Positive electrode active material, secondary battery, electronic device, and vehicle

Abstract

Provided is a positive electrode active material that is prevented from the decrease in a discharge capacity in a charge-discharge cycle. This positive electrode active material comprises cobalt, nickel and oxygen, in which the content of nickel relative to the total amount of cobalt and nickel, i.e., Ni / (Co+Ni), is more than 0.175 and equal to or less than 0.215, and the positive electrode active material has diffraction peaks at least two of 2θ = 18.526±0.1°, 2θ = 37.391±0.1°, 2θ = 37.628±0.1°, 2θ = 39.015±0.1°, 2θ = 44.947±0.1°, 2θ = 49.029±0.1° and 2θ = 58.857±0.1° when the positive electrode active material is analyzed by powder X-ray diffraction using CuKα1 line in the state charged to 4.5 V (vs.Li / Li+).

Description

Positive electrode active material, secondary battery, electronic device and vehicle

[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, there has been active development of various types of energy storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries. Demand for high-power, high-capacity lithium-ion secondary batteries has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable in today's information society as a rechargeable energy source.

[0004] In particular, there is a high demand for secondary batteries with a large discharge capacity per weight and excellent cycle characteristics for mobile electronic devices, etc. To meet this demand, improvements to the positive electrode active materials of the positive electrodes of secondary batteries have been actively pursued (e.g., Patent Documents 1 to 3). Research on the crystalline structure of positive electrode active materials has also been conducted (Non-Patent Documents 1 to 5).

[0005] X-ray diffraction (XRD) is one of the techniques used to analyze the crystalline structure of positive electrode active materials. XRD data can be analyzed using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 6. For example, the lattice constant of lithium cobalt oxide described in Non-Patent Document 7 can be referenced from ICSD. For Rietveld analysis, the analysis program RIETAN-FP (Non-Patent Document 8) can be used.

[0006] Also, image processing software such as ImageJ (Non-Patent Documents 9 to 11) is known. By using this software, for example, the shape of the positive electrode active material can be analyzed.

[0007] Microelectron diffraction is also effective for identifying the crystalline structure of the positive electrode active material, particularly the crystalline structure of the surface layer. For example, the analysis program ReciPro (Non-Patent Document 12) can be used to analyze the electron diffraction pattern.

[0008] Furthermore, fluorides such as fluorite (calcium fluoride) have long been used as fluxes in iron manufacturing and other processes, and their physical properties have been studied (Non-Patent Document 13).

[0009] Various research and development efforts are also being conducted on the reliability and safety of lithium-ion secondary batteries. For example, Non-Patent Document 14 describes the thermal stability of positive electrode active materials and electrolyte solutions.

[0010] Japanese Patent Application Laid-Open No. 2019-179758 WO2020 / 026078 Pamphlet Japanese Patent Application Laid-Open No. 2020-140954

[0011] Toyoki Okumura et al,”Correlation of lithium ion distribution and X−ray absorption near−edge structure in O3−and O2−lithium cobalt oxides from first−principle calculation”,Journal of Materials Chemistry,2012,22,p.17340−17348Motohashi,T.et al,”Electronic phase diagram of the layered cobalt oxide system Li▲x▼CoO▲2▼(0.0≦x≦1.0)”,Physical Review B,80(16);165114Zhaohui Chen et al,“Staging Phase Transitions in Li▲x▼CoO▲2▼”,Journal of The Electrochemical Society,2002,149(12)A1604−A1609G.G.Amatucci et.al.,“CoO▲2▼,The End Member of the Lix CoO▲2▼ Solid Solution”J.Electrochem.Soc.143(3)1114(1996).Atsushi Ueda and Tsutomu Ohzuku,“Solid−State Redox Reactions of LiNi▲1 / 2▼Co▲1 / 2▼O▲2▼(R3m)for 4 Volt Secondary Lithium Cells”Journal of The Electrochemical Society,Vol.141,No.8,August 1994.Belsky,A.et al.,“New developments in the Inorganic Crystal Structure Database(ICSD):accessibility in support of materials research and design”,Acta Cryst.,(2002)B58 364−369.Akimoto,J.;Gotoh,Y.;Oosawa, Y., "Synthesis and structure refinement of LiCoO₂ single crystals", Journal of Solid State Chemistry (1998) 141, p. 298 - 302. F. Izumi and K. Momma, Solid State Phenom., 130, 15 - 20 (2007) Rasband, W. S., ImageJ, U.S. National Institutes of Health, Bethesda, Maryland, USA, http: / / rsb.info.nih.gov / ij / , 1997 - 2012. Schneider, C. A., Rasband, W. S., Eliceiri, K. W., "NIH Image to ImageJ: 25 years of image analysis". Nature Methods 9, 671 - 675, 2012. Abramoff, M. D., Magelhães, P. J., Ram, S. J., "Image Processing with ImageJ". Biophotonics International, volume 11, issue 7, pp. 36 - 42, 2004. Seto, Y. & Ohtsuka, M., "Recipro: free and open - source multipurpose crystallographic software integrating a crystal model database and viewer, diffraction and microscopy simulators, and diffraction data analysis tools" (2022). J. Appl. Cryst. 55. W.E. Counts, R. Roy, and E.F. Osborne, "Fluoride Model Systems: II, The Binary Systems CaF₂ - BeF₂, MgF₂ - BeF₂, and LiF - MgF₂", Journal of the American Ceramic Society, 36[1]12 - 17 (1953). Kitano Shinya et al., GSYuasa Technical Report Vol. 2 No. 2 December 2015 P18 - 24.;

[0012] Lithium ion secondary batteries still have room for improvement in various aspects, such as discharge capacity, cycle characteristics, reliability, safety, and cost.

[0013] Therefore, there is a demand for positive electrode active materials that can improve issues such as discharge capacity, cycle characteristics, reliability, safety, and cost when used in secondary batteries.

[0014] An object of one embodiment of the present invention is to provide a positive electrode active material or composite oxide that can be used in a lithium ion secondary battery and that exhibits a suppressed decrease in discharge capacity during charge-discharge cycles. Another object is to provide a positive electrode active material or composite oxide that is less likely to lose its crystal structure even after repeated charge-discharge cycles. Another object is to provide a positive electrode active material or composite oxide that has a large discharge capacity. Another object is to provide a positive electrode active material or composite oxide that can be easily produced. Another object is to provide a positive electrode active material or composite oxide that has high thermal stability. Another object is to provide a secondary battery that is safe or highly reliable.

[0015] Another object of one embodiment of the present invention is to provide a power storage device or a manufacturing method thereof.

[0016] 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.

[0017] One aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, wherein the proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.025 and not greater than 0.215, the positive electrode active material having a surface layer portion and an interior portion, the concentration of the additive element in the surface layer portion being higher than the concentration of the additive element in the interior portion, and the additive element being one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

[0018] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, in which the proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and not more than 0.215, and the positive electrode active material has a surface layer portion and an interior portion, in which the average detected amount of the additive element in the surface layer portion is higher than the average detected amount of the additive element in the interior portion, and the additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

[0019] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.526 ± 0.1°, 2θ = 37.391 ± 0.1°, 2θ = 37.628 ± 0.1°, 2θ = 39.015 ± 0.1°, 2θ = 44.947 ± 0.1°, 2θ = 49.029 ± 0.1°, and 2θ = 58.857 ± 0.1°.

[0020] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, in which the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.351 ± 0.1°, 2θ = 37.412 ± 0.1°, 2θ = 38.974 ± 0.1°, 2θ = 44.865 ± 0.1°, 2θ = 48.864 ± 0.1°, and 2θ = 58.621 ± 0.1°.

[0021] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.7 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ=18.382±0.1°, 2θ=37.391±0.1°, and 2θ=44.886±0.1°.

[0022] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, the additive element being magnesium and fluorine, and the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), being greater than 0.175 and not more than 0.215, and the positive electrode active material having a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.516 ± 0.1°, 2θ = 37.391 ± 0.1°, 2θ = 37.586 ± 0.1°, 2θ = 38.995 ± 0.1°, 2θ = 44.947 ± 0.1°, 2θ = 49.039 ± 0.1°, and 2θ = 58.898 ± 0.1°.

[0023] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, the additive element being magnesium and fluorine, and the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), being greater than 0.175 and not more than 0.215, and the positive electrode active material having a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.608 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 37.792 ± 0.1°, 2θ = 39.015 ± 0.1°, 2θ = 44.999 ± 0.1°, 2θ = 49.101 ± 0.1°, and 2θ = 58.991 ± 0.1°.

[0024] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.403 ± 0.1°, 2θ = 37.412 ± 0.1°, 2θ = 38.985 ± 0.1°, 2θ = 44.875 ± 0.1°, 2θ = 48.916 ± 0.1°, and 2θ = 58.662 ± 0.1°.

[0025] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, in which the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.608 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 37.854 ± 0.1°, 2θ = 38.995 ± 0.1°, 2θ = 45.009 ± 0.1°, and 2θ = 59.073 ± 0.1°.

[0026] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.175 and is not more than 0.215, and the positive electrode active material has a voltage of 4.7 V (vs. Li / Li＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.413 ± 0.1°, 2θ = 36.774 ± 0.1°, 2θ = 37.412 ± 0.1°, and 2θ = 44.958 ± 0.1°.

[0027] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, in which the proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.075 and not more than 0.125, and the positive electrode active material has a surface layer portion and an interior portion, in which the average detected amount of the additive element in the surface layer portion is higher than the average detected amount of the additive element in the interior portion, and the additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

[0028] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.075 and is not more than 0.125, and the positive electrode active material has a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.434 ± 0.1°, 2θ = 37.401 ± 0.1°, 2θ = 39.005 ± 0.1°, 2θ = 44.896 ± 0.1°, 2θ = 48.957 ± 0.1°, and 2θ = 58.744 ± 0.1°.

[0029] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, in which the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.075 and is not more than 0.125, and the positive electrode active material has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.567 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 39.005 ± 0.1°, and 2θ = 44.978 ± 0.1°.

[0030] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, the additive element being magnesium and fluorine, and the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), being greater than 0.075 and not more than 0.125, and the positive electrode active material having a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.537 ± 0.1°, 2θ = 37.391 ± 0.1°, 2θ = 37.658 ± 0.1°, 2θ = 39.005 ± 0.1°, 2θ = 44.958 ± 0.1°, 2θ = 49.039 ± 0.1°, and 2θ = 58.898 ± 0.1°.

[0031] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, the additive element being magnesium and fluorine, and the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), being greater than 0.075 and not more than 0.125, and the positive electrode active material having a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.547 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 38.985 ± 0.1°, 2θ = 44.978 ± 0.1°, 2θ = 49.101 ± 0.1°, and 2θ = 59.073 ± 0.1°.

[0032] Another aspect of the present invention is a positive electrode active material having cobalt, nickel, oxygen, and an additive element, in which the proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.025 and not more than 0.075, and the positive electrode active material has a surface layer portion and an interior portion, in which the average detected amount of the additive element in the surface layer portion is higher than the average detected amount of the additive element in the interior portion, and the additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

[0033] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.025 and is not more than 0.075, and the positive electrode active material has a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.567 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 37.710 ± 0.1°, 2θ = 38.985 ± 0.1°, 2θ = 44.968 ± 0.1°, 2θ = 49.070 ± 0.1°, and 2θ = 58.980 ± 0.1°.

[0034] Another aspect of the present invention is a positive electrode active material containing cobalt, nickel, and oxygen, wherein the ratio of nickel to the sum of cobalt and nickel, Ni / (Co+Ni), is greater than 0.025 and is not more than 0.075, and the positive electrode active material has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using X-rays, the positive electrode active material has diffraction peaks at at least two of 2θ = 18.866 ± 0.1°, 2θ = 37.319 ± 0.1°, 2θ = 38.337 ± 0.1°, 2θ = 38.985 ± 0.1°, 2θ = 45.143 ± 0.1°, 2θ = 49.368 ± 0.1°, and 2θ = 59.515 ± 0.1°.

[0035] Another embodiment of the present invention is a secondary battery including the above positive electrode active material.

[0036] Another embodiment of the present invention is an electronic device including the above secondary battery.

[0037] Another embodiment of the present invention is a vehicle including the above secondary battery.

[0038] According to one embodiment of the present invention, a positive electrode active material or composite oxide that can be used in a lithium ion secondary battery and exhibits a suppressed decrease in discharge capacity during charge-discharge cycles can be provided. Alternatively, a positive electrode active material or composite oxide that is less likely to lose its crystal structure even after repeated charge-discharge cycles can be provided. Alternatively, a positive electrode active material or composite oxide that exhibits a large discharge capacity can be provided. Another object of the present invention is to provide a positive electrode active material or composite oxide that can be easily produced. Alternatively, a positive electrode active material or composite oxide that exhibits high thermal stability can be provided. Alternatively, a secondary battery that is safe or highly reliable can be provided.

[0039] According to one embodiment of the present invention, a power storage device or a manufacturing method thereof can be provided.

[0040] 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.

[0041] FIGS. 1A and 1B are cross-sectional views of a positive electrode active material. FIG. 2 is an example of a TEM image in which the crystal orientations are roughly consistent. FIG. 3A is an example of an STEM image in which the crystal orientations are roughly consistent. FIG. 3B is an FFT pattern of the region of the rock salt-type crystal RS, and FIG. 3C is an FFT pattern of the region of the layered rock salt-type crystal LRS. FIGS. 4A to 4C are diagrams illustrating a method for producing a positive electrode active material. FIGS. 5A and 5B are cross-sectional views of a positive electrode active material. FIG. 6 is a diagram illustrating the appearance of a secondary battery. FIGS. 7A to 7C are diagrams illustrating a method for producing a secondary battery. FIGS. 8A to 8H are diagrams illustrating an example of an electronic device. FIGS. 9A to 9D are diagrams illustrating an example of an electronic device. FIGS. 10A to 10C are diagrams illustrating an example of an electronic device. FIGS. 11A to 11C are diagrams illustrating an example of a vehicle. FIG. 12 is an XRD pattern of the positive electrode active material. FIGS. 13A and 13B are XRD patterns of the positive electrode active material. FIGS. 14A and 14B are XRD patterns of the positive electrode active material. FIG. 15 is an XRD pattern of the positive electrode active material. FIGS. 16A and 16B are XRD patterns of the positive electrode active material. FIGS. 17A and 17B are XRD patterns of the positive electrode active material. FIG. 18 is an XRD pattern of the positive electrode active material. FIGS. 19A and 19B are XRD patterns of the positive electrode active material. FIGS. 20A and 20B are XRD patterns of the positive electrode active material. FIG. 21 is an XRD pattern of the positive electrode active material. FIGS. 22A and 22B are XRD patterns of the positive electrode active material. FIGS. 23A and 23B are XRD patterns of the positive electrode active material. FIG. 24 is an XRD pattern of the positive electrode active material. FIGS. 25A and 25B are XRD patterns of the positive electrode active material. FIGS. 26A and 26B are XRD patterns of the positive electrode active material. FIG. 27 is an XRD pattern of the positive electrode active material. FIGS. 28A and 28B are XRD patterns of the positive electrode active material. FIGS. 29A and 29B are XRD patterns of the positive electrode active material. FIG. 30 is an XRD pattern of the positive electrode active material. FIGS. 31A and 31B are XRD patterns of the positive electrode active material. FIGS. 32A and 32B are XRD patterns of the positive electrode active material. FIG. 33 is an XRD pattern of the positive electrode active material. FIGS. 34A and 34B are XRD patterns of the positive electrode active material.Figures 35A and 35B are XRD patterns of the positive electrode active material. Figure 36 is an XRD pattern of the positive electrode active material. Figures 37A and 37B are XRD patterns of the positive electrode active material. Figures 38A and 38B are XRD patterns of the positive electrode active material.

