Lithium-ion secondary battery

Abstract

Provided is a new lithium-ion secondary battery. This lithium-ion secondary battery has a positive electrode and a negative electrode. The positive electrode has positive electrode active material particles including lithium, cobalt, oxygen, magnesium, fluorine, nickel, and aluminum. Each of the positive electrode active material particles includes a surface layer part having an edge region, and an internal part. The internal part has a layered rock-salt-type crystal structure of the space group R-3m. When the arrangement of bright spots on the surface of the positive electrode active material particle as observed in a cross-sectional STEM image of the surface through which the lithium is intercalated and deintercalated is defined as the first layer, at least a portion of the fourth to the ninth layers positioned in the direction of the internal part of the positive electrode active material particle has the characteristic of a spinel-type crystal structure. In a cobalt layer of the spinel-type crystal structure, Co2+ and Co3+ are alternately arranged.

Description

Lithium-ion rechargeable battery

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

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

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

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

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

[0006] Also, as image processing software, for example, ImageJ (Non-Patent Documents 8 to 10) is known. By using this software, for example, the shape of the positive electrode active material particles can be analyzed.

[0007] Microelectron diffraction is also effective for identifying the crystal structure of the positive electrode active material particles, particularly the crystal structure of the surface layer portion. For the analysis of the electron diffraction pattern, for example, the analysis program Recipro (Non-Patent Document 11) can be used. In addition, STEM (Scanning Transmission Electron Microscope) - EDX (Energy Dispersive X-ray Spectroscopy) can be used for elemental analysis of the positive electrode active material. Non-Patent Document 12 is known as the detection limit (also referred to as the lower detection limit) when using STEM-EDX.

[0008] As lithium cobaltate, LiCoO₂ with a layered rock salt-type crystal structure of space group R-3m, which is often used as the positive electrode active material of a secondary battery, ２ in addition to LiCoO₂ with a LiTiO₃-type crystal structure of space group Fd-3m ２ is known (Non-Patent Documents 13, Non-Patent Document 14). LiCoO₂ with a LiTiO₃-type crystal structure of space group Fd-3m ２ has a structure called LiTiO₃ structure, LT-LiCoO₂ structure, etc., and has lithium at the 16c position, cobalt at the 16d position, and oxygen at the 32e position in the Wyckoff positions (Non-Patent Document 15). Also, since the above crystal structure has the same basic skeleton as the spinel structure having atoms at the 8a position, 16d position, and 32e position, it is also called spinel-type LiCoO₂, modified spinel structure, spinel-related structure, structure having a spinel skeleton, or simply spinel structure without distinguishing them. ２ 型の結晶構造のLiCoO ２ は、Li ２ Ti ２ O ４ 構造、LT−LiCoO ２ 構造などとも呼ばれ、ワイコフ位置(Wyckoff Positions、非特許文献15)において16c位置にリチウム、16d位置にコバルト、及び32e位置に酸素を有する構造である。また、上記の結晶構造は、8a位置、16d位置、及び32e位置に原子を有するスピネル構造と基本骨格が同様であるため、スピネル型LiCoO ２ 、修正スピネル構造、スピネル関連構造、スピネル骨格を有する構造またはこれらを区別せず単にスピネル構造とも呼ばれる。

[0009] Japanese Patent Application Laid-Open No. 2018-206747, Japanese Patent Application Laid-Open No. 2022-070247 [[ID=K30]]

[0010] 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.17340−17348T.Motohashi,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−A1609A.Belsky,et al.,“New developments in the Inorganic Crystal Structure Database(ICSD):accessibility in support of materials research and design”,Acta Cryst.,(2002)B58 364−369.J.Akimoto,Y.Gotoh,Y.Oosawa,“Synthesis and structure refinement of LiCoO▲2▼ single crystals”Journal of Solid State Chemistry(1998)141,p.298−302.F.Izumi and K.Momma,“Three−Dimensional Visualization in Powder Diffraction”Solid State Phenom.130,15−20(2007)K.Momma and F.Izumi,”VESTA 3 for three−dimensional visualization of crystal,"Volumetric and morphology data" J. Appl. Cryst. (2011). 44, 1272−1276 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. Keiichi Fukunaga, Yukito Kondo, "Detection Limit by TEM / STEM-EDS", Microscopy, 53.3, pp. 134−139. (2018) Antaya, M., Cearns, K., Preston, J. S., Reimers, J. N., & Dahn, J. R. In situ growth of layered, spinel, and rock-salt LiCoO▲2▼ by laser ablation deposition. Journal of applied physics, 76(5), 2799−2806, (1994). Maiyalagan, T., Jarvis, K. A., Therese, S., Ferreira, P. J., & Manthiram,A. Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions. Nature communications, 5(1), 3949, (2014). W. Fischer, E. Koch, “14.2 Symbols and properties of lattice complexes”, International tables for crystallography Volume A, Fifth edition (ISBN: 0-7923-6590-9), Springer, (2005), pp. 848-872. ,

[0011] Lithium-ion secondary batteries still have room for improvement in various aspects, including output characteristics, discharge capacity, cycle characteristics, reliability, safety, and cost. For example, in order to suppress changes in the crystal structure of the surface of the positive electrode active material particles, the surface of the positive electrode active material particles is sometimes coated with an inert oxide, but this coating may inhibit the insertion and removal of lithium. If the insertion and removal of lithium ions is inhibited, there is a concern that the characteristics of the secondary battery will deteriorate, such as a decrease in discharge capacity during high-rate discharge (also called a decrease in output characteristics or a decrease in rate characteristics) and a decrease in charge and discharge capacity in low-temperature environments.

[0012] Therefore, one aspect of the present invention aims to provide positive electrode active material particles or composite oxides that can be used in lithium-ion secondary batteries and that promote the insertion and removal of lithium ions. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides that suppress the decrease in discharge capacity during high-rate discharge. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides that suppress the decrease in discharge capacity in low-temperature environments. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides that suppress the decrease in discharge capacity during charge-discharge cycles. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides whose crystal structure is less likely to collapse even after repeated charge-discharge. Alternatively, one aspect aims to provide positive electrode active material particles or composite oxides with a large discharge capacity. Alternatively, one aspect aims to provide a secondary battery with high safety or reliability, an electronic device having said secondary battery, or a vehicle having said secondary battery.

[0013] Furthermore, one aspect of the present invention aims to provide positive electrode active material particles, composite oxides, energy storage devices, or methods for producing the same.

[0014] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description, drawings, and claims.

[0015] One aspect of the present invention comprises a positive electrode and a negative electrode, the positive electrode having positive electrode active material particles comprising lithium, cobalt, oxygen, magnesium, fluorine, nickel, and aluminum, the positive electrode active material particles having a surface layer and an interior, the interior having a layered rock salt type crystal structure of space group R-3m, and in a cross-sectional STEM-EDX of the surface where lithium is inserted and deinserted from the positive electrode active material particles, magnesium, fluorine, and nickel are detected in the surface layer, and when the surface of the positive electrode active material particles observed in the cross-sectional STEM image of the surface where lithium is inserted and deinserted is considered as the first layer, at least a part of the fourth to ninth layers of the positive electrode active material particles has the characteristics of a spinel type crystal structure, and in the cobalt layer of the spinel type crystal structure Co ２＋ And, Co３＋ This is a lithium-ion secondary battery in which and are arranged alternately.

[0016] In the above, the spinel-type crystal structure in the cross-sectional STEM image is Co ２＋ Co ３＋ It is preferable that the cobalt site present has high brightness.

[0017] In the above, in the STEM-EELS analysis of the fourth to ninth layers of the positive electrode active material particles, Co ２＋ Magnesium and nickel were detected in the cobalt site where Co ３＋ It is preferable that nickel be detected at the cobalt site where it is present.

[0018] In the above, the positive electrode active material particles are Li ｘ CoO ２ When x in the middle is 0.1 < x ≤ 0.24, it is preferable to have an O3' type crystal structure.

[0019] According to one aspect of the present invention, positive electrode active material particles or composite oxides can be provided that can be used in lithium-ion secondary batteries and that promote the insertion and removal of lithium ions. Alternatively, positive electrode active material particles or composite oxides can be provided in which the decrease in discharge capacity during high-rate discharge is suppressed. Alternatively, positive electrode active material particles or composite oxides can be provided in which the decrease in discharge capacity in low-temperature environments is suppressed. Alternatively, positive electrode active material particles or composite oxides can be provided in which the decrease in discharge capacity during charge-discharge cycles is suppressed. Alternatively, positive electrode active material particles or composite oxides can be provided in which the crystal structure is less likely to collapse even after repeated charge-discharge. Alternatively, positive electrode active material particles or composite oxides can be provided in which the discharge capacity is large. Alternatively, a safe or highly reliable secondary battery, an electronic device having said secondary battery, or a vehicle having said secondary battery can be provided.

[0020] Furthermore, according to one aspect of the present invention, positive electrode active material particles, composite oxides, energy storage devices, or methods for producing the same can be provided.

[0021] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims.

[0022] Figures 1A to 1D illustrate the method for producing positive electrode active material particles. Figure 2 illustrates the method for producing positive electrode active material particles. Figures 3A to 3C illustrate the method for producing positive electrode active material particles. Figure 4A is a cross-sectional view illustrating the internal structure of a secondary battery, and Figure 4B is a cross-sectional view illustrating the positive electrode and electrolyte of a secondary battery. Figures 5A and 5B are cross-sectional views illustrating positive electrode active material particles. Figures 6A to 6F are cross-sectional views illustrating positive electrode active material particles. Figures 7A and 7B are schematic diagrams of the surface layer of positive electrode active material particles. Figure 8 is a HAADF-STEM image to illustrate the characteristics of the spinel type. Figure 9 is a schematic diagram of the crystal structure. Figure 10 illustrates the crystal structure of positive electrode active material particles. Figure 11 illustrates the crystal structure of conventional positive electrode active material particles. Figure 12 illustrates the crystal structure of positive electrode active material particles. Figure 13 is a diagram showing the XRD pattern calculated from the crystal structure. Figure 14 shows the XRD pattern calculated from the crystal structure. Figures 15A to 15G illustrate the positional relationship of the distribution in EDX radiation analysis. Figure 16A is an exploded perspective view of a coin-type secondary battery, Figure 16B is a perspective view of a coin-type secondary battery, and Figure 16C is a cross-sectional perspective view thereof. Figure 17A shows an example of a cylindrical secondary battery. Figure 17B shows an example of a cylindrical secondary battery. Figure 17C shows an example of multiple cylindrical secondary batteries. Figure 17D shows an example of an energy storage system having multiple cylindrical secondary batteries. Figures 18A and 18B are diagrams illustrating examples of secondary batteries, and Figure 18C shows the inside of a secondary battery. Figures 19A to 19C are diagrams illustrating examples of secondary batteries. Figures 20A and 20B show the external appearance of a secondary battery. Figures 21A to 21C illustrate a method for manufacturing a secondary battery. Figure 22A shows an example of the configuration of a battery pack, Figure 22B shows an example of the configuration of a battery pack, and Figure 22C shows an example of the configuration of a battery pack. Figure 23A is a perspective view of a battery pack showing one aspect of the present invention, Figure 23B is a block diagram of the battery pack, and Figure 23C is a block diagram of a vehicle having a battery pack. Figures 24A to 24D illustrate an example of a transport vehicle. Figure 24E illustrates an example of an artificial satellite.Figures 25A and 25B illustrate an energy storage device according to one aspect of the present invention. Figure 26A shows an electric bicycle, Figure 26B shows a secondary battery for an electric bicycle, and Figure 26C illustrates a scooter. Figures 27A to 27D illustrate an example of an electronic device. Figure 28A shows an example of a wearable device, Figure 28B shows a perspective view of a wristwatch-type device, and Figure 28C illustrates a side view of a wristwatch-type device.

[0023] The following describes embodiments for carrying out the present invention with reference to drawings and other illustrations. However, the present invention is not limited to the following embodiments. It is possible to modify the embodiments for carrying out the invention without departing from the spirit of the present invention.

[0024] In this specification, space groups are expressed using international notation (or Hermann-Mauguin notation) in short notation. Crystal planes and crystal directions are expressed using Miller indices. In crystallography, space groups, crystal planes, and crystal directions are expressed by superscripting numbers, but in this specification, due to formatting constraints, a minus sign (-) may be placed before the number instead of a superscript. Individual orientations indicating directions within a crystal are represented by [ ], collective orientations indicating all equivalent directions are represented by < >, individual crystal planes are represented by ( ), and collective planes with equivalent symmetry are represented by {}. Furthermore, for ease of understanding the structure, trigonal crystals represented by space group R-3m are generally represented as a composite hexagonal lattice, and in this specification, unless otherwise specified, space group R-3m will be represented as a composite hexagonal lattice. In addition, (hkl) as well as (hkil) may be used as Miller indices. Here, i is -(h+k).

[0025] In this specification, the term "particle" is not limited to spherical shapes (circular cross-sections), but may also refer to individual particles with elliptical, rectangular, trapezoidal, triangular, rounded quadrilateral, or asymmetrical cross-sections, and individual particles may also have irregular shapes.

[0026] Furthermore, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and detachable lithium contained in the positive electrode active material is detached. For example, LiCoO ２ Its theoretical capacity is 274 mAh / g, LiNiO ２ Its theoretical capacity is 275 mAh / g, LiMn ２ O ４ Its theoretical capacity is 148 mAh / g.

[0027] Furthermore, the extent to which insertable and detachable lithium remains in the positive electrode active material is determined by x in the composition formula, for example, Li. ｘ MO ２ The expression is denoted by x. Note that M represents a transition metal, and unless otherwise specified in this specification, M is cobalt and / or nickel. In the case of the positive electrode active material in a lithium-ion secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, Li ｘ MO ２ When a lithium-ion secondary battery using as the positive electrode active material is charged at 219.2 mAh / g, Li ０．２ MO ２ Alternatively, we can say x = 0.2. Li ｘ MO ２ For x to be small, for example, 0.1 < x ≤ 0.24.

[0028] If properly synthesized lithium cobalt oxide, before being used as the positive electrode, approximately satisfies the stoichiometric ratio, then LiCoO ２ And x = 1. Also, lithium cobalt oxide contained in a lithium-ion secondary battery when discharge has finished is also LiCoO ２ Therefore, we can say that x = 1. The state in which discharge has ended (discharge state) referred to here is the state in which the voltage becomes 3.0V or 2.5V or less when discharged with a current of 100mA / g or less.

[0029] Li ｘ MO ２ The charging and / or discharging capacities used to calculate x should preferably be measured under conditions that are free from or minimize the effects of short circuits and / or decomposition of the electrolyte. For example, data from lithium-ion secondary batteries that have experienced a sudden change in capacity, which may be attributed to a short circuit, should not be used to calculate x.

[0030] Furthermore, the space group of the positive electrode active material, etc., is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, "belonging to a certain space group," "being part of a certain space group," or "being a certain space group" can be rephrased as "being identified to a certain space group."

[0031] Furthermore, if the anion has a structure in which three layers are stacked with a slight offset from each other, such as ABCABC, it will be called a cubic close-packed structure. Therefore, the anion does not have to be strictly a cubic lattice. At the same time, since real crystals always have defects, the analytical results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) patterns such as electron diffraction patterns or TEM (Transmission Electron Microscope) images, spots may appear at positions slightly different from the theoretical positions. For example, if the deviation in orientation from the theoretical position is 5° or less, or 2.5° or less, it can be said that it has a cubic close-packed structure.

[0032] Furthermore, the distribution of an element refers to the region in which that element is continuously detected within a non-noise range using a certain continuous analytical method. A region in which an element is continuously detected within a non-noise range can also be defined as a region in which the element is always detected when the analysis is performed multiple times.

[0033] In this specification and other documents, positive electrode active material particles may be referred to as positive electrode active material, composite oxide, positive electrode material, positive electrode material, positive electrode material for secondary batteries, positive electrode material for lithium-ion secondary batteries, etc.

[0034] Furthermore, when describing the characteristics of individual particles in the following embodiments, it is not necessary for all particles to possess those characteristics. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected positive electrode active material particles possess those characteristics, it can be said that this is sufficient to improve the properties of the positive electrode active material and the secondary battery having it.

[0035] Unless otherwise specified, the materials of a secondary battery (positive electrode active material particles, negative electrode active material, electrolyte, separator, etc.) will be described in their state before degradation. Note that a decrease in discharge capacity due to aging and burn-in treatments during the secondary battery manufacturing process is not considered degradation. For example, a secondary battery consisting of a single cell or a battery pack can be considered to be in its pre-degradation state if it has a discharge capacity of 97% or more of its rated capacity. The rated capacity for secondary batteries for portable devices conforms to JIS C 8711:2019. For other secondary batteries, the specifications may conform to various JIS and IEC standards, including those for electric vehicle propulsion and industrial use, in addition to the above JIS standard.

[0036] In this specification, the state of a secondary battery before material degradation is referred to as the initial product or initial state, and the state after degradation (the state in which the secondary battery has a discharge capacity of less than 97% of its rated capacity) may be referred to as a used product or in use, or a used product or a used state.

[0037] In this specification, the (001) plane and the (003) plane, etc., may be collectively referred to as the (00l) plane. In this specification, the (00l) plane may also be referred to as the C plane, basal plane, etc. Furthermore, lithium in lithium cobalt oxide has a two-dimensional diffusion pathway. That is, the diffusion pathway of lithium can be said to exist along the plane. In this specification, the plane where the diffusion pathway of lithium is exposed, that is, the plane where lithium is inserted and removed (specifically, the plane other than the (00l) plane), may be referred to as the edge plane.

[0038] In this specification, secondary particles refer to particles formed by the aggregation of primary particles. Primary particles refer to particles that do not have visible grain boundaries. Single particles refer to particles that do not have visible grain boundaries. Single crystals refer to crystals in which grain boundaries do not exist within the particles, while polycrystalline crystals refer to crystals in which grain boundaries exist within the particles. Polycrystalline crystals can also be described as aggregates of multiple crystallites, and grain boundaries can be described as interfaces between two or more crystallites. In polycrystalline crystals, it is preferable that the orientation of the crystallites is aligned.

[0039] In this specification, the phrase "A and / or B" may be used, but this is just one example of how A alone, B alone, or A and B may be included.

[0040] A short circuit in a secondary battery can not only cause malfunctions in the charging and / or discharging operations of the secondary battery, but can also lead to overheating and ignition. To realize a safe secondary battery, it is desirable that short circuits be suppressed even at high charging voltages. The positive electrode of a battery according to one aspect of the present invention suppresses short circuits even at high charging voltages. Therefore, it is possible to create a battery that achieves both high discharge capacity and safety.

[0041] (Embodiment 1) In this embodiment, an example of a method for producing positive electrode active material particles 100, which are positive electrode active material of a battery according to one aspect of the present invention, will be described. Figures 1A to 3C are diagrams illustrating the method for producing positive electrode active material particles 100.

[0042] The method of adding the additive elements is crucial for producing the positive electrode active material particles 100. Simultaneously, good crystallinity within the positive electrode active material particles is also important.

[0043] Therefore, in the process of producing the positive electrode active material particles 100, it is preferable to first synthesize lithium cobalt oxide by mixing a first lithium source and a cobalt source and performing a heat treatment, then to mix the lithium cobalt oxide with a second lithium source and perform a heat treatment, and then to mix in an additive element source and perform a heat treatment.

[0044] In a method of synthesizing lithium cobalt oxide containing additive elements by simultaneously mixing a first lithium source and a cobalt source with an additive element source, it is difficult to increase the concentration of the additive elements on the surface layer of the positive electrode active material particles. Furthermore, if the additive element source is only mixed after the synthesis of lithium cobalt oxide without heating, the additive elements will only adhere to the lithium cobalt oxide without solid dissolving. Without sufficient heating, it is difficult to properly distribute the additive elements. Therefore, it is preferable to synthesize lithium cobalt oxide first, then mix in the additive element source, and then perform heat treatment.

[0045] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the likelihood that added elements, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site is Li ｘ CoO ２ When x is small, the effect of maintaining the R-3m layered rock salt crystal structure is lost. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to divalent cobalt and the evaporation of lithium.

[0046] [Initial Heating] Therefore, it is preferable to mix and heat with a second lithium source (also called initial heating) before mixing with the additive element source and heating. Here, it is preferable to use a material that functions as a flux as the second lithium source, for example lithium fluoride is suitable.

[0047] Furthermore, it is preferable to thoroughly mix the lithium cobalt oxide with the second lithium source. For example, the mixing can be done by ball milling.

[0048] In the process of thoroughly mixing lithium cobalt oxide with a second lithium source, the adhesion between lithium cobalt oxide particles is eliminated.

[0049] Furthermore, by adding a material that functions as a flux as a second lithium source, it is possible to suppress the re-adhesion of lithium cobalt oxide particles when the lithium cobalt oxide after initial heating is mixed with the added element source and heated in subsequent steps.

[0050] If lithium cobalt oxide particles are stuck together and then additive elements are added and heated, there is a risk that the additive elements will not be sufficiently distributed to the stuck areas. Therefore, when the sticking is released in a later process, such as a pressurizing process after coating the positive electrode current collector, surfaces with insufficient additive elements will be exposed, and degradation may progress from those surfaces when used in a secondary battery. For this reason, it is preferable to suppress the sticking of lithium cobalt oxide particles using the method described above before mixing in the additive element source and heating.

[0051] Furthermore, by adding a flux during the initial heating process, a melting point depression occurs near the surface of the lithium cobalt oxide when the lithium cobalt oxide after initial heating is mixed with the additive element source and heated in subsequent steps. This melting point depression makes it easier to distribute the additive elements well at a temperature where cation mixing is less likely to occur.

[0052] Therefore, the heating temperature in the initial heating is preferably above the melting point of the second lithium source. For example, when lithium fluoride is used as the second lithium source, the temperature is preferably higher than the melting point of lithium fluoride, which is 848°C (for example, 850°C or higher), and more preferably 900°C or higher. Furthermore, the heating temperature in the initial heating is preferably below the temperature used when synthesizing lithium cobalt oxide (for example, 950°C or lower). In other words, it is preferable to mix lithium cobalt oxide and lithium fluoride and heat them at a temperature of 900°C to 950°C as the initial heating.

[0053] Furthermore, by using lithium cobalt oxide that has undergone the initial heating described above, it is possible to suppress lithium deficiency that occurs due to the evaporation of lithium during the subsequent process of mixing and heating the added elements.

[0054] Lithium cobalt oxide that has undergone the initial heating described above preferably has a higher proportion of layered rock salt-type crystalline structure in the surface layer compared to lithium cobalt oxide before the initial heating. For example, in lithium cobalt oxide that has undergone the initial heating described above, it is preferable that the layered rock salt-type crystalline structure accounts for 35% or more, and more preferably 45% or more, in the portion within 2 nm from the surface. Furthermore, when EELS analysis is performed, it is preferable that the valence of cobalt is 2.35 or higher, and more preferably 2.45 or higher. A high proportion of layered rock salt-type crystalline structure is one factor indicating that lithium deficiency is suppressed.

