Positive active material

Abstract

To provide a positive electrode active material whose crystal structure does not easily collapse even after charging and discharging are repeated, and a positive electrode active material whose charging and discharging capacity is large.SOLUTION: A positive electrode active material includes lithium, cobalt, nickel, magnesium, and oxygen. A lattice constant of a-axis on the outermost layer of the positive electrode active material is larger than a lattice constant of the a-axis on the inside and a lattice constant of c-axis on the outermost surface is larger than that of a lattice constant of the c-axis on the inside. The change rate of the lattice constant of a-axis on the outermost surface and the lattice constant of a-axis on the inside is preferably more than 0 and 0.12 or less. The change rate of the lattice constant of c-axis on the outermost surface and the lattice constant of c-axis on the inside is preferably more than 0 and 0.18 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present invention relates to a product, a method, or a method of manufacture. 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 a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a method of manufacturing the same.

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

[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 to 3). Research is also being conducted on the crystal structure of positive electrode active materials (Non-Patent Documents 1 to 3).

[0005] X-ray diffraction (XRD) is also one of the techniques used to analyze the crystal structure of positive electrode active materials. By using ICSD (Inorganic Crystal Structure Database), which is introduced in Non-Patent Document 4, XRD data can be analyzed. [Prior art documents] [Patent Documents]

[0006] [License 1] Special Announcement No. 8-236114 [License 2] Special Announcement No. 2002-124262 [License 3] Special Announcement No. 2002-358953 [Non-licensed literature]

[0007] [Non-licensed Document 1] 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.17340-17348 [Non-licensed Document 2] Motohashi, T. et al, "Electronic phase diagram of the layered cobalt oxide system LixCoO2 (0.0≦x≦1.0) ", Physical Review B, 80(16);165114 [Non-licensed Document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-licensed Document 4] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., (2002) B58 364-369. [Overview of the project] [Problems that the invention aims to solve]

[0008] However, there is still room for improvement in lithium-ion secondary batteries and the cathode active materials used in them, in various aspects such as charge / discharge capacity, cycle characteristics, reliability, safety, and cost.

[0009] One aspect of the present invention aims to provide a positive electrode active material that, when used in a lithium-ion secondary battery, suppresses the decrease in charge / discharge capacity during charge / discharge cycles. Alternatively, it aims to provide a positive electrode active material whose crystal structure is resistant to collapse even after repeated charge / discharge cycles. Alternatively, it aims to provide a positive electrode active material with a large charge / discharge capacity. Alternatively, it aims to provide a secondary battery with high safety and reliability.

[0010] Another aspect of the present invention aims to provide a positive electrode active material, an energy storage device, or a method for producing the same.

[0011] 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 in the specification, drawings, and claims. [Means for solving the problem]

[0012] One aspect of the present invention is a positive electrode active material having lithium, cobalt, nickel, magnesium, and oxygen, wherein the lattice constant A of the a-axis of the outermost surface layer of the positive electrode active material is surfaceis a positive electrode active material in which the lattice constant A of the internal a-axis core is larger, and the lattice constant C of the c-axis in the outermost surface layer surface is larger than the lattice constant C of the internal c-axis core .

[0013] In the above, the rate of change R, obtained by dividing the difference Δ between the lattice constant A of the a-axis in the outermost surface layer surface and the lattice constant A of the internal a-axis core by the lattice constant A A core is preferably more than 0 and 0.12 or less, and the rate of change R obtained by dividing the difference Δ between the lattice constant C of the c-axis in the outermost surface layer A and the lattice constant C of the internal c-axis surface by the lattice constant C core is preferably more than 0 and 0.18 or less C core . C

[0014] In the above, it is preferable that the rate of change R A is 0.05 or more and 0.07 or less, and the rate of change R C is 0.09 or more and 0.12 or less.

[0015] In the above, it is preferable that the difference Δ between the lattice constant C of the c-axis in the outermost surface layer surface and the lattice constant C of the internal c-axis core is larger than the difference Δ between the lattice constant A of the a-axis in the outermost surface layer A and the lattice constant A of the internal a-axis surface core . C

[0016] Another aspect of the present invention is a positive electrode active material containing lithium, cobalt, nickel, magnesium, and oxygen, wherein at least a part of the outermost surface layer of the positive electrode active material has a layered rock salt-type crystal structure in which transition metal site layers and lithium site layers are alternately arranged, and a part of the lithium site layers contains a metal element having an atomic number larger than that of lithium.

[0017] ​​​​​In the above, the metallic element with an atomic number greater than lithium is preferably magnesium, cobalt, or aluminum.

[0018] In the above, it is preferable that the brightness of the lithium site layer in the cross-sectional TEM image of the outermost layer is 3% to 60% of the brightness of the transition metal site layer.

[0019] In the above, it is preferable that the nickel concentration in the outermost layer is 1 atomic percent or less, and the nickel concentration in the entire positive electrode active material is 0.05% to 4% of the cobalt concentration.

[0020] In the above, it is preferable that the outermost layer has a region in which bright spots indicating a rock salt type crystal structure belonging to space group Fm-3m or Fd-3m are observed in the micro-electron diffraction pattern, and bright spots indicating a layered rock salt type crystal structure belonging to space group R-3m are observed, and the interior has a region in which bright spots indicating a layered rock salt type crystal structure belonging to space group R-3m are observed in the micro-electron diffraction pattern.