[0042] 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.

[0043] 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 placing a superscript bar above the number. However, due to formatting constraints, in this specification, instead of placing a bar above the number, a minus sign (-) may be placed before the number. 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 {}. For ease of understanding the structure, trigonal crystals represented by the space group R-3m are generally expressed as a hexagonal composite hexagonal lattice. Unless otherwise specified, the space group R-3m will also be expressed as a composite hexagonal lattice in this specification. Miller indices may also be expressed as (hkil) rather than (hkl). Here, i is −(h+k). In this specification and the like, for the space group R-3m, crystal planes and the like are expressed as a composite hexagonal lattice unless otherwise specified.

[0044] In this specification and the like, the term "particle" is not limited to referring only to spherical particles (having a circular cross-sectional shape), and examples of the cross-sectional shape of individual particles include ellipsoids, rectangles, trapezoids, triangles, squares with rounded corners, and asymmetric shapes, and further, individual particles may have an irregular shape.

[0045] The theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated. For example, LiCoO ２ The theoretical capacity of LiNiO is 274 mAh / g. ２The theoretical capacity of LiMn is 274mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0046] The amount of lithium remaining in the positive electrode active material relative to the theoretical capacity can be determined by the x in the composition formula, for example, Li ｘ MO ２ In this specification, M represents a transition metal, and unless otherwise specified, M is the sum of cobalt and nickel. In the case of a positive electrode active material in a secondary battery, x = (theoretical capacity - charging capacity) / theoretical capacity. For example, LiMO ２ When a secondary battery using as a positive electrode active material is charged at 219.2 mAh / g, Li ０．２ MO ２ Or we can say x = 0.2. ｘ MO ２ In the above formula, "x" is small, for example, when 0.1<x≦0.24. The amount of lithium released from the positive electrode active material relative to the theoretical capacity is sometimes referred to as the depth of charge. In this specification and elsewhere, the depth of charge is expressed as 1−x.

[0047] When the lithium cobalt nickel oxide is approximately stoichiometric, LiMO ２ The occupancy rate of Li on the lithium site is x = 1. The secondary battery after discharge also has LiMO ２ In this case, x = 1. The end of discharge here refers to the state where the voltage is 2.5 V (lithium counter electrode) or less at a current of 100 mA / g, for example. In a lithium ion secondary battery, when the occupancy rate of lithium in the lithium site reaches x = 1 and no more lithium can enter, the voltage drops sharply. At this point, discharge can be said to be complete. Generally, LiMO ２ In a lithium ion secondary battery using LiMo, the discharge voltage drops sharply until it reaches 2.5 V, so the discharge is considered to have ended under the above conditions. Furthermore, when the positive electrode after discharge is analyzed by XRD etc., it is found that the positive electrode is a typical LiMo ２ It can be confirmed that the crystal structure is

[0048] Li ｘ MO ２It is preferable that the charge capacity and / or discharge capacity used to calculate x in the above should be measured under conditions that are free of or minimally affected by short circuits and / or decomposition of the electrolyte, etc. For example, data on a secondary battery that has experienced a sudden change in capacity that is considered to be due to a short circuit should not be used to calculate x.

[0049] 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."

[0050] Furthermore, if the anion arrangement is roughly close to cubic close packing, it can be considered cubic close packing. Cubic close packing of anions 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 need to be strictly cubic lattice. At the same time, because real crystals always have defects, analytical results do not necessarily have to be theoretical. For example, in FFT (fast Fourier transform) patterns such as electron diffraction patterns or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, a cubic close packing structure can be said to exist if the orientation from the theoretical positions is 5 degrees or less, or 2.5 degrees or less.

[0051] 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.

[0052] A cathode active material to which an additive element is added may be referred to as a composite oxide, a cathode material, a cathode ingredient, a cathode material for a secondary battery, or the like. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a compound. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a composition. In this specification and the like, the cathode active material of one embodiment of the present invention preferably includes a composite. The cathode active material refers to, for example, an aggregate of particles of lithium cobalt nickel oxide.

[0053] Furthermore, when describing the characteristics of individual particles of the positive electrode active material in the following embodiments, etc., it is not necessary for all particles to have that characteristic. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected particles of the positive electrode active material have that characteristic, it can be said that the effect of sufficiently improving the characteristics of the positive electrode active material and a secondary battery containing it is achieved.

[0054] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can suppress a decrease in charge / discharge capacity due to repeated charge / discharge.

[0055] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and / or discharging operations of the secondary battery, but may also lead to heat generation and fire. To achieve a safe secondary battery, it is preferable that the short circuit current be suppressed even at a high charging voltage. The positive electrode active material of one embodiment of the present invention suppresses the short circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high discharge capacity and safety can be obtained.

[0056] Unless otherwise specified, the materials (positive electrode active material, negative electrode active material, electrolyte, separator, etc.) contained in secondary batteries are described in their pre-degradation state. Note that a decrease in discharge capacity due to aging and burn-in treatments during secondary battery manufacturing is not considered to be degradation. For example, a lithium-ion secondary cell or lithium-ion secondary battery pack (hereinafter referred to as a lithium-ion secondary battery) can be said to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. For lithium-ion secondary batteries for portable devices, the rated capacity conforms to JIS C 8711:2019. For other lithium-ion secondary batteries, the rated capacity conforms to not only the above JIS standard but also various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.

[0057] In this specification and the like, the state of the materials of a secondary battery before deterioration is sometimes referred to as an initial product or initial state, and the state after deterioration (the state when the secondary battery has a discharge capacity of less than 97% of the rated capacity) is sometimes referred to as a product in use or in use state, or a used product or used state.

[0058] In this specification, ignition in a nail penetration test refers to the observation of a flame outside the exterior body, or the occurrence of thermal runaway in a secondary battery. For example, ignition can also be considered to have occurred if, after the completion of the nail penetration test, thermal decomposition products of the positive electrode and / or negative electrode are observed at a location 2 cm or more away from the nail penetration point.

[0059] For example, the positive electrode active material is layered rock salt type LiMO. ２ When using LiMO, the O / M (atomic ratio) is theoretically 2. On the other hand, due to thermal runaway, ２ When oxygen is released from the nail, the O / M (atomic ratio) decreases. Therefore, for example, if the O / M (atomic ratio) is less than 1.3 in EDX analysis at a location 2 cm or more away from the nail penetration point after the nail penetration test is completed, it can be said that thermal runaway has occurred, i.e., a fire has occurred.

[0060] The pyrolyzed products of the positive electrode and / or negative electrode also include, for example, aluminum oxide formed by oxidizing aluminum from the positive electrode current collector, and copper oxide formed by oxidizing copper from the negative electrode current collector.

[0061] On the other hand, even if sparks and / or smoke are observed, it is not considered to be a fire unless the fire spreads, i.e., unless the entire secondary battery goes into thermal runaway. For example, if a nail penetration test is performed on a secondary battery and no fire occurs, it can be said to be a non-fire-prone secondary battery.

[0062] Embodiment 1 In this embodiment, a positive electrode active material 100 of one embodiment of the present invention will be described with reference to FIGS. 1A and 1B.

[0063] 1A and 1B are cross-sectional views of a cathode active material 100 according to one embodiment of the present invention. As shown in FIG. 1A, the cathode active material 100 has a surface layer 100a and an interior 100b. In these figures, the boundary between the surface layer 100a and the interior 100b is indicated by a dashed line. In FIG. 1B, a portion of a grain boundary 101 is indicated by a dashed-dotted line. In the figures, (001) indicates the (001) plane of lithium cobalt nickel oxide. LiCo １−ｙ Ni ｙ O ２ belongs to the space group R-3m.

[0064] The positive electrode active material 100 preferably has high crystallinity. The positive electrode active material 100 is preferably a single particle (also referred to as a primary particle) rather than a secondary particle. The particles of the positive electrode active material 100 are more preferably single crystal.

[0065] In this specification, the surface layer 100a of the positive electrode active material 100 refers to, for example, a region extending from the surface toward the interior within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm perpendicular or approximately perpendicular from the surface toward the interior. Note that "approximately perpendicular" refers to an angle of 80° to 100°. Surfaces resulting from cracks and / or fissures may also be referred to as the surface. The surface layer 100a is synonymous with the near-surface, near-surface region, or shell.

[0066] The region of the positive electrode active material deeper than the surface layer 100a is referred to as the inner portion 100b, which is synonymous with the inner region or core.

[0067] The surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer portion 100a and the inner portion 100b. ２ O ３ This does not include metal oxides having no lithium sites that can contribute to charging and discharging, such as those having metal oxides attached thereto, carbonates chemically adsorbed after the preparation of the positive electrode active material, hydroxyl groups, etc. Note that the attached metal oxides refer to metal oxides whose crystal structure does not match that of the interior 100b, for example.

[0068] It also does not include the electrolyte, organic solvent, binder, conductive material, or compounds derived from these that are attached to the positive electrode active material 100.

[0069] The crystal grain boundary 101 refers to, for example, a portion where particles of the positive electrode active material 100 are adhered to each other, a portion where the crystal orientation changes within the positive electrode active material 100, i.e., a portion where the repetition of bright and dark lines in an STEM image or the like becomes discontinuous, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc. The crystal defect refers to a defect that can be observed in a cross-sectional TEM (transmission electron microscope), a cross-sectional STEM image, etc., that is, a structure in which atoms have entered between lattices, a cavity, etc. The crystal grain boundary 101 can be said to be one type of planar defect. The vicinity of the crystal grain boundary 101 refers to a region within 10 nm of the crystal grain boundary 101.

[0070] [Main Component] The positive electrode active material of a lithium-ion secondary battery must contain a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted and removed. The positive electrode active material 100 of one embodiment of the present invention preferably contains cobalt as the main component of the transition metal M responsible for the oxidation and reduction reaction. In this specification, the term "main component of the transition metal M" refers to the transition metal M with the highest atomic ratio. When there are multiple transition metals M with the highest atomic ratio, all of them can be considered as the main component. Furthermore, the positive electrode active material 100 preferably contains nickel in addition to cobalt. The presence of nickel allows for the positive electrode active material to have high thermal stability at temperatures above room temperature, for example, at 45°C or higher, more preferably at 65°C or higher.

[0071] The positive electrode active material 100 of one embodiment of the present invention contains lithium, cobalt, nickel, and oxygen. It is preferable that the positive electrode active material 100 further contains an additive element. Alternatively, the positive electrode active material 100 may contain lithium cobalt nickel oxide (LiCo １−ｙ Ni ｙ O ２ However, the positive electrode active material 100 of one embodiment of the present invention may have any crystal structure described later. Therefore, the composition of lithium cobalt nickel oxide is not strictly limited to Li:(Co+Ni):O=1:1:2.

[0072] In addition, the ratio of nickel to the sum of cobalt and nickel is Ni / (Co+Ni), that is, LiCo １−ｙ Ni ｙ O ２ In the formula, y is preferably greater than 0 and less than 0.5, more preferably 0.1 or greater and 0.3 or less, and even more preferably greater than 0.025 and 0.215 or less.

[0073] When Ni / (Co+Ni) is more than 0.025 and not more than 0.215, the alloy is heated at a high voltage, for example, 4.7 V (vs. Li / Li ＋ ) when charging ２ Therefore, even if charging and discharging are repeated, MO ２ It is believed that this makes it difficult for layers to shift, and improves the stability of the crystal structure.

[0074] LiCo １−ｙ Ni ｙ O ２ In the formula, y being 0.1 or more and 0.3 or less includes, for example, cases where Co:Ni=90:10 (atomic ratio), Co:Ni=80:20 (atomic ratio), or Co:Ni=70:30 (atomic ratio).

[0075] When the positive electrode active material 100 has an additional element, the additional element A can be one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

[0076] If the amount of the additive element A is too small, it will not be able to sufficiently chemically stabilize the positive electrode active material 100, but if the amount is too large, there is a concern that it will have an adverse effect on the charge / discharge capacity, etc. Therefore, among the additive elements A, fluorine, which becomes an anion, will be represented by F, and the other elements will be represented by A, and the composition of the positive electrode active material 100 will be represented by LiCo １−ｙ−ｚ Ni ｙ A ｚ O ２ F ｎ In this case, z+n is preferably greater than 0 and equal to or less than 0.1.

[0077] The additive element is preferably dissolved in the positive electrode active material 100. Therefore, for example, when performing a line analysis using STEM-EDX, the depth at which the amount of the additive element detected increases is preferably located deeper than the depth at which the amount of the transition metal M detected increases, i.e., closer to the interior of the positive electrode active material 100.

[0078] In this specification and the like, the depth at which the amount of a certain element detected increases in STEM-EDX line analysis refers to the depth at which measurement values ​​that can be determined not to be noise in terms of intensity, spatial resolution, etc. are continuously obtained.

[0079] These added elements further stabilize the crystal structure of the positive electrode active material 100. In this specification and the like, the added elements have the same meaning as a mixture or a part of a raw material.

[0080] The additive element does not necessarily have to include magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, or gallium.

[0081] [Crystalline Structure] The positive electrode active material 100 according to one embodiment of the present invention is in a discharged state, i.e., Li ｘ MO ２ In the case where x = 1 in the formula (I), it is preferable that the composite oxide has a layered rock-salt type crystal structure belonging to the space group R-3m. The layered rock-salt type composite oxide has a high discharge capacity, has two-dimensional lithium ion diffusion paths, is suitable for lithium ion insertion / extraction reactions, and is excellent as a positive electrode active material for secondary batteries. Therefore, it is particularly preferable that the inner portion 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock-salt type crystal structure.

[0082] On the other hand, the surface layer portion 100a of the cathode active material 100 according to one embodiment of the present invention preferably has a function of reinforcing the inner portion 100b so that the layered structure of the transition metal M and oxygen octahedra is not destroyed even when lithium is removed from the cathode active material 100 upon charging. Alternatively, the surface layer portion 100a preferably functions as a barrier film for the cathode active material 100. Alternatively, the surface layer portion 100a, which is the outer periphery of the cathode active material 100, preferably reinforces the cathode active material 100. Here, "reinforcement" refers to suppressing structural changes in the surface layer portion 100a and inner portion 100b of the cathode active material 100, such as oxygen desorption and / or shifting of the layered structure of the transition metal M and oxygen octahedra. And / or suppressing oxidative decomposition of the electrolyte on the surface of the cathode active material 100.