[0055] On the other hand, it is preferable that not the entire surface layer of lithium cobalt oxide has a layered rock salt crystal structure. For example, the solid solubility limit of magnesium is extremely low in pure lithium cobalt oxide. In order to solid dissolve magnesium and other additive elements at a sufficient concentration, it is preferable that the surface layer of lithium cobalt oxide also has the characteristics of a rock salt crystal structure. Therefore, it is preferable that the lithium cobalt oxide that has undergone the above initial heating has a layered rock salt crystal structure of less than 100% in the portion within 2 nm from the surface, and more preferably 90% or less. Furthermore, when EELS analysis is performed, it is preferable that the valence of cobalt is less than 3.00, and more preferably 2.90 or less.

[0056] In other words, the lithium cobalt oxide that has undergone the initial heating described above preferably has a layered rock salt-type crystalline structure of 35% or more and less than 100% in the portion within 2 nm from the surface, more preferably 35% or more and 90%, and even more preferably 45% or more and 90%. Furthermore, when EELS analysis is performed, the valence of cobalt is preferably 2.35 or more and less than 3.00, more preferably 2.35 or more and 2.90, and even more preferably 2.45 or more and 2.90.

[0057] Method 1 for producing positive electrode active material particles 100, which involves heat treatment and initial heating, will be explained using Figures 1A to 1D.

[0058] <Step S11> In step S11 shown in Figure 1B, a first lithium source (Li source 1) and a first cobalt source (Co source) are prepared as the starting materials, which are the first lithium and transition metal materials, respectively.

[0059] As the first lithium source, it is preferable to use a lithium-containing compound, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. The lithium source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0060] As a cobalt source, it is preferable to use a compound containing cobalt, such as tricobalt tetroxide or cobalt hydroxide.

[0061] The cobalt source should preferably have high purity; for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher should be used. By using a high-purity material, impurities in the positive electrode active material particles can be controlled. As a result, the capacity of the secondary battery is increased and / or the reliability of the secondary battery is improved.

[0062] In addition, it is preferable that the cobalt source has high crystallinity, for example, it is preferable that it has single crystal grains. The crystallinity of the cobalt source can be evaluated by TEM images, STEM images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, or by X-ray diffraction, electron diffraction, neutron diffraction, etc. The above methods for evaluating crystallinity can be applied not only to cobalt sources but also to the evaluation of other materials.

[0063] <Step S12> Next, as shown in Step S12 in Figure 1B, the first lithium source and cobalt source are crushed and mixed to produce a mixed material. Crushing and mixing can be done dry or wet. Wet crushing and mixing can produce finer particles. When wet crushing and mixing is performed, a solvent is prepared. As a solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the first lithium source and cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then crush and mix. By using dehydrated acetone of the above purity, the amount of impurities that may be mixed in can be reduced.

[0064] For grinding and mixing, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they produce less impurity. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0065] <Step S13> Next, as step S13 shown in Figure 1B, the mixed material is heated. The heating is preferably carried out at a temperature of 800°C to 1100°C, more preferably at 900°C to 1050°C, and even more preferably at 950°C to 1000°C. If the temperature is too low, the decomposition and melting of the first lithium source and cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to the evaporation of lithium from the first lithium source and / or the excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, inducing oxygen defects, etc.

[0066] If the heating time is too short, lithium cobalt oxide will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time is preferably between 1 hour and 100 hours, and more preferably between 2 hours and 20 hours.

[0067] The heating rate depends on the target temperature, but a rate between 80°C / h and 250°C / h is preferable. For example, when heating to 1000°C for 10 hours, the heating rate can be 200°C / h.

[0068] 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 lower, more preferably an atmosphere with a dew point of -80°C or lower. In this embodiment, heating will be 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, CH in the heating atmosphere is preferable. ４ CO, CO２ , and H ２ It is preferable that the concentrations of these impurities be 5 ppb (parts per billion) or less.

[0069] An atmosphere containing oxygen is preferred as the heating atmosphere. For example, one method is to continuously introduce dry air 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 having oxygen flow through the reaction chamber is called flow.

[0070] When the heating atmosphere is an oxygen-containing atmosphere, a method that does not involve flow may be used. For example, the reaction chamber may be depressurized and then filled with oxygen (which can also be called purging), so that the oxygen does not enter or leave the reaction chamber. For example, the reaction chamber may be depressurized to -970 hPa and then filled with oxygen to 50 hPa.

[0071] After heating, natural cooling is acceptable, but it is preferable that the cooling time from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary; it is sufficient if it cools to a temperature acceptable for the next step.

[0072] Heating in this process may be carried out using a rotary kiln or a roller hearth kiln. When using a rotary kiln, heating can be performed while stirring, whether in a continuous or batch system.

[0073] The container used to hold the material to be heated during heating is preferably an aluminum oxide crucible or an aluminum oxide setter (also called a sheath). An aluminum oxide crucible is made of a material that contains almost no impurities. In this embodiment, an aluminum oxide setter with a purity of 99.9% is used. It is preferable to cover the crucible or setter before heating because this prevents the material from volatilizing. Mullite-cordierite may also be used as the material for the crucible and setter.

[0074] Furthermore, it is preferable to use a used crucible rather than a new one. In this specification, a new crucible is defined as one that has undergone the heating process of adding lithium, transition metal M, and / or additive elements two or fewer times. A used crucible is defined as one that has undergone the heating process of adding lithium, transition metal M, and / or additive elements three or more times. This is because, when a new crucible is used, there is a risk that some of the material, including lithium fluoride, may be absorbed, diffused, migrated, and / or adhered to the casing during heating. If some of the material is lost as a result, there is a growing concern that the distribution of elements on the surface of the positive electrode active material particles will not be within a desirable range. On the other hand, this risk is less with a used crucible.

[0075] After heating is complete, the material may be crushed and sieved as needed. When collecting the heated material, it may be transferred from the crucible to a mortar before collection. A zirconium oxide mortar is preferable for this purpose. Zirconium oxide mortars are made of a material that does not easily release impurities. Specifically, a zirconium oxide mortar with a purity of 90% or higher, preferably 99% or higher, should be used. In addition, the same heating conditions as in step S13 can be applied to the heating processes described later, other than step S13.

[0076] <Step S14> Through the above steps, lithium cobalt oxide (LiCoO) shown in step S14 in Figure 1B is obtained. ２ ) can be synthesized. The lithium cobalt oxide (LiCoO) produced in this way can be synthesized. ２ ) is the starting material LiCoO in step S10 of Figure 1A. ２ It can be used as such.

[0077] Although examples of producing lithium cobalt oxide by a solid-phase method have been shown as in steps S11 to S14, lithium cobalt oxide may also be produced by a coprecipitation method. Alternatively, lithium cobalt oxide may be produced by a hydrothermal method.

[0078] <Step S15> In step S15 shown in Figure 1A, a second lithium source (Li source 2) is prepared. It is preferable to use lithium fluoride as the second lithium source.

[0079] <Step S16> Next, in step S16 shown in Figure 1A, lithium cobalt oxide and the second lithium source are mixed. The mixing in step S16 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, dry mixing is considered milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, for example, it is preferable to use zirconium oxide balls as the media.

[0080] <Step S17> Next, as shown in Step S17 in Figure 1A, the lithium cobalt oxide and the second lithium source are heated. The heating is preferably carried out at 800°C to 1000°C, more preferably at 850°C to 950°C, and even more preferably at 900°C to 950°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, more preferably 2 hours to 10 hours, and even more preferably 2 hours to 6 hours. Because this is the first heating of the lithium cobalt oxide, the heating in Step S17 is sometimes called initial heating. Alternatively, because it is heated before Step S33 shown below, it may be called preheating or pretreatment. By carrying out Steps S16 and S17, lithium cobalt oxide with a smooth surface can be obtained.

[0081] In addition, pre-synthesized lithium cobaltate may be used as step S14. In this case, steps S11 to S13 can be omitted. Even when using pre-synthesized lithium cobaltate, a lithium cobaltate with a smooth surface can be obtained by carrying out steps S16 and S17.

[0082] <Step S20> Next, as shown in step S20, it is preferable to add element A to the lithium cobalt oxide that has undergone initial heating. Adding element A to lithium cobalt oxide that has undergone initial heating allows for even addition of element A. Therefore, it is preferable to add element A after initial heating. The step of adding element A will be explained using Figures 1C and 1D.

[0083] <Steps S21 to S23> The process of preparing the additive element A source (A source) will be explained using Figure 1C. A lithium source may be prepared together with the additive element A source.

[0084] As additive element A, one or more elements selected from the additive elements described in the previous embodiment, such as magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron, can be used. Alternatively, one or two elements selected from bromine and beryllium can also be used.

[0085] <Step S21> Step S21 shown in Figure 1C will now be explained. When magnesium is selected as the additive element, the additive element source can be called a magnesium source (Mg source). As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate can be used. Multiple of the above-mentioned magnesium sources may also be used.

[0086] When fluorine is chosen as the additive element, the additive element source can be called a fluorine source (F source). Examples of such fluorine sources include lithium fluoride (LiF) and magnesium fluoride (MgF). ２ ), aluminum fluoride (AlF ３ ), cobalt fluoride (CoF ２ CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF) ２ ), cerium fluoride (CeF ３ CeF ４ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６ ) and the like can be used. Among them, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later. When lithium fluoride is used as the fluorine source, it can also be called the third lithium source.

[0087] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Another lithium source used in step S21 is lithium carbonate.

[0088] Furthermore, the fluorine source is fluorine (F ２ ), carbon fluoride, 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 A gas such as F) may be used and mixed into the atmosphere during the heating process described later. Alternatively, multiple fluorine sources may be used.

[0089] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF) is prepared as both the fluorine source and the magnesium source. ２ Prepare the following: Lithium fluoride and magnesium fluoride are LiF:MgF ２ Mixing lithium fluoride and magnesium fluoride in a molar ratio of approximately 65:35 yields the greatest effect in lowering the melting point. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride should be LiF:MgF２ Preferably, the ratio is x:1 (0 ≤ x ≤ 1.9), and LiF:MgF ２ = x: 1 (0.1 ≤ x ≤ 0.5) is more preferable, and LiF: MgF ２ A more preferable value is x = 1 (x = 0.33 or its vicinity). In this specification, "nearby" means a value greater than 0.9 times the value and less than 1.1 times the value.

[0090] <Step S22> Next, in step S22 shown in Figure 1C, the magnesium source and the fluorine source are crushed and mixed. This step can be performed by selecting from the crushing and mixing conditions described in step S12.

[0091] <Step S23> Next, in step S23 shown in Figure 1C, the material that has been crushed and mixed above is recovered to obtain the additive element A source (A source). The additive element A source shown in step S23 has multiple starting materials and can be called a mixture.

[0092] The particle size of the above mixture is preferably such that the D50 (median diameter) is 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less. Even when one material is used as the additive element source, the D50 (median diameter) is preferably such that it is 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0093] When the mixture is finely powdered in this way (including cases where only one additive element is present), it is easier to uniformly adhere the mixture to the surface of the lithium cobalt oxide particles when it is mixed with lithium cobalt oxide in a later process. When the mixture is uniformly adhered to the surface of the lithium cobalt oxide particles, it is preferable because it is easier to evenly distribute or diffuse the additive element onto the surface layer of the positive electrode active material particles 100 after heating.

[0094] <Step S21> A different step from that shown in Figure 1C will be explained using Figure 1D. In step S21 shown in Figure 1D, four types of additive element sources are prepared to be added to lithium cobalt oxide. In other words, Figure 1D shows different types of additive element sources than Figure 1C. A lithium source may also be prepared along with the additive element sources.

[0095] Four types of additive element sources are prepared: a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source). The magnesium and fluorine sources can be selected from the compounds described in Figure 1C. Nickel sources such as nickel oxide and nickel hydroxide can be used. Aluminum sources such as aluminum oxide and aluminum hydroxide can be used.

[0096] <Steps S22 and S23> Steps S22 and S23 shown in Figure 1D are the same as the steps described in Figure 1C.

[0097] <Step S31> Next, in step S31 shown in Figure 1A, the lithium cobalt oxide that has undergone initial heating is mixed with the additive element A source (A source).

[0098] In this embodiment, the number of magnesium atoms contained in the additive element A source is preferably 0.50% to 3.0%, more preferably 0.75% to 2.0%, and even more preferably 0.75% to 1.5%, relative to the number of cobalt atoms in lithium cobalt oxide.

[0099] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, dry mixing is generally milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconium oxide balls as the media.

[0100] In this embodiment, the mixing is performed dry at 150 rpm for 1 hour using a ball mill with zirconium oxide balls with a diameter of 1 mm. The mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0101] <Step S32> Next, in step S32 of Figure 1A, the materials mixed above are collected to obtain mixture 903. Sieving may be performed during collection as necessary.

[0102] Although Figures 1A to 1D illustrate a manufacturing method in which additive elements are added only after initial heating, the present invention is not limited to the above method. Additive elements may be added at other times, or added multiple times. The timing may also be varied depending on the element.

[0103] <Step S33> Next, in step S33 shown in Figure 1A, the mixture 903 is heated.

[0104] For example, as additive element source A, MgF ２ If LiF and MgF are present, ２ Since its eutectic point is around 742°C, it is preferable that the heating temperature in step S33 be 742°C or higher.

[0105] Also, LiCoO ２ :LiF:MgF ２ The mixture obtained by mixing in a molar ratio of 100:0.33:1 shows an endothermic peak around 830°C in differential scanning calorimetry (DSC test), therefore, a heating temperature of 830°C or higher is more preferable. Accordingly, the heating in step S33 is preferably carried out at 800°C to 1000°C, more preferably at 830°C to 950°C, and even more preferably at 850°C to 950°C. Furthermore, the heating time is preferably 1 hour to 60 hours, and more preferably 2 hours to 20 hours.

[0106] In the manufacturing method described in this embodiment, the second lithium source, LiF, added in steps S16 and S17 of Figure 1A may function as a flux. This function allows the heating temperature in step S33 to be lowered to below the decomposition temperature of lithium cobalt oxide, for example, between 742°C and 950°C, enabling the presence of additive elements such as magnesium in the surface layer and the production of positive electrode active material particles with good properties.

[0107] A supplement regarding heating time is provided. The heating time varies depending on conditions such as the heating temperature, the size of the lithium cobalt oxide in step S14, and its composition. When the lithium cobalt oxide is small, a lower heating temperature or shorter heating time may be preferable than when it is large.

[0108] <Step S34> Next, in step S34 shown in Figure 1A, the heated material is recovered to obtain positive electrode active material particles 100. At this time, the recovered particles can be crushed by sieving as needed. Through the above steps, positive electrode active material particles 100 according to one aspect of the present invention can be produced. The positive electrode active material particles according to one aspect of the present invention have a smooth surface.

[0109] 《Method 2 for Producing Positive Electrode Active Material Particles 100》 Next, a method 2 for producing positive electrode active material particles 100, which is an embodiment of the present invention and differs from method 1 for producing positive electrode active material particles 100, will be described with reference to Figures 2 to 3C. Method 2 for producing positive electrode active material particles differs from method 1 mainly in the number of times the additive elements are added and the mixing method. For other details, please refer to the description of method 1.

[0110] In Figure 2, steps S11 to S17 are performed in the same manner as in Figures 1A and 1B to prepare lithium cobalt oxide that has undergone initial heating.

[0111] <Step S20a> Next, as shown in step S20a, it is preferable to add element A1 to the lithium cobalt oxide that has undergone initial heating.

[0112] <Step S21> In steps S21 to S23 shown in Figure 3A, a first additive element source (A1 source) is prepared. The first additive element source can be selected from additive element A described in step S21 shown in Figure 1C. For example, as additive element A1, one or more selected from magnesium, fluorine, and calcium can be suitably used. Figure 3A illustrates the case where a magnesium source (Mg source) and a fluorine source (F source) are used as the first additive element source.

[0113] Steps S21 to S23 shown in Figure 3A can be carried out under the same conditions as steps S21 to S23 shown in Figure 1C. As a result, an additive element source (A1 source) can be obtained in step S23.

[0114] Furthermore, steps S31 to S33 shown in Figure 2 can be carried out in the same manner as steps S31 to S33 shown in Figure 1A.

[0115] <Step S34a> Next, the material heated in step S33 is recovered to produce lithium cobalt oxide having additive element A1. To distinguish it from the lithium cobalt oxide of step S14, it is called a composite oxide.

[0116] <Step S40> In step S40 shown in Figure 2, a second additive element source (source A2) is prepared. This will be explained with reference to Figures 3B and 3C.

[0117] <Step S41> In steps S41 to S43 shown in Figure 3B, a second additive element source (A2 source) is prepared. The additive element A2 contained in the second additive element source can be selected from the additive element A described in step S21 shown in Figure 1D. For example, as the additive element A2, one or more selected from nickel, boron, zirconium, and aluminum can be suitably used. Figure 3B illustrates the case where a nickel source (Ni source) and an aluminum source (Al source) are used as the second additive element source. For example, nickel hydroxide, nickel fluoride, etc. can be used as the nickel source. For example, aluminum hydroxide, aluminum fluoride, etc. can be used as the aluminum source.

[0118] The number of nickel atoms in the second additive element source (A2 source) is preferably 0.05% to 4.0%, more preferably 0.20% to 2.0%, and even more preferably 0.20% to 1.0%, relative to the number of cobalt atoms in lithium cobalt oxide. For example, when nickel hydroxide is used as the nickel source, when the number of moles of lithium cobalt oxide in step S10 is set to 100, the number of moles of nickel hydroxide contained in the second additive element source is preferably 0.05 to 4.0 (0.05 mol% to 4.0 mol%), more preferably 0.20 to 2.0 (0.20 mol% to 2.0 mol%), and even more preferably 0.20 to 1.0 (0.20 mol% to 1.0 mol%).

[0119] The number of aluminum atoms in the second additive element source (A2 source) is preferably 0.05% to 4.0%, more preferably 0.20% to 2.0%, and even more preferably 0.20% to 1.0%, relative to the number of cobalt atoms in lithium cobalt oxide. For example, when aluminum hydroxide is used as the aluminum source, when the number of moles of lithium cobalt oxide in step S10 is set to 100, the number of moles of aluminum hydroxide contained in the second additive element source is preferably 0.05 to 4.0 (0.05 mol% to 4.0 mol%), more preferably 0.20 to 2.0 (0.20 mol% to 2.0 mol%), and even more preferably 0.20 to 1.0 (0.20 mol% to 1.0 mol%).

[0120] Steps S41 to S43 shown in Figure 3B can be carried out under the same conditions as steps S21 to S23 shown in Figure 1D. As a result, an additive element source (A2 source) can be obtained in step S43.

[0121] Furthermore, Figure 3C shows a modified version of the steps described using Figure 3B. In step S41 shown in Figure 3C, a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, each is crushed. In other words, in step S43 shown in Figure 3C, multiple second additive element sources (A2 sources) are prepared.

[0122] <Steps S51 to S53> Next, steps S51 to S53 shown in Figure 2 can be carried out under the same conditions as steps S31 to S33 shown in Figure 1A. The heating in step S53 is preferably carried out at 800°C to 1000°C, more preferably at 800°C to 950°C, and even more preferably at 800°C to 900°C. The heating time is preferably 1 hour to 60 hours, more preferably 2 hours to 20 hours, and even more preferably 2 hours to 10 hours. It is preferable that the heating in step S53 is carried out at a lower heating temperature and for a shorter heating time than in step S33. Through the above steps, in step S54, positive electrode active material particles 100 according to one embodiment of the present invention can be produced. The positive electrode active material particles according to one embodiment of the present invention have a smooth surface.

[0123] As shown in Figures 2 to 3C, in manufacturing method 2, the addition of additive elements to lithium cobalt oxide is carried out separately as additive element A1 and additive element A2. By adding additive elements A1 and A2 separately, the depth distribution of each additive element can be changed. For example, it is possible to distribute additive element A1 at a higher concentration in the surface layer of the positive electrode active material particles compared to the interior layer, and to distribute additive element A2 at a higher concentration in the interior compared to the surface layer.

[0124] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0125] (Embodiment 2) This embodiment describes a battery and positive electrode active material particles according to one aspect of the present invention.

[0126] [Battery] A lithium-ion battery according to one aspect of the present invention comprises a positive electrode, a negative electrode, and an electrolyte. If the electrolyte contains an electrolyte solution, a separator is provided between the positive electrode and the negative electrode. Furthermore, an outer casing may be provided that covers at least a portion of the area around the positive electrode, the negative electrode, and the electrolyte.

[0127] This embodiment will primarily describe the positive electrode and positive electrode active material particles of a battery according to one aspect of the present invention. These positive electrode active material particles are the same positive electrode active material particles 100 whose manufacturing method was described in Embodiment 1. Further details regarding the remaining components of the lithium-ion battery according to one aspect of the present invention will be described in Embodiment 3.

[0128] Figure 4A is a schematic cross-sectional view illustrating the internal structure of a lithium-ion battery 10. The lithium-ion battery 10 includes a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22 on the positive electrode current collector 21, and the negative electrode 12 has a negative electrode current collector 31 and a negative electrode active material layer 32. As shown in the figure, the positive electrode active material layer 22 and the negative electrode active material layer 32 face each other with the separator 13 in between. Although not shown in Figure 4A, the electrolyte is contained in the voids of the positive electrode active material layer 22, the voids of the separator 13, and the voids of the negative electrode active material layer 32.

[0129] Although Figure 4A shows one positive electrode 11, one negative electrode 12, and one separator 13, the lithium-ion battery according to one embodiment of the present invention is not limited to this structure. It may also have a structure with two positive electrodes 11, two negative electrodes 12, and two separators 13, and even more electrodes may be stacked. Furthermore, instead of the stacked structure shown in Figure 4A, a wound structure may also be used.

[0130] Figure 4B is an enlarged view of area A, which is enclosed by a dashed line in Figure 4A.

[0131] The positive electrode active material layer 22 comprises positive electrode active material particles 100 (also called the first positive electrode active material), second positive electrode active material particles 200, and a conductive material 41. Although not shown in the figures, in addition to the positive electrode active material particles 100, the second positive electrode active material particles 200, and the conductive material 41, a binder may also be present.

[0132] Furthermore, the voids in the positive electrode active material layer 22 are preferably filled with electrolyte 51, as shown in the figure. For example, the proportion of the voids in the positive electrode active material layer 22 that are filled with electrolyte 51 is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, and most preferably 99% or more. Note that the voids in the positive electrode active material layer 22 refer to the regions in the positive electrode active material layer 22 other than the solid components (positive electrode active material particles, conductive material, etc.).

[0133] [Positive electrode] The positive electrode 11 has a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode active material layer 22 has positive electrode active material particles 100, and the positive electrode active material particles 100 are a group of particles consisting of multiple particles.

