and 7B are not completely identical corresponding views.

[0241] 7A shows the state in which the positive electrode 304, negative electrode 307, spacer 342, and washer 332 are stacked and sealed with the negative electrode can 302 and positive electrode can 301. Note that the electrolyte and separator described in the above embodiment are not shown in FIG. 7A. The spacer 342 and washer 332 are used to protect the interior or fix the position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 342 or washer 332 is made of stainless steel or an insulating material.

[0242] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0243] FIG. 7B is a perspective view of the completed coin-type lithium-ion battery 300.

[0244] In the coin-type lithium-ion battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, may be insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The 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.

[0245] It is preferable that the positive electrode 304 and the negative electrode 307 used in the coin-type lithium ion battery 300 each have an active material layer formed on only one surface.

[0246] As shown in FIG. 7C , a positive electrode 304, a negative electrode 307, and a negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303 to produce a coin-shaped lithium ion battery 300.

[0247] By using the positive electrode active material particles of the present invention in the coin-type lithium ion battery 300, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0248] [Cylindrical Lithium-ion Battery] An example of a cylindrical lithium-ion battery will be described with reference to Fig. 8A. As shown in Fig. 8A, a cylindrical lithium-ion battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0249] 8B is a schematic diagram showing a cross section of a cylindrical lithium-ion battery. The cylindrical lithium-ion battery shown in Fig. 8B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0250] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with an electrolyte layer 605 sandwiched therebetween. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. Inside the battery can 602, the wound battery element, in which the positive electrode, the negative electrode, and the separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. An electrolyte (not shown) of one embodiment of the present invention is injected into the battery can 602 in which the battery element is provided.

[0251] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector. While the lithium-ion battery 616 shown in Figures 8A to 8D has a cylinder whose height is greater than its diameter, this is not limiting. A lithium-ion battery whose diameter is greater than its height may also be used. This configuration, for example, can reduce the size of the lithium-ion battery.

[0252] 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. The positive electrode terminal 603 can be made of aluminum, and the negative electrode terminal 607 can be made of a metal material such as copper. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and this increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO ３ )-based ceramic materials, etc. can be used.

[0253] 8C shows an example of a power storage system 615. The power storage system 615 has multiple lithium-ion batteries 616 and is sometimes called a battery pack. The positive electrodes of each lithium-ion battery are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of each lithium-ion battery are electrically connected to the control circuit 620 via wiring 626. A protection circuit or the like that prevents overcharging or overdischarging can be used as the control circuit 620.

[0254] 8D shows an example of a power storage system 615. The power storage system 615 has a plurality of lithium ion batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of lithium ion batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of lithium ion batteries 616 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 615 to have a plurality of lithium ion batteries 616, a large amount of power can be extracted.

[0255] A plurality of lithium ion batteries 616 may be connected in parallel and then further connected in series.

[0256] A temperature control device may be provided between the plurality of lithium ion batteries 616. When the lithium ion batteries 616 are overheated, they can be cooled by the temperature control device, and when the lithium ion batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the influence of the outside air temperature.

[0257] 8D , the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of lithium ion batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of lithium ion batteries 616 via a conductive plate 614.

[0258] By using the positive electrode active material particles of the present invention in the cylindrical lithium ion battery 616, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0259] [Another Example of the Structure of the Lithium-Ion Battery] An example of the structure of the lithium-ion battery will be described with reference to FIGS. 9 and 10. FIG.

[0260] A lithium ion battery 913 shown in FIG. 9A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is impregnated with an electrolyte according to one embodiment of the present invention inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 9A , the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum), a composite material of metal and resin, or the like.

[0261] 9B, the housing 930 shown in Fig. 9A may be formed using a plurality of materials. For example, the lithium ion battery 913 shown in Fig. 9B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0262] The housing 930a can be made of an insulating material. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the lithium ion battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0263] 9C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and an electrolyte layer 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 electrolyte layer 933 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the electrolyte layer 933 may be stacked.

[0264] 10A to 10C may be used as a lithium ion battery 913 having a wound body 950a. The wound body 950a shown in Fig. 10A has a negative electrode 931, a positive electrode 932, and an electrolyte layer 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.