[0083] Therefore, the surface layer portion 100a preferably has a different crystal structure from the interior portion 100b. Furthermore, the surface layer portion 100a preferably has a composition and crystal structure that are more stable at room temperature (25°C) than the interior portion 100b. For example, at least a portion of the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention preferably has a rock salt crystal structure. Alternatively, the surface layer portion 100a preferably has both a layered rock salt crystal structure and a rock salt crystal structure. Alternatively, the surface layer portion 100a preferably has characteristics of both a layered rock salt crystal structure and a rock salt crystal structure.

[0084] The surface layer 100a is the region from which lithium ions are first released during charging, and is a region where the lithium concentration is likely to be lower than that of the interior 100b. In addition, it can be said that the atoms on the surface of the particles of the positive electrode active material 100 in the surface layer 100a are in a state where some of the bonds are broken. Therefore, the surface layer 100a is likely to become unstable, and is a region where deterioration of the crystal structure is likely to begin. For example, if the crystal structure of the layered structure consisting of transition metal M and oxygen octahedra in the surface layer 100a is displaced, this effect will be transmitted to the interior 100b, causing the layered crystal structure in the interior 100b to also be displaced, which is thought to lead to deterioration of the crystal structure of the entire positive electrode active material 100. On the other hand, if the surface layer 100a can be sufficiently stabilized, Li ｘ MO ２Even when x in the inner portion 100b is small, the layer structure consisting of the transition metal M and oxygen octahedra in the inner portion 100b can be made hard to break. Furthermore, it is possible to suppress the displacement of the layer consisting of the transition metal M and oxygen octahedra in the inner portion 100b. ｘ MO ２ When x is small, it means, for example, when x is 0.24 or less.

[0085] [Distribution of Additive Elements] To ensure that the surface layer portion 100a has a chemically stable composition and crystalline structure, the surface layer portion 100a preferably contains an additive element, and more preferably contains multiple additive elements. Furthermore, the surface layer portion 100a preferably has a higher average detected amount of one or more selected additive elements than the interior portion 100b. Furthermore, it is preferable that one or more selected additive elements contained in the positive electrode active material 100 have a concentration gradient. Furthermore, it is more preferable that the distribution of the additive elements in the positive electrode active material 100 differs depending on the additive element. For example, it is more preferable that the depth of the peak of the detected amount in the surface layer portion from the surface or the reference point in EDX-ray analysis described below differs depending on the additive element. Here, the peak of the detected amount refers to the maximum value of the detected amount in the surface layer portion 100a or within 50 nm from the surface. The detected amount refers to, for example, the count in EDX-ray analysis.

[0086] Preferably, the surface layer portion 100a and the inner portion 100b have the same main component (here, cobalt) and are connected to each other. This configuration allows the surface layer portion 100a to protect the inner portion 100b, providing excellent protection against internal short circuits when used in a secondary battery. For example, the structure of the positive electrode active material having the surface layer portion 100a can be considered to be non- or non-flammable even when a nail or the like is pierced from the outside of the secondary battery.

[0087] For example, by increasing the average detected amount of one selected from the additive elements, such as fluorine, in the surface layer portion 100a compared to the average detected amount in the inner portion 100b, excessive reaction between the positive electrode active material 100 and the electrolyte can be suppressed. Therefore, when used in a secondary battery, it is expected that safety against internal short circuits and the like in the secondary battery can be improved. In addition, corrosion resistance to hydrofluoric acid can be effectively improved.

[0088] Furthermore, it is more preferable that the average detected amount of one or more selected from the additive elements in the surface layer portion 100a be higher than the average in the interior portion 100b, thereby changing the conductivity of the surface of the positive electrode active material 100. For example, it is preferable that the powder resistance of the positive electrode active material 100 be increased. By making the positive electrode active material 100 have high powder resistance, it can be expected that the safety of the secondary battery against internal short circuits and the like will be improved when used in the secondary battery.

[0089] [Difference in Distribution of Added Element Depending on Crystal Plane] However, the added element does not necessarily have to have the same concentration gradient or distribution throughout the entire surface layer 100a of the positive electrode active material 100. Arrows X1-X2 in FIG. 1A show an example of the depth direction of a crystal plane other than the (001) plane of lithium cobalt nickel oxide in the positive electrode active material 100 of one embodiment of the present invention. Arrows Y1-Y2 also show an example of the depth direction of the (001) plane.

[0090] The surface parallel to (001) of the positive electrode active material 100 may have a different distribution of the additive element from the other surfaces. For example, the surface parallel to (001) indicated by arrows Y1-Y2 and its surface layer portion 100a may have a lower average detected amount of one or more additive elements compared to the surfaces other than the (001)-oriented surface indicated by arrows X1-X2. Alternatively, the surface parallel to (001) and its surface layer portion 100a may have a concentration of one or more additive elements selected from the additive elements that is less than 1 atomic %. Alternatively, the surface parallel to (001) and its surface layer portion 100a may have a peak of the detected amount of one or more additive elements that is shallower from the surface compared to the surfaces other than the (001)-oriented surface.

[0091] In the layered rock salt type crystal structure of R-3m, cations are arranged parallel to the (001) plane. ２The structure is composed of alternately stacked layers and lithium layers parallel to the (001) plane, and the diffusion path of lithium ions is also parallel to the (001) plane.

[0092] MO ２ Since the layer is relatively stable, it is more stable if the surface of the positive electrode active material 100 has a (001) orientation. The main diffusion path of lithium ions during charge and discharge is not exposed on the (001) plane.

[0093] On the other hand, the diffusion path of lithium ions is exposed on the surface other than the (001) orientation. Therefore, the surface and the surface layer 100a other than the (001) orientation are important regions for maintaining the diffusion path of lithium ions, and at the same time, they are regions from which lithium ions are first desorbed and are therefore prone to instability. Therefore, reinforcing the surface and the surface layer 100a other than the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.

[0094] High purity LiCo, which will be described in a later embodiment １−ｙ Ni ｙ O ２ In the manufacturing method of mixing the additive element after manufacturing the silicon nitride film and then heating the mixture, the additive element spreads mainly through the diffusion path of lithium ions, and therefore the distribution of the additive element in the surface other than the (001) orientation and in the surface layer 100a thereof can be easily controlled to a preferred range.

[0095] Furthermore, arrows Z1-Z2 are shown in FIG. 1B as an example of the depth direction of the (001) plane generated by the positive electrode active material 100 slipping parallel to the (001) plane. Arrows Z1-Z2 are similar to the plane parallel to (001) indicated by arrows Y1-Y2. That is, the average detected amount of one or more selected from the additive elements may be lower than that of a surface other than the (001)-oriented surface. Alternatively, the concentration of one or more selected from the additive elements may be less than 1 atomic %.

[0096] When a plurality of additive elements are contained as described above, the effects of the respective additive elements are synergistic and can contribute to further stabilization of the surface layer portion 100a.

[0097] However, if the surface layer 100a is occupied only by a compound of the added element and oxygen, it is not preferable because it makes it difficult to insert and extract lithium. Therefore, the surface layer 100a must contain at least cobalt or nickel, and also contain lithium in a discharged state, and have a path for the insertion and extraction of lithium.

[0098] In order to ensure sufficient paths for lithium insertion and desorption, it is preferable that the sum of the detected amounts of cobalt and nickel in the surface layer portion 100a is higher than that of the additional element.

[0099] [Approximate Matching] It is preferable that the crystal structure continuously changes from the interior 100b toward the surface due to the concentration gradient of the added element as described above. Alternatively, it is preferable that the crystal orientations of the surface layer 100a and the interior 100b are approximately the same.

[0100] For example, it is preferable that the crystal structure continuously change from the interior 100b of the layered rock salt type toward the surface and surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type.Alternatively, it is preferable that the orientation of the surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type, and the interior 100b of the layered rock salt type are approximately the same.

[0101] In this specification, the layered rock-salt crystal structure of a composite oxide containing lithium and a transition metal M and belonging to the space group R-3m refers to a crystal structure having a rock-salt ion arrangement in which cations and anions are alternately arranged, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Strictly speaking, the layered rock-salt crystal structure may have a distorted rock-salt crystal lattice.

[0102] The rock salt crystal structure refers to a cubic crystal structure, such as that of the space group Fm-3m, in which cations and anions are arranged alternately. Note that cation or anion defects may occur.

[0103] The fact that it has both the characteristics of the layered rock salt type and the rock salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, and the like.

[0104] In the rock salt type, there is no distinction in the cation sites, but in the layered rock salt type, there are two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by a transition metal M. The layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt type and the layered rock salt type. Among the bright spots in the electron diffraction pattern corresponding to the crystal planes that form this two-dimensional plane, when the central spot (transmitted spot) is set as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the rock salt type in an ideal state, and, for example, the (003) plane in the layered rock salt type. For example, rock salt type MgO and layered rock salt type LiCoO ２ When comparing the electron diffraction patterns of LiCoO ２ The distance between the bright spots on the (003) plane of LiCoO is observed to be about half the distance between the bright spots on the (111) plane of MgO. ２ In the case of a material with these two phases, the electron diffraction pattern shows a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to both the rock salt type and the layered rock salt type have strong brightness, while bright spots occurring only in the layered rock salt type have weak brightness.

[0105] Furthermore, when a layered rock-salt crystal structure is observed from a direction perpendicular to the c-axis in cross-sectional STEM images, layers observed with high brightness and layers observed with low brightness are observed alternately. This characteristic is not observed in the rock-salt structure, as there is no distinction in the cation sites. In the case of a crystal structure that has the characteristics of both the rock-salt and layered rock-salt structures, when observed from a specific crystal orientation, layers observed with high brightness and layers observed with low brightness are observed alternately in cross-sectional STEM images, and furthermore, metals with atomic numbers higher than that of lithium are present in some of the low-brightness layers, i.e., the lithium layers.

[0106] Layered rock salt crystals and the anions in rock salt crystals form a cubic close-packed structure (face-centered cubic lattice structure). Therefore, when layered rock salt crystals and rock salt crystals come into contact, there are crystal faces where the cubic close-packed structure formed by the anions is oriented in the same direction.

[0107] Alternatively, it can be explained as follows: Anions on the (111) plane of a cubic crystal structure have a triangular lattice. Layered rock salt structures have a space group of R-3m and a rhombohedral structure, but are generally expressed as a compound hexagonal lattice to make the structure easier to understand, and the (0001) plane of the layered rock salt structure has a hexagonal lattice. The triangular lattice on the cubic (111) plane has the same atomic arrangement as the hexagonal lattice on the (0001) plane of the layered rock salt structure. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structures.

[0108] However, since the space group of the layered rock salt type crystal is R-3m, which is different from the space group Fm-3m (space group of general rock salt type crystal) of the rock salt type crystal, the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt type crystal and the rock salt type crystal. In this specification, when the orientations of the cubic close-packed structures formed by anions in the layered rock salt type crystal and the rock salt type crystal are aligned, it may be said that the crystal orientations are approximately the same. In addition, having a three-dimensional structural similarity such that the crystal orientations are approximately the same, or having the same crystallographic orientation, is called topotaxis.

[0109] 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 (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron beam diffraction patterns, and the like. The determination can also be made based on the FFT pattern of a TEM image, the FFT pattern of a STEM image, etc. Furthermore, XRD (X-ray diffraction), neutron diffraction, etc. can also be used as materials for the determination.

[0110] 2 shows an example of a TEM image in which the orientations of the layered rock salt crystals LRS and RS are roughly the same. Images reflecting the crystal structure can be obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.

[0111] For example, in high-resolution TEM images, contrast originating from crystal planes can be observed. When an electron beam is incident perpendicularly to the c-axis of a layered rock-salt type composite hexagonal lattice, for example, due to the diffraction and interference of the electron beam, the contrast originating from the (0003) plane is observed as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, a repetition of bright and dark lines is observed in the TEM image, and the bright lines (for example, the L shown in Figure 2) ＲＳ and L ＬＲＳ When the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are roughly aligned, i.e., the crystal orientations are roughly aligned. Similarly, when the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are roughly aligned.

[0112] Furthermore, in HAADF-STEM images, contrast proportional to atomic number is obtained, and elements with higher atomic numbers are observed brighter. For example, in the case of layered rock-salt lithium cobalt nickel oxide belonging to the space group R-3m, the atomic numbers of cobalt (atomic number 27) and nickel (atomic number 28) are large, so the electron beam is strongly scattered at the positions of the cobalt and nickel atoms, and the arrangement of the cobalt and nickel atoms is observed as a bright line or an arrangement of highly bright dots. Therefore, when lithium cobalt nickel oxide with a layered rock-salt crystal structure is observed perpendicular to the c-axis, the arrangement of the cobalt and nickel atoms is observed perpendicular to the c-axis as a bright line or an arrangement of highly bright dots, and the arrangement of lithium atoms and oxygen atoms is observed as a dark line or a low-brightness region. The same is true when lithium cobalt nickel oxide contains fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.

[0113] Therefore, in an HAADF-STEM image, when repetitions of bright and dark lines are observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the atomic arrangements are roughly consistent, i.e., the crystal orientations are roughly consistent. Similarly, when the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can also be determined that the crystal orientations are roughly consistent.

[0114] 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.

[0115] Figure 3A shows an example of an STEM image in which the orientations of the layered rock-salt crystal LRS and the rock-salt crystal RS are roughly the same. Figure 3B shows the FFT pattern of the region of the rock-salt crystal RS, and Figure 3C shows the FFT pattern of the region of the layered rock-salt crystal LRS. The left side of Figures 3B and 3C shows the composition, JCPDS card number, and the d-value and angle calculated from these. The right side shows the measured values. The spot marked with O is the zeroth-order diffraction.

[0116] The spot marked A in Figure 3B is derived from the 11-1 reflection of the cubic crystal. The spot marked A in Figure 3C is derived from the 0003 reflection of the layered rock salt type. From Figures 3B and 3C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 3B is roughly parallel to the line passing through AO in Figure 3C. Here, "roughly coincident" and "roughly parallel" mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0117] In this way, in the FFT pattern and the electron beam diffraction pattern, when the orientations of the layered rock salt type crystal and the rock salt type crystal are roughly the same, the <0003> orientation of the layered rock salt type and the <11-1> orientation of the rock salt type may roughly coincide. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. A reciprocal lattice point being spot-like and not continuous with other reciprocal lattice points means high crystallinity.