[0134] <Positive Electrode Active Material Particles 100> The positive electrode active material particles 100 have the function of taking in lithium ions and releasing them during charging and discharging. The positive electrode active material particles used in one embodiment of the present invention can be made of a material that does not degrade much during charging and discharging (hereinafter also referred to as "charging and discharging"), even at high charging voltages (hereinafter also referred to as "high charging voltage"). Specifically, positive electrode active material particles (composite oxides) with a particle size (median diameter (D50)) of 10 μm or more and 50 μm or less, preferably 10 μm or more and 25 μm or less, obtained by the method for producing positive electrode active material particles described in Embodiment 1 can be used. The positive electrode active material particles 100 contain one or more of the additive elements X, Y, and Z. The additive elements X, Y, and Z will be described in detail in <Contained Elements>. Additive elements X, Y, and Z may be collectively referred to as additive element A.

[0135] The positive electrode active material particles 100 are the main constituent material of the positive electrode active material layer 22. The weight of the positive electrode active material particles 100 is preferably 50% or more, more preferably 60% or more, and more preferably 70% or more of the weight of the solid components of the positive electrode active material layer 22. If the particle size of the positive electrode active material particles 100 is too small, the surface area will become too large, which may lead to excessive reaction between the surface of the positive electrode active material particles and the electrolyte. For this reason, the particle size (median diameter (D50)) of the positive electrode active material particles is preferably 10 μm or more. Furthermore, if the particle size of the positive electrode active material particles is larger than the thickness of the active material layer, as described later, the particle density of the active material layer cannot be increased. Therefore, it is preferable that the largest particle size be 50 μm or less.

[0136] Particle size can be measured using a particle size analyzer (laser diffraction particle size distribution analyzer) that employs laser diffraction and scattering methods. D50 is the particle size at which the cumulative amount accounts for 50% of the cumulative curve of the particle size distribution measurement results. Particle size measurement is not limited to laser diffraction particle size distribution measurement; the major axis of the particle cross-section may also be measured by analysis using SEM (Scanning Electron Microscope) or TEM. As a method for measuring D50 from analysis using SEM or TEM, for example, 20 or more particles can be measured, a cumulative curve can be created, and the particle size at which the cumulative amount accounts for 50% can be defined as D50.

[0137] Furthermore, it is preferable that the difference in charging depth between all the active material particles in the positive electrode active material layer 22 (i.e., the positive electrode active material particles 100 and the second positive electrode active material particles 200) during charging and discharging is small. This is because if the difference in charging depth is large, particles with a higher charging depth are more likely to deteriorate. To mitigate the difference in charging depth, the conductive material 41 and / or binder in the positive electrode active material layer 22 do not necessarily have to be uniformly distributed. For example, particles near the current collector may have a higher charging depth, while particles further away from the current collector may have a lower charging depth. Therefore, it is preferable that the conductive material 41 in the region far from the current collector is greater than in the region near the current collector.

[0138] Alternatively, the positive electrode active material layer 22 preferably has a buffer layer that has the function of mitigating the difference in charging depth.

[0139] Unless otherwise specified in this specification, "charging voltage" shall be expressed with reference to the potential of lithium metal. Furthermore, in this specification, "high charging voltage" refers to a charging voltage of 4.5V or higher, preferably 4.55V or higher, more preferably 4.6V or higher, 4.65V or higher, or 4.7V or higher.

[0140] Furthermore, as stated above, in this specification, "high charging voltage" is defined as 4.6V or higher based on the potential when the negative electrode is lithium metal. However, when the negative electrode is a carbon material (e.g., graphite), 4.5V or higher shall be referred to as "high charging voltage." In short, in the case of a half-cell using lithium metal as the negative electrode, a charging voltage of 4.6V or higher shall be called a high charging voltage, and in the case of a full-cell using a carbon material (e.g., graphite) as the negative electrode, a charging voltage of 4.5V or higher shall be called a high charging voltage.

[0141] The positive electrode active material particles 100, which degrade less with repeated charging and discharging at high charging voltages, will be explained using Figures 5A to 6F.

[0142] Figures 5A and 5B are cross-sectional views of positive electrode active material particles 100 according to one embodiment of the present invention. Figures 6A to 6C show enlarged views of the area around A-B in Figure 5B. Figures 6D to 6F show enlarged views of the area around C-D in Figure 5B.

[0143] The positive electrode active material particles 100 have a layered rock salt type crystal structure belonging to space group R-3m, and a rock salt type crystal structure located on the surface side of the layered rock salt type crystal structure. Furthermore, if a carbon-containing coating or the like exists outside the positive electrode active material particles 100, the positive electrode active material particles 100 can be said to have a layered rock salt type crystal structure and a rock salt type crystal structure between the layered rock salt type crystal structure and the carbon-containing coating.

[0144] As shown in Figure 5A, the positive electrode active material particle 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.

[0145] The surface layer 100a of the positive electrode active material particles 100 refers to the region extending inward from the surface, perpendicular or nearly perpendicular to the surface, within 10 nm. Nearly perpendicular means an angle of 80° to 100°. Surfaces formed by cracks and / or fissures may also be considered the surface. The surface layer 100a is synonymous with the vicinity of the surface, the vicinity of the surface region, or the shell.

[0146] Furthermore, the region deeper than the surface layer 100a of the positive electrode active material particles is called the interior 100b. The interior 100b is synonymous with the interior region or core.

[0147] Furthermore, when the positive electrode active material particles 100 have a layered rock salt type crystalline structure of space group R-3m, the surface layer 100a has an edge region 100a1 and a basal region 100a2, as shown in Figure 5B. In Figures 5A and 5B, the straight line labeled (00l) represents the (00l) plane. Here, the edge region 100a1 has a surface exposed in a direction intersecting the (00l) plane, and the edge region 100a1 is defined as the region within 50 nm from the surface toward the interior, more preferably within 35 nm from the surface toward the interior, even more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm perpendicular or substantially perpendicular from the surface toward the interior. In this context, "intersecting" means that the angle formed by the perpendicular to the first surface ((00l) surface) and the normal to the second surface (the surface of the positive electrode active material particles 100) is between 10 degrees and 90 degrees, more preferably between 30 degrees and 90 degrees.

[0148] Furthermore, the basal region 100a2 has a surface parallel to the (00l) plane, and the basal region 100a2 is defined as the region within 50 nm from the surface inward, more preferably within 35 nm from the surface inward, even more preferably within 20 nm from the surface inward, and most preferably within 10 nm perpendicular or substantially perpendicular from the surface inward. Here, "parallel" means that the angle between the perpendicular of the first plane ((00l) plane) and the normal of the second plane (the surface of the positive electrode active material particles 100) is 0 degrees or more and 5 degrees or less, more preferably 0 degrees or more and 2.5 degrees or less.

[0149] The surface of the positive electrode active material particle 100 refers to the surface of the composite oxide including the surface layer 100a and the interior 100b. Furthermore, the surface of the positive electrode active material particle 100 in a cross-sectional HAADF-STEM image, etc., refers to the surface closest to the outside, where the first metal element with an atomic number greater than lithium is observed. More specifically, it refers to the point where the first metal element with an atomic number greater than lithium is observed, i.e., the point where the brightness peak exists in the cross-sectional HAADF-STEM image, etc.

[0150] The positive electrode active material particles 100 are aluminum oxide (Al) which does not have lithium sites that can contribute to charging and discharging. ２ O ３ This excludes metal oxides adhering to surfaces such as ), carbonates and hydroxyl groups chemically adsorbed after the production of the positive electrode active material particles. Adhered metal oxides refer to, for example, metal oxides whose crystal orientation does not match that of the interior 100b.

[0151] The general agreement of crystal orientation between two regions can be determined from TEM images, STEM images, HAADF-STEM images, ABF-STEM images, electron diffraction patterns, etc. It can also be determined from the FFT patterns of TEM images and STEM images. Furthermore, XRD and neutron diffraction can also be used as indicators.

[0152] Furthermore, the material does not contain electrolytes, electrolyte decomposition products, organic solvents, binders, conductive materials, or compounds derived therefrom that are attached to the positive electrode active material particles 100.

[0153] Since the positive electrode active material particles 100 are compounds containing a transition metal and oxygen that can be inserted into and removed from lithium, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) and oxygen, which undergo oxidation-reduction during lithium insertion and removal, are present and the region where they are absent is considered the surface of the positive electrode active material particles. Surfaces created by slip, cracks, and / or fissures may also be considered the surface of the positive electrode active material particles. When the positive electrode active material particles are subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material particles. As a protective film, single-layer or multi-layer films of carbon, metal, oxide, resin, etc. may be used.

[0154] <Elements contained> The positive electrode active material particles 100 contain lithium, cobalt, oxygen, and additive elements. Alternatively, the positive electrode active material particles 100 may contain lithium cobalt oxide (LiCoO ２ ) may have additive elements added to it. However, it is preferable that the positive electrode active material particles 100 in one embodiment of the present invention have the crystalline structure described later. For this reason, the composition of lithium cobalt oxide is not strictly limited to Li:Co:O = 1:1:2.

[0155] The positive electrode active material particles of a lithium-ion secondary battery need to contain a redox-capable transition metal in order to maintain charge neutrality even when lithium ions are inserted and removed. In one embodiment of the present invention, it is preferable that the positive electrode active material particles 100 mainly use cobalt as the transition metal responsible for the redox reaction. In addition to cobalt, at least one or more selected from nickel and manganese may be used. It is preferable that the cobalt content of the transition metals in the positive electrode active material particles 100 is 75 atomic percent or more, preferably 90 atomic percent or more, and more preferably 95 atomic percent or more, as this offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics.

[0156] Furthermore, if the cobalt content among the transition metals of the positive electrode active material particles 100 is 75 atomic percent or more, preferably 90 atomic percent or more, and more preferably 95 atomic percent or more, then lithium nickelate (LiNiO) ２ Compared to composite oxides in which nickel, such as ), makes up the majority of the transition metals, Li ｘ CoO ２Stability is better when x is small. This is thought to be because cobalt is less affected by strain due to the Jahn-Teller effect than nickel. In transition metal compounds, the strength of the Jahn-Teller effect varies depending on the number of electrons in the d orbital of the transition metal. In layered rock salt type composite oxides in which octahedral low-spin nickel(III) ions, such as lithium nickelate, make up the majority of the transition metal, the Jahn-Teller effect is significant, and strain is likely to occur in the layers consisting of octahedra of nickel and oxygen. Therefore, there is a growing concern that the crystal structure may collapse during charge-discharge cycles. Also, nickel ions are larger than cobalt ions and are close in size to lithium ions. Therefore, in layered rock salt type composite oxides in which nickel makes up the majority of the transition metal, such as lithium nickelate, there is a problem that cation mixing of nickel and lithium is likely to occur.

[0157] The additive elements in the positive electrode active material particles 100 are preferably one or more selected from magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, and beryllium. The sum of the transition metals among the additive elements is preferably less than 25 atomic percent, more preferably less than 10 atomic percent, and even more preferably less than 5 atomic percent.

[0158] In other words, the positive electrode active material particles 100 can be one or more of the following: lithium cobalt oxide having magnesium, lithium cobalt oxide having magnesium and aluminum, lithium cobalt oxide having magnesium and nickel, lithium cobalt oxide having magnesium, aluminum and nickel, lithium cobalt oxide having magnesium and fluorine, lithium cobalt oxide having magnesium, fluorine and nickel, lithium cobalt oxide having magnesium, fluorine, nickel and aluminum, etc.

[0159] Furthermore, it can be said that one or more of the following can be used as positive electrode active material particles 100: positive electrode active material particles having cobalt, oxygen, and magnesium; positive electrode active material particles having cobalt, oxygen, magnesium, and aluminum; positive electrode active material particles having cobalt, oxygen, magnesium, aluminum, and nickel; positive electrode active material particles having cobalt, oxygen, magnesium, and fluorine; positive electrode active material particles having cobalt, oxygen, magnesium, fluorine, and aluminum; positive electrode active material particles having cobalt, oxygen, magnesium, fluorine, and nickel; and positive electrode active material particles having cobalt, oxygen, magnesium, fluorine, nickel, and aluminum.

[0160] It is preferable that the additive elements are solid-dissolved in the positive electrode active material particles 100. For example, when performing STEM-EDX line analysis, it is preferable that the position where the additive elements begin to be detected in the depth direction is deeper than the position where the transition metal M begins to be detected, i.e., located inside the positive electrode active material particles 100. In STEM-EDX line analysis in the depth direction, the position where an element begins to be detected refers to the position where the amount of characteristic X-rays detected (count) due to that element begins to increase continuously.

[0161] These added elements further stabilize the crystal structure of the positive electrode active material particles 100, as will be described later.

[0162] Furthermore, the additive elements do not necessarily have to include magnesium, fluorine, nickel, aluminum, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, barium, bromine, or beryllium.

[0163] For example, if the positive electrode active material particles 100 are substantially free of titanium, the above-mentioned advantages, such as excellent cycle characteristics, become even greater. The weight of titanium contained in the positive electrode active material particles 100 is preferably 600 ppm or less, and more preferably 100 ppm or less. Furthermore, when the positive electrode active material particles 100 are subjected to STEM-EDX analysis, it is preferable that no characteristic X-rays attributable to titanium are detected, that is, that they are below the detection limit (for example, less than 0.3 atomic%).

[0164] For example, if the positive electrode active material particles 100 are substantially free of manganese, the above advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics become even greater. The weight of manganese contained in the positive electrode active material particles 100 is preferably 600 ppm or less, and more preferably 100 ppm or less.

[0165] The surface layer 100a is the region where lithium ions first desorb during charging, and the lithium concentration tends to be lower in this region than in the interior 100b. Furthermore, the atoms on the surface of the positive electrode active material particles 100 in the surface layer 100a can be described as having some of their bonds broken. Therefore, the surface layer 100a is prone to instability, and is a region where degradation of the crystal structure is likely to begin. On the other hand, if the surface layer 100a can be made sufficiently stable, Li ｘ CoO ２ Even when the internal x is small, for example, when x is 0.24 or less, the layered structure consisting of octahedrons of cobalt and oxygen in the internal 100b can be made less prone to breakage. Furthermore, the displacement of the layers consisting of octahedrons of cobalt and oxygen in the internal 100b can be suppressed.

[0166] In order to ensure a stable composition and crystal structure for the surface layer 100a, it is preferable that the surface layer 100a contains additive elements, and more preferably that it contains multiple additive elements. It is also preferable that the surface layer 100a has a higher concentration of one or more selected additive elements than the interior 100b. Furthermore, it is preferable that one or more selected additive elements in the positive electrode active material particles 100 have a concentration gradient. It is also preferable that the distribution of the positive electrode active material particles 100 differs depending on the additive elements. For example, it is preferable that the depth of the concentration peak from the surface differs depending on the additive element. Here, the concentration peak refers to the maximum concentration value in the surface layer 100a or below 50 nm from the surface.

[0167] [Distribution] The distribution of the added elements will be explained. Figures 6A to 6C are enlarged views of the area around A-B in Figure 5B, illustrating the edge region 100a1 of the positive electrode active material particles 100. Figures 6D to 6F are enlarged views of the area around C-D in Figure 5B, illustrating the basal region 100a2 of the positive electrode active material particles 100.

[0168] For example, some of the additive elements, such as magnesium, fluorine, silicon, phosphorus, boron, and calcium, preferably have a concentration gradient that increases from the interior 100b towards the surface, as shown by the gradient in Figures 6A and 6D. Additive elements having such a concentration gradient will be called additive elements X.

[0169] Another additive element, such as aluminum or manganese, preferably has a concentration gradient as shown by the density of the hatches in Figures 6B and 6E, and has a concentration peak in a region deeper than that of additive element X shown in Figures 6A and 6D. The concentration peak may be located in the surface layer 100a or deeper than the surface layer 100a. For example, it is preferable that the peak is in a region of 5 nm to 30 nm from the surface inward. An additive element having such a concentration gradient will be called additive element Y.

[0170] Another additive element, such as nickel, barium, etc., clearly exists in the edge region 100a1 as shown by the presence or absence of hatching and the density of hatching in FIGS. 6C and 6F, but may not substantially exist in the basal region 100a2. Here, "clearly exists" means that in the analysis of the cross-section STEM-EDX of the positive electrode active material particles 100, the characteristic X-ray energy spectrum of the element is detected. Also, "not substantially exist" means that in the analysis of the cross-section STEM-EDX of the positive electrode active material particles 100, the characteristic X-ray energy spectrum of the element is not detected. This is also referred to as the case where the element is below the detection limit in the STEM-EDX analysis. In this case, in the analysis in STEM-EDX, it is also said that the element is below the detection limit. The additive element having such a distribution is called additive element Z.

[0171] For example, magnesium, which is one of the additive elements X, has a valence of 2, and magnesium ions are more stable in the lithium sites than in the cobalt sites in the layered rock salt type crystal structure, so it is likely to enter the lithium sites. Note that magnesium existing in the cobalt sites or lithium sites in the layered rock salt type crystal structure is 6-coordinated with oxygen, and there are 6 oxygens around each magnesium element. The same is true for magnesium oxide of the rock salt type. Therefore, magnesium oxide can be expressed as, for example, Mg·n(O １／ｎ )(n = 6). When magnesium exists in the lithium sites of the surface layer portion 100a at an appropriate concentration, it becomes easier to maintain the layered rock salt type crystal structure. This is presumably because magnesium existing in the lithium sites functions as a pillar supporting the CoO ２ layers. Also, the presence of magnesium allows Li ｘ CoO ２When the internal x is, for example, 0.24 or less, the desorption of oxygen around the magnesium can be suppressed. Furthermore, the presence of magnesium is expected to increase the density of the positive electrode active material particles 100. In addition, if the magnesium concentration in the surface layer 100a is high, it is expected that the corrosion resistance to hydrofluoric acid produced when the electrolyte reacts with water will improve. On the other hand, if the magnesium concentration is insufficient, the surface layer 100a may be eroded by hydrofluoric acid and dissolved into the electrolyte, which may prevent sufficient suppression of the phase change in the interior 100b.

[0172] At appropriate concentrations, magnesium does not adversely affect lithium insertion and removal during charging and discharging, and the above benefits can be enjoyed. However, excessive magnesium may inhibit lithium insertion and removal. Furthermore, its effect on stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters not only lithium sites but also cobalt sites. In addition, excess magnesium compounds (oxides or fluorides, etc.) that do not substitute for lithium or cobalt sites may segregate on the surface of the positive electrode active material particles, potentially becoming a resistive component of the secondary battery. Moreover, as the magnesium concentration of the positive electrode active material particles increases, the discharge capacity of the positive electrode active material particles may decrease. This is thought to be because too much magnesium enters the lithium sites, reducing the amount of lithium that contributes to charging and discharging.

[0173] Therefore, it is preferable that the total amount of magnesium contained in the positive electrode active material particles 100 is appropriate. For example, the number of magnesium atoms is preferably 0.001 times or more and 0.1 times or less the number of cobalt atoms, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. The amount of magnesium contained in the total positive electrode active material particles 100 referred to here may be a value obtained by performing an elemental analysis of the entire positive electrode active material particles 100 using, for example, GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material particles 100.

[0174] Furthermore, aluminum, one of the additive elements Y, can be present in the cobalt site of the layered rock salt crystal structure. Since aluminum is a trivalent typical element and its valency does not change, lithium around the aluminum does not easily move during charging and discharging. Therefore, the lithium around the aluminum is CoO ２ It functions as a pillar supporting the layers and can suppress changes in the crystal structure. Furthermore, aluminum suppresses the leaching of surrounding cobalt, improving continuous charging resistance and / or storage resistance in a fully charged state. Also, because the Al-O bond is stronger than the Co-O bond, it can suppress the desorption of oxygen around the aluminum. These effects improve thermal stability. Therefore, including aluminum as an additive element can improve the safety when using positive electrode active material particles 100 in a secondary battery. It also allows for positive electrode active material particles 100 that are less prone to crystal structure collapse even after repeated charging and discharging.

[0175] On the other hand, an excess of aluminum may negatively affect the insertion and removal of lithium.

[0176] Therefore, it is preferable that the total amount of aluminum in the positive electrode active material particles 100 is appropriate. For example, the total number of aluminum atoms in the positive electrode active material particles 100 is preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.3% to 1.5% of the total number of cobalt atoms. Alternatively, 0.05% to 2% is preferred. Alternatively, 0.1% to 4% is preferred. The amount of aluminum in the positive electrode active material particles 100 referred to here may be, for example, the value obtained by elemental analysis of the entire positive electrode active material particles 100 using GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material particles 100.

[0177] Furthermore, nickel, one of the additive elements Z, is Ni ２＋ Ni ３＋ Ni ４＋ Ni ２＋is the most stable, and nickel has a higher trivalent ionization energy compared to cobalt. Therefore, it is known that nickel alone with oxygen does not form a spinel-type crystal structure. Therefore, nickel is considered to have an effect of suppressing the phase change from the layered rock salt type to the spinel-type crystal structure. Therefore, it is preferable that nickel exists in a region where it is likely to be observed that a phase change to a spinel-type crystal structure occurs after repeated charge and discharge, specifically, in a region deeper than 2 nm from the surface in the surface layer portion 100a.

[0178] Also, nickel can exist in either the cobalt site or the lithium site. When it exists in the cobalt site, the redox potential becomes lower compared to cobalt, leading to an increase in discharge capacity, which is preferable.

[0179] Also, when nickel exists in the lithium site, the deviation of the layered structure composed of octahedrons of cobalt and oxygen can be suppressed. Also, the volume change associated with charge and discharge is suppressed. Also, the elastic modulus increases, that is, the positive electrode active material particles 100 become harder. This is presumably because nickel existing in the lithium site also functions as a pillar supporting the layers of CoO ２ It is presumed that this is because it functions as a pillar supporting the layers of CoO. Therefore, it is particularly preferable that the crystal structure becomes more stable in the charged state at high temperatures, for example, 45 °C or higher.

[0180] On the other hand, if nickel is excessive, the influence of strain due to the Jahn-Teller effect is enhanced, which is not preferable. Also, if nickel is excessive, there is a possibility of having an adverse effect on the insertion and desorption of lithium.

[0181] Therefore, it is preferable that the total amount of nickel in the positive electrode active material particles 100 is appropriate. For example, the number of nickel atoms in the positive electrode active material particles 100 is preferably more than 0% and 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, it is preferable that it is more than 0% and 4% or less. Alternatively, it is preferable that it is more than 0% and 2% or less. Alternatively, it is preferable that it is more than 0% and 7.57.5% or less. Alternatively, it is preferable that it is more than 0% and 4% or less. The amount of nickel shown here may be, for example, a value obtained by elemental analysis of the entire positive electrode active material particles using GD-MS, ICP-MS, etc., or it may be based on the value of the raw material composition in the process of manufacturing the positive electrode active material particles.

