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

Abstract

Provided are lithium excess positive electrode active material particles having a stabilized crystal structure, and a secondary battery including said particles. The positive electrode active material particles contain lithium, a transition metal M (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru), oxygen, magnesium, and fluorine, wherein the ratio Li / M (atomic ratio) of the positive electrode active material particles is greater than 1, the positive electrode active material particles have a core and a shell outside the core, magnesium and fluorine are detected in greater amounts in the shell than in the core, and the crystal orientations of the core and the shell roughly coincide.

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] However, research and development is being conducted with the aim of achieving even higher capacities. Among these, positive electrode active materials known as lithium-rich or lithium-excess materials have attracted attention because they can store far more lithium ions than current lithium cobalt oxide, lithium nickel cobalt manganese oxide, etc. (Non-Patent Documents 1 to 5).

[0006] 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

[0007] Lithium-excess positive electrode active materials are known to have many advantages. For example, it is possible to increase the discharge capacity per weight of the positive electrode active material to 250 mAh / g or more, or even 300 mAh / g or more. At the same time, it is possible to increase the energy density per weight, for example, to 1000 Wh / kg or more. Furthermore, as the main transition metal, manganese, which is cheaper and more abundant, can be used instead of cobalt, which has cost and other issues.

[0008] On the other hand, lithium-excess positive electrode active materials have problems such as a large decrease in the initial discharge capacity relative to the initial charge capacity, poor rate characteristics, and a large decrease in voltage and / or discharge capacity in charge-discharge cycle tests. This is thought to be due to the fact that when lithium is released from lithium-excess positive electrode active material particles, a change in the crystal structure and / or release of oxygen occurs.

[0009] Therefore, an object of one embodiment of the present invention is to provide lithium-excess positive electrode active material particles or composite oxides in which a decrease in initial discharge capacity relative to an initial charge capacity is suppressed. Another object is to provide lithium-excess positive electrode active material particles or composite oxides with good rate characteristics. Another object is to provide lithium-excess positive electrode active material particles or composite oxides in which a decrease in voltage or discharge capacity during charge / discharge cycles is suppressed. Another object is to provide lithium-excess positive electrode active material particles or composite oxides in which a change in crystal structure during charging is suppressed. Another object is to provide lithium-excess positive electrode active material particles or composite oxides in which oxygen release is suppressed. Another object is to provide positive electrode active material particles or composite oxides with a high discharge capacity. Another object is to provide a secondary battery with high charge / discharge capacity, safety, or reliability.

[0010] 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.

[0011] 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.

[0012] In one embodiment of the present invention, the positive electrode active material particles have a core-shell structure, and the shell contains a large amount of an additive element such as magnesium. In addition, a fluoride salt that functions as a flux is used to effectively dope the additive element into the shell.

[0013] One aspect of the present invention is a cathode active material particle having lithium, a transition metal M (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru), oxygen, magnesium, and fluorine, wherein the cathode active material particle has an Li / M (atomic ratio) greater than 1, the cathode active material particle has a core and a shell outside the core, the shell has more magnesium and fluorine than the core, and the core and shell have roughly the same crystal orientation.

[0014] In the above, it is preferable that the 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, and beryllium than the core.

[0015] In the above, the core preferably has a layered rock salt type or disordered rock salt type crystal structure.

[0016] In the above, the shell preferably has a rock salt type or spinel type crystal structure.

[0017] Another aspect of the present invention is Li ｘ M ２−ｘ O ２(where M is one or more elements selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2) with an additive element source to prepare a mixture; and heating the mixture at 700°C or higher and 900°C or lower, wherein the additive element source is a fluorine source and a magnesium source.

[0018] In the above, it is preferable that the fluorine source is lithium fluoride and the magnesium source is magnesium fluoride.

[0019] According to one aspect of the present invention, it is possible to provide lithium-excess positive electrode active material particles or composite oxides in which a decrease in initial discharge capacity relative to an initial charge capacity is suppressed. Alternatively, it is possible to provide lithium-excess positive electrode active material particles or composite oxides with good rate characteristics. Alternatively, it is possible to provide lithium-excess positive electrode active material particles or composite oxides in which a decrease in voltage or discharge capacity during charge / discharge cycles is suppressed. Alternatively, it is possible to provide lithium-excess positive electrode active material particles or composite oxides in which a change in crystal structure during charging is suppressed. Alternatively, it is possible to provide lithium-excess positive electrode active material particles or composite oxides in which oxygen desorption is suppressed. Alternatively, it is possible to provide positive electrode active material particles or composite oxides with a high discharge capacity. Alternatively, it is possible to provide a secondary battery with high charge / discharge capacity, safety, or reliability.

[0020] 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.

[0021] 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.

[0022] FIG. 1 is a schematic cross-sectional view of a positive electrode active material particle of one embodiment of the present invention. FIGS. 2A to 2C are diagrams illustrating a crystal structure of a positive electrode active material particle of one embodiment of the present invention. FIGS. 3A and 3B are diagrams illustrating an example of a manufacturing method for a positive electrode active material of one embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a manufacturing method for a positive electrode active material of one embodiment of the present invention. FIGS. 5A to 5D are diagrams illustrating a positive electrode of one embodiment of the present invention. FIGS. 6A and 6B are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 7A to 7C are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 8A to 8D are diagrams illustrating a lithium-ion battery and a power storage system of one embodiment of the present invention. FIGS. 9A to 9C are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 10A to 10C are diagrams illustrating a lithium-ion battery of one embodiment of the present invention. FIGS. 11A to 11C are diagrams illustrating an electric vehicle of one embodiment of the present invention. FIGS. 12A to 12D are diagrams illustrating a transportation vehicle of one embodiment of the present invention. FIGS. 13A to 13C are diagrams illustrating a motorcycle or the like according to one embodiment of the present invention. FIGS. 14A to 14D are diagrams illustrating an electronic device or the like according to one embodiment of the present invention. FIGS. 15A to 15D are diagrams illustrating an example of space equipment. FIG. 16A is a cross-sectional STEM image of a complex oxide, and FIG. 16B is a STEM-EDX analysis result of the complex oxide. FIGS. 17A to 17F are SEM-EDX images of positive electrode active material particles. FIGS. 18A and 18B are SEM images of positive electrode active material particles. FIGS. 19A and 19B are charge / discharge curves of a secondary battery. FIGS. 20A to 20C are graphs illustrating charge / discharge cycle characteristics of a secondary battery. FIGS. 21A and 21B are charge / discharge curves of a secondary battery. FIGS. 22A to 22C are graphs illustrating charge / discharge cycle characteristics of a secondary battery.

[0023] 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.

[0024] 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.

[0025] In this specification and the like, when simply referring to a positive electrode active material or positive electrode active material particles, there are cases where the description refers to multiple positive electrode active material particles or 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.

[0026] 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.

[0027] 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 particles have a sufficient effect of improving the characteristics of a secondary battery having the positive electrode active material particles.

[0028] 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.

[0029] 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."

[0030] 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 arrangement, with cations occupying all octahedral positions. There may be one type of cation and one type of anion, or multiple types. There may be deficiencies of cations or anions.

[0031] Furthermore, in this specification, a layered rock salt crystal structure refers to a crystal structure that shares with the rock salt structure the fact that anions are arranged in a cubic close-packed manner, with cations and anions at octahedral positions arranged alternately. In addition, it is clear that multiple types of cations are present, and the arrangement of at least one of the cations forms a two-dimensional plane. Such lithium-rich oxide and lithium-rich positive electrode structures can also be referred to as layered structures. Layered lithium-rich oxides and lithium-rich positive electrodes can also be referred to as layered lithium-rich oxides, lithium-rich layered oxides, layered lithium-rich positive electrodes, lithium-rich layered positive electrodes, etc. Two-dimensional lithium ion formation in a two-dimensional plane allows for two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also exist. Furthermore, the cubic close-packing of anions does not necessarily have to be theoretical; distortions may occur depending on the type and / or arrangement of cations.

[0032] In this specification, the term "disordered rock salt" refers to a crystal structure that has a cubic crystal structure, anions are arranged in a cubic close-packed manner, and cations and anions at octahedral positions are arranged alternately, which is common to the rock salt structure. In addition, it is clear that there are multiple types of cations, and the arrangement of these cations is irregular. In lithium-rich positive electrode active material particles, the irregular arrangement of cations means that the ratio of the frequency of occurrence of each cation type at each cation site is almost fixed, and no significant difference is observed between cation sites. For example, in a HAADF-STEM (High-angle Annular Dark Field Scanning TEM, high-angle scattering annular dark field scanning transmission electron microscope) image, there is no significant difference in the contrast of the cation site. Note that there may be defects such as cation or anion deficiencies.

[0033] 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 ４The 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 have to be exact. For example, it can be a:1 (a is 1.9 or more and 2.1 or less). The spinel crystal structure is preferably determined from, for example, an STEM image, a TEM image, an electron diffraction pattern, an FFT (fast Fourier transform) pattern of a TEM image or an FFT pattern of a STEM image, STEM-EELS, etc.

[0034] 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 electron diffraction patterns or FFT patterns such as 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 relative to the theoretical positions is 5 degrees or less, or 2.5 degrees or less.

[0035] 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, cathode material, cathode ingredient, cathode material for secondary batteries, etc. Furthermore, the cathode active material particles of one embodiment of the present invention preferably contain a compound. Furthermore, the cathode active material particles of one embodiment of the present invention preferably contain a composition. Furthermore, the cathode active material particles of one embodiment of the present invention preferably contain a composite. Furthermore, the composite oxide refers to an oxide having multiple types of cations. Although the composite oxide has oxygen as an anion, it is not limited to oxygen, and may also contain other anions such as fluorine and chlorine in addition to oxygen.