[0265] The electrolyte layer 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0266] 10B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0267] 10C , wound body 950 a is covered with housing 930 to form lithium ion battery 913. Housing 930 is preferably provided with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0268] As shown in Fig. 10B, the lithium ion battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a lithium ion battery 913 with a larger charge / discharge capacity. For other elements of the lithium ion battery 913 shown in Figs. 10A and 10B, the descriptions of the lithium ion battery 913 shown in Figs. 9A to 9C can be referenced.

[0269] By using the positive electrode active material particles of the present invention in the lithium ion battery 913 having a wound body, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0270] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0271] Fifth Embodiment In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIG.

[0272] 11A , the electric vehicle is equipped with first batteries 1301 a and 1301 b as main driving lithium ion batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. By using the positive electrode active material particles of the present invention in the first batteries 1301 a and 1301 b, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0273] The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0274] The internal structure of the first battery 1301a may be a wound type or a stacked type. The first battery 1301a may use the all-solid-state battery described in Embodiment 6. By using the all-solid-state battery described in Embodiment 6 for the first battery 1301a, a high capacity can be achieved, safety can be improved, and the battery can be made smaller and lighter.

[0275] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple lithium ion batteries, it is possible to extract large amounts of power. The multiple lithium ion batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of lithium ion batteries is also called a battery pack.

[0276] In addition, in an in-vehicle lithium-ion battery, in order to cut off power from multiple lithium-ion batteries, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0277] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0278] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0279] The first battery 1301a will be described with reference to FIG. 11B.

[0280] FIG. 11B shows an example in which nine prismatic lithium-ion batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic lithium-ion batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also referred to as a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (e.g., from the road surface), it is preferable to fix multiple lithium-ion batteries using the fixing portions 1413 and 1414 and the battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0281] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0282] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein 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, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In—Ga oxide or an In—Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface where the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region is also a region with a uniform lattice arrangement. Furthermore, a CAAC-OS has a region where multiple crystalline regions are connected in the a-b plane direction, and the region may have distortion. Note that distortion refers to a portion where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with another uniform lattice arrangement in a region where multiple crystalline regions are connected. In other words, a CAAC-OS is an oxide semiconductor with a c-axis aligned and no clear orientation in the a-b plane direction.

[0283] Furthermore, since the control circuit unit 1320 can be used in low-temperature environments, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has a wider operating ambient temperature range than single-crystal Si, from −40° C. to 150° C., and its characteristics change less when the lithium-ion battery is heated than single-crystal Si. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150° C., whereas 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 unit 1320 can improve safety.

[0284] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for lithium-ion batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for lithium-ion batteries can be miniaturized.

[0285] Micro-short circuits are tiny short circuits that occur inside lithium-ion batteries. One of the causes of micro-short circuits is said to be local current concentration in parts of the positive electrode and negative electrode due to uneven distribution of positive electrode active material particles caused by repeated charge and discharge cycles, or the generation of by-products due to side reactions, which causes micro-short circuits.

[0286] In addition to detecting micro-short circuits, the control circuit 1320 can also be said to detect the terminal voltage of the lithium-ion battery and manage the charge / discharge state of the lithium-ion battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0287] FIG. 11C shows an example of a block diagram of the battery pack 1415 shown in FIG. 11B.

[0288] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the lithium-ion battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits for the lithium-ion battery is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0289] The switch unit 1324 can be configured by combining an n-channel transistor and a p-channel transistor. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO ｘThe switch portion 1324 may be formed using a power transistor having gallium oxide (x is a real number greater than 0). Furthermore, a memory element using an OS transistor can be freely arranged by stacking it on a circuit using a Si transistor, and thus integration can be easily achieved. By stacking the control circuit portion 1320 using an OS transistor on the switch portion 1324 and integrating them, it is possible to form it into a single chip, thereby enabling miniaturization.

[0290] The first batteries 1301a and 1301b mainly supply power to on-board equipment in the 42V system (high voltage system), while the second battery 1311 supplies power to on-board equipment in the 14V system (low voltage system). Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Using a lithium-ion battery as the second battery 1311 offers the advantage of being maintenance-free, but over long periods of use, such as three years or more, there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, even if the first batteries 1301a and 1301b have remaining capacity, the second battery 1311 is charged to maintain a full charge state by supplying power from the first battery to the second battery.