[0182] Furthermore, because compounds of fluorine, one of the additive elements X, with metals such as magnesium and cobalt are chemically stable, if the surface layer 100a is terminated with fluorine, the departure of oxygen from the positive electrode active material particles 100 can be suppressed. In particular, it is important that the lithium layer, which becomes the lithium diffusion pathway during charging and discharging, is terminated with fluorine. Figure 7 shows a schematic diagram of the surface layer 100a. The area shown by the dashed line in Figure 7A is the lithium diffusion pathway terminated with fluorine. Figure 7B is a diagram of the lithium diffusion pathway terminated with fluorine, similar to Figure 7A, drawn using VESTA (Non-Patent Literature 7). If the lithium diffusion pathway is not terminated with fluorine, the rock salt type wall containing MgO, which will be described later, will break down, and CoO ２ There is a risk that the layer displacement may not be suppressed.

[0183] Furthermore, since fluorine is a monovalent anion, if some of the oxygen in the surface layer 100a is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of cobalt ions accompanying lithium desorption is from trivalent to tetravalent when fluorine is absent, and from divalent to trivalent when fluorine is present, resulting in different oxidation-reduction potentials. Therefore, if some of the oxygen in the surface layer 100a of the positive electrode active material particles 100 is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. As a result, when the positive electrode active material particles 100 are used in a secondary battery, the charge-discharge characteristics, high-current characteristics, etc., can be improved. In addition, the presence of fluorine in the surface layer 100a, which is the part that comes into contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid. Furthermore, as explained in Embodiment 1, if the melting point of fluorides, including lithium fluoride, is lower than the melting point of other additive element sources, it can function as a flux (also called a fluxing agent) that lowers the melting point of other additive element sources.

[0184] Furthermore, as shown in Figures 6A and 6C, when the surface layer 100a contains both magnesium and nickel, divalent nickel may be able to exist more stably near divalent magnesium. Therefore, Li ｘ CoO ２ Even when the internal x is small, the elution of magnesium can be suppressed. Therefore, this can contribute to the stabilization of the surface layer 100a.

[0185] Furthermore, having multiple types of additive elements with different distributions, such as additive element X, additive element Y, and additive element Z, is preferable because it can stabilize the crystal structure over a wider area. For example, if the positive electrode active material particles 100 contain magnesium, which is one of the additive elements X, aluminum, which is one of the additive elements Y, and nickel, which is one of the additive elements Z, it can stabilize the crystal structure over a wider area than when it contains only one or two of the additive elements X, Y, and Z. Thus, when the positive electrode active material particles 100 contain three types of additive elements X, Y, and Z, surface stabilization can be sufficiently achieved by additive element X such as magnesium and additive element Z such as nickel, so additive element Y such as aluminum is not essential for the surface. Rather, it is preferable for aluminum to be widely distributed in deeper regions. For example, it is preferable for aluminum to be continuously detected in the region from the surface to a depth of 1 nm or more and 25 nm or less. It is preferable for aluminum to be widely distributed in this way because it can stabilize the crystal structure over a wider area.

[0186] Furthermore, when the additive element Z is abundantly present in the edge region 100a1 (also referred to as preferentially present or selectively present), as shown in Figures 6C and 6F, the stability of the crystal structure of the edge region 100a1 is improved, which is preferable. In the edge region 100a1, lithium ions enter and exit the positive electrode active material particles 100 during charging and discharging of the lithium-ion battery. Also, when the additive element Z has the distribution described above, for example, when the positive electrode active material particles 100 are lithium cobalt oxide, the effects of adding the additive element Z, such as a decrease in discharge voltage or a decrease in discharge capacity, can be minimized, which is preferable.

[0187] As described above, having multiple additive elements allows the effects of each additive element to synergistically contribute to further stabilization of the surface layer 100a. In particular, the presence of magnesium, nickel, and aluminum is highly preferable as it is effective in achieving a stable composition and crystal structure. Among these, it is preferable that the surface layer 100a of the positive electrode active material particles 100 has a region where magnesium is distributed closer to the surface than aluminum. Furthermore, in addition to the regions where magnesium and aluminum are distributed as described above, it is most preferable that the edge region 100a1 of the surface layer 100a of the positive electrode active material particles 100 has a region where the distribution of nickel and magnesium overlap.

[0188] <Crystal structure> <Li ｘ CoO ２ When x inside is 1 > The positive electrode active material particle 100 in one aspect of the present invention is in a discharge state, that is, Li ｘ CoO ２ When x = 1, it has a layered rock salt type crystal structure belonging to space group R-3m. Layered rock salt type composite oxides have high discharge capacity, possess a two-dimensional lithium ion diffusion pathway, and are suitable for lithium ion insertion / desorption reactions, making them excellent as positive electrode active material particles for secondary batteries. For this reason, it is particularly preferable that the interior 100b, which accounts for most of the volume of the positive electrode active material particle 100, has a layered rock salt type crystal structure.

[0189] On the other hand, in one aspect of the present invention, it is preferable that the surface layer 100a of the positive electrode active material particles 100 has a function to reinforce the layered structure of the interior 100b, which consists of an octahedron of transition metal M and oxygen, so that it does not break down even if lithium is removed from the positive electrode active material particles 100 due to charging. Alternatively, it is preferable that the surface layer 100a functions as a barrier film for the positive electrode active material particles 100. Alternatively, it is preferable that the surface layer 100a, which is the outer periphery of the positive electrode active material particles 100, reinforces the positive electrode active material particles 100. Reinforcement as used here means suppressing structural changes in the surface layer 100a and interior 100b of the positive electrode active material particles 100, including the desorption of oxygen, and / or suppressing the oxidative decomposition of the electrolyte on the surface of the positive electrode active material particles 100.

[0190] Therefore, it is preferable that the surface portion 100a has a different crystal structure from the interior portion 100b. Furthermore, it is preferable that the surface portion 100a has a composition and crystal structure that is more stable at room temperature (25°C) than the interior portion 100b. Specifically, at least a part of the surface portion 100a of the positive electrode active material particles 100 in one embodiment of the present invention has the characteristics of a rock salt type crystal structure. Furthermore, it is preferable that at least a part of the surface portion 100a has the characteristics of a spinel type crystal structure. Specifically, it is preferable to have a crystal structure with a spinel type skeleton. More specifically, LiTiO with space group Fd-3m, which has a crystal structure similar to a spinel structure. ２ It is preferable that the crystal structure has the characteristics of a type crystal structure. Furthermore, the surface layer 100a is a layered rock salt type, LiTiO with space group Fd-3m. ２ It is more preferable to have the characteristics of three crystal structures: type and rock salt type. Note that crystal structures with a spinel-type skeleton (e.g., LiTiO) ２ Since structures such as spinel types are sometimes collectively referred to as spinel structures, when we say that a crystal structure has the characteristics of a spinel type in this specification, we mean LiTiO with space group Fd-3m. ２ It can sometimes be reinterpreted as having the characteristics of a type crystal structure. Also, LiTiO with space group Fd-3m ２ The type of crystal structure is sometimes referred to as the spinel type crystal structure.

[0191] Furthermore, while it is preferable that some of the additive elements A, particularly magnesium, nickel, and aluminum, are present at a higher concentration in the surface layer 100a than in the interior 100b, it is also preferable that they be present randomly and dilutely in the interior 100b. When magnesium and aluminum are present at appropriate concentrations in the lithium sites of the interior 100b, it has the effect of making it easier to maintain a layered rock salt-type crystal structure, similar to the above. Also, when nickel is present at an appropriate concentration in the interior 100b, the displacement of the layered structure consisting of octahedra of transition metal M and oxygen can be suppressed, similar to the above. In addition, when the interior 100b contains both magnesium and nickel, divalent magnesium may be able to exist more stably near divalent nickel, so a synergistic effect of suppressing magnesium leaching can be expected.

[0192] Furthermore, due to the concentration gradient of the added element A as described above, it is preferable that the crystal structure changes continuously from the interior 100b toward the surface. Alternatively, it is preferable that the crystal orientations of the surface layer 100a and the interior 100b are roughly the same.

[0193] For example, it is preferable that the characteristics of the layered rock salt type change sequentially from the interior 100b of the layered rock salt type towards the surface, from the characteristics of the layered rock salt type to the characteristics of the spinel type, and then from the characteristics of the spinel type to the characteristics of the rock salt type. It is also preferable that this change in crystal structure is continuous. Furthermore, it is preferable that the crystal orientations of the three crystal structures—layered rock salt type, spinel type, and rock salt type—are roughly the same.

[0194] In this specification, the row of metallic elements with atomic numbers greater than lithium (also called a row of bright spots or arrangement of bright spots) observed in a cross-sectional HAADF-STEM image of the positive electrode active material particle 100, i.e., the closest to the surface and the outside, is referred to as the first layer. The row of metallic elements with atomic numbers greater than lithium, observed in the position next to the outside after the first layer, is referred to as the second layer. The same applies to the third layer and subsequent layers. In other words, the layers proceed inward from the first layer, second layer, third layer, fourth layer, and so on.

[0195] For example, the first to third layers in the edge region 100a1 preferably have characteristics of a rock salt type. The fourth to ninth layers preferably have characteristics of a spinel type. The tenth layer and beyond preferably have characteristics of a layered rock salt type.

[0196] An example of observing a region exhibiting spinel-type characteristics from the <110> direction in a cross-sectional HAADF-STEM image of the edge region 100a1 is described below. In this observation, the characteristics of the region change sequentially from layered rock salt type characteristics to spinel-type characteristics, and then from spinel-type characteristics to rock salt type characteristics, in the direction from the inside to the outside of the particle (depth direction). At this time, in the region exhibiting layered rock salt type characteristics, a first row (lithium layer) in which no clear bright spots are observed, and a second row (cobalt layer) adjacent to the first row in which clear bright spots are lined up, can be confirmed. When the first row is moved toward the outside of the particle, a first characteristic can be confirmed in the spinel-type characteristic region, in which bright spots of high luminance and areas in which no clear bright spots are observed are arranged alternately. Furthermore, when the second row is moved toward the outside of the particle, a second characteristic can be confirmed in the spinel-type characteristic region, in which bright spots of high luminance and bright spots of low luminance are arranged alternately. In other words, a region possessing the first and second characteristics described above can be called a region with spinel-type characteristics.

[0197] Furthermore, in cross-sectional HAADF-STEM images, etc., thin section samples may have multiple crystal structures in the depth direction. For example, a superposition of rock salt type and spinel type may result in having characteristics of both. Similarly, a superposition of spinel type and layered rock salt type may result in having characteristics of both.

[0198] In this specification, the layered rock salt crystal structure belonging to space group R-3m, which is found in composite oxides containing lithium and transition metals M including cobalt, refers to a crystal structure that has a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Furthermore, strictly speaking, the layered rock salt crystal structure may have a distorted lattice structure of the rock salt crystal.

[0199] Furthermore, a rock salt-type crystal structure refers to a cubic crystal structure in which cations and anions are arranged alternately. It is also acceptable for there to be vacancies in either the cations or anions.

[0200] Furthermore, the characteristics of layered rock salt crystal structures, spinel crystal structures, and rock salt crystal structures can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0201] Furthermore, in the region exhibiting spinel-type characteristics in the cross-sectional HAADF-STEM image, LiTiO of space group Fd-3m ２ It may have a crystal structure of the type Fd-3m. ２ For the type crystal structure, refer to ICSD (Inorganic Crystal Structure Database) col. code. 48128. LiTiO of space group Fd-3m ２ In this type of crystal structure, lithium is located at the 16c position, cobalt at the 16d position, and oxygen at the 32e position. Since the lithium at the 16c position is linearly aligned in the <110> direction, the movement of lithium during charging and discharging can be made smooth, which is preferable. Note that the 16c and 16d positions are equivalent in terms of site symmetry, so it is also possible to have cobalt at the 16c position, lithium at the 16d position, and oxygen at the 32e position.

[0202] The region exhibiting spinel-type characteristics is LiTiO in space group Fd-3m. ２ To determine whether it is a type of crystal structure, for example, it can be determined by checking whether an atom is present at position 8a in an ABF-STEM image or a HAADF-STEM image. If there is no atom at position 8a and an atom is present at position 16c, then it is LiTiO with space group Fd-3m. ２ It can be said that it is a crystal structure of type Fd-3m. In this specification, etc., LiTiO ２ A crystal structure of this type is sometimes called a spinel'-type crystal structure. Alternatively, if, by HAADF-STEM imaging and STEM-EELS analysis, sites where lithium is aligned in the <110> direction, sites where lithium and cobalt are aligned, and sites where cobalt is aligned are confirmed in a region exhibiting spinel-type characteristics, then the LiTiO of space group Fd-3m is identified. ２ LiCoO having a crystal structure of type ２ It can be said that LiTiO of the space group Fd-3m ２LiCoO having a crystal structure of type ２ The crystal structure has lithium diffusion pathways that allow lithium to move in the order of 16c to 8a, 8a to 16c, and 16c to 8a, meaning that lithium diffusion is possible in three dimensions, and therefore having this crystal structure is preferable from the viewpoint of charge-discharge characteristics.

[0203] In rock salt type, there is no distinction in the cation sites, but in layered rock salt type, there are two types of cation sites in the crystal structure: one is mostly occupied by lithium, and the other is occupied by the transition metal M. The layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are arranged alternately is the same for both rock salt type and 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 (transmission spot) is taken as the origin 000, the bright spot closest to the central spot is, for example, the (111) plane in the ideal state of rock salt type, 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 bright spots on the (003) plane are observed at a distance of approximately half the distance between the bright spots on the (111) plane of MgO. Therefore, in the analysis region, for example, rock salt type MgO and layered rock salt type LiCoO ２ When there are two phases, the electron diffraction pattern shows a plane orientation in which bright spots of high and low brightness are arranged alternately. Bright spots common to both rock salt and layered rock salt types have high brightness, while bright spots occurring only in the layered rock salt type have low brightness.

[0204] Furthermore, in cross-sectional STEM images, when a layered rock salt crystal structure is observed from a direction perpendicular to the c-axis, layers with high brightness and layers with low brightness are observed alternately. This characteristic is not seen in rock salt crystals because there is no distinction in the sites of cations. In the case of a crystal structure that has characteristics of both rock salt and layered rock salt crystals, when observed from a specific crystal orientation, layers with high brightness and layers with low brightness are observed alternately in cross-sectional STEM images, and furthermore, a metal with an atomic number greater than lithium is present in a part of the low-brightness layer, i.e., the lithium layer.

[0205] In rock salt crystal structures, there is no distinction between the sites of cations, i.e., metallic elements. Therefore, if rows of metallic elements with no difference in brightness overlap in cross-sectional HAADF-STEM images, it can be said that the structure exhibits characteristics of a rock salt crystal structure.

[0206] On the other hand, in the layered rock salt crystal structure, there are two types of sites for metallic elements, with lithium sites and transition metal M sites arranged alternately. In HAADF-STEM images, a contrast proportional to the square of the atomic number is obtained, with elements with larger atomic numbers appearing brighter. Therefore, when alternating rows of metallic elements with different brightness levels are observed in a cross-sectional HAADF-STEM image, it can be said that the structure has the characteristics of a layered rock salt.

[0207] Furthermore, in the HAADF-STEM image, if a pattern of alternating bright spots with low brightness is observed in the transition metal M site rows, it can be said to have spinel-type characteristics. Similarly, if a pattern of alternating bright spots and regions without clear bright spots is observed in the lithium site rows, it can also be said to have spinel-type characteristics. Figure 8 is an example of a HAADF-STEM image exhibiting spinel-type characteristics. In the lithium site rows, a pattern of alternating bright spots 110 and regions 111 without clear bright spots is observed.

[0208] The above LiTio ２ In regions having a Spinel-type crystal structure, it is preferable to have magnesium and nickel as additive elements at the lithium sites (Wyckoff position 16c). It is also preferable to have nickel as an additive element at the transition metal M sites (cobalt sites, Wyckoff position 16d). By having magnesium and nickel as additive elements at these positions, the surrounding crystal structure can be stabilized and the desorption of oxygen can be suppressed.

[0209] In ABF-STEM images, similar features can be observed compared to HAADF-STEM images, although the contrast is reversed. Therefore, if a pattern of alternating scotomas and areas without clear scotomas is observed in the lithium site rows of ABF-STEM images, it can be said that the lesion exhibits spinel-type characteristics.

[0210] The characteristics of a spinel type can also be determined from electron diffraction or TEM-FFT patterns.

[0211] Layered rock salt crystals, spinel type, LiTiO ２ The anions in the O3' type and rock salt type crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in the O3' type crystal, which will be discussed later, adopt a cubic close-packed structure. Therefore, layered rock salt type crystal structure, spinel type crystal structure, LiTiO ２ In the rock salt crystal structure and the rock salt crystal structure, there are crystal planes in which the orientation of the cubic close-packed structure composed of anions is aligned when in contact. For example, as shown in the schematic diagram of the crystal structure in Figure 9, the rock salt crystal structure and LiTiO ２ It is possible to adopt a structure in which the Spinel' type crystal structure and the layered rock salt type crystal structure are in contact with each other. Figure 9 shows the crystal structure near the surface of the positive electrode active material particle 100 of one embodiment of the present invention, which will be discussed from the examples described later. In the Spinel' type crystal structure, as shown in Figure 9, Co in the cobalt layer ２＋ And, Co ３＋ and are arranged alternately.

[0212] Alternatively, it can be explained as follows: The anions in the {111} plane of the cubic crystal structure have a triangular lattice. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the {111} plane of the cubic crystal has a similar atomic arrangement to the hexagonal lattice of the (0001) plane of the layered rock salt type. The consistency between the two lattices can be described as the orientation of the cubic close-packed structure being aligned.

[0213] However, the space group of the layered rock salt type is R-3m, which is different from the space group of the cubic crystal system of the rock salt type and spinel type. Therefore, the Miller indices of crystal planes that satisfy the above conditions are different for the layered rock salt type crystal compared to the rock salt type and spinel type. In this specification, it is sometimes said that the crystal orientations are roughly the same when the orientations of the cubic close-packed structure composed of anions are aligned in the layered rock salt type, spinel type, and rock salt type.

[0214] <Li ｘ CoO ２ State where x is small > The positive electrode active material particles 100 of one aspect of the present invention have the above-described distribution and / or crystal structure of additive element A in the discharge state, Li ｘ CoO ２ The crystal structure when x is small differs from that of conventional positive electrode active material particles. Here, x is small when 0.1 < x ≤ 0.24.

[0215] Using Figures 10 to 14, Li ｘ CoO ２ The change in crystal structure associated with the change in x within the material will be explained by comparing conventional positive electrode active material particles with positive electrode active material particles 100 according to one embodiment of the present invention.

[0216] Figure 11 shows the change in the crystal structure of conventional positive electrode active material particles. The conventional positive electrode active material particles shown in Figure 11 are lithium cobalt oxide (LiCoO2) which does not contain any additive element A. ２ )

[0217] Figure 11 shows R-3m O3 attached to Li ｘ CoO ２ This shows the crystal structure of lithium cobalt oxide at x=1. In this crystal structure, lithium occupies octahedral sites, and CoO is present in the unit cell. ２ Three layers are present. Therefore, this crystal structure is sometimes called an O3 type crystal structure. Note that CoO ２ A layer is defined as a structure in which octahedral structures, each with six oxygen atoms coordinated to cobalt, are continuous on a plane with shared edges. This is sometimes referred to as a layer composed of octahedra of cobalt and oxygen.

[0218] Furthermore, it is known that conventional lithium cobalt oxide exhibits increased lithium symmetry when x = approximately 0.5, resulting in a crystal structure belonging to the monoclinic space group P2 / m. This structure contains CoO in the unit cell. ２ It has one layer. Therefore, it is sometimes called O1 type or monoclinic O1 type.

[0219] Furthermore, when x = 0, the positive electrode active material particles have a crystal structure of the trigonal space group P-3m1, and also contain CoO in the unit cell.２ One layer is present. Therefore, this crystal structure is sometimes called O1 type or trigonal O1 type. Alternatively, the trigonal structure can be converted to a composite hexagonal lattice and called hexagonal O1 type.

[0220] Furthermore, conventional lithium cobalt oxide at x = approximately 0.12 has a crystal structure of space group R-3m. This structure is similar to that of trigonal O1 type CoO ２ The structure and LiCoO such as R-3m O3 ２ This structure can be described as a structure in which the and structures are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 type crystal structure. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 11, the c-axis of the H1-3 type crystal structure will be shown as half the unit cell to facilitate comparison with other crystal structures.

[0221] As an example, the H1-3 type crystal structure can be represented by the coordinates of cobalt and oxygen in the unit cell as follows: Co (0, 0, 0.42150 ± 0.00016), O1 (0, 0, 0.27671 ± 0.00045), and O2 (0, 0, 0.11535 ± 0.00045). O1 and O2 are oxygen atoms, respectively. The unit cell that should represent the crystal structure of the positive electrode active material particles can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, the unit cell that yields a smaller GOF (goodness of fit) value can be adopted.

[0222] Li ｘ CoO ２ When charging and discharging are repeated such that the internal x is 0.24 or less, the conventional lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0223] However, these two crystal structures are CoO ２ The layer displacement is large. As shown by the dotted line and arrow in Figure 11, in the H1-3 type crystal structure, CoO ２The layer deviates significantly from the discharged state R-3m O3. Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0224] Furthermore, these two crystal structures are CoO ２ The interlayer distance also changes significantly. Figure 12 shows the O3' type crystal structure, the H1-3 type crystal structure, and the O1 type crystal structure, and the CoO in each crystal structure. ２ The surface formed by the oxygen in the layer, and the next CoO ２ This indicates the distance between the planes formed by oxygen in the layer. In the H1-3 type crystal structure, this interplanar spacing is 2.77 Å and 3.06 Å, while in the O3' type crystal structure, which will be described later, this interplanar spacing is 3.13 Å. When this interplanar spacing changes significantly, as in the H1-3 type crystal structure, degradation such as cracking may occur, especially in the surface layer where lithium diffusion pathways exist.

[0225] Furthermore, these two crystal structures also have a large volume difference. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the R-3m O3 type crystal structure in the discharged state exceeds 3.5%, and is typically 3.9% or more.

[0226] In addition, the H1-3 crystal structure has a CoO structure similar to the trigonal O1 type. ２ A structure with continuous layers is likely to be unstable. Therefore, oxygen is thought to be easily released.

[0227] Therefore, repeated charging and discharging cycles that result in x being 0.24 or less cause the conventional lithium cobalt oxide crystal structure to break down. This breakdown of the crystal structure leads to a deterioration of the cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also makes it more difficult for lithium to be inserted and removed.

[0228] Furthermore, lithium cobalt oxide with x less than 0.24, where many Li atoms have been removed, also readily releases oxygen. Along with the release of oxygen, cobalt is released. ３＋ From Co ２＋ This can lead to a phase change from a layered rock salt crystal structure to a spinel crystal structure.