[0118] Furthermore, as described above, when the orientation of the cubic 11-1 reflection and the orientation of the layered rock salt 0003 reflection are approximately the same, depending on the incident orientation of the electron beam, spots not originating from the layered rock salt 0003 reflection may be observed in a reciprocal lattice space different from the orientation of the layered rock salt 0003 reflection. For example, the spot marked B in Figure 3C is originating from the layered rock salt 10-14 reflection. This spot may be observed at an angle of 52° to 56° (i.e., ∠AOB is 52° to 56°) from the orientation of the reciprocal lattice point originating from the layered rock salt 0003 reflection (A in Figure 3C), and at a point where d is 0.19 nm to 0.21 nm. Note that this index is merely an example and does not necessarily have to be identical. For example, reciprocal lattice points equivalent to 0003 and 1014 may also be used.

[0119] Similarly, spots not originating from the 11-1 reflection of the cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of the cubic crystal is observed. For example, the spot marked B in FIG. 3B originates from the 200 reflection of the cubic crystal. This is because a diffraction spot may be observed at an angle of 54° or more and 56° or less (i.e., ∠AOB is 54° or more and 56° or less) from the orientation of the reflection (A in FIG. 3B) originating from the 11-1 reflection of the cubic crystal. Note that this index is merely an example and does not necessarily have to match this. For example, a reciprocal lattice point equivalent to 11-1 and 200 may also be used.

[0120] It is known that layered rock-salt type positive electrode active materials, including lithium cobalt nickel oxide, tend to have the (0003) plane and its equivalents, as well as the (10-14) plane and its equivalents, as crystal planes. Therefore, by carefully observing the shape of the positive electrode active material using an SEM or the like, it is possible to thin-section the observation sample using an FIB or the like so that the electron beam is [1-210] incident in a TEM or the like, making it easier to observe the (0003) plane. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock-salt type so that the (0003) plane can be easily observed.

[0121] [Grain Boundary] When the positive electrode active material 100 of one embodiment of the present invention contains an additional element, it is more preferable that at least a part of the additional element is unevenly distributed in and near the grain boundary 101 in addition to the distribution described above.

[0122] In this specification and the like, uneven distribution refers to the concentration of an element in a certain region being different from that in other regions, and is synonymous with segregation, precipitation, non-uniformity, bias, or the mixture of areas with high concentration and areas with low concentration.

[0123] For example, it is preferable that the average detected amount of the additive element at and near the grain boundaries 101 of the positive electrode active material 100 is higher than the average detected amount at and near the grain boundaries 101 in the interior 100b.

[0124] The grain boundaries 101 are one type of planar defect. Therefore, like the grain surfaces, they tend to become unstable and are prone to change in the crystal structure. Therefore, if the concentration of the added element at and near the grain boundaries 101 is high, the change in the crystal structure can be more effectively suppressed.

[0125] [Li ｘ MO ２ The positive electrode active material 100 according to one embodiment of the present invention has a crystal structure in a charged state, that is, in a state where Li ｘ MO ２ It is preferable that the crystal structure when x is small is as follows:

[0126] The positive electrode active material 100 having Ni / (Co+Ni) of more than 0.175 and not more than 0.215, typically 0.2, has a resistance of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-nm NMR spectroscopy, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.526 ± 0.1 °, 2θ = 37.391 ± 0.1 °, 2θ = 37.628 ± 0.1 °, 2θ = 39.015 ± 0.1 °, 2θ = 44.947 ± 0.1 °, 2θ = 49.029 ± 0.1 °, and 2θ = 58.857 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.813 ± 0.02 (Å), c = 14.33 ± 0.02 (Å), and a unit cell volume of 98.17 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.813 ± 0.01 (Å), c = 14.33 ± 0.01 (Å), and the unit cell volume is 98.17 ± 1.4 (Å). ３ ) is more preferable. The crystallite size is preferably 100 nm or more, and more preferably 150 nm or more. In this specification, A±B means (A−B) or more and (A+B) or less.

[0127] In addition, the positive electrode active material 100 in which Ni / (Co+Ni) is greater than 0.175 and not more than 0.215, typically 0.2, has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １When analyzed by powder X-ray diffraction using 1000-1000 Hz, it preferably has diffraction peaks at least at 2θ=18.351±0.1°, 2θ=37.412±0.1°, 2θ=38.974±0.1°, 2θ=44.865±0.1°, 2θ=48.864±0.1°, and 2θ=58.621±0.1°. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a=2.808±0.02 (Å), c=14.43±0.02 (Å), and a unit cell volume of 98.55±1.6 (Å). ３ The lattice constants are preferably a = 2.808 ± 0.01 (Å), c = 14.43 ± 0.01 (Å), and the unit cell volume is 98.55 ± 1.4 (Å). ３ The crystallite size is preferably 70 nm or more, and more preferably 90 nm or more.

[0128] In addition, the positive electrode active material 100 in which Ni / (Co+Ni) is greater than 0.175 and not greater than 0.215, typically 0.2, has a voltage of 4.7 V (vs. Li / Li ＋ When analyzed by powder X-ray diffraction using CuKα1 radiation in a charged state, it preferably has diffraction peaks at at least two of 2θ=18.382±0.1°, 2θ=37.391±0.1°, and 2θ=44.886±0.1°. It also preferably has a crystalline structure belonging to the space group R-3m, with lattice constants a=2.808±0.02 (Å), c=14.40±0.02 (Å), and a unit cell volume of 98.32±1.6 (Å). ３ The lattice constants are preferably a = 2.808 ± 0.01 (Å), c = 14.40 ± 0.01 (Å), and the unit cell volume is 98.32 ± 1.4 (Å). ３ The crystallite size is preferably 80 nm or more, and more preferably 100 nm or more.

[0129] In addition, the positive electrode active material 100 having Ni / (Co+Ni) of more than 0.175 and not more than 0.215, typically 0.2, and containing magnesium as an additive element at 0.5 atomic % of the transition metal M and fluorine as an additive element at 1.5 atomic % of the transition metal M, has a low resistance of 4.5 V (vs. Li / Li ＋) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-nm IR, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.516 ± 0.1 °, 2θ = 37.391 ± 0.1 °, 2θ = 37.586 ± 0.1 °, 2θ = 38.995 ± 0.1 °, 2θ = 44.947 ± 0.1 °, 2θ = 49.039 ± 0.1 °, and 2θ = 58.898 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.812 ± 0.02 (Å), c = 14.32 ± 0.02 (Å), and a unit cell volume of 98.02 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.812 ± 0.01 (Å), c = 14.32 ± 0.01 (Å), and the unit cell volume is preferably 98.02 ± 1.4 (Å). ３ The crystallite size is preferably 100 nm or more, and more preferably 150 nm or more.

[0130] In addition, the positive electrode active material 100 having Ni / (Co+Ni) of more than 0.175 and not more than 0.215, typically 0.2, and containing magnesium as an additive element at 0.5 atomic % of the transition metal M and fluorine as an additive element at 1.5 atomic % of the transition metal M, has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-1000 Hz, it preferably has diffraction peaks at at least two of 2θ = 18.608 ± 0.1°, 2θ = 37.381 ± 0.1°, 2θ = 37.792 ± 0.1°, 2θ = 39.015 ± 0.1°, 2θ = 44.999 ± 0.1°, 2θ = 49.101 ± 0.1°, and 2θ = 58.991 ± 0.1°. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.812 ± 0.02 (Å), c = 14.25 ± 0.02 (Å), and a unit cell volume of 97.61 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.812 ± 0.01 (Å), c = 14.25 ± 0.01 (Å), and the unit cell volume is 97.61 ± 1.4 (Å). ３The crystallite size is preferably 50 nm or more, and more preferably 70 nm or more.

[0131] The positive electrode active material 100, in which Ni / (Co+Ni) is greater than 0.175 and not greater than 0.215, typically 0.2, and which is prepared by annealing after synthesis of lithium cobalt nickel oxide, has a voltage of 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-1200 Hz, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.403 ± 0.1 °, 2θ = 37.412 ± 0.1 °, 2θ = 38.985 ± 0.1 °, 2θ = 44.875 ± 0.1 °, 2θ = 48.916 ± 0.1 °, and 2θ = 58.662 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.809 ± 0.02 (Å), c = 14.39 ± 0.02 (Å), and a unit cell volume of 98.35 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.809 ± 0.01 (Å), c = 14.39 ± 0.01 (Å), and the unit cell volume is preferably 98.35 ± 1.4 (Å). ３ The crystallite size is preferably 100 nm or more, more preferably 130 nm or more.

[0132] In addition, the Ni / (Co+Ni) is more than 0.175 and not more than 0.215, typically 0.2, and the positive electrode active material 100 produced by annealing after synthesis of lithium cobalt nickel oxide has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-1000 Hz, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.608 ± 0.1 °, 2θ = 37.381 ± 0.1 °, 2θ = 37.854 ± 0.1 °, 2θ = 38.995 ± 0.1 °, 2θ = 45.009 ± 0.1 °, and 2θ = 59.073 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.812 ± 0.02 (Å), c = 14.24 ± 0.02 (Å), and a unit cell volume of 97.52 ± 1.6 (Å).３ The lattice constants are preferably a = 2.812 ± 0.01 (Å), c = 14.24 ± 0.01 (Å), and the unit cell volume is 97.52 ± 1.4 (Å). ３ The crystallite size is preferably 50 nm or more, more preferably 75 nm or more.

[0133] In addition, the Ni / (Co+Ni) is more than 0.175 and not more than 0.215, typically 0.2, and the positive electrode active material 100 produced by annealing after synthesis of lithium cobalt nickel oxide has a voltage of 4.7 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-1000 Hz, it preferably has diffraction peaks at at least two of 2θ=18.413±0.1°, 2θ=36.774±0.1°, 2θ=37.412±0.1°, and 2θ=44.958±0.1°. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a=2.809±0.02 (Å), c=14.36±0.02 (Å), and a unit cell volume of 98.13±1.6 (Å). ３ The lattice constants are preferably a = 2.809 ± 0.01 (Å), c = 14.36 ± 0.01 (Å), and the unit cell volume is 98.13 ± 1.4 (Å). ３ The crystallite size is preferably 50 nm or more, more preferably 75 nm or more.

[0134] The positive electrode active material 100 having Ni / (Co+Ni) of more than 0.075 and not more than 0.125, typically 0.1, has a low resistance at 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １When analyzed by powder X-ray diffraction using 1000-nm NMR spectroscopy, it preferably has diffraction peaks at least at two of the following angles: 2θ = 18.434 ± 0.1 °, 2θ = 37.401 ± 0.1 °, 2θ = 39.005 ± 0.1 °, 2θ = 44.896 ± 0.1 °, 2θ = 48.957 ± 0.1 °, and 2θ = 58.744 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.810 ± 0.02 (Å), c = 14.39 ± 0.02 (Å), and a unit cell volume of 98.42 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.810 ± 0.01 (Å), c = 14.39 ± 0.01 (Å), and the unit cell volume is 98.42 ± 1.4 (Å). ３ The crystallite size is preferably 100 nm or more, more preferably 130 nm or more.

[0135] In addition, the positive electrode active material 100 in which Ni / (Co+Ni) is greater than 0.075 and is not greater than 0.125, typically 0.1, has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-1000 Hz, it preferably has diffraction peaks at at least two of 2θ=18.567±0.1°, 2θ=37.381±0.1°, 2θ=39.005±0.1°, and 2θ=44.978±0.1°. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a=2.811±0.02 (Å), c=14.26±0.02 (Å), and a unit cell volume of 97.56±1.6 (Å). ３ The lattice constants are preferably a = 2.811 ± 0.01 (Å), c = 14.26 ± 0.01 (Å), and the unit cell volume is 97.56 ± 1.4 (Å). ３ The crystallite size is preferably 30 nm or more, and more preferably 45 nm or more.

[0136] In addition, a positive electrode active material 100 having Ni / (Co+Ni) exceeding 0.075 and not exceeding 0.125, typically 0.1, and containing magnesium as an additive element at 0.5 atomic % of the transition metal M and fluorine as an additive element at 1.5 atomic % of the transition metal M, has a low resistance at 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-nm NMR spectroscopy, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.537 ± 0.1 °, 2θ = 37.391 ± 0.1 °, 2θ = 37.658 ± 0.1 °, 2θ = 39.005 ± 0.1 °, 2θ = 44.958 ± 0.1 °, 2θ = 49.039 ± 0.1 °, and 2θ = 58.898 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.812 ± 0.02 (Å), c = 14.31 ± 0.02 (Å), and a unit cell volume of 98.02 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.812 ± 0.01 (Å), c = 14.31 ± 0.01 (Å), and the unit cell volume is 98.02 ± 1.4 (Å). ３ The crystallite size is preferably 100 nm or more, and more preferably 150 nm or more.

[0137] In addition, a positive electrode active material 100 having Ni / (Co+Ni) exceeding 0.075 and not exceeding 0.125, typically 0.1, and containing magnesium as an additive element at 0.5 atomic % of the transition metal M and fluorine as an additive element at 1.5 atomic % of the transition metal M, has a low resistance of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-nm NMR spectroscopy, it preferably has diffraction peaks at least at two of the following angles: 2θ = 18.547 ± 0.1 °, 2θ = 37.381 ± 0.1 °, 2θ = 38.985 ± 0.1 °, 2θ = 44.978 ± 0.1 °, 2θ = 49.101 ± 0.1 °, and 2θ = 59.073 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.810 ± 0.02 (Å), c = 14.26 ± 0.02 (Å), and a unit cell volume of 97.58 ± 1.6 (Å). ３The lattice constants are preferably a = 2.810 ± 0.01 (Å), c = 14.26 ± 0.01 (Å), and the unit cell volume is 97.58 ± 1.4 (Å). ３ The crystallite size is preferably 50 nm or more, more preferably 75 nm or more.

[0138] The positive electrode active material 100 having Ni / (Co+Ni) of more than 0.025 and not more than 0.075, typically 0.05, has a low resistance at 4.5 V (vs. Li / Li ＋ ) in a charged state, CuKα １ When analyzed by powder X-ray diffraction using 1000-nm NMR spectroscopy, it preferably has diffraction peaks at least at two of the following angles: 2θ = 18.567 ± 0.1 °, 2θ = 37.381 ± 0.1 °, 2θ = 37.710 ± 0.1 °, 2θ = 38.985 ± 0.1 °, 2θ = 44.968 ± 0.1 °, 2θ = 49.070 ± 0.1 °, and 2θ = 58.980 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.814 ± 0.02 (Å), c = 14.30 ± 0.02 (Å), and a unit cell volume of 98.07 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.814 ± 0.01 (Å), c = 14.30 ± 0.01 (Å), and the unit cell volume is 98.07 ± 1.4 (Å). ３ The crystallite size is preferably 100 nm or more, and more preferably 150 nm or more.