[0291] In this embodiment, an example in which lithium ion batteries are used for both the first battery 1301 a and the second battery 1311 is shown, but a lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. By using the positive electrode active material particles of the present invention in the above-mentioned lithium ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0292] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0293] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the lithium ion batteries used, and can perform rapid charging.

[0294] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The control circuit unit 1320 may also be provided in the connection cable or the charger's 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) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0295] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0296] Next, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0297] Furthermore, installing lithium-ion batteries in vehicles will enable next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), etc. Lithium-ion batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft.

[0298] 12A to 12D illustrate examples of transportation vehicles using one embodiment of the present invention. The automobile 2001 shown in FIG. 12A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor and an engine as a power source for traveling. When a lithium-ion battery is installed in a vehicle, an example of the lithium-ion battery described in the above embodiment is installed in one or more locations. By using the positive electrode active material particles of the present invention in a lithium-ion battery installed in a vehicle, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0299] 12A includes a battery pack 2200, which includes a battery module to which a plurality of lithium-ion batteries are connected. The battery pack 2200 further preferably includes a charge control device electrically connected to the battery module.

[0300] Furthermore, the automobile 2001 can charge its lithium-ion battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. The charging method and connector standards may be appropriately determined using a predetermined system such as CHAdeMO (registered trademark) or Combo. The external charging facility may be a charging station installed in a commercial facility, a household power source, or the like. For example, plug-in technology can be used to charge the power storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0301] Furthermore, although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the lithium-ion battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0302] 12B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The battery module of the transport vehicle 2002 is, for example, a four-cell unit of lithium-ion batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series to achieve a maximum voltage of 170 V. Apart from the number of lithium-ion batteries in the battery pack 2201, the battery pack 2201 has the same functions as those shown in FIG. 11B, and therefore a description thereof will be omitted. By using the positive electrode active material particles of the present invention in the lithium-ion batteries of the battery pack 2201, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0303] 12C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The battery module of the transport vehicle 2003 has, for example, one hundred or more lithium ion batteries with a nominal voltage of 3.0 V to 5.0 V connected in series to produce a maximum voltage of 600 V. Furthermore, except for the number of lithium ion batteries constituting the battery module of the battery pack 2202, the battery module has the same functions as that shown in FIG. 11B , and therefore a description thereof will be omitted. By using the positive electrode active material particles of the present invention in the lithium ion batteries of the module, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0304] Fig. 12D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 12D has wheels for takeoff and landing, it can also be considered part of a transportation vehicle, and has a battery pack 2203 that includes a battery module formed by connecting multiple lithium-ion batteries and includes the battery module and a charge control device.

[0305] The battery module of the aircraft 2004 is, for example, eight 4 V lithium ion batteries connected in series, with a maximum voltage of 32 V. Other than the number of lithium ion batteries constituting the battery module of the battery pack 2203, the battery module has the same functions as those shown in FIG. 11B, and therefore a description thereof will be omitted.

[0306] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0307] Embodiment 6 In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on a vehicle such as a motorcycle or a bicycle will be described.

[0308] 13A illustrates an example of an electric bicycle using the lithium-ion battery of one embodiment of the present invention. The lithium-ion battery of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 13A. The lithium-ion battery of one embodiment of the present invention may include a protection circuit.

[0309] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 13B . The power storage device 8702 includes a plurality of lithium-ion batteries 8701 of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. By using the positive electrode active material particles of the present invention for the lithium-ion battery 8701, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0310] The power storage device 8702 also includes a control circuit 8704 capable of controlling charging or detecting an abnormality of the lithium ion battery, an example of which is shown in Embodiment 8. The control circuit 8704 is electrically connected to the positive electrode and the negative electrode of the lithium ion battery 8701. This can greatly contribute to eliminating accidents such as fires caused by lithium ion batteries.

[0311] 13C illustrates an example of a two-wheeled vehicle using a lithium-ion battery of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 13C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. By using the positive electrode active material particles of the present invention in a lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0312] 13C can store a power storage device 8602 in an under-seat storage space 8604. The power storage device 8602 can be stored in the under-seat storage space 8604 even if the under-seat storage space 8604 is small.