[0229] Furthermore, when oxygen is released, cations such as cobalt that were bonded to the oxygen may dissolve into the electrolyte. If this progresses, it can lead to degradation in which holes are formed in the positive electrode active material particles, also known as pitting corrosion or pitting. At this time, strain and / or stress may occur in the positive electrode active material particles 100.

[0230] On the other hand, in the positive electrode active material particles 100 of one embodiment of the present invention shown in Figure 10, Li ｘ CoO ２ The change in crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less is less than that of conventional positive electrode active material particles. More specifically, the change in CoO between the state where x is 1 and the state where x is 0.24 or less ２ The displacement of the layers can be reduced. As described in the previous embodiment, by adding an additive element such as magnesium together with a fluoride that functions as a flux, and heating in an oxygen-containing atmosphere, preferably at 850°C to 950°C, the additive element can be distributed in the surface layer 100a at a sufficient concentration. Therefore, even if lithium detaches from the positive electrode active material particles 100 and x becomes 0.24 or less, the phase change suppression effect of magnesium can suppress the phase change to an H1-3 type crystal structure. For example, this is the case when a rock salt type crystal structure containing MgO is converted to an internal CoO ２ It can also be described as functioning as a barrier that prevents layers from shifting.

[0231] Although the lithium layer in the surface layer 100a functions as a lithium diffusion pathway, the area surrounding the lithium diffusion pathway is the region in the surface layer 100a where degradation is most likely to occur first, and lithium alone is insufficient to suppress the phase change. Therefore, as described above, the presence of magnesium at the lithium sites is necessary.

[0232] Furthermore, the change in volume when compared per cobalt atom can be reduced. Therefore, the positive electrode active material particles 100 of one aspect of the present invention are less prone to structural collapse even when repeatedly charged and discharged such that x is 0.24 or less, and are less prone to cracking, thus achieving excellent cycle characteristics. In addition, because the volume change is small, it is easy to maintain the conductive path even in secondary batteries that require high-density packing. Furthermore, the positive electrode active material particles 100 of one aspect of the present invention are Li ｘ CoO ２ When x is 0.24 or less, it can adopt a more stable crystal structure than conventional positive electrode active material particles. Therefore, the positive electrode active material particle 100 in one aspect of the present invention is Li ｘ CoO ２ When the internal value of x is maintained at 0.24 or less, thermal runaway due to structural changes is less likely to occur. Therefore, the safety of the secondary battery is further improved, which is desirable.

[0233] Li ｘ CoO ２ Figure 10 shows the crystal structure of the interior 100b of the positive electrode active material particle 100 when the internal x is approximately 1 and 0.2. The interior 100b occupies most of the volume of the positive electrode active material particle 100 and is a part that greatly contributes to charging and discharging, therefore CoO ２ The shifting of layers and changes in volume are arguably the most problematic aspects.

[0234] When x = 1, the positive electrode active material particle 100 has the same R-3m O3 crystal structure as conventional lithium cobalt oxide.

[0235] However, when x is 0.24 or less, for example, about 0.2 or about 0.12, the positive electrode active material particles 100 have a crystal structure different from that of conventional lithium cobalt oxide, which has an H1-3 type crystal structure. In this specification, "about 0.2" means 0.16 or more and 0.24 or less.

[0236] When x = approximately 0.2, the positive electrode active material particles 100 of one embodiment of the present invention have a crystal structure that belongs to the trigonal space group R-3m. This is CoO ２The layer symmetry is the same as that of O3. Therefore, this crystal structure will be called the O3' type crystal structure. This crystal structure is shown in Figure 10, labeled R-3m O3'.

[0237] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25. Furthermore, the lattice constant of the unit cell is such that the a-axis is 2.797≦a≦2.837(×10⁻¹⁰). −１ (nm) is preferred, and 2.807 ≤ a ≤ 2.827 (×10 −１ nm) is more preferable, and typically a = 2.817 (×10 −１ The value is (nm). The c-axis is 13.681 ≤ c ≤ 13.881 (×10). −１ c = 13.781 (nm) is preferred, 13.751 ≤ c ≤ 13.811 is more preferred, and typically c = 13.781 (×10) −１ It is (nm).

[0238] In the O3' type crystal structure, ions such as cobalt, nickel, and magnesium occupy the six-coordinate positions to oxygen. Lighter elements such as lithium may occupy the four-coordinate positions to oxygen.

[0239] As shown by the dotted line in Figure 10, the CoO of R-3m(O3) in the discharged state and the O3' type crystal structure are different. ２ There is almost no misalignment of the layers.

[0240] Furthermore, the difference in volume per unit number of cobalt atoms between the discharged state R-3m(O3) and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0241] Thus, in the positive electrode active material particles 100 of one aspect of the present invention, Li ｘ CoO ２When x is small, that is, when a large amount of lithium is desorbed, the change in crystal structure is suppressed compared to conventional positive electrode active material particles. Furthermore, the change in volume per unit of the same number of cobalt atoms is also suppressed. Therefore, the crystal structure of positive electrode active material particles 100 is less likely to collapse even when repeatedly charging and discharging in a manner where x is 0.24 or less. As a result, the decrease in charge / discharge capacity during charge / discharge cycles is suppressed in positive electrode active material particles 100. Also, because more lithium can be stably utilized than in conventional positive electrode active material particles, positive electrode active material particles 100 have a high discharge capacity per unit weight and per unit volume. Therefore, by using positive electrode active material particles 100, secondary batteries with high discharge capacity per unit weight and per unit volume can be manufactured.

[0242] The positive electrode active material particles 100 are Li ｘ CoO ２ It has been confirmed that when x is between 0.15 and 0.24, it may have an O3' type crystal structure, and it is presumed that it also has an O3' type crystal structure when x is greater than 0.24 and less than or equal to 0.27. However, the crystal structure is Li ｘ CoO ２ Because it is affected not only by x but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., it is not necessarily limited to the range of x mentioned above.

[0243] Therefore, the positive electrode active material particle 100 is Li ｘ CoO ２ When x is greater than 0.1 and less than or equal to 0.24, the entire interior 100b of the positive electrode active material particle 100 does not have to have an O3' type crystal structure. It may contain other crystal structures, or a part of it may be amorphous.

[0244] Also Li ｘ CoO ２ To make the internal x small, it is generally necessary to charge with a high charging voltage. Therefore Li ｘ CoO ２A state where x is small can be rephrased as a state where the device is charged at a high charging voltage. For example, when CC / CV charging is performed at a voltage of 4.6V or higher relative to the potential of lithium metal in an environment of 25°C, the H1-3 type crystal structure appears in conventional positive electrode active material particles. Therefore, a charging voltage of 4.6V or higher relative to the potential of lithium metal can be said to be a high charging voltage.

[0245] Therefore, the positive electrode active material particles 100 of one aspect of the present invention are preferable because they can maintain a crystal structure with R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6V or higher at 25°C. Furthermore, they are preferable because they can adopt an O3' type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65V or higher and 4.7V or lower at 25°C.

[0246] Even with the positive electrode active material particles 100, an H1-3 type crystal structure may only be observed when the charging voltage is further increased. Furthermore, as mentioned above, the crystal structure is affected by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., so even at lower charging voltages, for example, when the charging voltage is 4.5V or more and less than 4.6V at 25°C, the positive electrode active material particles 100 of one embodiment of the present invention may take on an O3' type crystal structure.

[0247] Furthermore, when graphite is used as the negative electrode active material in a secondary battery, for example, the voltage of the secondary battery will decrease by the amount of the graphite's potential compared to the above. The potential of graphite is approximately 0.05V to 0.2V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystal structure is observed when the voltage obtained by subtracting the graphite's potential from the above voltage is obtained.

[0248] Furthermore, while Figure 10 shows that lithium is present at all lithium sites with equal probability in the O3' type crystal, this is not the only case. It may be concentrated in some lithium sites, or, for example, in the monoclinic O1(Li) shown in Figure 11... ０．５ CoO ２ It may have symmetries such as ). The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0249] Furthermore, the O3' type crystal structure has CdCl randomly placed lithium between the layers. ２ It can also be said that this CdCl has a crystal structure similar to that of the type. ２ A crystal structure similar to this type is lithium nickelate Li ０．０６ NiO ２ The crystal structure is similar to that when charged to this level, but in pure lithium cobalt oxide or layered rock salt-type cathode active material particles containing a large amount of cobalt, CdCl is typically used. ２ It is known that it does not adopt a specific crystal structure.

[0250] Furthermore, it is preferable that the concentration gradient of additive element A is similar at multiple locations on the surface layer 100a of the positive electrode active material particles 100. In other words, it is preferable that the reinforcement derived from additive element A is uniformly present on the surface layer 100a. Even if there is reinforcement in a part of the surface layer 100a, if there are parts without reinforcement, stress may concentrate in those parts. If stress concentrates in a part of the positive electrode active material particles 100, defects such as cracks may occur from there, which may lead to cracking of the positive electrode active material particles and a decrease in discharge capacity.

[0251] However, the additive element A does not necessarily have to have a similar concentration gradient across the entire surface layer 100a of the positive electrode active material particles 100. An example of the distribution of additive element X near C-D in Figure 5B is shown in Figure 6D, and an example of the distribution of additive element Y near C-D is shown in Figure 6E.

[0252] Here, the region near C-D has a layered rock salt type crystal structure of R-3m, and the surface is (001) oriented. The (001) oriented surface may have a different distribution of additive element A than the other surfaces. For example, the (001) oriented surface and its surface layer 100a may have a distribution of one or more concentration peaks selected from additive elements X and Y that is limited to a shallower portion from the surface compared to surfaces other than the (001) oriented surface. Alternatively, the (001) oriented surface and its surface layer 100a may have lower concentrations of one or more elements selected from additive elements X and Y compared to the other orientations. Alternatively, the (001) oriented surface and its surface layer 100a may have one or more elements selected from additive elements X and Y below the detection limit.

[0253] In the layered rock salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This is CoO ２ It can be said that the structure consists of layers and lithium layers stacked alternately parallel to the (001) plane. Therefore, the diffusion pathways of lithium ions also exist parallel to the (001) plane.

[0254] CoO ２ Since the layer is relatively stable, the surface of the positive electrode active material particles 100 is more stable when it is oriented in the (001) direction. The main diffusion pathway of lithium ions during charging and discharging is not exposed on the (001) plane.

[0255] On the other hand, the lithium ion diffusion pathways are exposed on surfaces other than those oriented in the (001) direction. Therefore, the surfaces and surface layer 100a other than those oriented in the (001) direction are important regions for maintaining the lithium ion diffusion pathways, but at the same time, they are prone to instability because they are the regions where lithium ions first desorb. For this reason, reinforcing the surfaces and surface layer 100a other than those oriented in the (001) direction is extremely important for maintaining the overall crystal structure of the positive electrode active material particles 100.

[0256] Therefore, in another embodiment of the positive electrode active material particles 100 of the present invention, it is important that the distribution of the added element A on the surfaces other than (001) and their surface layer 100a1 is as shown in Figures 6A to 6C. On the other hand, on the (001) surface and its surface layer 100a, the concentration of the added element A may be low or absent, as described above.

[0257] As described in Embodiment 1, high-purity LiCoO ２ In the manufacturing method in which the additive element A is mixed in and heated after the initial manufacturing, the additive element A spreads mainly through the diffusion pathway of lithium ions. Therefore, it is easier to bring the distribution of the additive element A on surfaces other than (001) and its surface layer 100a within a desirable range.

[0258] <Grain Boundaries> In addition to the distribution described above, it is more preferable that at least a portion of the additive element A in the positive electrode active material particles 100 of one aspect of the present invention is concentrated in the grain boundaries and their vicinity. A crystal grain is a region in which atoms or molecules are arranged regularly and repeatedly in three dimensions with a constant period. A crystal grain boundary is the interface between crystal grains. The vicinity of a crystal grain boundary refers to the region within 10 nm of the grain boundary.

[0259] In this specification, "non-uniformity" refers to a situation where the concentration of an element in one region differs from that in other regions. It is synonymous with segregation, precipitation, heterogeneity, bias, or a mixture of areas with high and low concentrations.

[0260] For example, it is preferable that the magnesium concentration at and near the grain boundaries of the positive electrode active material particles 100 is higher than that of the interior 100b outside the grain boundaries. It is also preferable that the fluorine concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries. Furthermore, it is preferable that the nickel concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries. Furthermore, it is preferable that the aluminum concentration at and near the grain boundaries is higher than that of the interior 100b outside the grain boundaries.

[0261] Grain boundaries are a type of surface defect. Therefore, like surfaces, they tend to be unstable and prone to initiating changes in crystal structure. For this reason, increasing the concentration of additive element A at and near the grain boundaries can more effectively suppress changes in crystal structure.

[0262] Furthermore, if the magnesium and fluorine concentrations are high at and near the grain boundaries, even if cracks occur along the grain boundaries of the positive electrode active material particles 100 according to one embodiment of the present invention, the magnesium and fluorine concentrations will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material particles after cracks have occurred.

[0263] <Analysis Method> A certain positive electrode active material particle is Li ｘ CoO ２Whether or not the positive electrode active material particle 100 of the present invention has an O3' type crystal structure when x is small depends on Li ｘ CoO ２ The presence of positive electrode active material particles with a small x value can be determined by analyzing them using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc.

[0264] XRD is particularly favored because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material particles with high resolution, compare the crystallinity and crystal orientation, analyze the periodic distortion of the lattice and crystallite size, and obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling a secondary battery. Among XRD methods, powder XRD provides diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material particles 100, which occupies most of the volume of the positive electrode active material particles 100.

[0265] When analyzing crystallite size using powder XRD, it is preferable to measure while excluding the influence of the orientation of positive electrode active material particles due to pressure, etc. For example, it is preferable to extract positive electrode active material particles from the positive electrode obtained by disassembling a secondary battery, and measure them after obtaining a powder sample.

[0266] Furthermore, while it is preferable to obtain the XRD diffraction pattern when calculating the crystallite size using only the positive electrode active material, it may also be obtained in the positive electrode state, which includes a current collector, binder, and conductive material in addition to the positive electrode active material. However, in the positive electrode state, the positive electrode active material may be oriented due to the effects of pressurization during the manufacturing process. Since strong orientation may prevent accurate calculation of the crystallite size, it is more preferable to obtain the XRD diffraction pattern by removing the positive electrode active material layer from the positive electrode, removing some of the binder and other components from the positive electrode active material layer using a solvent, and then filling it into a sample holder.

[0267] For calculating crystallite size, for example, a Bruker D8 ADVANCE can be used, with CuKα as the X-ray source, 2θ between 15° and 90°, increase 0.005, and a LYNXEYE XE-T detector. The diffraction pattern obtained with these settings and the literature value for lithium cobaltate (ICSD col. code. 172909) can be used. The Rietveld method can be used with DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and settings can be as follows, for example: Emission Profile: CuKa5. lam Background: Chebychev polynomia: l, 5th Instrument Primary radius: 280mm Secondary radius: 280mm Linear PSD 2Th Angular range: 2.9 FDS angle: 0.3 Full Axial Convolution Filament length: 12mm Sample length: 15mm Receiving Slit Length: 12mm Primary Sollers: 2.5 Secondary Sollers: 2.5 Corrections Specimen displacement: Refine LP Factor: 0

[0268] It is preferable to use the value of LVol-IB, which is the crystallite size corrected by the integral width criterion calculated using the above method, as the crystallite size.

[0269] Since lithium cobalt oxide is prone to (001) orientation, setting the preferred orientation to (001) may yield a better GOF (goodness of fit). The preferred orientation can be the March-Dollase function or Spherical Harmonics. Furthermore, in the Rietveld method, if the preferred orientation is less than 0.8 or greater than 1.2, the sample orientation may be too strong, making it unsuitable for determining crystallite size. In such cases where the Rietveld method is unsuitable, it is preferable to determine the crystallite size using other refinement techniques that yield a better GOF. For example, the Whole-Powder Pattern Decomposition (WPPD) method can be employed.

[0270] Furthermore, with the full pattern resolution method, not only the crystallite size but also the lattice constant can be calculated without being affected by the orientation of the sample.

[0271] In one aspect of the present invention, the positive electrode active material particles 100 are Li ｘ CoO ２ A key feature is that the change in crystal structure is minimal when x is 1 and when it is 0.24 or less. Materials in which the crystal structure changes significantly when charged at high voltage, and in which crystal structures with large changes account for more than 50%, are undesirable because they cannot withstand repeated high-voltage charging and discharging.

[0272] It is also important to note that simply adding additive elements may not result in the formation of an O3' type crystal structure. For example, even if lithium cobalt oxide has magnesium and fluorine, or lithium cobalt oxide has magnesium and aluminum, the structure may differ depending on the concentration and distribution of the additive elements. ｘ CoO ２ There are two cases: one where x is 0.24 or less and the O3' type crystal structure accounts for 60% or more, and another where the H1-3 type crystal structure accounts for 50% or more.

[0273] Also, in the case of the positive electrode active material particles 100 of one embodiment of the present invention, when x is too small, such as 0.1 or less, or when the charging voltage exceeds 4.9 V, a crystal structure of the H1-3 type or trigonal O1 type may occur. Therefore, in order to determine whether the positive electrode active material particles 100 are of one embodiment of the present invention, analysis of the crystal structure including XRD and information such as the charge capacity or charging voltage are required.

[0274] However, the positive electrode active material particles in a state where x is small may change the crystal structure when exposed to air. For example, the crystal structure may change from the O3' type to the H1-3 type. Therefore, it is preferable to handle all samples for crystal structure analysis in an inert atmosphere such as an argon atmosphere.

[0275] On the other hand, even when handled in an argon atmosphere, the crystal structure of the positive electrode after disassembling the secondary battery may change with time. Therefore, it is preferable to adopt a method that can be measured quickly as needed.

[0276] In the case of XRD, in order to quickly observe the main peaks, the detector and / or the measurement start angle etc. can be appropriately changed. For example, it is preferable to measure the main peaks within 13 minutes from the start of measurement.

[0277] Also, whether the distribution of the additive elements possessed by the positive electrode active material particles is in the state as described above can be determined by analyzing using, for example, XPS, EDX, EPMA (Electron Probe Micro Analyzer), etc.

[0278] Also, the crystal structure of the surface layer portion 100a, crystal grain boundaries, etc. can be analyzed by electron diffraction of the cross section of the positive electrode active material particles 100.

[0279] <Charging method> The charging for determining whether the composite oxide is the positive electrode active material particles​

[0280] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry containing positive electrode active material particles, a conductive material, and a binder.

[0281] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the voltage of the secondary battery and the potential of the positive electrode will differ. In this specification, unless otherwise specified, the voltage and potential refer to the potential of the positive electrode.

[0282] The electrolyte consists of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, with 1 mol / L lithium hexafluoride phosphate (LiPF) added as the electrolyte. ６ A preparation made by adding ( ) and 2 wt% vinylene carbonate (VC) as an additive can be used.

[0283] A 25 μm thick porous polypropylene film can be used as the separator.

[0284] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0285] The coin cell manufactured under the above conditions is charged with an arbitrary voltage (e.g., 4.50V, 4.55V, 4.58V, 4.60V, 4.62V, 4.65V, 4.70V, 4.75V, or 4.80V). The charging method is not particularly limited as long as it can be charged at any voltage for a sufficient amount of time. In this specification, when approximately 4.6V is mentioned, it refers to a voltage between 4.58V and 4.62V. For example, when charging with CCCV, the current in CC charging can be between 20mA / g and 100mA / g. CV charging can be terminated at between 2mA / g and 10mA / g. It is desirable to charge with such small current values ​​in order to observe the phase change of the positive electrode active material particles. The charging temperature should be 25°C or 45°C. After charging in this manner, the coin cell can be disassembled in a glove box under an argon atmosphere and the positive electrode can be removed to obtain positive electrode active material particles with any charging capacity. When performing various analyses afterward, it is preferable to seal the device in an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the device in a sealed container in an argon atmosphere. It is also preferable to remove the positive electrode as soon as possible after charging is complete and use it for analysis. Specifically, it is preferable to do this within one hour after charging is complete, and more preferably within 30 minutes.

[0286] Furthermore, when analyzing the crystal structure of the charged state after multiple charge-discharge cycles, for example, charging can be performed by constant current charging at a current value of 20 mA / g to 100 mA / g up to any voltage (e.g., 4.50 V, 4.55 V, 4.58 V, 4.60 V, 4.62 V, 4.65 V, 4.70 V, 4.75 V, or 4.80 V), then constant voltage charging until the current value becomes 2 mA / g to 10 mA / g, and discharging can be performed by constant current discharge at 20 mA / g to 100 mA / g up to 2.5 V. Alternatively, discharging can be performed by constant current discharge at 20 mA / g to 200 mA / g up to 3.0 V.

[0287] Furthermore, when analyzing the crystal structure of the discharged state after multiple charge-discharge cycles, for example, constant current discharge can be performed up to 2.5V with a current value of 20mA / g to 200mA / g. Alternatively, constant current discharge can be performed up to 3.0V with a current value of 20mA / g to 200mA / g.

[0288] <XRD> The equipment and conditions for XRD measurement are not particularly limited. For example, measurements can be taken with the following equipment and conditions: XRD equipment: Bruker AXS, D8 ADVANCE; X-ray: CuKα1; Output: 40KV, 40mA; Slit width: Div. Slit, 0.5°; Detector: LynxEye; Scanning 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.

[0289] If the sample to be measured is a powder, it can be set up by placing it in a glass sample holder or by sprinkling the sample onto a grease-coated silicon anti-reflective plate. If the sample to be measured is a positive electrode, the positive electrode can be attached to a substrate with double-sided tape, and the positive electrode active material layer can be set up to match the measurement surface required by the instrument. If the positive electrode active material layer is higher than the measurement surface required by the instrument, the diffraction pattern will shift overall to the higher angle side, and if it is lower, it will shift overall to the lower angle side. In this case, it is preferable to correct the shift in the diffraction pattern using crystal structure analysis software or the like.

[0290] Figures 13 and 14 show the ideal powder XRD patterns calculated from the O3' type crystal structure and the H1-3 type crystal structure model using CuKα1 line. For comparison, Li ｘ CoO ２ LiCoO inside x=1 ２ The ideal XRD patterns calculated from the crystal structures of O3 and trigonal O1 at x=0 are also shown. ２ (O3) and CoO ２ The pattern (O1) was created using Reflex Powder Diffraction, one of the modules in Materials Studio (BIOVIA), based on crystal structure information obtained from ICSD. The range of 2θ was set to 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562 × 10⁻¹⁰ −１０m and λ² were left unset, and Monochromator was set to single. The XRD pattern for the H1-3 type crystal structure was created using the same method as above, based on the information of the H1-3 type crystal structure shown in Figure 11. The XRD pattern for the O3' type crystal structure was created by estimating the crystal structure from the XRD pattern of the positive electrode active material particles of one embodiment of the present invention, fitting it using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and creating the XRD pattern in the same manner as the others.