[0139] In addition, the positive electrode active material 100 in which Ni / (Co+Ni) is greater than 0.025 and is not greater than 0.075, typically 0.05, has a voltage of 4.6 V (vs. Li / Li ＋ ) in a charged state, CuKα １When analyzed by powder X-ray diffraction using 1000-nm IR, it preferably has diffraction peaks at least two of the following angles: 2θ = 18.866 ± 0.1 °, 2θ = 37.319 ± 0.1 °, 2θ = 38.337 ± 0.1 °, 2θ = 38.985 ± 0.1 °, 2θ = 45.143 ± 0.1 °, 2θ = 49.368 ± 0.1 °, and 2θ = 59.515 ± 0.1 °. It also has a crystalline structure belonging to the space group R-3m, with lattice constants a = 2.819 ± 0.02 (Å), c = 14.06 ± 0.02 (Å), and a unit cell volume of 96.74 ± 1.6 (Å). ３ The lattice constants are preferably a = 2.819 ± 0.01 (Å), c = 14.06 ± 0.01 (Å), and the unit cell volume is 96.74 ± 1.4 (Å). ３ The crystallite size is preferably 150 nm or more, and more preferably 200 nm or more.

[0140] <Analysis Method> Whether or not a certain positive electrode active material is the positive electrode active material 100 of one embodiment of the present invention having the above-described crystal structure in a charged state can be determined by analyzing a positive electrode including the positive electrode active material in a charged state using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.

[0141] In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, it can obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery as it is, etc. Among XRD methods, powder XRD can obtain diffraction peaks that reflect the crystalline structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100.

[0142] When analyzing the crystallite size by powder XRD, it is preferable to measure the crystallite size while excluding the influence of orientation due to pressure, etc. For example, it is preferable to take out the positive electrode active material from the positive electrode obtained by disassembling a secondary battery, prepare a powder sample, and then measure the sample.

[0143] However, since the crystalline structure of the positive electrode active material in a charged state may change when exposed to air, it is preferable to handle all samples used for crystalline structure analysis in an inert atmosphere such as an argon atmosphere.

[0144] Furthermore, whether or not the distribution of the additive elements contained in a certain positive electrode active material is in the state described above can be determined by analysis using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0145] The crystal structure of the surface layer 100 a, the grain boundaries 101 , etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100 .

[0146] <Charging Method> In order to determine whether a certain positive electrode active material or composite oxide is the positive electrode active material 100 of one embodiment of the present invention, the positive electrode active material or composite oxide is charged at a predetermined potential (vs. Li / Li ＋ To do this, for example, a reference battery or coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) may be prepared using lithium as the counter electrode and charged.

[0147] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive material, and a binder.

[0148] The electrolyte contained in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF ６ ) is used, and the electrolyte may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7 with 2 wt % vinylene carbonate (VC).

[0149] The coin cell prepared under the above conditions is charged at a desired voltage (e.g., 4.5 V, 4.6 V, or 4.7 V). The charging method is not particularly limited as long as charging is performed at the desired voltage for a sufficient period of time. For example, when charging by CCCV, the CC charging current can be set to 20 mA / g or more and 100 mA / g or less. CV charging can be terminated at 2 mA / g or more and 10 mA / g or less. To observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value. On the other hand, if the current does not reach 2 mA / g or more and 10 mA / g or less even after long-term CV charging, it is considered that the current is being consumed not for charging the positive electrode active material but for decomposing the electrolyte. Therefore, CV charging may be terminated after a sufficient time has elapsed. In this case, a sufficient time can be, for example, 1.5 hours or more and 3 hours or less. The temperature is 25°C or 45°C. After charging in this manner, the coin cell can be disassembled in an argon-atmosphere glove box and the positive electrode removed to obtain a positive electrode active material with the desired charge capacity. When various analyses are performed after this, it is preferable to seal the battery in an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the battery in a sealed container in an argon atmosphere. Furthermore, it is preferable to quickly remove the positive electrode and subject it to analysis after charging is complete. Specifically, it is preferable to perform the analysis within 1 hour, and more preferably within 30 minutes, after charging is complete.

[0150] <<XRD>> The XRD measurement apparatus and conditions are not particularly limited as long as appropriate adjustment and calibration are performed. For example, measurements can be performed using the following apparatus and conditions: XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: Cu Output: 40 kV, 40 mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm The standard sample used for adjustment and calibration can be, for example, NIST (National Institute of Standards and Technology) standard aluminum oxide sintered plate SRM 1976.

[0151] If the measurement sample is a powder, it can be set by placing it on a glass sample holder, or by sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.

[0152] The characteristic X-rays may be monochromated using a filter or by using XRD data analysis software after obtaining an XRD pattern. For example, the CuKα ２ Excluding the peak due to the line, CuKα １ It is possible to extract only the line peaks. The software can also be used to remove background noise.

[0153] In this specification, when the 2θ value of a certain diffraction peak is mentioned, it means the 2θ value at which the peak top of the diffraction peak appears in the XRD pattern after fitting with a calculation model. The crystal structure analysis software used for fitting is not particularly limited, but for example, TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker) can be used.

[0154] <EDX> Preferably, one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. Furthermore, it is more preferable that the depth from the surface of the peak of the detected amount differs depending on the additive element in the positive electrode active material 100. The concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 using a focused ion beam (FIB) or the like, and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0155] Among EDX measurements, EDX area analysis is performed by scanning an area and evaluating the area two-dimensionally. EDX area analysis is performed by linear scanning and evaluating the distribution of atomic concentrations within the positive electrode active material. Linear analysis is also used to refer to data extracted from a linear area of ​​EDX area analysis. Point analysis is used to measure an area without scanning.

[0156] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration and detection amount of the added element in the surface layer 100a, the interior 100b, and near the grain boundary 101 of the positive electrode active material 100. Furthermore, EDX ray analysis can analyze the concentration distribution and maximum value of the added element. Furthermore, analysis that thins the sample, such as STEM-EDX, is more suitable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.

[0157] Since the positive electrode active material 100 is a compound containing a transition metal and oxygen capable of lithium insertion / extraction, the interface between a region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced upon lithium insertion / extraction and oxygen is present and a region where it is not present is defined as the surface of the positive electrode active material. When the positive electrode active material is subjected to analysis, a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material. The protective film may be a single-layer or multilayer film of carbon, metal, oxide, resin, etc.

[0158] In STEM-EDX ray analysis or the like, the element profile does not change sharply in principle or due to measurement errors, 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, it is important to consider whether the transition metal M is greater than the average value M of the amount detected inside. ＡＶＥ and the average background value M ＢＧ The point where the oxygen concentration is 50% of the sum of the average value of the detected amount of oxygen inside the ＡＶＥ and the average background value O ＢＧThe reference point is the point where the sum of the internal and background is 50%. If the transition metal M and oxygen are different from each other in terms of the 50% point of the sum of the internal and background, this is considered to be due to the influence of metal oxides, carbonates, etc. containing oxygen adhering to the surface. Therefore, the average value M of the internal detected amount of the transition metal M is used. ＡＶＥ and the average background value M ＢＧ In the case of a positive electrode active material having a plurality of transition metals M, the M of the element with the largest count in the inner portion 100b can be used. ＡＶＥ and M ＢＧ The reference point can be determined using the following formula:

[0159] The average value M of the background of the transition metal M ＢＧ can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, from the outside of the positive electrode active material, avoiding the vicinity where the detected amount of transition metal M starts to increase. ＡＶＥ can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, at a depth of 30 nm or more, preferably more than 50 nm, from the region where the counts of the transition metal M and oxygen are saturated and stable, for example, the region where the detected amount of the transition metal M starts to increase. ＢＧ and the average value of the amount of oxygen detected inside O ＡＶＥ can also be found in the same way.

[0160] The surface of the positive electrode active material 100 in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between the region where an image derived from the crystalline structure of the positive electrode active material is observed and the region where it is not observed, and is the outermost region 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 are observed. Alternatively, it is the intersection of the tangent line drawn to the brightness profile from the surface toward the bulk of the STEM image and the axis in the depth direction. The surface in a STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.

[0161] Furthermore, the spatial resolution of STEM-EDX is approximately 1 nm. Therefore, the maximum value of the additive element profile may deviate by approximately 1 nm. For example, even if the maximum value of the additive element profile of magnesium or the like is outside the surface obtained above, the difference between the maximum value and the surface can be considered an error if it is less than 1 nm.

[0162] In addition, a peak in STEM-EDX-ray analysis refers to the detected intensity in each element profile or the maximum value of the characteristic X-rays for each element. Note that noise in STEM-EDX-ray analysis may be a measured value with a half-width less than the spatial resolution (R), for example, R / 2 or less.

[0163] The influence of noise can be reduced by scanning the same location multiple times under the same conditions. For example, the integrated values ​​measured over six scans can be used as the profile of each element. The number of scans is not limited to six; more scans can be performed and the average can be used as the profile of each element.

[0164] The STEM-EDX analysis can be performed, for example, as follows: First, a protective film is vapor-deposited on the surface of the positive electrode active material. For example, carbon can be vapor-deposited using an ion sputtering device (MC1000 manufactured by Hitachi High-Technologies).

[0165] Next, the positive electrode active material is sliced ​​to prepare a STEM cross-section sample. For example, the slice processing can be performed using an FIB-SEM device (Hitachi High-Tech XVision 200TBS). Pickup is performed using an MPS (microprobing system), and the finishing conditions can be, for example, an acceleration voltage of 10 kV.

[0166] STEM-EDX ray analysis can be performed using, for example, a STEM device (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W (two-pronged) EDX detector. During EDX ray analysis, the emission current of the STEM device is set to 6 μA or more and 10 μA or less, and a portion of the thinned sample with minimal depth and unevenness is measured. The magnification is, for example, approximately 150,000 times. The conditions for EDX ray analysis can be drift correction, a line width of 42 nm, a pitch of 0.2 nm, and six or more frames.

[0167] When EDX area analysis or EDX point analysis is performed on the positive electrode active material 100 of one embodiment of the present invention, the average detected amount of each added element, particularly added element X, in the surface layer portion 100a is preferably higher than that in the interior portion 100b.

[0168] <Additional features>

[0169] A coating portion may be attached to at least a portion of the surface of the positive electrode active material 100. Figures 5A and 5B show examples of the positive electrode active material 100 to which a coating portion 104 is attached.

[0170] The coating portion 104 is preferably formed by the accumulation of decomposition products of the electrolyte and the organic electrolytic solution during charging and discharging. ｘ MO ２ When repeated charging is performed so that x in the positive electrode active material 100 decreases, the presence of a coating portion derived from the electrolyte on the surface of the positive electrode active material 100 is expected to improve charge-discharge cycle characteristics. This is due to reasons such as suppressing an increase in impedance on the surface of the positive electrode active material or suppressing cobalt elution. The coating portion 104 preferably contains, for example, carbon, oxygen, and fluorine. Furthermore, when LiBOB and / or SUN (suberonitrile) are used as the electrolyte, a high-quality coating portion is easily obtained. Therefore, a coating portion 104 containing one or more elements selected from boron, nitrogen, sulfur, and fluorine may be a high-quality coating portion and is therefore preferred. Furthermore, the coating portion 104 does not have to cover the entire positive electrode active material 100. For example, it is sufficient for the coating portion 104 to cover 50% or more of the surface of the positive electrode active material 100, with 70% or more being more preferable and 90% or more being even more preferable.

[0171] This embodiment can be used in combination with other embodiments.

[0172] Embodiment 2 In this embodiment, an example of a method for manufacturing a positive electrode active material 100, which is one embodiment of the present invention, will be described.

[0173] <<Method 1 for Producing Positive Electrode Active Material>> Method 1 for producing positive electrode active material 100 will be described with reference to FIG. 4A.

[0174] <Step S11> In step S11 shown in FIG. 4A, a lithium source (Li source), a cobalt source (Co source), and a nickel source (Ni source) are prepared as starting materials for lithium and transition metals, respectively.

[0175] The ratio of nickel to the sum of cobalt and nickel is Ni / (Co+Ni), i.e., LiCo １−ｙ Ni ｙ O ２ In the formula, y is preferably more than 0.001 and less than 0.5, and more preferably more than 0.025 and 0.215 or less.

[0176] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and it is preferable to use a material with a purity of, for example, 99.99% or higher.

[0177] As the cobalt source, it is preferable to use a compound containing cobalt, such as cobalt oxide or cobalt hydroxide.

[0178] As the nickel source, it is preferable to use a compound containing nickel, such as nickel oxide or nickel hydroxide.

[0179] The cobalt source and nickel source preferably have high purity. For example, materials with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher are used. By using high-purity materials, impurities in the positive electrode active material can be controlled. As a result, the capacity and / or reliability of the secondary battery are increased.

[0180] <Step S12> Next, in step S12 shown in FIG. 4A , the lithium source, cobalt source, and nickel source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed by either a dry or wet method. The wet method is preferred because it allows for finer pulverization and mixing of particles. When using the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then pulverize and mix them. Using dehydrated acetone with the above purity can reduce potential impurities.

[0181] A ball mill, a bead mill, or the like can be used as a means for pulverizing and mixing. When using a ball mill, aluminum oxide balls or zirconium oxide balls are preferably used as pulverizing media. Zirconium oxide balls are preferred because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, the peripheral speed should be set to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 628 mm / s (rotation speed 300 rpm, ball mill diameter 40 mm).

[0182] <Step S13> Next, in step S13 shown in FIG. 4A , the mixed material is heated. Heating is preferably performed at a temperature of 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably at approximately 950°C. If the temperature is too low, the decomposition and melting of the lithium source and cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium evaporation from the lithium source and / or excessive reduction of the transition metal M. For example, cobalt and / or nickel may change from trivalent to divalent, which may induce oxygen defects.

[0183] If the heating time is too short, lithium cobalt nickel oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less.

[0184] The temperature rise rate depends on the heating temperature reached, but is preferably 80° C. / h to 250° C. / h. For example, when heating at 1000° C. for 10 hours, the temperature rise rate should be 200° C. / h.

[0185] Heating is preferably carried out in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of -50°C or less, more preferably an atmosphere with a dew point of -80°C or less. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In addition, in order to suppress impurities that may be mixed into the material, the CH ４ , CO, CO ２ , and H ２ The impurity concentrations of the above should be 5 ppb (parts per billion) or less.

[0186] An oxygen-containing atmosphere is preferred as the heating atmosphere. For example, dry air can be continuously introduced into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and allowing oxygen to flow through the reaction chamber is called flow.

[0187] When the heating atmosphere is an atmosphere containing oxygen, a method of not allowing oxygen to flow may be used. For example, a method of reducing the pressure of the reaction chamber and then filling it with oxygen (which may also be called purging) may be used to prevent the oxygen from entering or leaving the reaction chamber. For example, the reaction chamber may be reduced in pressure to -970 hPa and then filled with oxygen to 50 hPa.

[0188] After heating, the material may be cooled naturally, but it is preferable that the time required for the temperature to drop from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not necessarily required, as long as the material is cooled to a temperature acceptable for the next step.