[0036] 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.

[0037] Unless otherwise specified, the materials (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) contained in the secondary battery are described in their pre-degradation state. A decrease in discharge capacity due to aging and / or burn-in treatment 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.

[0038] 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.

[0039] The positive electrode active material particle 100 according to one embodiment of the present invention includes lithium, a transition metal M, oxygen, and an additive element. The positive electrode active material particle 100 is preferably a compound obtained by adding the additive element to a lithium-excess positive electrode active material particle.

[0040] [Lithium-excess positive electrode active material particles] Lithium-excess positive electrode active material particles are particles having a composition of Li ｘ M 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.) Note that part of O may be substituted with other anions such as F and / or Cl.

[0041] Li ｘ M ２−ｘ O ２As is clear from the expression (1<x<2), the Li / M (atomic ratio) of the lithium-excess positive electrode active material particles is greater than 1. It is also preferable that the Li / M ratio is greater than 1 in the positive electrode active material particles 100 of one embodiment of the present invention, in which an additive element is added to the lithium-excess positive electrode active material particles.

[0042] Examples of lithium-excess positive electrode active material particles include layered rock salt type composite oxides and disordered rock salt type composite oxides.

[0043] <Layered Rock Salt Type> The layered rock salt type lithium-excess positive electrode active material particles (also called lithium-excess layered oxide) contain Li ２ MnO ３ And LiMO ２ (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru) in a certain ratio. ２ For example, LiCoO ２ , LiNiO ２ , LiNi ａ Co ｂ Mn ｃ O ２ (a+b+c=1), etc. The layered rock salt type crystal structure may also be referred to as a layered or layered structure. Similarly, layered rock salt type lithium-excess positive electrode active material particles may also be referred to as a layered lithium-excess positive electrode, lithium-excess layered positive electrode, etc.

[0044] 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 LiMO ２ A 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.

[0045] 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.

[0046] As the layered rock salt type lithium-excess positive electrode active material particles, 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 Mn １／２ O ２ ) also written as Li １．２ Mn ０．６ Ni ０．２ O ２ , LiCoO ２ -Li ２ MnO ３ Also written as Li (Li ｘ／３ Mn ２ｘ／３ Co １−ｘ ) O ２(0≦x≦1) etc. can be used.

[0047] Especially Li １．２ Mn ０．６ Ni ０．２ O ２ Such a lithium secondary battery having Mn and Ni as the transition metal M, in which the atomic ratio of Li / transition metal is 1.1 or more and 1.3 or less, and the atomic ratio of Ni / (Mn+Ni) is 0.1 or more and 0.3 or less, is preferable because it can achieve both a large discharge capacity exceeding 200 mAh / g and a relatively high discharge capacity retention rate during cycling.

[0048] <Irregular rock salt type> Irregular rock salt type lithium-excess positive electrode active material particles are particles having a composition of Li ｘ M 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), and refers to a composite oxide having a rock-salt crystal structure and in which the arrangement of cations is irregular. Note that some of the O may be substituted with other anions such as F and / or Cl.

[0049] Examples of combinations of elements contained in the irregular rock salt type lithium-excess positive electrode active material particles that can be used 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-Mn-O-F, and Li-Mo-O-F.

[0050] [Additive Element] The positive electrode active material particles 100 preferably contain, as an additive element, one or more selected from magnesium, fluorine, titanium, aluminum, nickel, cobalt, manganese, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium.

[0051] [Core-Shell Structure] As shown in FIG. 1, the positive electrode active material particle 100 has a core 102 and a shell 101 outside the core.

[0052] The core 102 has the characteristics of the lithium-excess positive electrode active material particles. For example, it has the same crystal structure and / or composition as the lithium-excess positive electrode active material particles. Therefore, the core 102 preferably has a layered rock salt type or disordered rock salt type crystal structure and preferably has the above-mentioned composition.

[0053] The shell 101 contains a larger amount of the additive element than the core 102. In other words, the shell 101 has a higher concentration and / or detectable amount of the additive element than the core 102. In addition, it is preferable that the concentration and / or detectable amount of the additive element is higher on the outer side of the shell 101.

[0054] For example, in XPS analysis, the surface sensitivity increases when the photoelectron take-off angle is shallow, i.e., when the photoelectron take-off angle is small, compared to when the photoelectron take-off angle is close to 90°. Therefore, when XPS analysis is performed on the positive electrode active material particle 100 while changing the photoelectron take-off angle, it is preferable that the concentration and / or the amount of detection of the added element is higher when the take-off angle is shallow than when the take-off angle is close to 90°.

[0055] When magnesium is used as the additive element, the atomic ratio of Mg / M (M is the sum of one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru) when XPS analysis of the positive electrode active material particles 100 is performed at a take-off angle of 45° is preferably 3% or more, more preferably 4% or more, and even more preferably 5% or more. When XPS analysis is performed at a take-off angle of 15°, the atomic ratio of Mg / M is preferably 3% or more, more preferably 5% or more, and even more preferably 7% or more.

[0056] When fluorine is used as the additive element, the atomic ratio of F / M when XPS analysis of the positive electrode active material particles 100 is performed at a takeoff angle of 45° is preferably 15% or more, more preferably 20% or more, and even more preferably 30% or more. When XPS analysis is performed at a takeoff angle of 15°, the atomic ratio of F / M is preferably 15% or more, more preferably 25% or more, and even more preferably 35% or more.

[0057] However, if the concentration and / or detected amount of the additive element in the shell 101 is too high, the diffusion of lithium may be hindered, which may result in an increase in internal resistance, a decrease in charge / discharge capacity, etc. Therefore, the concentration and / or detected amount of the additive element in the XPS analysis is preferably not more than twice the concentration of lithium, and more preferably not more than the concentration of lithium.

[0058] When an element not contained in the core 102 is used as an additive element, it is preferable that the element be detected in the shell 101. When an element also contained in the core 102 is used as an additive element, it is preferable that the element be detected in the core 102 as well, and that the concentration and / or detected amount of the element in the shell 101 be higher than that in the core 102.

[0059] The shell 101 contains more additive elements than the core 102, and therefore has a different composition from the core 102. Therefore, the crystal structure of the shell 101 also preferably differs from that of the core 102. For example, the shell 101 preferably has a rock-salt type, an irregular rock-salt type, or a spinel type crystal structure.

[0060] However, the core 102 and the shell 101 may have the same crystal structure. For example, the core 102 and the shell 101 may both have an irregular rock-salt crystal structure, although the elements and / or ratios of the elements that make up the core 102 and the shell 101 are different.

[0061] The shell 101, which is a region including the surface of the positive electrode active material particle 100 or a region close to the surface, has a rock salt or spinel crystal structure containing a large amount of added elements, which is expected to have the effect of suppressing side reactions with the electrolyte solution and / or electrolyte.

[0062] If the shell 101 is too thin, the surface and bulk of the positive electrode active material particle 100 may not be sufficiently stabilized, so the thickness of the shell 101 is preferably 1 nm or more, more preferably 2 nm or more. It can also be 3 nm or more, or 5 nm or more. On the other hand, a thinner shell 101 makes it easier to increase the charge / discharge capacity. Therefore, the thickness of the shell 101 is preferably 10 nm or less.

[0063] <Approximate Matching of Orientations> When the crystal structures of the shell 101 and the core 102 are different, it is preferable that the orientations of the two crystal structures approximately match. The approximately matching of the orientations makes it possible to obtain a stable shell 101, and therefore, it is possible to more effectively suppress the release of oxygen from the core 102, the elution of cations, and the like.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] When the crystal planes of the layered rock salt and the rock salt structure coincide, 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 techniques, such as selected area diffraction and nanobeam diffraction, depending on the particle size and / or the range of the rock salt structure of the shell 101.

[0068] For example, in a HAADF-STEM image, contrast proportional to the atomic number is obtained, and elements with larger atomic numbers are observed brighter. ｘ M ２−ｘ O ２ In the case where M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, and 1<x<2, M is the transition metal with the largest atomic number, so the electron beam is strongly scattered at the position of the transition metal M, and if there is an arrangement of transition metals M, it is observed as an arrangement of dots with strong brightness.

[0069] Therefore, in an 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 M on the (001) 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 element 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 bands is 5 degrees or less or 2.5 degrees or less, or when the difference in spacing between multiple bright bands is within 15%, it can be determined that the crystal planes are roughly consistent, i.e., the crystal orientations are roughly consistent.

[0070] Therefore, in a HAADF-STEM image, if an array of highly bright dots, i.e., bright bands, 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.

[0071] 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.

[0072] 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 can be obtained on whether the

[001] direction in a region of a layered rock salt structure having a crystal structure of space group C2 / m or R-3m roughly coincides with the <111> direction in a region of a rock salt structure having a crystal structure of space group Fm-3m. If the crystal orientations coincide by 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.

[0073] In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not concentric rings connected to other reciprocal lattice points. Spot-like reciprocal lattice points that are not connected to other reciprocal lattice points indicate high crystallinity.

[0074] 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.

[0075] 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 incident at

[120] . 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 M can be easily observed.

[0076] The crystal structures of the shell 101 and the core 102 roughly coincide with each other, so that the shell 101, which contains a large amount of the additive element, functions as a pillar supporting the crystal structure of the positive electrode active material particle 100. 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 100. In other words, the presence of the additive element stabilizes the crystal structure of the surface and / or bulk of the positive electrode active material particle 100. Therefore, it is possible to suppress changes in the crystal structure and / or oxygen desorption during charging of the positive electrode active material particle 100.