[0291] As shown in Figure 13, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°).

[0292] However, as shown in Figure 14, peaks do not appear at these positions in the H1-3 type crystal structure and trigonal O1. Therefore, Li ｘ CoO ２ The appearance of diffraction peaks at 2θ = 19.25 ± 0.12° (19.13° to 19.37°) and 2θ = 45.47 ± 0.10° (45.37° to 45.57°) when x is small is a characteristic feature of the positive electrode active material particle 100 in one embodiment of the present invention.

[0293] Furthermore, for the O3' type crystal structure, if the value of x in the XRD pattern shown in Figure 13 is slightly larger, for example, when charging is performed with a voltage slightly lower than 4.60V (4.56V, 4.57V, 4.58V, or 4.59V) as the upper limit of the charging voltage, the above peak will appear shifted to the lower angle side. For example, when charging is performed with a charging voltage of 4.58V as the upper limit, the positive electrode active material particles 100 have diffraction peaks at 2θ = 18.85 ± 0.20° and 2θ = 45.15 ± 0.10°.

[0294] This can also be described as the positions where the XRD diffraction peaks appear being close together in the crystal structures at x=1 and x≦0.24. More specifically, for the main diffraction peaks in the crystal structures at x=1 and x≦0.24 where 2θ is between 42° and 46°, the difference in 2θ is 0.7° or less, more preferably 0.5° or less.

[0295] In one aspect of the present invention, the positive electrode active material particles 100 are Li ｘ CoO ２ When x is small, it has an O3' type crystal structure, but not all of it has to be an O3' type crystal structure. It may contain other crystal structures, and part of it may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that the O3' type crystal structure accounts for 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3' type crystal structure accounts for 50% or more, more preferably 60% or more, and even more preferably 66% or more, it is possible to obtain cathode active material particles with sufficiently excellent cycle characteristics.

[0296] Furthermore, even after 5 or more charge-discharge cycles, 30 or more charge-discharge cycles, 50 or more charge-discharge cycles, or 100 or more charge-discharge cycles from the start of measurement, it is preferable that the O3' type crystal structure accounts for 35% or more, more preferably 40% or more, and even more preferably 43% or more when Rietveld analysis is performed.

[0297] Furthermore, the sharpness of diffraction peaks in the XRD pattern indicates high crystallinity. Therefore, it is preferable for each diffraction peak after charging to be sharp, i.e., have a narrow full width at half maximum (FWHM). The FWHM varies depending on the XRD measurement conditions or the value of 2θ, even for peaks arising from the same crystalline phase. Under the measurement conditions described above, for peaks observed with 2θ = 43° to 46°, the FWHM is preferably 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. It is not necessary for all peaks to satisfy this requirement. If some peaks satisfy this requirement, it can be said that the crystal phase has high crystallinity. Such high crystallinity contributes to the stabilization of the crystal structure after sufficient charging.

[0298] Furthermore, the crystallite size of the O3' type crystal structure of the positive electrode active material particles 100 is the same as that of LiCoO in the discharged state. ２ It only drops to about 1 / 20th of (O3). Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, Li ｘ CoO ２When x is small, a clear peak of the O3' type crystal structure can be observed. On the other hand, conventional LiCoO ２ Even if a portion of the crystal structure resembles the O3' type, the crystallite size will be smaller, and the peaks will be broad and small. The crystallite size can be determined from the full width at half maximum of the XRD peaks.

[0299] <XPS> In XPS (X-ray Photoelectron Spectroscopy), when using monochromatic aluminum Kα X-rays for inorganic oxides, it is possible to analyze regions from the surface to a depth of approximately 2 to 8 nm (usually less than 5 nm). Therefore, the concentration of each element can be quantitatively analyzed in a region that is about half the depth of the surface layer 100a. Furthermore, the bonding state of elements can be analyzed by narrow-scan analysis. The quantitative accuracy of XPS is usually around ±1 atomic percent, and the detection limit is approximately 1 atomic percent, although this varies depending on the element.

[0300] In one aspect of the present invention, it is preferable that the concentration of one or more selected additive elements in the positive electrode active material particles 100 is higher in the surface layer 100a than in the interior 100b. This is equivalent to saying that it is preferable that the concentration of one or more selected additive elements in the surface layer 100a is higher than the average concentration of the positive electrode active material particles 100 as a whole. For example, it can be said that it is preferable that the concentration of one or more selected additive elements from the surface layer 100a, measured by XPS, is higher than the average concentration of additive elements of the positive electrode active material particles 100 as a whole, measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry). For example, it is preferable that the concentration of magnesium in at least a portion of the surface layer 100a, measured by XPS, is higher than the average magnesium concentration of the positive electrode active material particles 100 as a whole. It is also preferable that the concentration of nickel in at least a portion of the surface layer 100a is higher than the average nickel concentration of the positive electrode active material particles 100 as a whole. Furthermore, it is preferable that the concentration of aluminum in at least a portion of the surface layer 100a is higher than the average concentration of aluminum in the entire positive electrode active material particles 100. Also, it is preferable that the concentration of fluorine in at least a portion of the surface layer 100a is higher than the average concentration of fluorine in the entire positive electrode active material particles 100.

[0301] In one embodiment of the present invention, the surface and surface layer 100a of the positive electrode active material particles 100 do not contain carbonates, hydroxyl groups, etc., that have been chemically adsorbed after the production of the positive electrode active material particles 100. Furthermore, the surface of the positive electrode active material particles 100 does not contain electrolyte, binder, conductive material, or compounds derived therefrom. Therefore, when quantifying the elements contained in the positive electrode active material particles, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc., which can be detected by surface analysis such as XPS. For example, XPS can separate the types of bonds through analysis, and corrections may be made to exclude C-F bonds derived from the binder.

[0302] Furthermore, before subjecting the sample to various analyses, the positive electrode active material particles and positive electrode active material layer may be washed to remove electrolyte, binder, conductive material, or compounds derived therefrom that adhere to the surface of the positive electrode active material particles. In this case, lithium may dissolve into the solvent used for washing, but even if this occurs, the added elements are unlikely to dissolve, so it will not affect the atomic ratio of the added elements.

[0303] Furthermore, the concentrations of the added elements may be compared in ratio to cobalt. Using the ratio to cobalt is preferable because it reduces the influence of carbonates and the like that chemically adsorbed after the production of the positive electrode active material particles. For example, the ratio of the number of atoms of magnesium to cobalt, Mg / Co, determined by XPS analysis is preferably 0.400 or more and 1.20 or less, more preferably 0.400 or more and 1.00 or less, more preferably 0.400 or more and 0.900 or less, and more preferably 0.400 or more and 0.700 or less.

[0304] Furthermore, for example, the ratio of nickel to cobalt atoms, Ni / Co, determined by XPS analysis, is preferably 0.050 or more and 0.200 or less, more preferably 0.050 or more and 0.150 or less, more preferably 0.050 or more and 0.100 or less, and more preferably 0.050 or more and 0.070 or less.

[0305] Furthermore, for example, the ratio of aluminum to cobalt atoms, Al / Co, determined by XPS analysis, is preferably 0.010 or more and 0.100 or less, more preferably 0.010 or more and 0.050 or less, and even more preferably 0.010 or more and 0.040 or less.

[0306] Furthermore, for example, the ratio of fluorine to magnesium atoms F / Mg determined by XPS analysis is preferably 0.100 or more and 1.00 or less, more preferably 0.100 or more and 0.800 or less, more preferably 0.100 or more and 0.500 or less, more preferably 0.100 or more and 0.300 or less, and more preferably 0.100 or more and 0.200 or less.

[0307] Being within the above range indicates that these additive elements are not attached to a narrow range on the surface of the positive electrode active material particles 100, but are widely distributed at a favorable concentration in the surface layer portion 100a of the positive electrode active material particles 100. That is, as a result of XPS analysis of the positive electrode active material particles 100, being within the above range means that even when charging and discharging are repeated such that x becomes 0.24 or less, the crystal structure is less likely to collapse, and excellent cycle characteristics can be realized. Also, good insertion and desorption of lithium in the positive electrode active material particles 100 become possible, and excellent rate characteristics can be realized.

[0308] When performing XPS analysis, for example, monochromatic aluminum Kα rays can be used as the X-rays. Also, as the energy resolution, it is preferable to use an XPS apparatus having an energy resolution such that the full width at half maximum of the Ag3d5 / 2 peak (112 eV) in the XPS spectrum of an Ag sample is 1.0 eV ± 0.1 eV. Also, the take-off angle may be, for example, 45°. For example, it can be measured under the following XPS apparatus and measurement conditions. Measuring apparatus: QuanteraII manufactured by PHI Co., Ltd. X-rays: Monochromatic Al Kα (1486.6 eV) Energy resolution: The full width at half maximum of the Ag3d5 / 2 peak is 1.0 eV ± 0.1 eV Detection area: 100 μmφ Detection depth: Approximately 4 to 5 nm (take-off angle 45°) Measurement spectrum: Wide scan, narrow scan of each detected element

[0309] When XPS analysis is performed on the positive electrode active material particles 100 of one aspect of the present invention, the peak (Mg1s peak) indicating the binding energy between magnesium and other elements is preferably 1303.0 eV or more and less than 1305.0 eV, and more preferably about 1304.0 eV. This is a value different from the binding energy of magnesium fluoride, which is 1306.0 eV, and is a value close to the binding energy of magnesium oxide.

[0310] In XPS analysis of positive electrode active material particles 100 according to one aspect of the present invention, the measured XPS spectrum is corrected so that the C1s peak matches a reference value (284.8 eV), that is, the entire spectrum is shifted. This reduces the influence of differences in XPS equipment, differences in measurement conditions, etc., on the XPS measurement.

[0311] Furthermore, in XPS analysis of the positive electrode active material particles 100 according to one embodiment of the present invention, when analyzing the Mg1s peak and determining the ratio of peak components derived from "O-Mg-O" bonds, peak components derived from "O-Mg-F" bonds, and peak components derived from "F-Mg-F" bonds, it is preferable to have a peak component derived from O-Mg-O bonds. Also, while a peak component derived from "O-Mg-F" bonds may be included, it is preferable that it accounts for 30% or less of the total of the three peak components, more preferably 20% or less, more preferably 10% or less, and even more preferably below the detection limit. Also, while a peak component derived from "F-Mg-F" bonds may be included, it is preferable that it accounts for 10% or less of the total, and even more preferably below the detection limit.

[0312] In other words, in the XPS analysis of positive electrode active material particles 100 according to one aspect of the present invention, when the ratio of peak components derived from "O-Mg-O" bonds, peak components derived from "O-Mg-F" bonds, and peak components derived from "F-Mg-F" bonds is analyzed, it is preferable that the peak component derived from "O-Mg-O" bonds is 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferable that it is 100%.

[0313] This section describes a method for analyzing the Mg1s peak in an XPS spectrum obtained through XPS analysis. In analyzing the Mg1s peak, the peak component derived from the O-Mg-O bond is designated as Fit Peak 1, the peak component derived from the O-Mg-F bond as Fit Peak 2, and the peak component derived from the F-Mg-F bond as Fit Peak 3. These three fit peaks are then combined, and the ratio of the combined peaks that minimizes the difference between this combined peak and the Mg1s peak in the XPS spectrum obtained through XPS analysis is calculated. The area ratio of Fit Peak 1, Fit Peak 2, and Fit Peak 3 at this time can be assumed to represent the relative abundance of the O-Mg-O bond, O-Mg-F bond, and F-Mg-F bond, and the analysis results can be output accordingly.

[0314] In the above XPS spectrum analysis method, the energy value (Ep1) at the maximum value (also called the peak top) of fitted peak 1 is MgO-coated LiCoO ２ The energy value at the maximum value of the Mg1s peak when measured separately using the standard sample can be referenced. Furthermore, the energy value at the maximum value of the fitted peak 3 (Ep3) is the same as that of magnesium fluoride (MgF ２ For example, the energy value at the maximum value of the Mg1s peak when MGH18XB (purity 99.9% (3N) up) from the High Purity Chemical Laboratory is measured separately as a standard sample can be referenced. Also, the energy value at the maximum value of Fit Peak 2 (Ep2) can be an intermediate value between Ep1 and Ep3. Furthermore, Ep1 is located on the lower energy side compared to Ep3. The energy value at the maximum value of the peak is also called the peak position.

[0315] In XPS analysis of positive electrode active material particles 100 according to one embodiment of the present invention, the analysis result of the Mg1s peak being within the above preferred range can be determined from the peak position and the full width at half maximum (FWHM) of the peak. For example, the FWHM of the Mg1s peak is preferably 1.0 eV to 3.0 eV, more preferably 1.0 eV to 2.8 eV, and particularly preferably 1.0 eV to 2.6 eV. In the above, the peak position of the Mg1s peak is on the lower energy side than the energy value at the maximum value of the Mg1s peak when magnesium fluoride is measured separately as a standard sample.

[0316] <EDX> It is preferable that one or more of the additive elements in the positive electrode active material particles 100 have a concentration gradient. It is even more preferable that the depth of the concentration peaks from the surface differs depending on the additive element. The concentration gradient of the additive elements can be evaluated, for example, by exposing the cross-section of the positive electrode active material particles 100 using FIB (Focused Ion Beam) and analyzing the cross-section using EDX, EPMA (Electron Probe Microanalysis), etc.

[0317] Within EDX analysis, measuring while scanning within a region and evaluating that region in two dimensions is called EDX surface analysis. Measuring while scanning linearly and evaluating the distribution of atomic concentration within positive electrode active material particles is called line analysis. Furthermore, sometimes line analysis is also used to refer to the extraction of linear region data from EDX surface analysis. Measuring a region without scanning is called point analysis.

[0318] EDX surface analysis (e.g., elemental mapping) allows for quantitative analysis of the concentration of additive elements in the surface layer 100a, interior 100b, and near grain boundaries of the positive electrode active material particles 100. EDX radiation analysis allows for analysis of the concentration distribution and maximum value of the additive elements. Furthermore, analysis using thinned samples, such as STEM-EDX, is preferable because it allows for analysis of the concentration distribution in the depth direction from the surface to the center of the positive electrode active material particles in a specific region, without being affected by the distribution in the depth direction.

[0319] Since the positive electrode active material particles 100 are compounds containing a transition metal and oxygen that can insert and remove lithium, the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) and oxygen, which undergo oxidation and reduction during lithium insertion and removal, are present and the region where they are absent, is defined as the surface of the positive electrode active material particles. When the positive electrode active material particles are subjected to analysis, a protective film may be applied to the surface, but the protective film is not included in the positive electrode active material particles. As the protective film, single-layer or multi-layer films of carbon, metal, oxide, resin, etc., may be used.

[0320] In STEM-EDX ray analysis, due to the principle or measurement errors, the graph of the detected characteristic X-rays of an element does not change sharply, making it difficult to precisely determine the surface. Therefore, when referring to the depth direction in STEM-EDX ray analysis, the detected amount of characteristic X-rays of the transition metal M is considered to be the average value M of the detected characteristic X-rays of the transition metal M inside the surface. ＡＶＥ And the average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ The point where the sum of the two is 50%, or where the amount of oxygen characteristic X-rays detected is equal to the average value of the amount of oxygen characteristic X-rays detected inside. ＡＶＥ And the average value of the detected characteristic X-rays of background oxygen O ＢＧ The reference point is the point at which the sum of the above is 50%. Note that if the detected amount of characteristic X-rays of the transition metal M is different from the point at which the detected amount of characteristic X-rays of oxygen sum of the average detected amount of characteristic X-rays of oxygen inside the body and the average detected amount of characteristic X-rays of oxygen in the background is 50%, it is thought to be due to the influence of oxygen-containing metal oxides, carbonates, etc. adhering to the surface, and therefore the detected amount of characteristic X-rays of the transition metal M is different from the point at which the detected amount of characteristic X-rays of oxygen is different from the point at which the sum of the average detected amount of characteristic X-rays of oxygen inside the body and the average detected amount of characteristic X-rays of oxygen in the background is 50%. ＡＶＥ And the average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ The point at 50% of the sum of these can be adopted as the reference point. Also, in the case of positive electrode active material particles having multiple transition metals M, the transition metal element M that has the highest amount of characteristic X-rays detected inside is selected. ＡＶＥ and M ＢＧ The above reference points can be determined using this method.

[0321] The average value M of the detected characteristic X-rays of the above transition metal M in the background. ＢＧ For example, the average value M of the detected characteristic X-rays of the transition metal M can be determined by averaging the range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material particles, while avoiding the vicinity where the detection amount of characteristic X-rays of the transition metal M begins to increase. ＡＶＥ The average value of the background characteristic X-ray O is obtained by averaging a range of 2 nm or more, preferably 3 nm or more, from a depth of 30 nm or more, preferably more than 50 nm, in the region where the detection amount of characteristic X-rays of transition metal M and oxygen saturates and stabilizes, for example, from the region where the detection amount of characteristic X-rays of transition metal M begins to increase. ＢＧ and the average value of the detected amount of characteristic X-rays of the internal oxygen O ＡＶＥ This can be calculated in a similar manner.

[0322] Furthermore, the surface of the positive electrode active material particles 100 in cross-sectional STEM images, etc., is defined as the boundary between the region where an image originating from the crystal structure of the positive electrode active material particles is observed and the region where it is not observed, and is the outermost region where atomic columns originating from the nuclei of metal elements with atomic numbers greater than lithium among the metal elements constituting the positive electrode active material particles are confirmed.

[0323] Furthermore, in STEM-EDX analysis, a peak refers to the maximum value of a convex shape appearing on the graph of characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element. Noise in STEM-EDX analysis can include measurements with a width at half maximum (FWHM) below the spatial resolution (R), for example, R / 2 or less.

[0324] Scanning the same location multiple times under the same conditions can reduce the effects of noise. For example, the cumulative value measured by two scans can be used as the detected value for each element. The number of scans is not limited to two; more scans can be performed, and the cumulative value can be used as the detected value for each element.

[0325] For elemental quantification in EDX analysis, a standardless quantification method can be employed, using the k-factor built into the analytical instrument and / or analytical software. Furthermore, when determining elemental concentrations from the quantification results, the elements to be considered (also called the denominator elements) preferably include the elements used in the target material, raw materials, and pre-analysis treatment. For example, these can be the 14 elements carbon, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, titanium, iron, cobalt, nickel, and gallium.

[0326] STEM-EDX radiation analysis can be performed, for example, as follows: First, a protective film is deposited on the surface of the positive electrode active material particles. For example, carbon can be deposited using an ion sputtering apparatus (Hitachi High-Tech MC1000).

[0327] Next, the positive electrode active material particles are thinned to prepare a STEM cross-sectional sample. For example, thinning can be performed using a FIB-SEM device (Hitachi High-Tech XVision 200TBS). In this case, pickup is performed using an MPS (microprobing system), and the finishing conditions can be set to, for example, an acceleration voltage of 10kV.

[0328] STEM-EDX ray analysis can be performed using, for example, a STEM instrument (Hitachi High-Tech HD-2700) and an EDAX Octane T Ultra W EDX detector. An example of the conditions for EDX ray analysis using the Hitachi High-Tech HD-2700 is to set the emission current of the STEM instrument to 6 μA to 10 μA and measure areas of the thinned sample with little depth and unevenness. The magnification can be, for example, around 150,000x. The conditions for EDX ray analysis can be drift-corrected, with a line width of 42 nm, a pitch of 0.2 nm, and 6 or more frames.

[0329] To achieve high spatial resolution in STEM-EDX ray analysis, it is preferable to have a small electron beam diameter (also called beam diameter, probe diameter, or probe diameter). In STEM-EDX ray analysis, the beam diameter is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less. Furthermore, to increase the analytical sensitivity in STEM-EDX ray analysis, it is preferable to increase the electron beam current (also called probe current). Therefore, it is preferable that the apparatus used for STEM-EDX ray analysis be equipped with a spherical aberration correction device (Cs collector) that can reduce the beam diameter and increase the beam current.

[0330] Furthermore, in positive electrode active material particles 100 having magnesium and fluorine as additive elements, it is preferable that the distribution of fluorine has a region that overlaps with the distribution of magnesium. For example, it is preferable that the difference in depth direction between the peak of fluorine concentration or detected amount and the peak of magnesium concentration or detected amount is within 10 nm, more preferably within 3 nm, even more preferably within 1 nm, and still more preferably within 0.5 nm.

[0331] Furthermore, in positive electrode active material particles 100 having nickel as an additive element, the peak of nickel concentration or detected amount in the surface layer 100a is preferably located on the surface of the positive electrode active material particle 100, or within a depth of 3 nm from the reference point toward the center, and more preferably within a depth of 1 nm. Furthermore, in positive electrode active material particles 100 having magnesium and nickel, the distribution of nickel is preferably in a region that overlaps with the distribution of magnesium. For example, the difference in depth between the peak of nickel concentration or detected amount and the peak of magnesium concentration or detected amount is preferably within 3 nm, and more preferably within 1 nm.

[0332] Furthermore, if the positive electrode active material particles 100 contain aluminum as an additive element, when EDX radiation analysis is performed, it is preferable that the peaks of concentration or detection amount of magnesium, nickel, or fluorine are closer to the surface than the peaks of concentration or detection amount of aluminum in the surface layer 100a. In other words, it is preferable that the peak of concentration or detection amount of aluminum in the surface layer 100a is located further inward than the peaks of concentration or detection amount of magnesium, nickel, or fluorine. For example, it is preferable that the peak of concentration or detection amount of aluminum is located on the surface of the positive electrode active material particles 100, or at a depth of 0.5 nm to 50 nm from a reference point toward the center, and more preferably at a depth of 5 nm to 50 nm.

[0333] Here, we will explain how to represent the positional relationships of elemental distributions when performing EDX radiation analysis, using Figures 15A to 15G. Figures 15A to 15F are schematic diagrams showing the concentration distribution or detection amount distribution of the first element e1 and the second element e2. Figure 15G is a schematic diagram showing the concentration distribution or detection amount distribution of the first element e1, the second element e2, and the third element e3.

[0334] For example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15A, the position where the concentration or detection amount of the second element e2 is maximum is located further inside than the position where the concentration or detection amount of the first element e1 is maximum. Also, for example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15B, the position where the concentration or detection amount of the second element e2 is maximum is located further inside than the position where the concentration or detection amount of the first element e1 is maximum. Also, for example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15C, the position where the concentration or detection amount of the first element e1 is maximum is located further inside than the position where the concentration or detection amount of the second element e2 is maximum. Furthermore, for example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15D, the position where the concentration or detection amount of the second element e2 is maximum is located further inside than the position where the concentration or detection amount of the first element e1 is maximum. Furthermore, for example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15E, the position where the concentration or detection amount of the first element e1 is maximum is located further inside than the position where the concentration or detection amount of the second element e2 is maximum. Furthermore, for example, if the concentration distribution or detection amount distribution of the first element e1 and the second element e2 is as shown in Figure 15F, the position where the concentration or detection amount of the second element e2 is maximum is located further inside than the position where the concentration or detection amount of the first element e1 is maximum.