[0313] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0314] Embodiment 7 In this embodiment, an example of mounting a lithium-ion battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a lithium-ion battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants (PDAs), sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0315] 14A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into a 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 includes a lithium ion battery 2107. By using the positive electrode active material particles of the present invention in the lithium ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0316] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0317] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0318] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0319] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0320] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0321] 14B shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a lithium-ion battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. By using the positive electrode active material particles of the present invention in a lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0322] Fig. 14C shows an example of a robot. A robot 6400 shown in Fig. 14C includes a lithium ion battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0323] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0324] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0325] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0326] The robot 6400 includes a lithium-ion battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. By using the positive electrode active material particles of the present invention in the lithium-ion battery, the secondary battery can have a high capacity, a high discharge capacity, and excellent cycle characteristics.

[0327] 14D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a lithium-ion battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0328] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a lithium-ion battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal region. By using the positive electrode active material particles of the present invention in the lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0329] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0330] Embodiment 8 In this embodiment, an example in which a lithium-ion battery according to one embodiment of the present invention is mounted on space equipment will be described.

[0331] 15A shows an artificial satellite 6800 as an example of space equipment. The artificial satellite 6800 has a body 6801, a solar panel 6802, an antenna 6803, and a lithium-ion battery 6805. The solar panel may be called a solar cell module.

[0332] When sunlight is irradiated onto the solar panel 6802, the power required for the operation of the satellite 6800 is generated. However, for example, in a situation where sunlight is not irradiated onto the solar panel or where the amount of sunlight irradiating the solar panel is small, the generated power is small. Therefore, there is a possibility that the power required for the operation of the satellite 6800 will not be generated. In order to operate the satellite 6800 even in a situation where the generated power is small, it is preferable to provide a lithium ion battery 6805 in the satellite 6800. By using the positive electrode active material particles of the present invention in the lithium ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0333] The satellite 6800 can generate a signal. The signal is transmitted via the antenna 6803, and can be received by, for example, a receiver installed on the ground or another satellite. By receiving the signal transmitted by the satellite 6800, the position of the receiver that received the signal can be measured, for example. As described above, the satellite 6800 can constitute, for example, a satellite positioning system.

[0334] Alternatively, the artificial satellite 6800 may be configured to include a sensor. For example, by including a visible light sensor, the artificial satellite 6800 may have the function of detecting sunlight reflected from an object on the ground. Alternatively, by including a thermal infrared sensor, the artificial satellite 6800 may have the function of detecting thermal infrared rays emitted from the earth's surface. As described above, the artificial satellite 6800 may function as, for example, an earth observation satellite.

[0335] FIG. 15B shows a probe 6900 equipped with a solar sail (also called a sun sail) as an example of space equipment. The probe 6900 includes a body 6901, a solar sail 6902, and a lithium-ion battery 6905. By using the positive electrode active material particles of the present invention in the lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained. When photons emitted from the sun strike the surface of the solar sail 6902, momentum is transferred to the solar sail 6902. Therefore, the surface of the solar sail 6902 preferably has a thin film with high reflectivity and preferably faces the sun.

[0336] The solar sail 6902 may also be designed to be folded up small until it leaves the atmosphere, and then deployed into a large sheet shape outside the Earth's atmosphere (outer space) as shown in Figure 15B.

[0337] FIG. 15C shows a spacecraft 6910 as an example of space equipment. The spacecraft 6910 has a body 6911, a solar panel 6912, and a lithium-ion battery 6913. By using the positive electrode active material particles of the present invention in the lithium-ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained. The body 6911 can have, for example, a pressurized compartment and a non-pressurized compartment. The pressurized compartment may be designed to accommodate a crew member. Electricity generated by sunlight irradiating the solar panel 6912 can be charged into the lithium-ion battery 6913.

[0338] 15D shows a rover 6920 as an example of space equipment. The rover 6920 has a body 6921 and a lithium ion battery 6923. By using the positive electrode active material particles of the present invention in the lithium ion battery, a secondary battery with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained. The rover 6920 may also have a solar panel 6922.

[0339] The rover 6920 may be designed to accommodate a crew member. The lithium ion battery 6923 may be charged with electricity generated by sunlight irradiating the solar panel 6912, or the lithium ion battery 6923 may be charged with electricity generated by other power sources, such as a fuel cell, a radioisotope thermoelectric converter, or the like.