[0189] In this embodiment, the heating temperature was 900° C., the heating time was 10 hours, the heating atmosphere was dry air at a flow rate of 10 L / min, and the temperature rise rate was 200° C. / h.

[0190] The heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be carried out while stirring, whether in a continuous or batch system.

[0191] The crucible used for heating is preferably an aluminum oxide crucible. Aluminum oxide crucibles are made of a material that does not easily release impurities. In this embodiment, an aluminum oxide crucible with a purity of 99.9% is used. It is preferable to heat the crucible with a lid on, as this can prevent the material from volatilizing.

[0192] Furthermore, it is preferable to use a crucible that has been used multiple times rather than a new crucible. In this specification, a new crucible refers to one that has undergone two or fewer heating processes with materials containing lithium, transition metal M, and / or additive elements. A multiple-use crucible refers to one that has undergone three or more heating processes with materials containing lithium, transition metal M, and / or additive elements. This is because using a new crucible may result in some of the materials, including lithium fluoride, being absorbed, diffused, migrated, and / or adhered to the sheath during heating. This loss of material may increase concerns that the distribution of elements, particularly in the surface layer of the positive electrode active material, may not fall within the desired range. On the other hand, this risk is less likely with a multiple-use crucible.

[0193] After heating, the material may be crushed and sieved as necessary. The heated material may be recovered by transferring it from the crucible to a mortar and then recovering it. It is preferable to use a mortar made of agate or partially stabilized zirconium oxide. Agate or partially stabilized zirconium oxide mortars are made of materials that do not easily release impurities. Specifically, a mortar made of agate or partially stabilized zirconium oxide with a purity of 90% or more, preferably 99% or more, is used. Heating conditions equivalent to those of step S13 can also be applied to heating steps other than step S13, which will be described later.

[0194] <Step S14> By the above steps, lithium cobalt nickel oxide (LiCo １−ｙ Ni ｙ O ２ ) can be synthesized.

[0195] <<Preparation Method 2 of Positive Electrode Active Material>> Next, a description will be given of a preparation method 2 of a positive electrode active material, which is an embodiment of the present invention and differs from preparation method 1 of a positive electrode active material, with reference to FIGS. 4B and 4C . Preparation method 2 of a positive electrode active material differs from preparation method 1 of a positive electrode active material in the presence or absence of an additive element. Addition of the additive element chemically stabilizes the surface of the positive electrode active material, thereby suppressing deterioration of the crystal structure during charge-discharge cycles. The description of preparation method 1 can be referred to for other details.

[0196] The additive element may be mixed simultaneously with the lithium source, cobalt source, and nickel source, but it is more preferable to synthesize lithium cobalt nickel oxide containing no additive element, and then mix in the additive element source and perform heat treatment.

[0197] In a method of synthesizing lithium cobalt nickel oxide containing an additive element by simultaneously mixing an additive element source with a lithium source, a cobalt source, and a nickel source, it is difficult to increase the concentration of the additive element in the surface layer portion 100a. Furthermore, if the additive element source is simply mixed without heating after synthesizing lithium cobalt nickel oxide, the additive element will simply adhere to the lithium cobalt nickel oxide without dissolving in the lithium cobalt nickel oxide. Without sufficient heating, it is difficult to achieve a good distribution of the additive element. Therefore, it is preferable to mix the additive element source after synthesizing lithium cobalt nickel oxide and then perform a heat treatment. This heat treatment after mixing the additive element source is sometimes called annealing.

[0198] However, if the annealing temperature is too high, cation mixing occurs, increasing the possibility that the additive element, such as magnesium, will enter the transition metal M site. Furthermore, if the heat treatment temperature is too high, there is concern about adverse effects such as the reduction of cobalt and nickel to divalent states and the evaporation of lithium.

[0199] Therefore, it is preferable to mix a material that functions as a flux (also called a fluxing agent) with the additive element source. Any material that has a lower melting point than lithium cobalt nickel oxide can function as a flux. For example, fluorine compounds such as lithium fluoride are suitable. Adding a flux lowers the melting points of the additive element source and lithium cobalt nickel oxide. Lowering the melting point makes it easier to distribute the additive elements well at a temperature where cation mixing is unlikely to occur.

[0200] Fluorides are LiF and MgF ２ According to Non-Patent Document 13, when LiF and MgF ２ Since the eutectic point of is around 742°C, it is preferable to set the heating temperature to 742°C or higher in the heating step after mixing the additive element.

[0201] <Steps S11 to S14> First, similarly to the positive electrode active material preparation method 1, lithium cobalt nickel oxide is synthesized through steps S11 to S14.

[0202] <Step S20> Next, as shown in step S20 in Fig. 4C, an additional element A is prepared in lithium cobalt nickel oxide. A lithium source may be prepared together with the additional element source (A source).

[0203] The additive element A can be any of the additive elements described in the previous embodiment. Specifically, one or more elements selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium can be used. Figure 4C shows an example in which magnesium and fluorine are selected as the additive element A.

[0204] When magnesium is selected as the additive element, the source of the additive element can be called a magnesium source. As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used. Furthermore, a plurality of the above-mentioned magnesium sources may be used.

[0205] When fluorine is selected as the additive element, the source of the additive element can be called a fluorine source (F source). Examples of the fluorine source include lithium fluoride (LiF), magnesium fluoride (MgF ２ ), aluminum fluoride (AlF ３ ), titanium fluoride (TiF ４ ), cobalt fluoride (CoF ２ , CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF ２ ), cerium fluoride (CeF ３ , CeF ４ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0206] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as a lithium source. Another lithium source that can be used in step S21 is lithium carbonate.

[0207] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ５ F ２ , O ６ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0208] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF) is prepared as the fluorine source and magnesium source. ２ Lithium fluoride and magnesium fluoride are prepared as LiF:MgF ２ The effect of lowering the melting point is greatest when the molar ratio is about 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is set to LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x: 1 (x = near 0.33) is more preferable. In this specification, "near" refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.

[0209] 4C, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0210] 4B, the pulverized and mixed materials are collected to obtain a source of the additional element A. The source of the additional element A shown in step S23 includes a plurality of starting materials and can be called a mixture.

[0211] The particle size of the mixture is preferably D50 (median diameter) of 600 nm to 10 μm, more preferably 1 μm to 5 μm. Even when a single material is used as the additive element source, the D50 (median diameter) is preferably 600 nm to 10 μm, more preferably 1 μm to 5 μm.

[0212] Such a finely powdered mixture (including the case where only one kind of additive element is included) makes it easy to uniformly adhere the mixture to the surface of the lithium cobalt nickel oxide particles when mixed with the lithium cobalt nickel oxide in a later step. If the mixture is uniformly adhered to the surface of the lithium cobalt nickel oxide particles, it is easy to uniformly distribute or diffuse the additive element in the surface layer portion 100a of the composite oxide after heating, which is preferable.

[0213] 4B , lithium cobalt nickel oxide is mixed with a source of additional element A. The ratio of the sum M of the numbers of cobalt and nickel atoms in the lithium cobalt oxide to the number Mg of magnesium atoms in the source of additional element A is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0214] The mixing in step S31 is preferably performed under milder conditions than those in step S12 so as not to destroy the shape of the lithium cobalt nickel oxide particles. For example, it is preferable to perform the mixing under conditions with a lower rotation speed or shorter time than those in step S12. It can also be said that a dry method provides milder conditions than a wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconium oxide balls as media, for example.

[0215] In this embodiment, dry mixing is performed in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour in a dry room with a dew point of −100° C. or higher and −10° C. or lower.

[0216] <Step S32> Next, in step S32 of Fig. 4B, the mixed materials are collected to obtain a mixture 903. When collecting the materials, they may be crushed and then sieved, if necessary.

[0217] <Step S33> Next, in step S33 shown in FIG. 4B , the mixture 903 is heated. This can be performed by selecting from the heating conditions described in step S13. The heating time is preferably 2 hours or more. At this time, the pressure inside the furnace may exceed atmospheric pressure in order to increase the oxygen partial pressure in the heating atmosphere. This is because if the oxygen partial pressure in the heating atmosphere is insufficient, cobalt and nickel may be reduced, and lithium cobalt nickel oxide or the like may no longer be able to maintain a layered rock salt type crystal structure.

[0218] Here, a supplementary note about the heating temperature will be provided. The lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the lithium cobalt nickel oxide and the additive element source proceeds. The temperature at which the reaction proceeds may be any temperature at which interdiffusion of elements contained in the lithium cobalt nickel oxide and the additive element source occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, but the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ ) solid-phase diffusion occurs. Therefore, the heating temperature in step S33 should be 650° C. or higher.

[0219] Of course, the reaction is more likely to proceed if the temperature is equal to or higher than the melting point of one or more of the materials contained in the mixture 903. For example, LiF and MgF are used as the additive element source. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0220] Also, LiCoO ２ :LiF:MgF ２ A mixture 903 obtained by mixing the components so that the molar ratio was 100:0.33:1 exhibits an endothermic peak at around 830° C. in differential scanning calorimetry (DSC). Therefore, the lower limit of the heating temperature is more preferably 830° C. or higher.

[0221] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0222] The upper limit of the heating temperature is set to be lower than the decomposition temperature of lithium cobalt nickel oxide. At temperatures around the decomposition temperature, there is a concern that lithium cobalt nickel oxide may decompose, albeit only slightly. Therefore, the upper limit of the heating temperature is more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0223] In consideration of these, the heating temperature in step S33 is preferably 650°C or higher and 1130°C or lower, more preferably 650°C or higher and 1000°C or lower, even more preferably 650°C or higher and 950°C or lower, and even more preferably 650°C or higher and 900°C or lower. Also, it is preferably 742°C or higher and 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, it is preferably 800°C or higher and 1100°C or lower, or 830°C or higher and 1130°C or lower, more preferably 830°C or higher and 1000°C or lower, even more preferably 830°C or higher and 950°C or lower, and even more preferably 830°C or higher and 900°C or lower.

[0224] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0225] In the manufacturing method described in this embodiment, some materials, for example, LiF as a fluorine source, may function as a flux, which allows the heating temperature to be lowered to a temperature lower than the decomposition temperature of lithium cobalt oxide, for example, 742° C. or higher and 950° C. or lower, and allows the additive elements to be distributed in the surface layer portion, thereby enabling the manufacture of a positive electrode active material with excellent characteristics.

[0226] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF will volatilize when heated, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, etc., LiCoO ２ There is a possibility that Li on the surface reacts with F in the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0227] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization of LiF in the mixture 903.

[0228] The heating in this step is preferably performed so as not to cause adhesion between particles of the mixture 903. If the particles of the mixture 903 adhere to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the additive elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the additive elements (e.g., magnesium and fluorine) in the surface layer portion.

[0229] Furthermore, it is believed that uniform distribution of an additive element (e.g., fluorine) in the surface layer portion results in a smooth cathode active material with few irregularities. Therefore, in order to maintain or further smooth the surface after the heating in step S15 in this process, it is preferable that the particles of mixture 903 do not adhere to each other.

[0230] Furthermore, when heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and then not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen may cause the fluorine source to evaporate, which is undesirable in terms of maintaining surface smoothness.

[0231] When heating is performed using a roller hearth kiln, the mixture 903 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 903 .

[0232] Regarding the heating time, the heating time varies depending on conditions such as the heating temperature, the size and composition of the lithium cobalt nickel oxide in step S14. When the lithium cobalt nickel oxide is small, a lower temperature or a shorter heating time may be preferable than when the lithium cobalt nickel oxide is large.

[0233] 4B and 4C illustrate a production method in which heating is performed after mixing the additive element A source, but this is not a limitation of one embodiment of the present invention. Heating in step S33 may be performed without mixing the additive element A source. By heating the lithium cobalt nickel oxide in step S14 in step S33, the crystallinity of the lithium cobalt nickel oxide can be expected to be improved. Furthermore, the effect of alleviating distortion, misalignment, and the like resulting from differences in contraction, etc., of the lithium cobalt nickel oxide can be expected.

[0234] <Step S34> Next, in step S34 shown in FIG. 4B , the heated material is recovered and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. Through the above steps, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

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

[0236] Embodiment 3 In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG.

[0237] <Configuration Example of Secondary Battery> Hereinafter, a secondary battery shown in FIG. 6 will be described as an example, in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.

[0238] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may also have a conductive material (synonymous with a conductive additive) and a binder. The positive electrode active material is the positive electrode active material described in the previous embodiment.

[0239] The positive electrode active material described in the above embodiment may be mixed with another positive electrode active material.

[0240] Other examples of the positive electrode active material 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:

[0241] Other positive electrode active materials include LiMn ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0242] The conductive material may be a carbon-based material such as acetylene black, or may be a carbon nanotube, graphene, or a graphene compound.

[0243] In this specification and the like, graphene compounds include multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Graphene compounds contain carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings is sometimes called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a curved shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0244] In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0245] In this specification, reduced graphene oxide refers to a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. A single reduced graphene oxide can function, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is 2 atomic % or more and 15 atomic % or less. By achieving these carbon and oxygen concentrations, reduced graphene oxide can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D of the G band to the D band in a Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0246] Graphene compounds may have excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds may also have a sheet-like shape. Graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. Even thin graphene compounds may have very high conductivity, allowing a small amount of graphene to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive material can increase the contact area between the active material and the conductive material. It is preferable that the graphene compound covers 80% or more of the active material. It is preferable that the graphene compound clings to at least a portion of the active material particles. It is also preferable that the graphene compound overlaps at least a portion of the active material particles. It is also preferable that the shape of the graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a portion of the active material particles. The graphene compound may also have holes.

[0247] When active material particles having a small particle size, for example, 1 μm or less, are used, the specific surface area of ​​the active material particles is large, and more conductive paths connecting the active material particles are required. In such cases, it is preferable to use a graphene compound that can efficiently form conductive paths even in a small amount.

[0248] Because of the properties described above, graphene compounds are particularly effective as conductive materials for secondary batteries that require rapid charging and rapid discharging. For example, rapid charging and rapid discharging characteristics may be required for secondary batteries for two-wheeled or four-wheeled vehicles, secondary batteries for drones, etc. Rapid charging characteristics may also be required for mobile electronic devices, etc. Rapid charging and discharging refers to charging and discharging at, for example, 200 mA / g, 400 mA / g, or 1000 mA / g or more.

[0249] The plurality of graphenes or graphene compounds are formed so as to partially cover the plurality of granular positive electrode active material particles or to be attached to the surfaces of the plurality of granular positive electrode active material particles, and are therefore preferably in surface contact with each other.

[0250] Here, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphenes or graphene compounds together. When an active material is covered with a graphene net, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or no binder can be used, thereby improving the ratio of active material to the electrode volume and electrode weight. In other words, the discharge capacity of a secondary battery can be increased.

[0251] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO ２ , SiO ｘ (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a median diameter (D50) of 1 μm or less, more preferably 100 nm or less.

[0252] [Binder] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Furthermore, as the binder, fluororubber can be used.