[0335] The expression "having a region where the distributions overlap" will be explained using the example of the positional relationship shown in Figure 15G for the concentration distributions or detection amount distributions of the first element e1, the second element e2, and the third element e3. In this specification, "having a region where the distributions of two elements overlap" means, for example, that the position where the maximum value occurs in the concentration distribution or detection amount distribution of at least one element is located within the range where the concentration or detection amount in the concentration distribution or detection amount distribution of the other element is 1 / 5 or more of the maximum value. Note that if the detection intensity of the background in EDX analysis is 1 / 5 or more of the above "maximum value", then "1 / 5 of the maximum value" in the above text shall be referred to as "background detection intensity (also called the detection limit)".

[0336] For example, in the positional relationship shown in Figure 15G, the position (p2) where the concentration distribution or detection amount distribution of the second element e2 is at its maximum value is located within the range (hatched area in the figure) where the concentration or detection amount of the first element e1 is at or above 1 / 5 of the maximum value (or the lower detection limit). Therefore, the first element e1 and the second element e2 have a region where their distributions overlap. On the other hand, the position (p3) where the concentration distribution or detection amount distribution of the third element e3 is at its maximum value is not located within the range (hatched area in the figure) where the concentration or detection amount of the first element e1 is at or above 1 / 5 of the maximum value (or the lower detection limit). Therefore, the first element e1 and the third element e3 cannot be said to have a region where their distributions overlap.

[0337] Furthermore, in the case of the positional relationship shown in Figure 15G, it can be said that the distribution of the second element e2 and the distribution of the third element e3 are located more inward than the distribution of the first element e1. Alternatively, it can be said that the distribution of the second element e2 and the distribution of the third element e3 are biased towards the inward side compared to the distribution of the first element e1.

[0338] <Powder Resistance Measurement> The positive electrode active material particles 100 according to one aspect of the present invention have a stable crystal structure even at high voltages. Because the crystal structure of the positive electrode active material particles is stable in the charged state, the decrease in charge / discharge capacity due to repeated charge and discharge can be suppressed. As a feature of the positive electrode active material particles 100 having the above-mentioned excellent properties, in the above <XRD>, Li ｘ CoO ２ It was explained that when x is small, it has an O3' type and / or monoclinic O1(15) type crystal structure. Furthermore, in the above <EDX> section, the preferred distribution of additive element A (e.g., Mg, Al, Ni) when the positive electrode active material particles 100 are subjected to STEM-EDX analysis was explained. Furthermore, in the above <XPS> section, the preferred ratio of additive element A (e.g., Mg, Al, Ni) when the positive electrode active material particles 100 are subjected to XPS analysis was explained. Moreover, the positive electrode active material particles 100 of one embodiment of the present invention also have distinctive features in terms of the volume resistivity of the powder.

[0339] One characteristic of the positive electrode active material particles 100 according to one aspect of the present invention is that the volume resistivity of the positive electrode active material particles 100 in powder form is 1.0 × 10⁻¹⁴ at a pressure of 64 MPa. ８ Ω・cm or more 1.0×10 １０ It is preferable that the volume resistivity is Ω·cm or less. The positive electrode active material particles 100 having the above volume resistivity have a stable crystal structure even at high voltages, and this can serve as an indicator that the surface layer 100a, which is important for the stability of the crystal structure of the positive electrode active material particles in the charged state, has been formed well.

[0340] Furthermore, the volume resistivity of the positive electrode active material particles 100 in powder form is 1.0 × 10⁻⁶ at a pressure of 64 MPa. ８ Ω・cm or more 1.0×10 ９ It is more preferable that it be Ω·cm or less, and 1.0 × 10 ８ Ω・cm or more 5.0×10 ８It is even more preferable that the volume resistivity is Ω·cm or less. The positive electrode active material particles 100 having the above volume resistivity have a stable crystal structure even at high voltages, and can serve as an indicator that the surface layer 100a, which is important for the stability of the crystal structure of the positive electrode active material particles in the charged state, has been formed well, and can also serve as an indicator that good lithium insertion and removal is possible in the positive electrode active material particles.

[0341] A method for measuring the volume resistivity of a powder of positive electrode active material particles 100 according to one aspect of the present invention will be described.

[0342] For measuring the volume resistivity of a powder, it is preferable to have a device with terminals for resistance measurement and a mechanism for applying pressure to the powder being measured. It is preferable to have four terminals (also called four probes) for resistance measurement. As a measuring device having terminals for resistance measurement and a mechanism for applying pressure to the powder (sample) being measured, for example, the MCP-PD600 manufactured by Nitto Seiko Analytech Co., Ltd. can be used. For the four-probe method, the Lorestar-GXII or Highrestar-UX can be used for the device. The Lorestar-GXII can be used for measuring low-resistance samples, and the Highrestar-UX can be used for measuring high-resistance samples. Furthermore, it is preferable to have a stable environment such as a dry room for measurement. As for the dry room environment, for example, a temperature environment of 25°C and a dew point environment of minus 40°C or lower is preferable.

[0343] The measurement of the volume resistivity of a powder using the measuring device described above will now be explained. First, the powder sample is placed in the measuring section. The measuring section has a structure in which the powder sample and the terminals for resistance measurement are in contact, and it is also possible to apply pressure to the powder sample. The measuring section also has a structure for measuring the volume of the powder sample. Specifically, the measuring section has a cylindrical space into which the powder sample is placed. The structure for measuring the volume of the powder sample described above makes it possible to measure the volume occupied by the powder at that time by measuring the height of the powder placed in the space.

[0344] In measuring the volume resistivity of a powder, the electrical resistance and volume of the powder are measured while pressure is applied to the powder. Multiple pressure conditions can be used. For example, the electrical resistance and volume of the powder can be measured at pressures of 13 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa. The volume resistivity of the powder can be calculated from the measured values ​​of electrical resistance and volume.

[0345] When performing the measurements described above, the volume resistivity of the positive electrode active material particles 100 in powder form according to one embodiment of the present invention is 1.0 × 10⁻¹⁴ at a pressure of 64 MPa. ８ Ω・cm or more 1.0×10 １０ When the value is Ω·cm or less, it exhibits favorable cycle characteristics in charge-discharge cycle tests under high voltage conditions, and 1.0 × 10 ８ Ω・cm or more 1.0×10 ９ When the volume resistivity is Ω·cm or less, it exhibits favorable cycle characteristics in charge-discharge cycle tests under high voltage conditions, and also exhibits favorable discharge characteristics in discharge rate tests. ８ Ω・cm or more 5.0×10 ８ When the value is Ω·cm or less, it exhibits even more favorable discharge characteristics in the discharge rate test.

[0346] <EPMA> The concentration of additive elements in the positive electrode active material particles 100 can be analyzed using EDX, but it can also be analyzed using EPMA. EPMA has a higher detection capability (also known as a lower detection limit) than EDX when analyzing elements present in trace amounts in a sample. Therefore, it is preferable to use EPMA when analyzing regions where additive elements are present in trace amounts.

[0347] In EPMA analysis, the cross-section of the positive electrode active material particles 100 is exposed by mechanical polishing, ion polishing, FIB, etc., and the cross-section is analyzed. As an EPMA apparatus, for example, the JEOL JXA-iHP200F electron probe microanalyzer can be used.

[0348] Because EPMA uses a wavelength-dispersive detector, it has a higher ability to detect trace elements compared to EDX, which uses an energy-dispersive detector. On the other hand, the spatial resolution of EPMA analysis is inferior to that of EDX (especially STEM-EDX). Therefore, STEM-EDX is suitable for analysis focusing on the detailed distribution of additive elements in the surface layer 100a of the positive electrode active material particles 100, while EPMA analysis is suitable for analysis of trace amounts of additive elements in the interior 100b. Note that because EPMA and EDX use different analytical methods, the concentration values ​​obtained when analyzing the same region using each method may not match.

[0349] The additive elements in the interior 100b of the positive electrode active material particles 100 are preferably magnesium and nickel in trace amounts. For example, in EPMA analysis, the ratio of the number of magnesium (Mg) to cobalt (Co) atoms in the interior 100b, Mg / Co, is preferably 0.005 or more and 0.03 or less, and more preferably around 0.01. By uniformly having the amount of magnesium shown here in the interior 100b, Li ｘ CoO ２ This is preferable because it can suppress changes in the crystal structure when the internal x is small.

[0350] Furthermore, in EPMA analysis, the ratio of nickel (Ni) to cobalt (Co) atoms in internal 100b, Ni / Co, is preferably 0.003 or more and 0.01 or less, and more preferably around 0.007. On the other hand, in EPMA analysis, the number of titanium atoms in internal 100b is preferably below the detection limit. For example, the detection limit for the number of titanium atoms is 0.2 at% when analyzing the interior of lithium cobalt oxide using JXA-iHP200F.

[0351] Furthermore, the interior 100b may contain aluminum in amounts undetectable or at the detection limit in EPMA analysis. The presence of aluminum in the interior 100b can stabilize the surrounding crystal structure. For example, the detection limit for the number of aluminum atoms is 0.1 at% when analyzing the interior of lithium cobalt oxide using JXA-iHP200F.

[0352] <Microelectron Diffraction Pattern> Similar to Raman spectroscopy, it is preferable that the microelectron diffraction pattern also shows the characteristics of the rock salt type crystal structure along with the crystal structure of the layered rock salt. However, in STEM images and microelectron diffraction patterns, taking into account the differences in sensitivity mentioned above, it is preferable that the characteristics of the rock salt type crystal structure do not become too strong in the surface layer 100a, especially at the outermost surface (for example, at a depth of 1 nm from the surface). This is because having an additive element such as magnesium in the lithium layer while maintaining a layered rock salt type crystal structure is preferable to having the outermost surface covered with a rock salt type crystal structure, as this ensures a diffusion pathway for lithium and provides a stronger function in stabilizing the crystal structure.

[0353] Therefore, when obtaining, for example, an ultramicroelectron diffraction pattern from a region with a depth of 1 nm or less from the surface and an ultramicroelectron diffraction pattern from a region with a depth of 3 nm to 10 nm, it is preferable that the difference between the lattice constants calculated from these patterns be small.

[0354] For example, the difference in lattice constants calculated from measurement points at a depth of 1 nm or less from the surface and measurement points at a depth of 3 nm to 10 nm is 0.1 × 10⁻¹⁰ with respect to the a-axis. −１０ It is preferable that it is less than or equal to m, and 1.0 × 10 for the c axis. −１０ It is preferable that it is less than or equal to m. Also, for the a-axis, 0.03 × 10 −１０ It is more preferable that it is less than or equal to m, and with respect to the c axis 0.6 × 10 −１０ It is more preferable if it is less than or equal to m. Also, for the a-axis, 0.04 × 10 −１０ It is even more preferable that it be less than or equal to m, and 0.3 × 10 for the c axis. −１０ It is even more preferable if it is less than or equal to m.

[0355] <Second Positive Electrode Active Material Particles> In one embodiment of the present invention, the positive electrode may have, in addition to the positive electrode active material particles 100, second positive electrode active material particles different from the positive electrode active material particles 100. The second positive electrode active material particles 200, like the positive electrode active material particles 100, have the function of taking in and releasing lithium ions during charging and discharging. The second positive electrode active material particles 200 used in one embodiment of the present invention can be made of a material that is similar to the positive electrode active material particles 100 except for the particle size, and which does not degrade as much during charging and discharging (hereinafter also referred to as "charging and discharging") even at high charging voltages. Specifically, in the method for producing positive electrode active material particles described in Embodiment 1, positive electrode active material particles (composite oxides) with a particle size (median diameter (D50)) of 0.1 μm or more and less than 9 μm, preferably 1 μm or more and 5 μm or less, obtained by reducing the particle size of the starting material and shortening the heating treatment by lowering the temperature. The second positive electrode active material particles 200 preferably contain one or more of the additive elements X, Y, and Z, similar to the positive electrode active material particles 100 described above.

[0356] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0357] (Embodiment 3) In this embodiment, each element constituting the battery will be described.

[0358] [Positive Electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has positive electrode active material particles and may further have at least one of a conductive material and a binder. The positive electrode active material particles can be the positive electrode active material particles 100 described in Embodiment 1 and Embodiment 2.

[0359] The positive electrode current collector can be made of, for example, metal foil. The positive electrode can be formed by applying a slurry to the metal foil and drying it. Pressing may also be applied after drying. The positive electrode is formed by creating an active material layer on the positive electrode current collector.

[0360] A slurry is a liquid material used to form an active material layer on a positive electrode current collector. It contains an active material, a binder, and a solvent, and preferably also contains a conductive material. The slurry is sometimes called an electrode slurry or an active material slurry. When forming a positive electrode active material layer, a positive electrode slurry is used, and when forming a negative electrode active material layer, a negative electrode slurry is used.

[0361] The positive electrode active material particles have the function of taking in and releasing lithium ions during charging and discharging. The positive electrode active material particles 100 used in one embodiment of the present invention described above can be made of a material that does not degrade much during charging and discharging, even at high charging voltages.

[0362] <Binder> As a binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluororubber can also be used as a binder.

[0363] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, or starch. It is even preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0364] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose as the binder.

[0365] You may use a combination of several of the binders mentioned above.

[0366] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials have excellent adhesive and elastic properties, but their viscosity can be difficult to adjust when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. As a material with particularly excellent viscosity-modifying properties, a water-soluble polymer may be used. As a water-soluble polymer with particularly excellent viscosity-modifying properties, the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, or starch can be used.

[0367] Furthermore, cellulose derivatives such as carboxymethylcellulose can be made more soluble by using salts such as sodium or ammonium salts of carboxymethylcellulose, thereby increasing their effectiveness as viscosity modifiers. Increased solubility also improves the dispersibility with active materials or other components when preparing electrode slurries. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0368] Water-soluble polymers stabilize viscosity by dissolving in water, allowing for stable dispersion of active materials and other materials used as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of the active material. Additionally, cellulose derivatives such as carboxymethylcellulose often possess functional groups like hydroxyl or carboxyl groups, and these functional groups allow the polymers to interact with each other, resulting in a broad coverage of the active material surface.

[0369] When a binder covers or is in contact with the surface of the active material, it is expected to act as a passivation film, suppressing the decomposition of the electrolyte. Here, a "passivation film" is a film that does not conduct electricity, or has extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Furthermore, it is even more desirable for the passivation film to suppress electrical conductivity while still allowing lithium ions to conduct.

[0370] <Conductive Materials> Conductive materials, also called conductivity imparters or conductivity enhancers, are typically made of carbon. By attaching conductive materials between multiple active materials, the multiple active materials are electrically connected to each other, increasing conductivity. Note that "attachment" does not only refer to physical contact between the active materials and the conductive material, but also includes cases where covalent bonds are formed, bonds are formed by van der Waals forces, the conductive material covers a portion of the surface of the active material, the conductive material fits into surface irregularities of the active material, or where they are electrically connected even without physical contact.

[0371] The active material layers, such as the positive electrode active material layer and the negative electrode active material layer, preferably contain a conductive material.

[0372] As conductive materials, one or more of the following can be used: carbon black such as acetylene black and furnace black; graphite such as artificial graphite and natural graphite; carbon fibers such as carbon nanofibers and carbon nanotubes; and graphene compounds.

[0373] As carbon fibers, for example, mesophase pitch carbon fibers and isotropic pitch carbon fibers can be used. Alternatively, carbon nanofibers or carbon nanotubes can be used. Carbon nanotubes can be fabricated, for example, by vapor deposition.

[0374] In this specification, graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is defined as a material having carbon, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. This two-dimensional structure formed by a six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a bent shape. Graphene compounds may also be rolled up to resemble carbon nanofibers.

[0375] The content of conductive material relative to the total amount of active material layer is preferably 1 wt% to 10 wt%, and more preferably 1 wt% to 5 wt%.

[0376] Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene compounds enable surface contact with low contact resistance. Therefore, a smaller amount of graphene compound can improve the electrical conductivity between the granular active material and the graphene compound compared to conventional conductive materials. Consequently, the ratio of the active material in the active material layer can be increased. This, in turn, can increase the discharge capacity of the battery.

[0377] Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes, readily penetrate minute spaces. These minute spaces refer, for example, to regions between multiple active materials. By combining a carbon-containing compound that readily penetrates minute spaces with a sheet-like carbon-containing compound such as graphene, which can impart conductivity across multiple particles, the electrode density can be increased, and excellent conductive paths can be formed. A battery obtained by the manufacturing method according to one embodiment of the present invention can have high capacity density and stability, making it effective as an in-vehicle battery.

[0378] <Positive Electrode Current Collector> As the current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, aluminum alloys to which elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, have been added can be used. Alternatively, it may be formed from a metallic element that reacts with silicon to form a silicide. Metallic 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 various shapes such as foil, plate, sheet, mesh, perforated metal, or expanded metal as appropriate. The current collector should preferably have a thickness of 5 μm or more and 30 μm or less.

[0379] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a negative electrode active material, a conductive material, and a binder.

[0380] <Negative electrode active material> As the negative electrode active material, for example, alloy materials or carbon materials can be used.

[0381] Furthermore, the negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger 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. Compounds containing these elements may also be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ Mg ２ Sn, SnS ２ , V ２ Sn ３ FeSn ２ CoSn ２ Ni ３ Sn ２ ,Cd ６ Sn ５ Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ LaSn ３ La ３ Co ２ Sn ７ CoSb ３ Examples include InSb and SbSn. Here, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0382] In this specification, "SiO" refers to silicon monoxide, for example. Alternatively, SiO refers to SiO ｘ It can also be expressed as follows. Here, x preferably has a value of 1 or a value in the vicinity of 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0383] Carbon materials such as graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon fibers (carbon nanotubes), graphene, and carbon black can be used.

[0384] 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, spheroidal graphite having a spherical shape can be used as artificial graphite. For example, MCMB may have a spherical shape and is therefore preferable. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, which may also be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0385] Graphite exhibits a potential as low as lithium metal (0.05V to 0.3V vs. Li / Li) when lithium ions are inserted into it (during the formation of lithium-graphite intercalation compounds). ＋ This allows lithium-ion batteries using graphite to exhibit a high operating voltage. Furthermore, graphite is preferable because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0386] Furthermore, titanium dioxide (TiO) is used as the negative electrode active material. ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ Oxides such as those listed above can be used.

[0387] Furthermore, as the negative electrode active material, lithium and a nitride of a transition metal, Li ３ Li with an N-type structure ３−ｘ M ｘ N (M = Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N has a large discharge capacity (900 mAh / g, 1890 mAh / cm²). ３ ) indicates a preference.

[0388] When lithium and transition metal nitrides are used, lithium ions are contained in the negative electrode active material, so the positive electrode active material particles do not contain lithium ions. ２ O ５ , Cr ３ O ８ It is preferable that it be combined with materials such as the above. Furthermore, even when a material containing lithium ions is used for the positive electrode active material particles, lithium and a nitride of a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material particles beforehand.

[0389] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. As for materials that undergo a conversion reaction, 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 ,Cd ３ N, Ge ３ N ４ Nitrides such as NiP ２ FeP ２ CoP ３ Phosphates such as FeF ３ BiF ３ Examples of fluorides include the following.

[0390] Furthermore, another form of the negative electrode is one that does not have negative electrode active material at the end of battery manufacturing. As an example of a negative electrode without negative electrode active material, one can have only a negative electrode current collector at the end of battery manufacturing, in which lithium ions that detach from the positive electrode active material particles during battery charging deposit as lithium metal on the negative electrode current collector, forming a negative electrode active material layer. Batteries using such a negative electrode are sometimes called negative electrode-free (anode-free) batteries or negative electrode-less (anode-less) batteries.

[0391] When using a negative electrode without a negative electrode active material, a film may be provided on the negative electrode current collector to homogenize the deposition of lithium. As a film to homogenize the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As a solid electrolyte, sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. Among these, polymer-based solid electrolytes are suitable as a film to homogenize the deposition of lithium because it is relatively easy to form a uniform film on the negative electrode current collector. Alternatively, as a film to homogenize the deposition of lithium, for example, a metal film that forms an alloy with lithium can be used. As a metal film that forms an alloy with lithium, for example, a magnesium metal film can be used. Since lithium and magnesium form a solid solution over a wide composition range, it is suitable as a film to homogenize the deposition of lithium.

[0392] Furthermore, when using a negative electrode without negative electrode active material, a negative electrode current collector with irregularities can be used. When using a negative electrode current collector with irregularities, the recesses in the negative electrode current collector become cavities where lithium can easily be deposited, thus suppressing the formation of dendrite-like shapes when lithium is deposited.

[0393] The conductive material and binder that the negative electrode active material layer can have can be the same materials as the conductive material and binder that the positive electrode active material layer can have.

[0394] <Negative Electrode Current Collector> In addition to the same materials as the positive electrode current collector, copper and other materials can also be used for the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0395] [Electrolyte] A secondary battery has an electrolyte containing carrier ions. In this specification, the electrolyte is not limited to one containing an organic solvent that is liquid at room temperature, but also includes solid electrolytes, and electrolytes containing both an organic solvent that is liquid at room temperature and a solid electrolyte that is solid at room temperature (semi-solid electrolytes) are also included. Note that a solution in which lithium salt is dissolved in an organic solvent that is liquid at room temperature is sometimes called an electrolyte solution.

[0396] <Organic solvents that are liquid at room temperature> Examples of organic solvents that are liquid at room temperature are described below.

[0397] The organic solvent, which is liquid at room temperature, is preferably an aprotic organic solvent. For example, one or more of the following can be used: 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 (EP), propyl propionate (PP), methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc.

[0398] By using one or more flame-retardant and low-volatility ionic liquids (room-temperature molten salts) as organic solvents that are liquid at room temperature, it is possible to prevent the battery cell from rupturing and igniting even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in organic solvents include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, or aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in organic solvents include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0399] Furthermore, the lithium salt to be dissolved in the above organic solvent is, for example, LiPF ６ LiClO ４ LiAsF ６ LiBF ４LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ Li ２ B １０ Cl １０ Li ２ B １２ Cl １２ LiCF ３ SO ３ LiC ４ F ９ SO ３ LiC (CF ３ SO ２ ) ３ LiC(C ２ F ５ SO ２ ) ３ ,LiN(CF ３ SO ２ ) ２ ,LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), and LiN(C ２ F ５ SO ２ ) ２ You may use one or more selected from the above.

[0400] <Additives> The above organic solvent may contain additives. Additives can suppress the reaction decomposition of the electrolyte that may occur on the positive or negative electrode surface when the secondary battery is operated at high voltage and / or high temperature. Examples of additives include vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate) borate (LiBOB). LiBOB is particularly preferred because it easily forms a good film. VC or FEC are preferred because they can form a good film on the negative electrode during aging or initial charging of the secondary battery, improving cycle characteristics.