[0077] Therefore, the positive electrode active material particles 100 can be made to have a reduced decrease in the initial discharge capacity relative to the initial charge capacity, or to have good rate characteristics, or to have a reduced decrease in voltage or discharge capacity during charge / discharge cycles.

[0078] <Example of roughly matching orientation> For the shell 101 and the core 102 to have different crystal structures and roughly matching orientations, they must share a common anion packing structure and there must be no significant mismatch in their lattice constants. More precisely, taking into account different space groups, there must be no significant mismatch in the metal-metal distance and 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), this refers to the (111) plane. In the case of a layered rock salt structure, this refers to the (001) plane for R-3m, the (001) plane for C / 2m, and the (001) plane for P2 / m. In the case of a spinel structure (Fd-3m), this refers to the (111) plane. When there are multiple types of metals and they are arranged in a regular pattern, the plane on which the same type of metal is most abundant is sometimes called the metal layer.

[0079] With regard to the metal-metal distance and the interlayer distance, if the core 102 / shell 101 ratio is 0.94 or more and 1.06 or less, the crystal structures can be roughly identical.

[0080] Below, an example will be given in which the shell 101 and the core 102 have different crystal structures, but the crystal orientations can be roughly the same.

[0081] First, an example will be described in which the core 102 has the crystal structure and composition of layered rock salt type lithium-excess positive electrode active material particles, and the shell 101 has the rock salt type crystal structure.

[0082] The layered rock salt type lithium-rich positive electrode active material particles are Li ２ MnO ３ And LiMO ２ (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru) are mixed and synthesized in a certain ratio, so the metal-to-metal distance and the interlayer distance of the core 102 are ２ MnO ３ And LiMO ２ It is thought that the value will be somewhere between. ２ MnO ３The experimental values ​​of the metal-metal distance and interlayer distance are shown in Fig. 1. Similarly, LiMO ２ As an example of the known LiCoO ２ , LiNiO ２ , LiNi １／２ Mn １／２ O ２ , and LiNi １／３ Mn １／３ Co １／３ O ２ The experimental values ​​are shown. The interlayer distance is 2.342 Å or more and 2.382 Å or less, and the metal-metal distance is 2.816 Å or more and 2.887 Å or less, all with four significant figures.

[0083] The upper part of Figure 2A shows Li, which belongs to the space group C2 / m. ２ MnO ３ The (001) plane of the crystal structure of Li is shown in the figure, and the plane perpendicular to the (001) plane is shown in the figure below. ２ MnO ３ The (001) plane of the crystal structure is the plane where the metal is arranged in layers. For clarity, the (001) plane in the upper part of Figure 2A shows only one metal layer and the oxygen layers above and below it. The plane perpendicular to these in the lower part shows only the bonds between one metal layer and the oxygen layers above and below it.

[0084] In addition, ICSD Collection Code: 73370 Li ２ MnO ３ The crystal structure of the present invention has a metal layer in which Li and Mn are mixed, and a layer of only Li. Both are parallel or approximately parallel to the a-axis and b-axis. In addition, the metal sites of the layer in which Li and Mn are mixed are partially occupied by Li and Mn. However, to simplify the diagram, in Figure 2A, the element with the larger occupancy rate is shown as a representative for the layer in which Li and Mn are mixed. Li ２ MnO ３ The metal sites of Li are not in an equilateral triangle configuration. ２ MnO ３ The metal-to-metal distance in the above can be determined by the following two methods.

[0085] One method is to calculate the average interatomic distance in a layer containing both Li and Mn. The Li-only layer was not included in the calculation because the atomic positions are slightly off-plane. The metal-metal distance calculated using this method was 2.842 Å with four significant digits.

[0086] The other is that when the metal-metal distance is x, the a-axis length of 4.921 Å is (√3)x, the b-axis length of 8.526 Å is 3x, and the product of the a-axis length and the b-axis length is 41.95645 Å. ２ is 3 (√3) x ２ This is a method for calculating x assuming that the metal-metal distance is 2.842 Å. The metal-metal distance calculated using this method was 2.842 Å with four significant digits. Thus, the metal-metal distances calculated using the two methods were the same up to four significant digits.

[0087] The upper part of Figure 2B shows LiMO ２ As an example, LiCoO, which has the space group R-3m ２ The (001) plane of the crystal structure of LiCoO is shown in the figure, and the plane perpendicular to the (001) plane is shown in the bottom. ２ The (001) plane of the crystal structure is the plane where the metal is arranged in layers. For clarity, the (001) plane in the upper part of Figure 2B shows only one metal layer and the oxygen layers above and below it. The plane perpendicular to these in the lower part shows only the bonds between one metal layer and the oxygen layers above and below it.

[0088] Because the concentration and / or detected amount of the additive element is higher in the shell 101 than in the core 102, it is believed that the metal-metal distance and interlayer distance of the shell 101 will have values ​​somewhere between those of the rock-salt oxide of the additive element and the crystal structure of the core 102. Here, magnesium, cobalt, nickel, and manganese are taken as examples of additive elements, and Table 1 shows experimental values ​​of the metal-metal distance and interlayer distance of known MgO, CoO, NiO, and MnO. In all cases, the interlayer distance is 2.412 Å or more and 2.567 Å or less, and the metal-metal distance is 2.954 Å or more and 3.144 Å or less, with four significant digits.

[0089] The upper part of Figure 2C shows the (111) plane of the crystal structure of MgO, which has the space group Fm-3m, as an example of a rock-salt oxide of an added element, and the lower part shows a schematic diagram of a plane perpendicular to the (111) plane. The (111) plane of the MgO crystal structure is a plane on which metal is arranged in layers. For clarity, the (111) plane in Figure 2C shows only one metal layer and the oxygen layers above and below it. In a plane perpendicular to this, only the bonds between one metal layer and the oxygen layers above and below it are shown.

[0090] As shown in Figures 2A to 2C, although these oxides have different space groups, they share the common feature of cubic close-packed oxygen and alternating cations and anions. As shown by the dotted lines in Figures 2A to 2C, the cations are all present in hexacoordinate octahedral positions.

[0091] Table 1 shows the relative values ​​of each distance when the metal-metal distance and interlayer distance of MgO are set to 1. ２ MnO ３ and LiCoO ２ Since the interlayer distance varies depending on the layer position, the average value is shown.

[0092] When the metal-metal distance and interlayer distance of MgO are taken as 1, the relative values ​​of the interlayer distance and metal-metal distance are both 0.94 to 1.06, and it is clear that there is no significant mismatch between these crystal structures. Therefore, when core 102 has the composition and crystal structure of the layered rock salt type lithium-excess positive electrode active material particles exemplified above, and shell 101 contains magnesium, cobalt, nickel, and / or manganese as an added element and has a rock salt type crystal structure, the crystal structures of shell 101 and core 102 can roughly match.

[0093]

[0094] Next, an example will be described in which the core 102 has the crystal structure and composition of an irregular rock-salt type lithium-excess positive electrode active material particle, and the shell 101 has a rock-salt type crystal structure. Because the irregular rock-salt type crystal structure of the core 102 is the same as the rock-salt type crystal structure of the shell, the two can be compared in terms of lattice constant.

[0095] In Non-Patent Document 5, Li, which is a lithium-excess positive electrode active material having an irregular rock salt crystal structure, １．０５ Mn ０．８５ Ti ０．１ O ２ , Li １．１０ Mn ０．７０ Ti ０．２ O ２ and Li １．１５ Mn ０．５５ Ti ０．３ O ２ It has been shown that the lattice constant a of is 4.16 Å to 4.17 Å.

[0096] Here, magnesium is taken as an example of an added element. The lattice constant a of MgO is 4.217 Å.

[0097] From these, it is clear that the lattice constant a of the irregular rock salt type lithium-excess positive electrode active material particles / the lattice constant a of MgO is 0.986 or more and 0.989 or less, and there is no large mismatch between these crystal structures.

[0098] Therefore, when the core 102 has the composition and crystal structure of the irregular rock salt type lithium-excess positive electrode active material particles exemplified above, and the shell 101 contains magnesium as an added element and has a rock salt type crystal structure, the crystal orientation of the shell 101 and the core 102 can be roughly the same.

[0099] Next, an example will be described in which the core 102 or the shell 101 has a spinel crystal structure. When evaluating whether the crystal orientation roughly matches between the spinel crystal structure and other crystal structures, it is preferable to compare the oxygen stacking and the relative value of the interlayer distance of the oxygen layers.

[0100] Examples of spinel-type quartz crystals containing Li and Mn (space group: Fd-3m) include LiMn ２ O ４ The spinel-type oxygen layers are stacked in a cubic close-packed manner, with ABCABC stacking in the <111> direction.

[0101] The oxygen layers of the rock salt type are also cubic close-packed, with ABCABC stacking in the <111> direction. The oxygen layers of the layered rock salt type R-3m are also cubic close-packed, with ABCABC stacking in the

[001] direction. The oxygen layers of the layered rock salt type C / 2m are also cubic close-packed, with ABCABC stacking in the direction roughly perpendicular to the c-plane.

[0102] Therefore, spinel-type LiMn ２ O ４ If the interlayer distance of the stacking of oxygen layers and the oxygen-oxygen distance are consistent, the crystal orientation will roughly match the rock salt structure (Fm-3m) and the layered rock salt structure (R-3m, C / 2m).