[0340] The content of this embodiment can be appropriately combined with the content of other embodiments. [Explanation of symbols] 101 Positive electrode active material particle 101A: Positive electrode active material particle, 101B: Positive electrode active material particle, 101C: Positive electrode active material particle, 101D: Positive electrode active material particle, 101E: Positive electrode active material particle, 101F: Positive electrode active material particle, 101G: Positive electrode active material particle, 102: Positive electrode active material particle, 200: Core, 201: First shell, 202: Second shell,

Claims

Positive electrode active material particles containing lithium, a transition metal M1 (M1 is one or more selected from Ni, Co, Mn, and V), oxygen, and magnesium, the positive electrode active material particles have a core, a first shell on the outside of the core, and a second shell on the outside of the first shell, the first shell and the second shell each have more cobalt than the core; The positive electrode active material particles, wherein the second shell has more magnesium than the core and the first shell. 　 Positive electrode active material particles containing lithium, a transition metal M2 (M2 is one or more selected from Mn, Cr, Mo, Nb, V, Fe, Ni, Ti, and Ru), oxygen, magnesium, and fluorine, The positive electrode active material particles have a Li / M2 (atomic ratio) greater than 1, the positive electrode active material particles have a core, a first shell on the outside of the core, and a second shell on the outside of the first shell, the first shell and the second shell have more cobalt than the core; The positive electrode active material particles, wherein the second shell has more magnesium than the core and the first shell. 　 In claim 1 or claim 2, the positive electrode active material particles contain fluorine, The positive electrode active material particles, wherein the second shell has more fluorine than the first shell. 　 The positive electrode active material particles according to claim 3 , wherein the second shell has more fluorine than the core. 　 In claim 4, The core, the first shell, and the second shell have crystal orientations that are substantially the same.

5. The positive electrode active material particle according to claim 4, wherein the second shell contains one or more elements selected from titanium, aluminum, nickel, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, beryllium, europium, gadolinium, and antimony in a larger amount than the core and the second shell. 　 In claim 5, the first shell is present in at least a part of a region having a depth of 3 nm to 50 nm from the surface of the positive electrode active material particle, The positive electrode active material particle, wherein the second shell is present in at least a part of a region having a depth of 0.5 nm or more and less than 3 nm from the surface of the positive electrode active material particle. 　 In claim 6, The positive electrode active material particles are secondary particles. 　 a step of mixing a first composite oxide having lithium, a transition metal M1 (M1 is one or more selected from Ni, Co, Mn, and V), and oxygen, and having a layered rock-salt crystal structure of space group R-3m, with a solution containing cobalt to prepare a first mixture; a step of subjecting the first mixture to a first heating to produce a second composite oxide; mixing the second composite oxide with a magnesium source and a fluorine source to prepare a second mixture; and a step of subjecting the second mixture to a second heating process to produce positive electrode active material particles. Li ｘ M2 ２−ｘ O ２ (M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2) and a solution containing cobalt to prepare a first mixture; a step of subjecting the first mixture to a first heating to produce a second composite oxide; mixing the second composite oxide with a magnesium source and a fluorine source to prepare a second mixture; and a step of subjecting the second mixture to a second heating process to produce positive electrode active material particles. 　 In claim 8 or claim 9, the cobalt-containing solution comprises an aqueous cobalt sulfate solution; the magnesium source comprises magnesium fluoride; The method for producing positive electrode active material particles, wherein the fluorine source comprises lithium fluoride. 　 In claim 10, The first heating has a heating temperature of 250° C. or more and 900° C. or less, and a heating time of 2 hours or more and 10 hours or less, The method for producing positive electrode active material particles, wherein the second heating is performed at a heating temperature of 700° C. or more and 900° C. or less for a heating time of 2 hours or more and 10 hours or less. 　 a step of mixing a first composite oxide containing lithium, a transition metal M1 (M1 being one or more selected from Ni, Co, Mn, and V), and oxygen, and having a layered rock-salt crystal structure of space group R-3m, with a cobalt source, a magnesium source, and a fluorine source to prepare a mixture; and heating the mixture to prepare positive electrode active material particles. Li ｘ M2 ２−ｘ O ２ (M2 is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2), with a cobalt source, a magnesium source, and a fluorine source to prepare a mixture; and heating the mixture to prepare positive electrode active material particles. 　 In claim 14, The heating temperature is 700° C. or more and 900° C. or less, and the heating time is 2 hours or more and 10 hours or less.

Images