[0253] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, and starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0254] Alternatively, it is preferable to use, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0255] The binder may be used in combination with two or more of the above.

[0256] [Current Collector] The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0257] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also have a conductive material and a binder.

[0258] [Negative Electrode Active Material] As the negative electrode active material, for example, an alloy-based material and / or a carbon-based material can be used.

[0259] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying / de-alloying reaction with lithium can be used. For example, a material containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger charge-discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, a compound containing these elements may 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.

[0260] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO ｘHere, x preferably has a value close to 1. For example, x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less. Alternatively, x is preferably 0.2 or more and 1.2 or less. Alternatively, x is preferably 0.3 or more and 1.5 or less.

[0261] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0262] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0263] 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 secondary batteries to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high charge / discharge capacity per unit volume, relatively little volume expansion, low cost, and greater safety than lithium metal.

[0264] 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 oxide (WO ２ ), molybdenum oxide (MoO ２ ) and other oxides can be used.

[0265] In addition, as the negative electrode active material, a composite 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 ３ has a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0266] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, can be used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the composite nitride of lithium and a transition metal can be used as the negative electrode active material, even when a material containing lithium ions is used as the positive electrode active material, by first removing the lithium ions contained in the positive electrode active material.

[0267] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0268] The conductive material and binder that can be contained in the negative electrode active material layer can be the same as the conductive material and binder that can be contained in the positive electrode active material layer.

[0269] [Negative electrode current collector] The negative electrode current collector can be made of the same material as the positive electrode current collector. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0270] [Electrolyte] The electrolyte contains a solvent and an electrolyte. The solvent for the electrolyte 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), 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 sultone, or any combination and ratio of two or more of these.

[0271] 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 secondary battery from exploding and / or catching fire even if the internal temperature of the secondary battery rises due to an internal short circuit, overcharging, or the like. 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.

[0272] 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 ) (CF３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ These lithium salts may be used alone or in any combination and ratio of two or more thereof.

[0273] The electrolyte used in the secondary battery is preferably a highly purified electrolyte with a low content of granular dust 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.

[0274] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), dinitrile compounds such as succinonitrile and adiponitrile, fluorobenzene, and ethyleneglycolbis(propionitrile)ether may be added to the electrolyte solution. The concentration of each of the added materials may be, for example, 0.1 wt % to 5 wt % of the total solvent. VC and LiBOB are particularly preferred because they are likely to form a good coating portion.

[0275] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0276] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0277] 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.

[0278] Examples of polymers that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0279] In addition, instead of an electrolytic solution, a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator and / or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0280] [Separator] The secondary battery preferably has a separator. Examples of separators that can be used include paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.

[0281] 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).

[0282] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0283] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0284] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the discharge capacity per volume of the secondary battery can be increased.

[0285] [Exterior Body] The exterior body of the secondary battery can be made of, for example, a metal material such as aluminum and / 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.

[0286] <Laminated Secondary Battery and Method for Fabricating the Same> An example of an external view of a laminated secondary battery 500 is shown in FIGS. 6 and 7. As shown in FIGS. 6 and 7, the secondary battery 500 includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511. The laminated secondary battery has a flexible structure, and when mounted in an electronic device having at least a flexible portion, the secondary battery can also be bent to accommodate deformation of the electronic device. An example of a method for fabricating the laminated secondary battery will be described with reference to FIGS. 7A to 7C.

[0287] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 7B shows the stacked negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0288] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0289] Next, as shown in Fig. 7C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding or the like may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0290] Next, an electrolyte solution (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0291] By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 can have a high discharge capacity and excellent cycle characteristics.

[0292] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0293] Embodiment 4 In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS. 8A to 8C. FIG.

[0294] 8A to 8G show examples in which the secondary battery having the positive electrode active material described in the above embodiment is mounted in an electronic device. Examples of electronic devices to which the secondary battery is applied include television devices (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 machines, personal digital assistants, sound reproducing devices, and large game machines such as pachinko machines.

[0295] Furthermore, a secondary battery having a flexible shape can be incorporated along the curved surfaces of the inner or outer walls of houses, buildings, etc., and the interior or exterior of automobiles.

[0296] 8A shows an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long lifetime can be provided.

[0297] FIG. 8B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 installed therein is also bent. FIG. 8C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.

[0298] FIG. 8D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display portion 7102, operation buttons 7103, and a secondary battery 7104. FIG. 8E shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's arm in a bent state, the housing deforms, causing a change in the curvature of part or the entire secondary battery 7104. Note that the degree of curvature at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or the entire main surface of the housing or the secondary battery 7104 changes when the radius of curvature is in the range of 40 mm to 150 mm. High reliability can be maintained when the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0299] 8F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0300] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0301] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 also includes a touch sensor, and can be operated by touching the screen with a finger or a stylus. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0302] The operation button 7205 can have 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 7205 can be freely set by an operating system incorporated in the portable information terminal 7200.

[0303] The portable information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is possible by communicating with a wirelessly enabled headset.

[0304] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0305] The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight portable information terminal with a long life can be provided. For example, the secondary battery 7104 shown in FIG. 8E can be incorporated into the housing 7201 in a curved state or into the band 7203 in a bendable state.

[0306] The portable information terminal 7200 preferably has a sensor. For example, a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is preferably mounted as the sensor.

[0307] 8G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can also function as a portable information terminal.

[0308] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0309] The display device 7300 also includes an input / output terminal, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed by wireless power supply without using the input / output terminal.

[0310] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0311] An example in which the secondary battery having good cycle characteristics shown in the above embodiment is mounted on an electronic device will be described with reference to FIGS. 8H, 9, and 10. FIG.

[0312] By using a secondary battery of one embodiment of the present invention as a secondary battery in daily electronic devices, products that are lightweight and have a long life can be provided. For example, daily electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For secondary batteries in these products, a stick-shaped secondary battery that is easy for users to hold, small, lightweight, and has a large discharge capacity is desired.

[0313] FIG. 8H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 8H, the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 that includes a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and / or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 8H has external terminals so that it can be connected to a charging device. Because the secondary battery 7504 is the tip portion when held, it is desirable that the total length be short and the weight be light. The secondary battery of one embodiment of the present invention has a high discharge capacity and good cycle characteristics, making it possible to provide a compact and lightweight electronic cigarette 7500 that can be used for a long period of time.

[0314] 9A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0315] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 9A . The eyeglasses-type device 4000 includes a frame 4000 a and a display unit 4000 b. Mounting the secondary battery on the temples of the curved frame 4000 a makes it possible to provide the eyeglasses-type device 4000 with a lightweight design, a good weight balance, and a long continuous use time. The inclusion of the secondary battery of one embodiment of the present invention allows for a configuration that can accommodate space savings associated with a smaller housing.

[0316] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b and / or the earphone unit 4001c. By including the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0317] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0318] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0319] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted inside the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0320] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0321] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0322] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0323] FIG. 9B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0324] 9C shows a side view of the display portion 4005a. The side view of the display portion 4005a also shows a state in which a secondary battery 913 is built in the display portion 4005a. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and is small and lightweight.

[0325] 9D shows an example of a wireless earphone. Here, the wireless earphone is shown as having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0326] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0327] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0328] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played back on the main units 4100a and 4100b. If the main units 4100a and 4100b have microphones, the sound picked up by the microphones can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the devices to be used as, for example, translation devices.

[0329] The secondary battery 4103 included in the main body 4100a can be charged from the secondary battery 4111 included in the case 4110. The coin-type secondary battery, the cylindrical secondary battery, or the like described in the above embodiments can be used as the secondary battery 4111 and the secondary battery 4103. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 as a positive electrode has high energy density. By using the secondary battery 4103 and the secondary battery 4111 as the secondary battery, a configuration that can accommodate space saving associated with miniaturization of wireless earphones can be realized.

[0330] 10A 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 secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0331] 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 rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be a highly reliable electronic device with a long operating time.

[0332] Fig. 10B shows an example of a robot. A robot 6400 shown in Fig. 10B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0333] 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.

[0334] 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.

[0335] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. Furthermore, 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.

[0336] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component inside the robot 6400. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be a highly reliable electronic device with a long operating time.

[0337] Fig. 10C shows an example of an aircraft 6500. The aircraft 6500 shown in Fig. 10C includes a propeller 6501, a camera 6502, a secondary battery 6503, and the like, and has the function of flying autonomously.

[0338] For example, image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of an obstacle when moving. Furthermore, the electronic component 6504 can estimate the remaining battery charge from a change in the storage capacity of the secondary battery 6503. The flying object 6500 includes the secondary battery 6503 according to one embodiment of the present invention therein. By using the secondary battery according to one embodiment of the present invention in the flying object 6500, the flying object 6500 can be an electronic device with a long operating time and high reliability.

[0339] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0340] Embodiment 5 In this embodiment, an example in which a secondary battery including the positive electrode active material of one embodiment of the present invention is mounted on a vehicle will be described.

[0341] When a secondary battery is installed in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs) can be realized.

[0342] FIG. 11 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 11A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized. Furthermore, the automobile 8400 includes a secondary battery. For example, secondary battery modules can be arranged on the floor of the interior of the vehicle. The secondary battery not only drives the electric motor 8406 but also supplies power to light-emitting devices such as a headlight 8401 and a room light (not shown).

[0343] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0344] The automobile 8500 shown in FIG. 11B can charge its secondary battery by receiving power from an external charging facility using a plug-in system and / or a wireless power supply system. FIG. 11B shows a state in which a ground-mounted charging device 8021 charges a secondary battery 8024 mounted on the automobile 8500 via a cable 8022. The charging method and connector specifications may be determined as appropriate using a predetermined system, such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device, such as an AC-DC converter.

[0345] 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 the road and / or 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 vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped and / or moving. Electromagnetic induction and / or magnetic resonance methods can be used for such contactless power supply.

[0346] 11C is an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 11C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0347] 11C can store a secondary battery 8602 in under-seat storage 8604. Even if under-seat storage 8604 is small, secondary battery 8602 can be stored in under-seat storage 8604. Secondary battery 8602 is removable, and when charging, secondary battery 8602 can be carried indoors, charged, and stored before riding.

[0348] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to reducing the weight of the vehicle, thereby improving the cruising range. Furthermore, the secondary battery installed in the vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. Avoiding the use of a commercial power source during peak power demand can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, such as cobalt, can be reduced.

[0349] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0350] In this example, a positive electrode active material according to one embodiment of the present invention was prepared, and its crystal structure after charge was analyzed.

[0351] <Preparation of Positive Electrode Active Material> The sample prepared in this example will be described with reference to the preparation method shown in FIG.

[0352] <Sample 1> In step S11 of FIG. 4A, lithium carbonate (Li ２ CO ３ ) as a cobalt (Co) source, and tetracobalt trioxide (Co ３ O ４ ) as a nickel (Ni) source and nickel hydroxide (Ni(OH) ２ The components were weighed out so that the atomic ratio of Li:Co:Ni was 1:0.8:0.2.

[0353] Next, in step S12, the lithium source, cobalt source, and nickel source were wet mixed using a ball mill. Dehydrated acetone was used as the solvent, and zirconium oxide balls (1 mm diameter) were used as the grinding media. 20 mL of dehydrated acetone, 22 g of zirconium oxide balls (1 mm diameter), and a total of 10 g of the lithium source, cobalt source, and nickel source were placed in a 45 mL capacity mixing ball mill. The ball mill rotation speed was 300 rpm (ball mill diameter: 40 mm), and the treatment time was 20 hours.

[0354] Next, in step S13, the mixture obtained above was heated in a muffle furnace at 900° C. for 10 hours in a dry air atmosphere at a flow rate of 10 L / min.

[0355] In the above process, LiCo ０．８ Ni ０．２ O ２ This was designated as Sample 1.

[0356] <Sample 2> Steps S11 to S14 in FIG. 4B were performed in the same manner as in Sample 1 to prepare LiCo ０．８ Ni ０．２ O ２ Next, in step S20 of FIG. 4B, magnesium and fluorine were selected as the source of the additional element A to be added. In step S21 of FIG. 4C, magnesium fluoride (MgF) was added as the magnesium (Mg) source. ２ ) and lithium fluoride (LiF), with lithium fluoride used as the fluorine source. LiF:MgF ２ were weighed out so as to give a molar ratio of 1:3.

[0357] Next, in step S22 of FIG. 4C, a magnesium source (Mg source) and a fluorine source were mixed together to obtain a source of the additional element A.

[0358] Next, in step S31 of FIG. 4B, MgF ２ was weighed out so that LiCo was 0.5 mol % of the transition metal M and LiF was 0.17 mol % of the transition metal M. ０．８ Ni ０．２ O ２The mixture was dry mixed with the above. The mixture was stirred at a rotation speed of 150 rpm for 1 hour. This was a gentler stirring condition than that used to obtain the A source. Finally, the mixture was sieved with a sieve having 300 μm openings to obtain a mixture 903 with a uniform particle size (step S32).

[0359] Next, in step S33, mixture 903 was heated. The heating conditions were 850°C and 2 hours. During heating, a lid was placed on the crucible containing mixture 903. An oxygen atmosphere was created, and the flow rate was 10 L / min. A positive electrode active material containing Mg and F was obtained by heating (step S34). This was designated sample 2.

[0360] <Sample 3> Sample 3 was prepared in the same manner as Sample 2 except that no additional element was added in step S20.

[0361] <Sample 4> In step S11, lithium carbonate (Li) was used as a lithium (Li) source. ２ CO ３ ) as a cobalt (Co) source, and tricobalt tetroxide (Co ３ O ４ ) and nickel hydroxide (Ni(OH) as a nickel (Ni) source. ２ Sample 4 was prepared in the same manner as Sample 1, except that the components Li, Co, and Ni were weighed out so that the atomic ratio was Li:Co:Ni=1:0.9:0.1.

[0362] <Sample 5> In step S11, lithium carbonate (Li) was used as a lithium (Li) source. ２ CO ３ ) as a cobalt (Co) source, and tricobalt tetroxide (Co ３ O ４ ) as a nickel (Ni) source and nickel hydroxide (Ni(OH) ２ Sample 5 was prepared in the same manner as Sample 2, except that the components Li, Co, and Ni were weighed out so that the atomic ratio was Li:Co:Ni=1:0.9:0.1.

[0363] <Sample 6> In step S11, lithium carbonate (Li) was used as a lithium (Li) source. ２ CO ３ ) as a cobalt (Co) source, and tricobalt tetroxide (Co３ O ４ ) as a nickel (Ni) source and nickel hydroxide (Ni(OH) ２ Sample 6 was prepared in the same manner as Sample 1, except that the components Li, Co, and Ni were weighed out so that the atomic ratio was Li:Co:Ni=1:0.95:0.05.