[0103] In the rock-salt crystal structure of the space group Fm-3m, the metal-metal distance is the same as the oxygen-oxygen distance. Similarly, the interlayer distance of the metal layers is the same as the interlayer distance of the oxygen layers. LiCoO ２ In layered rock salt structures of space group R-3m, such as LiCoO, the metal-metal distance is the same as the oxygen-oxygen distance. ２ In layered rock salt structures such as Li, oxygen and metal are arranged alternately, and the average interlayer distance of the metal layers is the same as the average interlayer distance of the oxygen layers. ２ MnO ３ In the layered rock salt structure of space group C / 2m, oxygen and metal are arranged alternately in the direction perpendicular to the (001) plane, and the average interlayer distance of the metal layers is the same as the average interlayer distance of the oxygen layers. Of the methods for determining metal-metal distances, the latter method described above can also be applied to determining oxygen-oxygen distances. In other words, the oxygen-oxygen distance within the same plane is the same as the metal-metal distance previously determined. Therefore, the metal-metal distances shown in Table 1 can be said to be the same as the oxygen-oxygen distances. Similarly, the interlayer distance of the metal layers can be said to be the same as the interlayer distance of the oxygen layers.

[0104] LiMn ２ O ４The oxygen positions on the (111) plane of the SiO2 are shifted from the triangular lattice positions. Therefore, we assume that the oxygen atoms are arranged in the same plane as the triangular lattice positions, and the distance between the triangular lattices is the oxygen-oxygen distance. The oxygen-oxygen distance calculated under this assumption is 2.908 Å, which is 0.98 relative to the oxygen-oxygen distance of MgO.

[0105] LiMn ２ O ４ Since the oxygen positions of LiMn are shifted from the (111) plane, the average of the oxygen positions on the (111) plane is taken as the oxygen position on the (111) plane, and the distance of the oxygen layers in the

[111] direction calculated using the oxygen positions on the (111) plane is assumed to be the interlayer distance of the oxygen layers. The interlayer distance of the oxygen layers calculated under this assumption is 2.375 Å, and the relative value to the interlayer distance of the oxygen layers of MgO is 0.98. ２ O ４ In the case of MgO, the relative values ​​of both the oxygen-oxygen distance and the oxygen layer interlayer distance are in the range of 0.94 to 1.06.

[0106] Therefore, the core 102 is LiMn ２ O ４ When the shell 101 has a spinel-type structure such as LiMn ２ O ４ When the core 102 has a spinel-type structure such as the above, the crystal orientation can be approximately the same as that of the core 102 having a layered rock-salt type and / or disordered rock-salt type crystal structure.

[0107] The particle diameter of the positive electrode active material particles 100 is preferably 500 nm or less, more preferably 250 nm or less, and even more preferably about 100 nm, in order to suppress the diffusion resistance of lithium within the particles. On the other hand, if the particle diameter is too small, disadvantages such as a tendency for aggregation to occur may occur. Therefore, the diameter is preferably 25 nm or more, and more preferably 50 nm or more.

[0108] Unless otherwise specified, the present specification and the like will describe the characteristics of the primary particles of the positive electrode active material particles 100, but the positive electrode active material particles may have secondary particles formed by aggregation, adhesion, and / or sintering of a plurality of primary particles. The presence of secondary particles is preferable because the particle size becomes larger, making it easier to apply the particles to a current collector, etc.

[0109] When the positive electrode active material particle 100 has secondary particles, the shell 101 may be formed for each primary particle that the secondary particle has. Alternatively, the shell 101 may be formed for each secondary particle as a single particle. In other words, a primary particle without a shell 101 may be present inside a secondary particle. Alternatively, an additive element may be used as a sintering aid when granulating the primary particles into secondary particles.

[0110] It is preferable that shell 101 has a rock salt or spinel crystal structure, but it is not necessary that only shell 101 has a rock salt or spinel crystal structure. For example, a part of core 102 may have a rock salt or spinel crystal structure.

[0111] Furthermore, the shell 101 does not necessarily need to cover the entire surface of the positive electrode active material particle 100. However, in order to function as a pillar, the shell 101 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 100.

[0112] Furthermore, the shell 101 does not have to have a rock-salt or spinel-type crystal structure entirely. For example, a portion of the shell may be amorphous, or it may have another crystal structure. Similarly, the core 102 does not have to have a layered rock-salt or disordered rock-salt crystal structure entirely. For example, a portion of the shell may be amorphous, or it may have another crystal structure.

[0113] [Analysis] <Composition> The composition of the positive electrode active material particle 100 according to one embodiment of the present invention is preferably evaluated by combining a plurality of analyses. For example, among the elements contained in the positive electrode active material particle 100, the ratios of the main components lithium, transition metal M, and oxygen are preferably determined by ICP-MS (inductively coupled plasma mass spectrometry) or the like. The ratios of the additive elements are preferably determined by an analysis with high detection sensitivity for trace elements, such as GD-MS (glow discharge mass spectrometry).

[0114] <Distribution of Additional Element> The distribution of the additional element in the positive electrode active material particle 100 according to one embodiment of the present invention is preferably evaluated by, for example, cross-sectional analysis of the positive electrode active material particle 100 .

[0115] For example, cross-sectional STEM-EDX is preferable because of its high spatial resolution. To further increase the spatial resolution in STEM-EDX ray analysis, it is preferable that the 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.

[0116] Cross-sectional EPMA (electron probe microanalyzer) is also preferred because it has a low detection limit for elements.

[0117] Multiple analyses can be combined for evaluation as needed.

[0118] The interface between the shell 101 and the core 102 is a series of points showing a detection amount closest to 50% of the sum of the detection amount of the element in the center of the positive electrode active material particle 100 and the detection amount of the element most abundant near the surface of the positive electrode active material particle 100. When there are multiple added elements, the element that is easiest to detect and / or quantify is selected based on the composition of the positive electrode active material particle 100. For example, if there is an added element that is not contained in the core 102, it is preferable to select this added element. It is also preferable to select an element whose characteristic X-ray spectrum overlaps little with the element contained in the core 102. It is also preferable to select an element that is more abundantly detected near the surface.

[0119] <Surface> The positive electrode active material particles of one embodiment of the present invention are compounds containing a transition metal M and oxygen, capable of lithium insertion / extraction. Therefore, in this specification and the like, the interface between a region where the transition metal M and oxygen, which are oxidized and reduced upon lithium insertion / extraction, 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.

[0120] 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 charging and discharging, such as lithium-rich positive electrode active material particles, carbonates, hydroxyl groups, etc. that are chemically adsorbed after the production of the positive electrode active material particles. Note that the attached metal oxides refer to metal oxides whose crystal structure does not generally match that of the lithium-excess positive electrode active material particles, for example.

[0121] 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.

[0122] In STEM-EDX-ray analysis or the like, in principle or due to measurement errors, the graph of the detected amount of characteristic X-rays of the 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 or the like, the detected amount of characteristic X-rays of the transition metal M is set 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 ＢＧThe reference point is the point where the detected amount of the characteristic X-rays of the transition metal M is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal transition metal M and the average value of the detected amount of the characteristic X-rays of the background transition metal M. If the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal oxygen and the average value of the detected amount of the characteristic X-rays of the background oxygen is different from the point where the detected amount of the characteristic X-rays of oxygen is 50% of the sum of the average value of the detected amount of the characteristic X-rays of the internal oxygen and the average value of the detected amount of the characteristic X-rays of the background oxygen, this is considered to be due to the influence of metal oxides, carbonates, etc. containing oxygen attached to the surface, and therefore, the detected amount of the characteristic X-rays of the transition metal M is different from the point where ... oxygen is different from the sum of the average value of the detected amount of the 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 In the case of the 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 can be used as the reference point. ＡＶＥ and M ＢＧ The reference point can be determined using the following formula:

[0123] 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 the detected amount of characteristic X-rays of the transition metal M within a range of 2 nm or more, preferably 3 nm or more, from the outside of the positive electrode active material particle 100, while 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 the detected amounts of characteristic X-rays of the transition metal M and oxygen in a region where the detected amounts are saturated and stable, for example, in a 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.

[0124] Furthermore, the surface of a positive electrode active material particle in a cross-sectional STEM (scanning transmission electron microscope) image or the like refers to 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. The surface in an STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.

[0125] The STEM observation and STEM-EDX analysis are performed on a thin section sample, which is prepared by forming a protective film on the surface of a positive electrode active material and then processing the resulting sample into a thin section.

[0126] Carbon can be used for the protective film. Carbon films can be formed by vapor deposition using the carbon coating unit of an ion sputtering device, or by depositing carbon using an FIB. Carbon films formed using an FIB have less oxygen contamination and are therefore more suitable for oxide analysis.

[0127] The thinning process can be performed, for example, using an FIB-SEM device (NX5200 manufactured by Hitachi High-Tech). In this case, the sample is picked up using an MPS (microprobing system), and the accelerating voltage is gradually reduced from a high accelerating voltage to a low accelerating voltage, for example, 30 kV, 10 kV, 5 kV, (2 kV if necessary), to remove the damaged layer. It is also preferable to measure the depth and the area of ​​the thinned sample with minimal unevenness.

[0128] In EDX measurement of the surface layer portion of the positive electrode active material particles, a magnification that can obtain sufficient information within a few nanometers from the surface is preferable, for example, a magnification that allows the electron beam scanning pitch for EDX area analysis to be approximately 0.3 nm, or a measurement magnification of approximately 160,000 times (320,000 times, doubled on the screen display for drift correction).