[0401] The additive may include a compound shown in the following general formula (G1). The following general formula (G1) is a compound having two cyano groups and can be called a dinitrile compound.

[0402]

[0403] In the above general formula (G1), R represents a hydrocarbon having 1 to 5 carbon atoms. Preferably, in the above general formula (G1), R represents a hydrocarbon having 2 to 4 carbon atoms.

[0404] Specific examples of the above general formula (G1) include succinonitrile, glutalonitrile, adiponitrile (ADN), or ethylene glycol bis(propionitrile) ether (EGBE).

[0405] The structural formula (H1) of succinonitrile is shown below.

[0406]

[0407] The structural formula (H2) of glutaronitrile is shown below.

[0408]

[0409] The structural formula (H3) of adiponitrile is shown below.

[0410]

[0411] The structural formula (H4) of ethylene glycol bis(propionitrile) ether is shown below.

[0412]

[0413] One or more dinitrile compounds can be used as additives.

[0414] Furthermore, fluorobenzene may be added to the above organic solvent. The concentration of the additive can be, for example, 0.1 wt% to 5 wt% of the total electrolyte. PS or EGBE is preferred because it can form a good film on the positive electrode during charging and discharging, improving cycle characteristics. FB is preferred because it improves the wettability of the organic solvent to the positive and negative electrodes. Dinitrile compounds are preferred because the nitrile groups are oriented toward the positive and negative electrodes, inhibiting oxidative decomposition of the organic solvent, thus improving high-voltage resistance. Furthermore, when a current collector having copper is used in the negative electrode, dinitrile compounds are preferred because they can prevent the dissolution of copper during over-discharge. Considering the use of secondary batteries at high voltages, it is preferable to add nitrile compounds.

[0415] The electrolyte does not need to be liquid at room temperature; a semi-solid material called a polymer gel electrolyte may be used as the organic solvent. Using a polymer gel electrolyte enhances safety against leakage and other issues. It also allows for thinner and lighter battery cells.

[0416] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide-based gels, polypropylene oxide-based gels, fluorine-based polymer gels, and the like can be used.

[0417] 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 resulting polymer may also have a porous structure.

[0418] [Separator] When the electrolyte contains an electrolyte solution, a separator is placed between the positive electrode and the negative electrode. As the separator, for example, materials such as paper and other cellulose fibers, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyimide, or polyurethane can be used. It is preferable that the separator be processed into a bag shape and placed so as to enclose either the positive electrode or the negative electrode.

[0419] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, hydroxide material, fluorine material, polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles, silicon oxide particles, and magnesium oxide. Examples of hydroxide materials include magnesium hydroxide and aluminum hydroxide. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid and para-aramid).

[0420] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and improving the reliability of secondary batteries. Coating with fluorine-based materials facilitates better adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thereby enhancing the safety of secondary batteries.

[0421] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0422] By using a multi-layered separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the secondary battery.

[0423] [Outer Covering] The outer covering of a battery can be made of metal materials such as aluminum, stainless steel, or titanium, or resin materials. A film-like outer covering can also be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film or metal foil made of aluminum, stainless steel, titanium, copper, nickel, etc. is placed on a film made of polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide resin or polyester resin is placed on the metal thin film as the outer surface of the outer covering. Such a multilayer film can be called a laminate film. In this case, the name of the material of the metal layer in the laminate film may be used to refer to it, such as aluminum laminate film, stainless steel laminate film, titanium laminate film, copper laminate film, nickel laminate film, etc.

[0424] The material or thickness of the metal layer in the laminate film can affect the flexibility of the battery. For batteries where flexibility or weight reduction is important, it is preferable to use an aluminum laminate film having a polypropylene layer, an aluminum layer, and a nylon layer as the outer casing. Here, the thickness of the aluminum layer is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and more preferably 20 μm or less. If the aluminum layer is thinner than 10 μm, there is a concern that the gas barrier properties will decrease due to pinholes in the aluminum layer, so it is desirable that the thickness of the aluminum layer be 10 μm or more.

[0425] For batteries where physical strength or safety is important, it is preferable to use a stainless laminate film having a polypropylene layer, a stainless steel layer, and a nylon layer as an outer casing. Furthermore, a polyethylene terephthalate layer may be provided on the nylon layer. Here, the thickness of the stainless steel layer is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and more preferably 20 μm or less. If the stainless steel layer is thinner than 10 μm, there is a concern that the gas barrier properties will decrease due to pinholes in the stainless steel layer, so it is desirable that the thickness of the stainless steel layer be 10 μm or more. In this specification, stainless steel refers to steel (an alloy of iron and carbon) containing about 12% or more chromium, and can be broadly classified into martensitic, ferritic, or austenitic types in terms of composition. It also includes stainless steel to which one or more elements selected from Ti, Nb, Mo, Cu, Ni, or Si have been added.

[0426] Alternatively, for example, it is preferable to use a titanium laminate film having a polypropylene layer, a titanium layer, and a nylon layer. Furthermore, a polyethylene terephthalate layer may be provided on the nylon layer. Here, the thickness of the titanium layer is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and more preferably 20 μm or less. If the titanium layer is thinner than 10 μm, there is a concern that the gas barrier properties will decrease due to pinholes in the titanium layer, so it is desirable that the thickness of the titanium layer be 10 μm or more.

[0427] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0428] (Embodiment 4) In this embodiment, an example of the shape of a secondary battery having a positive electrode manufactured by the manufacturing method described in the previous embodiment will be explained.

[0429] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 16A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 16B is an external view, and Figure 16C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

[0430] Note that Figure 16A is a schematic diagram to show the overlapping of components (up / down relationship and positional relationship) for clarity. Therefore, Figures 16A and 16B are not perfectly identical corresponding diagrams.

[0431] In Figure 16A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with a gasket between the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 16A. The spacer 322 and washer 312 are used to protect the inside or fix the position within the can when the positive electrode can 301 and the negative electrode can 302 are pressed together. The spacer 322 and washer 312 are made of stainless steel or an insulating material.

[0432] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0433] Figure 16B is a perspective view of the completed coin-type rechargeable battery.

[0434] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, which are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0435] Furthermore, the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300 may each have the active material layer formed on only one side.

[0436] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel or aluminum to prevent corrosion caused by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0437] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 16C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are pressed together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0438] By having the above configuration, a coin-type secondary battery 300 with high discharge capacity and excellent cycle characteristics can be obtained.

[0439] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be described with reference to Figure 17A. As shown in Figure 17A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery can (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery can (outer casing) 602 are insulated by a gasket (insulating packing) 610.

[0440] Figure 17B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 17B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0441] Inside the hollow cylindrical battery can 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery can 602 is closed at one end and open at the other. The battery can 602 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (for example, stainless steel), which are corrosion resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel and aluminum, etc., to prevent corrosion by the electrolyte. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and insulating plate 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0442] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector.

[0443] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0444] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Metal materials such as aluminum can be used for the positive electrode terminal 603, and copper can be used for the negative electrode terminal 607. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the rise in the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. PTC elements include barium titanate (BaTiO ３ ) semiconductor ceramics and the like can be used.

[0445] Figure 17C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging and / or over-discharging.

[0446] Figure 17D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to the conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0447] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0448] Furthermore, a temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0449] Furthermore, in Figure 17D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0450] [Other structural examples of secondary batteries] Structural examples of secondary batteries will be explained using Figures 18 and 19.

[0451] The secondary battery 913 shown in Figure 18A has a wound body 950 with terminals 951 and 952 provided inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 18A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum), a composite material of metal and resin, etc.

[0452] Furthermore, as shown in Figure 18B, the housing 930 shown in Figure 18A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 18B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0453] An insulating material can be used for the housing 930a. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. For the housing 930b, for example, a metal material can be used.

[0454] Furthermore, the structure of the wound body 950 is shown in Figure 18C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0455] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 19. The wound body 950a shown in Figure 19A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0456] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 932, a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0457] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0458] As shown in Figure 19B, the negative electrode 931 is electrically connected to terminal 951 by ultrasonic bonding, welding, or crimping. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952 by ultrasonic bonding, welding, or crimping. Terminal 952 is electrically connected to terminal 911b.

[0459] As shown in Figure 19C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure to prevent the battery from rupturing.

[0460] As shown in Figure 19B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 19A and 19B can be referenced from the description of the secondary battery 913 shown in Figures 18A to 18C.

[0461] <Laminated Rechargeable Battery> Next, an example of an external view of a laminated rechargeable battery is shown in Figures 20A and 20B. Figures 20A and 20B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0462] Figure 21A shows the external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., the tab region. Note that the area or shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 21A.

[0463] <Method for Manufacturing Laminated Secondary Batteries> An example of a method for manufacturing laminated secondary batteries, whose external appearance is shown in Figure 20A, will be explained using Figures 21B and 21C.

[0464] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 21B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, for example, ultrasonic welding may be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0465] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0466] Next, as shown in Figure 21C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as an inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0467] Next, the electrolyte is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0468] By using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode 503, a secondary battery 500 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0469] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be explained with reference to Figure 22.

[0470] Figure 22A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 22B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 includes a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0471] The interior of the secondary battery 513 may have a structure with a wound body or a structure with a laminated body.

[0472] In the secondary battery pack 531, for example as shown in Figure 22B, a control circuit 590 is located on a circuit board 540. The circuit board 540 is electrically connected to terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0473] Alternatively, as shown in Figure 22C, the system may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0474] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0475] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0476] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0477] (Embodiment 5) This embodiment shows an example of a vehicle having a secondary battery according to one aspect of the present invention.

[0478] As for vehicles, secondary batteries can typically be applied to automobiles. Examples of automobiles include next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHEVs or PHVs), and secondary batteries can be applied as one of the power sources installed in these vehicles. Vehicles are not limited to automobiles. For example, examples of vehicles include trains, monorails, ships, submersibles (deep-sea exploration vessels, unmanned submersibles), flying objects (helicopters, unmanned aerial vehicles (drones), airplanes, rockets, artificial satellites), electric bicycles, electric motorcycles, etc., and secondary batteries according to one aspect of the present invention can be applied to these vehicles.

[0479] As shown in Figure 23C, electric vehicles are equipped with a first battery 1301a, 1301b as the main secondary battery for driving, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called a cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a, 1301b.

[0480] The internal structure of the first battery 1301a may be a wound type as shown in Figure 18C or Figure 19A, or a stacked type as shown in Figure 20A or Figure 20B.

[0481] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0482] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and is provided on the first battery 1301a.

[0483] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. In the case where there is a rear motor 1317 on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0484] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio system 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0485] Next, the first battery 1301a will be explained using Figure 23A.

[0486] Figure 23A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0487] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as BTOS (Battery operating system or Battery oxide semiconductor).

[0488] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the metal oxide, it is preferable to use a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium). In particular, it is preferable that the In-M-Zn oxide applicable as the metal oxide is CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may also be used as the metal oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. This specific direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. Furthermore, a crystalline region is a region with periodicity in its atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region with a aligned lattice arrangement.

[0489] Furthermore, "CAC-OS" is a mosaic-like structure formed by the separation of the material into a first region and a second region, with the first region distributed within the film (hereinafter also referred to as a cloud-like structure). In other words, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed. However, it may be difficult to observe a clear boundary between the first region and the second region.

[0490] For example, in the CAC-OS of In-Ga-Zn oxide, EDX mapping obtained using EDX confirms that it has a structure in which regions mainly composed of In (first region) and regions mainly composed of Ga (second region) are unevenly distributed and mixed.

[0491] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulation due to the second region work complementaryly to give CAC-OS a switching function (on / off function). In other words, CAC-OS has conductive function in part of the material, insulating function in part of the material, and semiconductor function as a whole. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I) can be achieved. ｏｎ This enables high field-effect mobility (μ) and good switching operation.

[0492] Oxide semiconductors can take on diverse structures, each possessing different properties. One embodiment of the present invention may include two or more of amorphous oxide semiconductors, polycrystalline oxide semiconductors, a-like OS, CAC-OS, nc-OS, and CAAC-OS.

[0493] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from -40°C to 150°C, and even if the secondary battery overheats, the change in characteristics is smaller compared to single crystals. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode. The secondary battery and control circuit unit 1320 using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0494] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. Functions to eliminate the 10 causes of instability include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0495] Furthermore, "micro-short" refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short time and small location can cause a large voltage change, the abnormal voltage value may affect subsequent estimations.

[0496] One of the causes of micro-short circuits is said to be that, due to the uneven distribution of positive electrode active material particles after multiple charge-discharge cycles, localized current concentration occurs in parts of the positive and negative electrodes, causing parts of the separator to malfunction, or micro-short circuits to occur due to the generation of by-reactants from side reactions.

[0497] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0498] Next, Figure 23B shows an example of a block diagram of the battery pack 1415 shown in Figure 23A.

[0499] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current or the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and / or overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch of the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0500] The switch section 1324 can be constructed by combining n-channel or p-channel transistors. The switch section 1324 is not limited to a switch having a Si transistor using single-crystal silicon, but may also be formed using power transistors such as Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0). Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, a control circuit section 1320 using OS transistors can be stacked on the switch section 1324 and integrated into a single chip. Since the volume occupied by the control circuit unit 1320 can be reduced, miniaturization becomes possible.

[0501] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage HV) onboard equipment, while the second battery 1311 supplies power to 14V (low-voltage LV) onboard equipment. Lead-acid batteries are often used for the second battery 1311 due to cost advantages. Lead-acid batteries have the disadvantage of higher self-discharge and are prone to degradation due to a phenomenon called sulfation compared to lithium-ion batteries. Using a lithium-ion battery for the second battery 1311 offers the advantage of being maintenance-free, but after long-term use, for example more than three years, there is a risk of malfunctions occurring that are difficult to detect at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, it will be impossible to start the motor even if the first batteries 1301a and 1301b have remaining capacity. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery to keep it constantly charged to a full charge state.

[0502] This embodiment shows an example in which lithium-ion batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor.

[0503] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0504] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0505] Although not shown in the diagram, when an electric vehicle is connected to an external charger, the charger's plug or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some cases, a control circuit is provided in the charger, and the functions of the battery controller 1302 are not used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the control circuit is also provided in the charger's plug or connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. Furthermore, the ECU uses either a CPU or a GPU.

[0506] External chargers installed at charging stations and other locations may have a 100V-200V outlet, or a 3-phase 200V and 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0507] For rapid charging, a rechargeable battery capable of withstanding high-voltage charging is desired to achieve short charging times.

[0508] Furthermore, by using graphene as a conductive material, it is possible to suppress capacity degradation even when the electrode layer is thickened and the load is increased, and maintain high capacity. As a synergistic effect, a secondary battery with significantly improved electrical characteristics can be realized. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide vehicles with a long driving range, specifically a driving range of 500 km or more on a single charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0509] In particular, the secondary battery of this embodiment described above can achieve a higher operating voltage by using the positive electrode active material particles 100 described in Embodiments 1 and 2, and can increase its usable capacity as the charging voltage increases. Furthermore, by using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, it is possible to provide a secondary battery for vehicles with excellent cycle characteristics.

[0510] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0511] By mounting the secondary battery shown in any one of Figures 17D, 19C, or 23A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs) can be realized. Furthermore, secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, satellites, space probes, planetary probes, or spacecraft. One embodiment of the present invention allows for high-capacity secondary batteries. Therefore, one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0512] Figures 24A to 24D illustrate a transport vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 24A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on the vehicle, one or more examples of the secondary battery shown in Embodiment 4 are installed in one location. The automobile 2001 shown in Figure 24A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device electrically connected to the secondary battery module.

[0513] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the secondary battery of the automobile 2001. When charging, the charging method or connector specifications may be carried out as appropriate in accordance with the prescribed methods of CHAdeMO (registered trademark) or Combo. The charging facility may be a charging station installed in a commercial facility or a household power supply. For example, the energy storage device mounted on the automobile 2001 can be charged by supplying power from an external source using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an ADC converter.

[0514] Although not shown in the diagram, a power receiving device can also be mounted on the vehicle, and power can be supplied contactlessly from a ground-based power transmission device for charging. In this contactless power supply method, by incorporating the power transmission device into the road or exterior wall, charging can be performed not only when the vehicle is stopped but also while it is in motion. Furthermore, this contactless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or in motion. For such contactless power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0515] Figure 24B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a nominal voltage of 3.0V to 5.0V. The battery pack 2201 has the same functions as Figure 24A, except for differences in the number of secondary batteries constituting the secondary battery module, so the explanation is omitted.

[0516] Figure 24C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 secondary batteries with a nominal voltage of 3.0V to 5.0V in series. Therefore, secondary batteries with small variation in characteristics are required. By using secondary batteries that use the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, it is possible to manufacture secondary batteries with stable battery characteristics, enabling low-cost mass production from a yield standpoint. Furthermore, since it has the same functions as Figure 24A except for differences in the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the explanation is omitted.

[0517] Figure 24D shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Figure 24D can be considered a type of transport vehicle because it has wheels for takeoff and landing, and has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0518] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functions as Figure 24A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0519] Figure 24E shows an example of a satellite 2005 equipped with a secondary battery 2204. It is preferable that the secondary battery 2204 is mounted inside the satellite 2005, covered with a heat-insulating material.

[0520] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0521] (Embodiment 6) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in a building will be described with reference to Figures 25A and 25B.

[0522] The house shown in Figure 25A has a power storage device 2612 having a secondary battery, which is one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611, etc. Alternatively, the power storage device 2612 may be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0523] The electricity stored in the energy storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

[0524] Figure 25B shows an example of an energy storage device according to one aspect of the present invention. As shown in Figure 25B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Furthermore, a synergistic effect on safety can be obtained by using a secondary battery with the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode in the energy storage device 791. The secondary battery with the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by the energy storage device 791 having a secondary battery.

[0525] A control device 790 is installed in the energy storage device 791, and the control device 790 is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0526] Power is supplied from the commercial power supply 701 to the distribution board 703 via the service drop connection section 710. Power is also supplied to the distribution board 703 from the energy storage device 791 and the commercial power supply 701, and the distribution board 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0527] The general load 707 is, for example, an electronic device such as a television or a personal computer, and the energy storage load 708 is, for example, an electronic device such as a microwave oven, refrigerator, or air conditioner.

[0528] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during one day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during one day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0529] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked via the router 709 on electronic devices such as televisions or personal computers. Furthermore, it can be checked via the router 709 on portable electronic devices such as smartphones or tablets. Additionally, the amount of electricity demand predicted by the prediction unit 712 for each time period (or hourly) can be checked on the display unit 706, electronic devices, and portable electronic devices.

[0530] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0531] (Embodiment 7) In this embodiment, as an example of mounting a secondary battery in a vehicle, an example is shown in which a lithium-ion battery according to one aspect of the present invention is mounted in a motorcycle and a bicycle.

[0532] Figure 26A shows an example of an electric bicycle using a power storage device according to one aspect of the present invention. The power storage device according to one aspect of the present invention can be applied to the electric bicycle 8700 shown in Figure 26A. The power storage device according to one aspect of the present invention includes, for example, a plurality of batteries and a protection circuit.

[0533] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 is also portable, and Figure 26B shows it detached from the bicycle. The power storage device 8702 also has multiple storage batteries 8701, which are part of a power storage device according to one embodiment of the present invention, and the remaining battery level can be displayed on a display unit 8703. The power storage device 8702 also has a control circuit 8704 that can control the charging of the secondary battery or detect abnormalities. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. Furthermore, by combining it with a secondary battery that uses the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, a synergistic effect on safety can be obtained. The secondary battery and control circuit 8704 that use the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0534] Figure 26C shows an example of a motorcycle using a power storage device according to one embodiment of the present invention. The scooter 8600 shown in Figure 26C is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply electricity to the turn signals 8603. Furthermore, the power storage device 8602, which houses multiple secondary batteries using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, can have a high capacity and contribute to miniaturization.

[0535] Furthermore, the scooter 8600 shown in Figure 26C can accommodate the power storage device 8602 in the under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0536] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0537] (Embodiment 8) This embodiment describes an example in which a secondary battery, which is one aspect of the present invention, is mounted on an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0538] Figure 27A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By providing a secondary battery 2107 that uses the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0539] The mobile phone 2100 can run various applications such as making mobile phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0540] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0541] Furthermore, the mobile phone 2100 is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless communication-enabled headset to enable hands-free calling.

[0542] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows it to directly exchange data with other information terminals via a connector. It can also be charged via the external connection port 2104. However, charging may be performed wirelessly without using the external connection port 2104.

[0543] Furthermore, it is preferable that the mobile phone 2100 has sensors. Preferably, the sensors include, for example, human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, touch sensors, pressure sensors, or acceleration sensors.

[0544] Figure 27B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery to be mounted on an unmanned aerial vehicle 2300.

[0545] Figure 27C shows an example of a robot. The robot 6400 shown in Figure 27C is equipped with a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0546] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0547] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0548] The upper camera 6403 and the lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407.

[0549] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0550] Figure 27D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0551] The cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that may become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal region. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6306 to be mounted on the cleaning robot 6300.

[0552] Figure 28A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0553] For example, a secondary battery according to one embodiment of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 28A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 with good weight balance and a long continuous usage time can be made. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0554] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. The secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0555] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0556] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0557] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply and receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0558] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and the secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. The secondary battery using the positive electrode active material particles 100 described in Embodiments 1 and 2 as the positive electrode has a high energy density and can realize a configuration that can accommoda...

Claims

It has a positive electrode and a negative electrode, The positive electrode has positive electrode active material particles comprising lithium, cobalt, oxygen, magnesium, fluorine, nickel, and aluminum. The positive electrode active material particles are, It has a surface layer and an interior, and the interior has a layered rock salt type crystalline structure of space group R-3m. In the STEM-EDX cross-section of the surface where lithium is inserted into and removed from the positive electrode active material particles, magnesium, fluorine, and nickel were detected in the surface layer. When the surface of the positive electrode active material particles observed in a cross-sectional STEM image of the surface where lithium is inserted and removed is considered as the first layer, at least a portion of the fourth to ninth layers of the positive electrode active material particles has the characteristics of a spinel-type crystal structure. In the cobalt layer of the spinel-type crystal structure mentioned above, Co ２＋ And, Co ３＋ and are arranged alternately. Lithium-ion rechargeable battery. 　 In claim 1, In the cross-sectional STEM image, the spinel-type crystal structure is Co ２＋ Co ３＋ A lithium-ion secondary battery with high brightness in the cobalt sites where it is present. 　 In claim 2, In STEM-EELS analysis of the fourth to ninth layers of the positive electrode active material particles, The aforementioned Co ２＋ Magnesium and nickel were detected in the cobalt site where it is present, The aforementioned Co ３＋ A lithium-ion secondary battery in which nickel is detected at the cobalt site where nickel is present. 　 In any one of claims 1 to 3, the positive electrode active material particles are Li ｘ CoO ２ A lithium-ion secondary battery having an O3' type crystal structure when x in the middle is 0.1 < x ≤ 0.24.

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