[0364] <Sample 11> In step S11, lithium carbonate (Li) was used as a lithium (Li) source. ２ CO ３ ) as a cobalt (Co) source, and tricobalt tetroxide (Co ３ O ４ ) as a nickel (Ni) source and nickel hydroxide (Ni(OH) ２ Sample 11 was prepared in the same manner as Sample 1, except that the components Li, Co, and Ni were weighed out so that the atomic ratio was Li:Co:Ni=1:0.99:0.01.

[0365] <Sample 12> In step S11, lithium carbonate (Li) was used as a lithium (Li) source. ２ CO ３ ) as a cobalt (Co) source, and tricobalt tetroxide (Co ３ O ４ ) as a nickel (Ni) source and nickel hydroxide (Ni(OH) ２ Sample 12 was prepared in the same manner as Sample 2, except that the components Li, Co, and Ni were weighed out so that the atomic ratio was Li:Co:Ni=1:0.99:0.01.

[0366] The preparation conditions for Samples 1 to 6, 11 and 12 are shown in Table 1.

[0367]

[0368] <XRD> After the positive electrode active materials of Samples 1, 4 and 6 were prepared, the crystal structures thereof were analyzed by XRD before they were used in half cells.

[0369] Furthermore, half cells were assembled for Samples 1 to 6, Sample 11, and Sample 12, and charged at 4.5 V, 4.6 V, or 4.7 V, and the crystal structure was analyzed using XRD.

[0370] The conditions for the half-cell are explained below. First, the above-mentioned positive electrode active material was prepared. Acetylene black (AB) was prepared as a conductive material. Polyvinylidene fluoride (PVDF) was prepared as a binder. These were mixed in a weight ratio of positive electrode active material:AB:PVDF=95:3:2 to prepare a slurry. The slurry was then applied to an aluminum current collector. NMP was used as the solvent for the slurry.

[0371] After the slurry was applied to the current collector, the solvent was evaporated. A positive electrode was obtained by the above steps. The amount of active material carried on the positive electrode was approximately 7 mg / cm. ２ It was decided.

[0372] The electrolyte solution used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, to which 2 wt% vinylene carbonate (VC) was added as an additive. The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF ６ ) was used. Polypropylene was used as the separator.

[0373] A lithium metal counter electrode was prepared, and a coin-shaped half cell equipped with the above positive electrode was formed.

[0374] The charging conditions were a charging voltage of 4.5V, 4.6V or 4.7V, a charging method of CCCV (constant current 68.5mA / g, upper limit voltage each voltage, end current 1.37mA / g), and a charging temperature of 25°C.

[0375] In both cases, immediately after charging was completed, the charged half-cell was disassembled in an argon atmosphere glove box, the positive electrode was removed, and the electrolyte was removed by washing with DMC (dimethyl carbonate). The removed positive electrode was attached to a flat substrate with double-sided tape and sealed in an airtight sample holder in an argon atmosphere. The positive electrode active material layer was set to match the measurement surface required by the device. XRD measurements were performed at room temperature, regardless of the temperature during charging.

[0376] The XRD measurement was performed using the following equipment and conditions: XRD equipment: D8 ADVANCE manufactured by Bruker AXS X-ray source: Cu Output: 40 kV, 40 mA Divergence angle: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 75°, or 15° to 70° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm The obtained XRD pattern was analyzed using the analysis software DIFFRAC.EVA to separate the background and CuKα ２ The line peaks were removed.

[0377] 12 shows XRD patterns of Samples 1, 4, and 6 after the positive electrode active materials were prepared and before they were used in half cells (hereinafter, sometimes referred to as "after synthesis"). 13A to 14B show enlarged patterns of a portion of FIG. 15.

[0378] Fig. 15 shows the XRD patterns of Sample 1 when the charging voltages were 4.5 V, 4.6 V, and 4.7 V. Figs. 16A to 17B show enlarged partial patterns of Fig. 15 .

[0379] Fig. 18 shows the XRD patterns of Sample 2 when the charging voltages were 4.5 V, 4.6 V, and 4.7 V. Figs. 19A to 20B show enlarged partial patterns of Fig. 18.

[0380] Fig. 21 shows the XRD patterns of Sample 3 when the charging voltages were 4.5 V, 4.6 V, and 4.7 V. Figs. 22A to 23B show enlarged partial patterns of Fig. 21.

[0381] Fig. 24 shows the XRD patterns of Sample 4 when the charging voltages were 4.5 V, 4.6 V, and 4.7 V. Figs. 25A to 26B show enlarged partial patterns of Fig. 24.

[0382] Fig. 27 shows the XRD patterns of Sample 5 when the charging voltages were 4.5 V, 4.6 V, and 4.7 V. Figs. 28A to 29B show enlarged partial patterns of Fig. 27.

[0383] Fig. 30 shows the XRD pattern of Sample 6 when the charging voltage was 4.7 V. Figs. 31A to 32B show enlarged patterns of a part of Fig. 30 .

[0384] Fig. 33 shows the XRD pattern of Sample 11 when the charging voltage was 4.6 V. Figs. 34A to 35B show enlarged partial patterns of Fig. 33 .

[0385] Fig. 36 shows the XRD pattern of Sample 12 when the charging voltage was 4.6 V. Figs. 37A to 38B show enlarged partial patterns of Fig. 36 .

[0386] Table 2 shows the angles at which the main peaks appear and their intensity ratios for the XRD patterns of Samples 1, 4, and 6 before use in the half cell, as well as the XRD patterns at each charging voltage for Samples 1 to 6. In Table 2, a hyphen (-) indicates that no clear peak was observed. Note that the 2θ value may shift overall due to shaking of the measurement surface when setting the sample in the XRD analyzer. For example, all peaks in a certain XRD pattern may shift in the same direction by up to about 0.1°. In this case, correction may be performed using analysis software such as DIFFRAC.TOPAS, and the corrected results may be used.

[0387]

[0388] The crystalline structure of the positive electrode active material was analyzed using DIFFRAC.TOPAS for the XRD patterns of Samples 1, 4, and 6 after synthesis, as well as the XRD patterns at each charge voltage of Samples 1 to 6. All space groups were R-3m. Table 3 shows the lattice constant, crystallite size, and unit cell volume. The crystallite size was calculated using Lvol-1B with a Scherrer constant k = 1. The charge capacity at each voltage is also shown for some samples. For samples with XRD patterns both after synthesis and in the charged state, the rate of change in the a-axis lattice constant Δa, the rate of change in the c-axis lattice constant Δc, and the rate of change in unit cell volume ΔV are also shown. Note that if the value increases after synthesis, the rate of change is indicated as a positive value, and if the value decreases, the rate of change is indicated as a negative value.

[0389]

[0390] The unit cell of Sample 1 after synthesis had the cobalt and oxygen coordinates Co(0,0,0.5) and O(0,0,0.2394).

[0391] The unit cell of Sample 4 after synthesis had the cobalt and oxygen coordinates Co(0,0,0.5) and O(0,0,0.238).

[0392] The unit cell of Sample 6 after synthesis had the cobalt and oxygen coordinates Co(0,0,0.5) and O(0,0,0.2391).

[0393] 12 to 38 and Tables 2 and 3, the lattice constants of the a-axis and c-axis and the unit cell volume tend to increase as Ni / (Co+Ni) increases, which conforms to Vegard's law.

[0394] Furthermore, Samples 1 to 6, in which Ni / (Co+Ni) is 0.05 or more and 0.2 or less, exhibited relatively clear peaks in the XRD patterns after charging to 4.6 V, suggesting that they had stable crystal structures. On the other hand, Samples 11 and 12, in which Ni / (Co+Ni) was 0.01, exhibited unclear peaks in the XRD patterns after charging to 4.6 V, suggesting that their crystal structures were beginning to collapse. Therefore, it was considered preferable for Ni / (Co+Ni) to exceed 0.01.

[0395] In addition, in sample 6 where Ni / (Co+Ni) is 0.05, CoO ２ The XRD pattern is believed to be that of CoO (O1). ２ (O1) structure is LiMO ２ From CoO ２ Since the layers are formed with misalignment, repeated charge and discharge through this structure may easily cause the crystal structure to collapse, which may adversely affect cycle characteristics. Therefore, it can be said that Ni / (Co+Ni) is more preferably greater than 0.05, and even more preferably 0.1 or greater.

[0396] Furthermore, the higher the Ni / (Co+Ni), the smaller the rate of change in unit cell volume ΔV tends to be. This is a desirable property for all-solid-state secondary batteries and the like, where volume change during charging and discharging is a problem.

[0397] On the other hand, the lower the Ni / (Co+Ni), the smaller the rate of change in the a-axis lattice constant Δa, which is expected to improve the stability of the crystal structure. Therefore, Ni / (Co+Ni) is preferably 0.3 or less, and more preferably 0.215 or less.

[0398] 100: Positive electrode active material, 100a: Surface layer, 100b: Interior, 101: Grain boundary, 104: Coating

Claims

1. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is between 0.1 and 0.

3. The positive electrode active material has a surface layer having a rock salt-type crystalline structure and an interior having a layered rock salt-type crystalline structure. The average amount of the additive element detected in the surface layer is higher than the average amount of the additive element detected in the interior. The positive electrode active material wherein the additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium.

2. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.5V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.526 ± 0.1°, and 2θ = 37.391 ± 0.1°, and 2θ = 37.628 ± 0.1°, and 2θ = 39.015 ± 0.1°, and 2θ = 44.947 ± 0.1°, and 2θ = 49.029 ± 0.1°, and At least two of the angles within 2θ = 58.857 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

3. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.351 ± 0.1°, and 2θ = 37.412 ± 0.1°, and 2θ = 38.974 ± 0.1°, and 2θ = 44.865 ± 0.1°, and 2θ = 48.864 ± 0.1°, and At least two of the angles within 2θ = 58.621 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

4. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.7V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.382 ± 0.1°, and 2θ = 37.391 ± 0.1°, and At least two of the angles within 2θ = 44.886 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

5. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The aforementioned additive elements are magnesium and fluorine. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.5V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.516 ± 0.1°, and 2θ = 37.391 ± 0.1°, and 2θ = 37.586 ± 0.1°, and 2θ = 38.995 ± 0.1°, and 2θ = 44.947 ± 0.1°, and 2θ = 49.039 ± 0.1°, and At least two of the angles within 2θ = 58.898 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

6. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The aforementioned additive elements are magnesium and fluorine. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.608 ± 0.1°, and 2θ = 37.381 ± 0.1°, and 2θ = 37.792 ± 0.1°, and 2θ = 39.015 ± 0.1°, and 2θ = 44.999 ± 0.1°, and 2θ = 49.101 ± 0.1°, and At least two of the angles within 2θ = 58.991 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

7. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.5V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.403 ± 0.1°, and 2θ = 37.412 ± 0.1°, and 2θ = 38.985 ± 0.1°, and 2θ = 44.875 ± 0.1°, and 2θ = 48.916 ± 0.1°, and At least two of the angles within 2θ = 58.662 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

8. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.608 ± 0.1°, and 2θ = 37.381 ± 0.1°, and 2θ = 37.854 ± 0.1°, and 2θ = 38.995 ± 0.1°, and 2θ = 45.009 ± 0.1°, and At least two of the angles within 2θ = 59.073 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

9. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.175 and less than or equal to 0.

215. The positive electrode active material is 4.7V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.413 ± 0.1°, and 2θ = 36.774 ± 0.1°, and 2θ = 37.412 ± 0.1°, and At least two of the angles within 2θ = 44.958 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

10. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.075 and less than or equal to 0.

125. The positive electrode active material has a surface layer having a rock salt-type crystalline structure and an interior having a layered rock salt-type crystalline structure. The average amount of the additive element detected in the surface layer is higher than the average amount of the additive element detected in the interior. The additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium, in the positive electrode active material.

11. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.075 and less than or equal to 0.

125. The positive electrode active material is 4.5 V (vs. Li / Li ＋ ) when charged and analyzed by powder X-ray diffraction 2θ = 18.434 ± 0.1°, and 2θ = 37.401 ± 0.1°, and 2θ = 39.005 ± 0.1°, and 2θ = 44.896 ± 0.1°, and 2θ = 48.957 ± 0.1°, and At least two of the angles within 2θ = 58.744 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

12. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.075 and less than or equal to 0.

125. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.567 ± 0.1°, and 2θ = 37.381 ± 0.1°, and 2θ = 39.005 ± 0.1°, and At least two of the angles within 2θ = 44.978 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

13. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The aforementioned additive elements are magnesium and fluorine. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.075 and less than or equal to 0.

125. The positive electrode active material is 4.5V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.537 ± 0.1°, and 2θ = 37.391 ± 0.1°, and 2θ = 37.658 ± 0.1°, and 2θ = 39.005 ± 0.1°, and 2θ = 44.958 ± 0.1°, and 2θ = 49.039 ± 0.1°, and At least two of the angles within 2θ = 58.898 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

14. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The aforementioned additive elements are magnesium and fluorine. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.075 and less than or equal to 0.

125. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.547 ± 0.1°, and 2θ = 37.381 ± 0.1°, and 2θ = 38.985 ± 0.1°, and 2θ = 44.978 ± 0.1°, and 2θ = 49.101 ± 0.1°, and At least two of the angles within 2θ = 59.073 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

15. The positive electrode active material contains cobalt, nickel, oxygen, and additive elements. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.025 and less than or equal to 0.

075. The positive electrode active material has a surface layer having a rock salt-type crystalline structure and an interior having a layered rock salt-type crystalline structure. The average amount of the additive element detected in the surface layer is higher than the average amount of the additive element detected in the interior. The additive element is one or more selected from magnesium, fluorine, calcium, aluminum, silicon, vanadium, copper, and gallium, in the positive electrode active material.

16. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.025 and less than or equal to 0.

075. The positive electrode active material is 4.5V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.567 ± 0.1°, and 2θ = 37.381 ± 0.1°, and 2θ = 37.710 ± 0.1°, and 2θ = 38.985 ± 0.1°, and 2θ = 44.968 ± 0.1°, and 2θ = 49.070 ± 0.1°, and At least two of the angles within 2θ = 58.980 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

17. The positive electrode active material contains cobalt, nickel, and oxygen. The proportion of nickel in the sum of cobalt and nickel, Ni / (Co+Ni), is It is greater than 0.025 and less than or equal to 0.

075. The positive electrode active material is 4.6V (vs.Li / Li ＋ When analyzed by powder X-ray diffraction while the device is charged, 2θ = 18.866 ± 0.1°, and 2θ = 37.319 ± 0.1°, and 2θ = 38.337 ± 0.1°, and 2θ = 38.985 ± 0.1°, and 2θ = 45.143 ± 0.1°, and 2θ = 49.368 ± 0.1°, and At least two of the angles within 2θ = 59.515 ± 0.1° have diffraction peaks due to CuKα 1 line. Cathode active material.

18. A secondary battery having the positive electrode active material according to claims 1 to 17.

19. An electronic device having a secondary battery as described in claim 18.

20. A vehicle having a secondary battery as described in claim 18.