[0129] Standardless quantification can be used to quantify elements in STEM-EDX analysis. This method uses a k-factor, an element-specific coefficient pre-set in the analytical instrument and / or analytical software. Furthermore, when calculating element concentrations from quantitative results, the target elements (also referred to as denominator elements) preferably include the target material, raw materials, the mesh on which the thin section sample is placed, the instrument components, and the elements used in thin section processing. For example, the target elements are preferably 15 elements: C, O, F, Mg, Al, Si, P, S, Ca, Ti, Mn, Fe, Co, Ni, and Ga. The net count, which indicates the total number of detected counts, and the concentration can be output as desired. Furthermore, when simply referring to the detected amount of a certain element, it includes the characteristic X-ray count and concentration. Furthermore, concentration includes weight % and atomic %.

[0130] Furthermore, the spatial resolution of STEM-EDX depends on the probe diameter. Therefore, the maximum value of the additive element profile may deviate by approximately 1 nm depending on conditions such as the probe diameter. For example, even if the maximum value of the additive element profile of magnesium or the like is located 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.

[0131] In addition, a peak in STEM-EDX-ray analysis refers to a convex maximum value that appears in a graph of the amount of characteristic X-ray detected for each element, or the maximum value of the characteristic X-ray 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, less than R / 2.

[0132] The effect of noise can be reduced by scanning the same location multiple times under the same conditions or by increasing the number of frames.

[0133] <Particle Size Distribution Analysis Using Cross-Sectional SEM Image of Positive Electrode> For example, the particle size distribution of the positive electrode active material particles 100 can be calculated from a cross-sectional SEM image of the positive electrode active material particles 100 by the following method.

[0134] 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 100 sufficient for image analysis. For example, it is preferable to cut out a range from which 100 or more cross sections of the positive electrode active material particles 100 can be obtained.

[0135] 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.

[0136] Next, the cut-out first image is binarized using image processing software, and particle analysis is performed.

[0137] 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.

[0138] 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.

[0139] 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).

[0140]

[0141] In this way, the 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.

[0142] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0143] 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.

[0144] [Fabrication Method 1] First, using FIG. 3A, ｘ M 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) and then adding the additive element source will be described. ｘ M ２−ｘ O ２ Although the synthesis method is not particularly limited, in this embodiment, an example in which a solid phase method is adopted will be described.

[0145] First, in step S11 of FIG. 3A, a lithium (Li) source and an M source are prepared. For example, lithium carbonate (Li ２ CO ３ ), lithium hydroxide (LiOH) and / or lithium oxide (Li ２ O) and the like can be used. As the M source, oxides, hydroxides, carbonates, etc. of transition metals M can be used. For example, manganese oxide (Mn ２ O ３ , MnO ２ and / or MnO), manganese carbonate (MnCO ３ ), nickel oxide (NiO ２ ), nickel carbonate (NiCO ３ ), nickel hydroxide (Ni(OH) ２), cobalt oxide (Co ２ O ３ ), cobalt hydroxide (Co(OH) ２ ), chromium oxide (Cr ２ O ３ ), molybdenum dioxide (MoO ２ ), niobium oxide (NbO, Nb ２ O ５ ), vanadium oxide (V ２ O ３ ), iron oxide (Fe ２ O ３ ), titanium oxide (TiO ２ ), ruthenium oxide (RuO ２ ) etc. can be used.

[0146] Next, in step S12, the lithium source and the M source are mixed to prepare a mixture 901 (step S13). Pulverization during the mixing process is useful for reducing the particle size. For pulverization, it is preferable to use a bead mill and / or a ball mill. A planetary ball mill can be used as the ball mill. The bead mill and / or ball mill may be either a dry type or a wet type. Furthermore, if heat is generated during mixing and pulverization, it is preferable to perform the process while cooling.

[0147] Next, in step S14, the first mixture 901 prepared above is heated. A higher heating temperature increases productivity by shortening the heating time, but too high a heating temperature increases the particle size of the primary particles, potentially resulting in a decrease in charge / discharge capacity. Furthermore, transition metals are more likely to be reduced, potentially reducing Mn from tetravalent to trivalent, preventing the synthesis of a composite oxide with the intended composition. A shorter heating time is preferable for higher productivity, but too short a heating time can result in insufficient reaction. Therefore, the heating temperature is preferably 700°C or higher and 1200°C or lower, and more preferably 800°C or higher and 1050°C or lower. The heating time is preferably 15 minutes or higher and 100 hours or lower, and more preferably 2 hours or higher and 20 hours or lower. The heating time here refers to the time during which the heating temperature is maintained, excluding the time during which the temperature is increased or decreased.

[0148] Layered and irregular rock salt Li ｘ M２−ｘ O ２ The heating for producing the Li may be carried out in an oxidizing atmosphere containing oxygen, or in an inert atmosphere such as argon or nitrogen. １．２ Mn ０．６ Ni ０．２ O ２ When preparing a composite oxide in which the valence of Mn is tetravalent or close to tetravalent, it is preferable to heat in an atmosphere containing oxygen. ３＋ , V ３＋ , Cr ３＋ , Co ２＋ Li including etc. ｘ M ２−ｘ O ２ When preparing a film, it may be preferable to heat in an inert atmosphere.

[0149] In this heating step, if the amount of first mixture 901 per heating container is too large, the first mixture 901 may not be in sufficient contact with the atmosphere, which may result in partial insufficient reaction. Therefore, it is preferable to heat the mixture in multiple heating containers as needed. When heating the mixture in multiple heating containers, these are mixed after heating. For this mixing, a bead mill, a ball mill, a mortar, a mixer rotor, and / or a mixer can be used.

[0150] In the above process, Li ｘ M ２−ｘ O ２ A composite oxide 902 represented by the following formula is obtained (step S16).

[0151] Next, in step S23, a source of the additive element (A) 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.

[0152] When magnesium is used as an additive element, magnesium oxide (MgO) and / or magnesium fluoride (MgF ２When 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.

[0153] The fluorides of these typical metal elements function as fluxes in the subsequent heating step, and can promote the diffusion and doping of the additive elements in the shell 101. The mixture containing the fluorides has a melting point of Li ｘ M ２−ｘ O ２ In particular, a mixture of a combination having a eutectic point of 1000°C, preferably 900°C or less in an oxygen-containing atmosphere is suitable because it is likely to become liquid at a relatively low temperature.

[0154] After functioning as a flux, fluorine may be lost due to volatilization or the like, so even if fluorine is added as an additive element, there may be cases where fluorine is not detected in the positive electrode active material particles 100 after production.

[0155] Next, in step S31, the composite oxide 902 and the additive element source are mixed to prepare a second mixture 903 (step S32). For this mixing, the description of step S12 can be referred to.

[0156] Next, in step S33, the second mixture is heated. If the heating temperature is too low, doping of the additive element may become non-uniform and / or insufficient. Therefore, the heating temperature is preferably 500°C or higher, more preferably 700°C or higher, and even more preferably 800°C or higher. On the other hand, if the temperature is too high, there is a risk that the composite oxide 902 may be thermally decomposed, or that particles may sinter together, resulting in an unnecessarily large particle size. Therefore, the heating temperature is preferably 1050°C or lower. Furthermore, in order to suppress the volatilization of fluorides such as lithium fluoride, a heating temperature of 900°C or lower is more preferable.

[0157] The shorter the heating time, the higher the productivity, but if the heating time is too short, the diffusion and doping of the additive element may be insufficient. The heating time is, for example, preferably from 15 minutes to 100 hours, and more preferably from 2 hours to 20 hours.

[0158] In the heating step of step S33, the composite oxide 902 and the additive element source are partially melted, and the additive elements, including magnesium, are effectively diffused and doped. Because of the partial melting, the crystal structure of the shell 101 is influenced by the crystal structure of the core 102, and the crystal structures of the shell 101 and core 102 generally coincide. The shell 101 thus formed stabilizes the crystal structures of the surface and bulk of the positive electrode active material particle 100. This effectively suppresses changes in the crystal structure and / or oxygen release during charging of the positive electrode active material particle 100.

[0159] The optimum ranges for the heating temperature and heating time may differ depending on the particle size of the composite oxide 902 .

[0160] Through the above steps, the positive electrode active material particles 100 can be produced (step S34).

[0161] [Preparation Method 2] In Preparation Method 1, Li ｘ M ２−ｘ O ２ In this example, a composite oxide represented by the formula (I) was synthesized, and then an additive element was added and heated. However, the method for producing positive electrode active material particles according to one embodiment of the present invention is not limited to this. The additive element may be added at a different timing or multiple times. The timing may vary depending on the element. In Production Method 2, an example in which an additive element is added at a different timing than in Production Method 1 will be described with reference to FIG. 3B .

[0162] In the manufacturing method 2 shown in FIG. ｘ M 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) in the process of preparing a composite oxide. That is, in step S11, a lithium source, an M source, and an additive element source are mixed and heated to synthesize. Even in such a preparation process, it is possible to make the shell 101 contain a large amount of the additive element by adjusting the additive element and heating conditions. For example, Li ｘ M ２−ｘ O ２ By using an additive element having a low solid solubility limit in the composite oxide represented by the formula (I), the shell 101 containing a large amount of the additive element can be formed.

[0163] Except for the timing of adding the additive element, reference can be made to Fabrication Method 1 and FIG. 3A.

[0164] 4, a more specific example of the manufacturing method 1, manufacturing method 1-1, will be described. In this manufacturing method, manganese and nickel are used as the transition metal M, and magnesium and fluorine are used as the additive elements.

[0165] First, in step S11 of FIG. 4, a lithium (Li) source, a manganese (Mn) source, and a nickel (Ni) source are prepared. For example, the lithium source is lithium carbonate (Li ２ CO ３ As a manganese source, for example, manganese carbonate (MnCO ３ As the nickel source, for example, nickel carbonate (NiCO ３ ) can be used.

[0166] Next, in step S12, the lithium source, manganese source, and nickel source are mixed to prepare a mixture 901 (step S13). In this preparation method, a ball mill is used for the mixing, and the mixture is mixed while cooling. Zirconia balls with a diameter of 3 mm are used as the media for the ball mill.

[0167] Next, in step S14, the first mixture 901 prepared above is heated. In this preparation method, heating is performed while dry air is flowing. To distinguish it from other steps, the heating in step S14 may be referred to as the first heating.

[0168] Next, if the materials are heated separately in a plurality of containers in step S14, mixing is carried out in step S15. For mixing, it is preferable to use a bead mill, a ball mill, a mortar, a mix rotor, and / or a mixer.

[0169] In the above process, Li ｘ M ２−ｘ O ２ A composite oxide 902 represented by the following formula is obtained (step S16).

[0170] Next, in step S21, a magnesium source and a fluorine source are prepared. In this production method, magnesium fluoride and lithium fluoride are used as the magnesium source and the fluorine source. Magnesium fluoride and lithium fluoride are a combination that easily become liquid at a relatively low temperature, with a eutectic point of around 742°C. Therefore, they are suitable as a flux that must function below the decomposition temperature of the composite oxide.

[0171] Next, in step S22, the magnesium source and the fluorine source are pulverized and mixed. While the pulverization and mixing method is not particularly limited, in this production method, a ball mill is used to perform wet mixing and pulverization. Zirconia balls with a diameter of 1 mm are used as the ball mill media. Next, if necessary, the mixed media can be removed by sieving, and the solvent can be dried.

[0172] Through the above steps, the additive element source is obtained (step S23).

[0173] Next, in step S31, the composite oxide 902 and the additive element source are mixed to prepare a second mixture 903 (step S32). For this mixing, the description of step S12 can be referred to.

[0174] Next, in step S33, the second mixture 903 is heated. In this manufacturing method, the heating is performed while oxygen is flowing. To distinguish it from other steps, the heating in step S33 may be referred to as second heating.

[0175] Through the above steps, the positive electrode active material particles 100 can be produced (step S34). In this production method, Production Method 1 and FIG. 3A can be referred to as appropriate.

[0176] This embodiment mode can be combined with the contents of other embodiment modes as appropriate.

[0177] Embodiment 3 In this embodiment, a structure of a lithium ion battery will be described.

[0178] [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.

[0179] The positive electrode active material particles described in the above embodiment may be mixed with other positive electrode active material particles.

[0180] 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:

[0181] FIG. 5A shows an example of a schematic cross-sectional view of a positive electrode.

[0182] 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. Although not shown, it is preferable to provide a conductive carbon coating layer between the active material and the current collector 550. By providing a conductive carbon coating layer, the interface resistance between the aluminum foil and the active material and the variation in that resistance can be reduced.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] Specific examples of carbon materials that can be used as the conductive additive include carbon black (furnace black, acetylene black, graphite, etc.).

[0188] FIG. 5A illustrates carbon black 553 as a conductive additive.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] <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.

[0201] 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.

[0202] 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.

[0203] The binder may be used in combination with two or more of the above.

[0204] When the binder covers the surface of the active material or contacts the surface and 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" refers to 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.

[0205] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as aluminum, stainless steel, gold, platinum, aluminum, titanium, or other metals, or alloys thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable that the current collector have a thickness of 5 μm to 30 μm.

[0206] [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.

[0207] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy material and / or a carbon material can be used.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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, CeSb ３ , 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.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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 ８ It is preferable that the negative electrode active material be a nitride of lithium and a transition metal, since it can be combined with a material such as the above. Even when a material containing lithium ions is used for the positive electrode active material particles, 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 particles.

[0216] 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 , FeP２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0217] 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).

[0218] 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.

[0219] <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.

[0220] [Electrolyte] The electrolyte contains an organic solvent, but the organic solvent does not necessarily have to be liquid at room temperature, for example, 25°C, and may be solid or semi-solid at room temperature. The organic solvent is preferably liquid over a wide temperature range, including 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 below freezing to high temperatures.

[0221] 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.

[0222] The organic solvent may contain an additive. The additive can suppress reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Examples of additives that can be used include vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate)borate (LiBOB). LiBOB is particularly preferred because it easily forms a good coating. VC or FEC is preferred because it can form a good coating on the negative electrode during aging of the secondary battery or during charging in the early stages of use, thereby improving the cycle characteristics.

[0223] 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.

[0224] 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.

[0225] 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 solution 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0232] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0233] 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.

[0234] 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.

[0235] [Separator] When a separator is disposed between the positive electrode and the negative electrode, the separator can be formed, for example, from 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, or polyurethane. The porosity of the separator can be 35% to 90%, preferably 60% to 85%. A separator using polypropylene can have a porosity of 35% to 45%. A separator using polyimide can have a porosity of 75% to 85%. The thickness of the separator is preferably 10 μm to 80 μm, more preferably 20 μm to 60 μm. A separator using polyimide can have a high porosity and can be made thick (typically, a thickness of 50 μm to 60 μm).

[0236] The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0237] 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).

[0238] 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.

[0239] [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.

[0240] This embodiment can be used in combination with other embodiments.

[0241] Embodiment 4 In this embodiment, an example of a lithium ion battery will be described.

[0242] [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, 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.

[0243] 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.

[0244] [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.

[0245] 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.

[0246] 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.

[0247] 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 .

[0248] FIG. 7B is a perspective view of the completed coin-type lithium-ion battery 300.

[0249] 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.

[0250] 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.

[0251] 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.

[0252] 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.

[0253] [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.

[0254] 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.

[0255] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and negative electrode 606 are wound with an electrolyte layer 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. An electrolyte (not shown) is poured into the interior of the battery can 602 in which the battery element is provided.

[0256] 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.

[0257] 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.

[0258] 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.

[0259] 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.

[0260] A plurality of lithium ion batteries 616 may be connected in parallel and then further connected in series.

[0261] 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.

[0262] 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.

[0263] 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.

[0264] [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.

[0265] The 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 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.

[0266] 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.

[0267] 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.

[0268] 9C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0269] 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 includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0270] The separator 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0276] Fifth Embodiment In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIG.

[0277] 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.

[0278] 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.

[0279] The internal structure of the first battery 1301a may be a wound type or a stacked type.

[0280] 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.

[0281] 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.

[0282] 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.

[0283] 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.

[0284] The first battery 1301a will be described with reference to FIG. 11B.

[0285] 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.

[0286] 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).

[0287] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M2-Zn oxide (wherein the element M2 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.

[0288] 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.

[0289] 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.

[0290] 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.

[0291] 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.

[0292] FIG. 11C shows an example of a block diagram of the battery pack 1415 shown in FIG. 11B.

[0293] 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).

[0294] 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.

[0295] 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.

[0296] 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.

[0297] 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.

[0298] 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.

[0299] 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.

[0300] 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.

[0301] 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.

[0302] 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.

[0303] 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.

[0304] 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.

[0305] 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.

[0306] 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.

[0307] 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.

[0308] 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.

[0309] 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.

[0310] 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.

[0311] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0312] 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.

[0313] 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.

[0314] 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.

[0315] The power storage device 8702 also includes a control circuit 8704 capable of controlling charging or detecting an abnormality of the lithium ion battery. 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.

[0316] 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.

[0317] 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.

[0318] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0319] 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.

[0320] 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 has 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.

[0321] 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.

[0322] 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.

[0323] 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.

[0324] 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.

[0325] 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.

[0326] 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.

[0327] 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.

[0328] 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.

[0329] 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.

[0330] 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.

[0331] 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.

[0332] 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.

[0333] 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.

[0334] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0335] 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.

[0336] 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.

[0337] 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.

[0338] 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.

[0339] 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.

[0340] 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.

[0341] 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.

[0342] 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.

[0343] 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.

[0344] 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.

[0345] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0346] In this example, Li ｘ M ２−ｘ O ２ (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti and Ru, 1<x<2) １．２ Mn ０．６ Ni ０．２ O ２ The positive electrode active material particles were prepared by adding fluorine and magnesium as additive elements and heating the mixture, and the properties of the particles were evaluated.

[0347] <Preparation of Positive Electrode Active Material> A method for preparing positive electrode active material particles in this example will be described with reference to the preparation method shown in FIG.

[0348] First, in step S11, lithium carbonate was prepared as the Li source, manganese carbonate as the Mn source, and nickel carbonate as the Ni source, and these were weighed out so that the molar ratio of Li:Mn:Ni was 1.2:0.6:0.2.

[0349] Next, in step S12, the mixture was wet mixed using a ball mill with dehydrated acetone as a solvent while cooling. Zirconia balls with a diameter of 3 mm were used as the ball mill media, and mixing was carried out for 2 hours. The dehydrated acetone was then dried in a drying oven at 55°C, and the mixing media was removed with a sieve to obtain a first mixture.

[0350] Next, in the first heating step S14, a muffle furnace was used to heat the sample while flowing dry air. The heating conditions were 1000°C and 10 hours. The temperature increase rate was 200°C / hour. The temperature decrease rate was 200°C / hour or less.

[0351] Through the above process, Li １．２ Mn ０．６ N ｉ０．２ O ２ A composite oxide represented by the formula:

[0352] Next, magnesium fluoride and lithium fluoride were prepared as the Mg source and F source in step S21. ２ The components were weighed so that the molar ratio was 1:3.

[0353] Next, in step S22, the mixture was wet-mixed using a ball mill and dehydrated acetone as a solvent. Zirconia balls with a diameter of 1 mm were used as the ball mill media, and mixing was carried out for 20 hours. The dehydrated acetone was then dried in a drying oven at 55°C, and the mixing media was removed with a sieve to obtain the additive element source.

[0354] Next, in step S31, Li １．２ Mn ０．６ Ni ０．２ O ２ : MgF ２The additive element sources were weighed so that the molar ratio of the additives was 3:0.03:0.01, and the mixture was dry-mixed using a ball mill. Zirconia balls with a diameter of 1 mm were used as the ball mill media, and the mixture was mixed for 20 minutes. The mixing media was then removed using a sieve to obtain a second mixture.

[0355] Next, in the second heating step S33, a muffle furnace was used to heat the sample while flowing oxygen. The heating conditions were 900°C and 20 hours. The temperature increase rate was 200°C / hour. The temperature decrease rate was 200°C / hour or less.

[0356] The positive electrode active material particles produced by the above steps were designated as Sample 1.

[0357] Sample 2 was prepared by heating in the same manner as Sample 1, except that no additive element source was added.

[0358] Sample 3 was prepared in the same manner as Sample 1, except that in step S14, the mixture was heated using two heating containers, and in step S15, the mixture was mixed using a mortar and a mix rotor, and the temperature of the second heating was set to 800°C.

[0359] Sample 4 was prepared in the same manner as Sample 3 except that the temperature of the second heating was set to 900°C.

[0360] Sample 5 was prepared in the same manner as Sample 3 except that the temperature of the second heating was set to 1000°C.

[0361] The preparation conditions for Samples 1 to 5 are shown in Table 2.

[0362]

[0363] <STEM-EDX-ray analysis> Li １．２ Mn ０．６ N ｉ０．２ O ２In order to evaluate whether the composite oxide represented by the formula (1), i.e., the composite oxide 902 in FIG. 4, was synthesized as intended, a carbon protective film was formed on the composite oxide, and then a thin specimen was prepared by FIB processing, and STEM-EDX analysis was performed. The STEM and EDX equipment and measurement conditions were as follows: Analysis equipment: JEM-ARM200F NEOARM manufactured by JEOL Ltd. Acceleration voltage: 200 kV Magnification accuracy: ±3% Emission current: 5 μA or more and 15 μA or less Observation mode: C6 X-ray detector: Dual SDD (158 mm ２ x 2) JEOL JED-2300T Energy resolution: 133 eV or less Solid angle: 2.2 sr Dwell time: 50 μsec Number of frames: Approximately 400 Number of captured pixels: 256 x 256 EDX analyzer: Thermo Fisher Analysis software: Thermo Fisher Pathfinder

[0364] In FIG. １．２ Mn ０．６ N ｉ０．２ O ２ 16B shows the cross-sectional STEM image of a complex oxide represented by the formula (1). Figure 16B shows the results of STEM-EDX analysis of the region corresponding to the bulk of the complex oxide, indicated by the dashed line in Figure 16A. The horizontal axis in Figure 16B corresponds to the direction of the arrow in Figure 16A. The denominators of the concentrations on the vertical axis are 15 elements: C, O, F, Mg, Al, Si, P, S, Ca, Ti, Mn, Fe, Co, Ni, and Ga. Figure 16B also shows a profile obtained by taking a three-term moving average.

[0365] As shown in FIG. 16B, Li １．２ Mn ０．６ N ｉ０．２ O ２ The concentrations of oxygen, manganese, and nickel were stable in the region corresponding to the bulk of the composite oxide, expressed as: Furthermore, the atomic ratio, where Ni is taken as 1, was Mn:Ni:O = 3.1:1.0:9.7. This indicates that a composite oxide was synthesized with a feed ratio of roughly Mn:Ni:O = 3:1:10.

[0366] <SEM-EDX and SEM> To evaluate the distribution of the additive element source on the surface of the positive electrode active material particles, SEM-EDX images were obtained before and after the second heating in the production process of Sample 1. Figures 17A to 17C are SEM-EDX images of the second mixture before the second heating, i.e., in the process of Sample 1. Figures 17D to 17F are SEM-EDX images of Sample 1 after the second heating. Note that Figures 17A and 17D are SEM-EDX images of oxygen, Figures 17B and 17E are SEM-EDX images of fluorine, and Figures 17C and 17F are SEM-EDX images of magnesium.

[0367] 17B and 17C, multiple bright particles thought to be lithium fluoride or magnesium fluoride were observed. However, in FIGS. 17E and 17F after the second heating, these were not observed, and the source of the additional element was spread over the entire surface of the positive electrode active material particles.

[0368] Next, to observe the shape of the positive electrode active material particles, SEM images were taken for Sample 1 and Sample 2. Fig. 18A is an SEM image of Sample 1, and Fig. 18B is an SEM image of Sample 2 to which no additive element source was added.

[0369] <XPS> Next, to evaluate the shell composition of the positive electrode active material particles before and after the second heating, XPS analysis was performed under the following measurement conditions. The results are shown in Tables 3 and 4 as quantitative values. The unit is atomic %.

[0370] Measurement equipment: PHI Quantera II X-ray source: Monochromated Al (1486.6 eV) Detection area: 100 μmφ Detection depth: Approximately 5.3 nm (take-off angle 45 °), approximately 1.9 nm (take-off angle 15 °) Measurement spectrum: Wide, Li1s, Mn2p, Ni2p3 / 2, O1s, Mg1s, F1s, C1s, S2p Note that for Li, the nearby Mn3p is removed by calculation, so the quantitative error is larger than usual. Also, since Ni Auger overlaps with Mn and Mn Auger overlaps with Ni, the quantitative error is larger than usual. In addition, the standard deviation and detection limit were calculated from the 45 ° data.

[0371]

[0372]

[0373] As shown in Table 3, when comparing Sample 1 before and after the second baking, i.e., comparing Mixture 903 and Positive Electrode Active Material Particles 100 in the flowchart of FIG. 4 , the proportion of magnesium increases after the second baking compared to before the second baking. This is thought to be because magnesium present locally in magnesium fluoride spreads to the entire surface of the positive electrode active material particles. Because XPS detects elements near the surface, it can be said that magnesium is present on the surface of the positive electrode active material particles of Sample 1.

[0374] The Mg / (Mn + Ni) atomic ratio of Sample 1 measured by XPS was 5.8 at% at a take-off angle of 45° and 7.3 at% at a take-off angle of 15°. The shallower the take-off angle, the higher the magnesium concentration, indicating that the magnesium concentration is higher the closer to the surface. Furthermore, compared to the Mg / (Mn + Ni) atomic ratio of 1.25 at% for Sample 1 measured in the raw material, i.e., the weighed value at the time of synthesis, the magnesium concentration is higher at both take-off angles of 45° and 15°. Therefore, it can be said that the magnesium concentration at the depth detectable by XPS, i.e., in the shell, is higher than in the bulk.

[0375] Similarly, the proportion of fluorine increased after the second baking compared to before the second baking. This is thought to be because the fluorine present locally in the magnesium fluoride and lithium fluoride spread to the entire surface of the positive electrode active material particles. Because XPS detects elements near the surface, it can be said that fluorine is present on the surface of the positive electrode active material particles of Sample 1.

[0376] The F / (Mn + Ni) atomic ratio of Sample 1 measured by XPS was 31.7 at% at a take-off angle of 45° and 35.6 at% at a take-off angle of 15°. The shallower the take-off angle, the higher the fluorine concentration, indicating that the fluorine concentration is higher the closer to the surface. Furthermore, compared to the F / (Mn + Ni) atomic ratio of 2.92 at% for Sample 1 measured in the raw material, i.e., the weighed value at the time of synthesis, the fluorine concentration is higher at both take-off angles of 45° and 15°. Therefore, it can be said that the fluorine concentration in the depth detectable by XPS, i.e., the shell, is higher than that in the bulk.

[0377] In addition, the F / O atomic ratio of Sample 1 measured by XPS was 15.0 at% when the take-off angle was 45° and 15.6 at% when the take-off angle was 15°. The F / Mg atomic ratio was 5.5 when the take-off angle was 45° and 4.9 when the take-off angle was 15°.

[0378] As shown in Table 4, when comparing Samples 3 to 5 before and after the second firing, Samples 3 and 4 showed the same tendency as Sample 1 with respect to magnesium and fluorine.

[0379] The Mg / (Mn + Ni) atomic ratio of Sample 3 measured by XPS was 8.3 at% at a take-off angle of 45° and 11.3 at% at a take-off angle of 15°. The Mg / (Mn + Ni) atomic ratio of Sample 4 was 7.5 at% at a take-off angle of 45° and 7.8 at% at a take-off angle of 15°. The magnesium concentration was higher at shallower take-off angles in both cases, demonstrating that the magnesium concentration is higher closer to the surface. Furthermore, when compared with the Mg / (Mn + Ni) atomic ratio of 1.25% in the raw material (i.e., the weighed value at the time of synthesis), the magnesium concentration at the depth detectable by XPS, i.e., in the shell, can be said to be higher than that in the bulk.

[0380] On the other hand, the atomic ratio of Mg / (Mn+Ni) in Sample 5 was 4.7 at % when the take-off angle was 45° and 5.2 at % when the take-off angle was 15°, and the magnesium concentration was lower than that of Samples 1, 3 and 4.

[0381] The F / (Mn + Ni) atomic ratio of Sample 3 measured by XPS was 46.6 at% at a take-off angle of 45° and 58.1 at% at a take-off angle of 15°. The F / (Mn + Ni) atomic ratio of Sample 4 was 37.4 at% at a take-off angle of 45° and 46.6 at% at a take-off angle of 15°. The fluorine concentration was higher at shallower take-off angles in both cases, demonstrating that the fluorine concentration is higher closer to the surface. Furthermore, a comparison with the F / (Mn + Ni) atomic ratio of 2.88% in the raw material (i.e., the weighed value at the time of synthesis) indicates that the fluorine concentration in the depth detectable by XPS, i.e., the shell, is higher than that in the bulk.

[0382] On the other hand, the atomic ratio of F / (Mn+Ni) of sample 5 was 11.6 at % when the take-off angle was 45° and 12.9 at % when the take-off angle was 15°, which was a lower fluorine concentration than samples 1, 3 and 4.

[0383] The F / O atomic ratio of Sample 3 was 24.2 at% when the take-off angle was 45° and 27.2 at% when the take-off angle was 15°. The F / O atomic ratio of Sample 4 was 19.3 at% when the take-off angle was 45° and 20.8 at% when the take-off angle was 15°. The F / O atomic ratio of Sample 5 was 5.8 at% when the take-off angle was 45° and 5.0 at% when the take-off angle was 15°.

[0384] The atomic ratio of F / Mg for sample 3 was 5.6 at a take-off angle of 45° and 5.1 at a take-off angle of 15°. The atomic ratio of F / Mg for sample 4 was 5.0 at a take-off angle of 45° and 6.0 at a take-off angle of 15°. The atomic ratio of F / Mg for sample 5 was 2.5 at a take-off angle of 45° and 2.5 at a take-off angle of 15°.

[0385] <Charge / Discharge Curve and Charge / Discharge Cycle Characteristics> Next, in order to evaluate the electrochemical characteristics, half cells were prepared using the positive electrode active material particles of Samples 1 to 5, and a charge / discharge cycle test was carried out.

[0386] [Fabrication of Positive Electrode] Samples 1 to 5 were prepared as positive electrode active material particles, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder. PVDF was dissolved in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 5%. Next, the positive electrode active material, AB, and PVDF were mixed in a weight ratio of 90:5:5 to prepare a slurry, which was then applied to an aluminum positive electrode current collector. NMP was used as the solvent for the slurry. After the slurry was applied to the positive electrode current collector, the solvent was evaporated.

[0387] Thereafter, in order to increase the density of the positive electrode active material layer on the positive electrode current collector, a pressing process was performed using a roll press machine. The pressing process was performed under a linear pressure of 210 kN / m. The upper and lower rolls of the roll press machine were both set at 120°C.

[0388] A positive electrode was obtained by the above steps. The amount of the positive electrode active material supported per area of ​​the positive electrode was about 5 mg / cm. ２ By this manufacturing method, positive electrodes including Samples 1 to 5 were manufactured.

[0389] [Fabrication of Half Cells] Coin-shaped half cells (also referred to as coin cells) were fabricated using the above-described positive electrodes, lithium metal foil, separators, electrolytes, coin cell positive electrode cans, and coin cell negative electrode cans. The coin-shaped half cells were CR2032 type (diameter 20 mm, height 3.2 mm).

[0390] The electrolyte was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 1 mol / L of lithium hexafluorophosphate (LiPF ６ ) was dissolved in a solution.

[0391] A porous polypropylene film was used as the separator.

[0392] A charge-discharge cycle test was performed using the half cell prepared as described above. Charging was performed at CC (constant current) 0.1 C with a cut-off voltage of 4.8 V. Discharging was performed at CC 0.1 C with a cut-off voltage of 2.0 V. In this example, 1 C was 300 mA / g. The ambient temperature was 25°C.

[0393] The charge-discharge curves for the first cycle and the second cycle of the half cells containing Samples 1 and 2 are shown in Figure 19A and Figure 19B, respectively. The cycle characteristics of the discharge capacity per weight of the positive electrode active material particles for the half cells containing Samples 1 and 2 are shown in Figure 20A, the discharge capacity retention rate in Figure 20B, and the discharge energy density in Figure 20C. The discharge capacity retention rate was calculated assuming that the maximum discharge capacity in the charge-discharge cycle test was 100%.

[0394] 20A to 20C, Sample 1, which was heated with the addition of an additive element source, had better cycle characteristics than Sample 2, which was heated without the addition of an additive element source. The initial discharge capacity of Sample 1 was 233.7 mAh / g, and the 30th discharge capacity was 211.7 mAh / g.

[0395] Fig. 21A shows the charge-discharge curves for the first cycle and Fig. 21B shows the charge-discharge curves for the second cycle of the half cells containing Samples 3 to 5. Fig. 22A shows the cycle characteristics of the discharge capacity of the half cells containing Samples 3 to 5, Fig. 22B shows the discharge capacity retention rate, and Fig. 22C shows the discharge energy density.

[0396] 22A to 22C, Samples 3 and 4, in which the second heating times were 800° C. and 900° C., respectively, exhibited good discharge capacity and cycle characteristics. Sample 4 had better cycle characteristics than Sample 3.

[0397] As described above, it has become clear that lithium-excess positive electrode active material particles containing magnesium and fluorine as additive elements and having high magnesium and fluorine concentrations in the shell exhibit good discharge capacity and cycle characteristics.

[0398] 100: Positive electrode active material particle, 100a: Positive electrode active material particle, 101: Shell, 102: Core, 300: Lithium ion battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 332: Washer, 342: Spacer, 500: Lithium ion battery, 506: Negative electrode, 507: Positive electrode, 508: Adhesive region, 509: Exterior body, 510: Negative electrode lead electrode, 511: Positive electrode lead electrode, 550: Current collector, 553: Carbon black, 554: Graphene, 555: carbon fiber, 561: positive electrode active material particles, 562: second active material, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: electrolyte layer, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 613: safety valve mechanism, 614: conductive plate, 615: power storage system, 616: lithium ion battery, 620: control circuit, 621: wiring, 622: wiring, 623: wiring, 624: conductor, 625: insulator, 626: wiring, 627: wiring, 628: conductive plate, 911a: terminal, 911b: terminal , 913: lithium ion battery, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 931a: negative electrode active material layer, 932: positive electrode, 932a: positive electrode active material layer, 933: separator, 950: wound body, 950a: wound body, 951: terminal, 952: terminal, 1300: prismatic lithium ion battery, 1301a: first battery, 1301b: first battery, 1302: battery controller, 1303: motor controller, 1304: motor, 1305: gear, 1306: DCDC circuit, 1307: electric power steering, 1308: heater, 1309: Defogger, 1310: DCDC circuit, 1311: second battery, 1312: inverter, 1313: audio, 1314: power window, 1315: lamps, 1316: tires, 1317: rear motor, 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 1324: switch section, 1413: fixing section, 1414: fixing section, 1415: battery pack, 1421: wiring, 1422: wiring, 2001: automobile, 2002: transport vehicle, 2003: transport vehicle, 2004: aircraft, 2100: mobile phone, 2101: housing, 2102: display section,2103: operation buttons, 2104: external connection port, 2105: speaker, 2106: microphone, 2107: lithium ion battery, 2200: battery pack, 2201: battery pack, 2202: battery pack, 2203: battery pack, 2300: unmanned aerial vehicle, 2301: lithium ion battery, 2302: rotor, 2303: camera, 6300: cleaning robot, 6301: housing, 6302: display unit, 6303: camera, 6304: brush, 6305: operation buttons, 6306: lithium ion battery, 6310: dust, 6400: robot, 6401: illuminance sensor, 6402: microphone, 6403: upper camera, 6404: speaker, 6405: display unit, 6406: lower camera, 6407: obstacle sensor, 6408: Mobile mechanism, 6409: lithium ion battery, 6800: artificial satellite, 6801: airframe, 6802: solar panel, 6803: antenna, 6805: lithium ion battery, 6900: probe, 6901: airframe, 6902: solar sail, 6905: lithium ion battery, 6910: spacecraft, 6911: airframe, 6912: solar panel, 6913: lithium ion battery, 6920: rover, 6921: airframe, 6922: solar panel, 6923: lithium ion battery, 8600: scooter, 8601: side mirror, 8602: power storage device, 8603: turn signal light, 8604: under-seat storage, 8700: electric bicycle, 8701: lithium ion battery, 8702: power storage device, 8703: display unit, 8704: control circuit,

Claims

Positive electrode active material particles having lithium, transition metal M (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti and Ru), oxygen, magnesium, and fluorine, wherein the positive electrode active material particles have a Li / M (atomic ratio) greater than 1, the positive electrode active material particles have a core and a shell outside the core, the shell has more magnesium and fluorine than the core, the core and the shell have substantially the same crystal orientation, positive electrode active material particles. 　 In claim 1, the shell has more of one or more selected from titanium, aluminum, nickel, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium than the core, positive electrode active material particles. 　 In claim 1, the core has a layered rock salt type or irregular rock salt type crystal structure, positive electrode active material particles. 　 In claim 1, the shell has a rock salt type or spinel type crystal structure, positive electrode active material particles. Li ｘ M ２−ｘ O ２ A step of mixing a composite oxide represented by (M is one or more selected from Mn, Ni, Co, Cr, Mo, Nb, V, Fe, Ti, and Ru, 1 < x < 2) and a source of additive elements to produce a mixture a step of heating the mixture at 700 °C or higher and 900 °C or lower, the method for producing positive electrode active material particles, wherein the additive element source is a fluorine source and a magnesium source. 　 In claim 5, the fluorine source is lithium fluoride, the magnesium source is magnesium fluoride, the method for producing positive electrode active material particles.

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