[0021] In the above, the spin density attributable to one or more of the following is 2.0 × 10⁻¹⁰ 17 spins / g or more 1.0×10 21 It is preferable that the spins / g value be less than or equal to 1 / 2.

[0022] In the above, the positive electrode active material contains aluminum, and it is preferable that the concentration of aluminum in the entire positive electrode active material is 0.05% or more and 4% or less of the cobalt concentration.

[0023] In the above, in energy-dispersive X-ray analysis of the cross-section of the positive electrode active material, it is preferable that the peak of aluminum concentration is located at a depth of 5 nm to 30 nm from the surface toward the center.

[0024] Another aspect of the present invention is a lithium-ion secondary battery having a positive electrode active material, wherein the positive electrode active material comprises lithium, cobalt, nickel, magnesium, and oxygen, and the lattice constant of the a-axis of the outermost surface layer of the positive electrode active material is A surface The lattice constant A of the internal a-axis is core Larger than the lattice constant C of the c-axis of the outermost surface layer of the positive electrode active material. surface The lattice constant C of the internal c-axis is core It is a larger lithium-ion rechargeable battery.

[0025] Another aspect of the present invention is an electronic device having the above-mentioned secondary battery. [Effects of the Invention]

[0026] According to one aspect of the present invention, a positive electrode active material can be provided that, when used in a lithium-ion secondary battery, suppresses the decrease in charge / discharge capacity during charge / discharge cycles. Alternatively, a positive electrode active material can be provided that maintains its crystal structure even after repeated charge / discharge cycles. Alternatively, a positive electrode active material with a large charge / discharge capacity can be provided. Alternatively, a safe or highly reliable secondary battery can be provided.

[0027] Furthermore, according to one aspect of the present invention, a positive electrode active material, an energy storage device, or a method for producing the same can be provided.

[0028] 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. [Brief explanation of the drawing]

[0029] [Figure 1] Figure 1A is a cross-sectional view of the positive electrode active material, and Figures 1B, 1C1, and 1C2 are partial cross-sectional views of the positive electrode active material. [Figure 2]Figures 2A1 to 2C2 show partial cross-sectional views of the positive electrode active material. [Figure 3] Figure 3 is a cross-sectional view of the positive electrode active material. [Figure 4] Figure 4 illustrates the charging depth and crystal structure of the positive electrode active material. [Figure 5] Figure 5 shows the XRD pattern calculated from the crystal structure. [Figure 6] Figure 6 illustrates the charging depth and crystal structure of the positive electrode active material in the comparative example. [Figure 7] Figure 7 shows the XRD pattern calculated from the crystal structure. [Figure 8] Figures 8A to 8C show the lattice constants calculated from XRD. [Figure 9] Figures 9A to 9C show the lattice constants calculated from XRD. [Figure 10] Figure 10 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 11] Figure 11 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 12] Figure 12 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 13] Figure 13 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 14] Figure 14 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 15] Figure 15 is a diagram illustrating the method for preparing the positive electrode active material. [Figure 16] Figures 16A and 16B are cross-sectional views of the active material layer when a graphene compound is used as the conductive material. [Figure 17] Figures 17A and 17B illustrate an example of a secondary battery. [Figure 18] Figures 18A to 18C illustrate an example of a secondary battery. [Figure 19] Figures 19A and 19B illustrate an example of a secondary battery. [Figure 20] Figures 20A to 20C illustrate a coin-type rechargeable battery. [Figure 21] Figures 21A to 21D illustrate a cylindrical secondary battery. [Figure 22] Figures 22A and 22B illustrate an example of a secondary battery. [Figure 23] Figures 23A to 23D illustrate examples of secondary batteries. [Figure 24] Figures 24A and 24B illustrate examples of secondary batteries. [Figure 25] Figure 25 illustrates an example of a secondary battery. [Figure 26] Figures 26A to 26C illustrate a laminate-type secondary battery. [Figure 27] Figures 27A and 27B illustrate laminate-type secondary batteries. [Figure 28] Figure 28 shows the external appearance of a secondary battery. [Figure 29] Figure 29 shows the external appearance of a secondary battery. [Figure 30] Figures 30A to 30C illustrate the method for manufacturing a secondary battery. [Figure 31] Figures 31A to 31H illustrate an example of an electronic device. [Figure 32] Figures 32A to 32C illustrate an example of an electronic device. [Figure 33] Figure 33 illustrates an example of an electronic device. [Figure 34] Figures 34A to 34D illustrate an example of an electronic device. [Figure 35] Figures 35A to 35C show examples of electronic devices. [Figure 36] Figures 36A to 36C illustrate an example of a vehicle. [Figure 37] Figures 37A to 37D are SEM images of the surface of the positive electrode active material. [Figure 38] Figure 38A is a cross-sectional TEM image of the positive electrode active material. Figures 38B and 38C are selected-field electron diffraction images of a portion of Figure 38A. [Figure 39]Figures 39A and 39B show micro-electron diffraction patterns of the positive electrode active material. [Figure 40] Figure 40A is a cross-sectional TEM image of the positive electrode active material. Figures 40B and 40C are micro-electron diffraction images of a portion of Figure 40A. [Figure 41] Figure 41A is a cross-sectional TEM image of the positive electrode active material. Figures 41B and 41C are micro-electron diffraction images of a portion of Figure 41A. [Figure 42] Figures 42A to 42C are cross-sectional STEM images of the positive electrode active material. [Figure 43] Figure 43A is a cross-sectional STEM image of the positive electrode active material, which is a rotated version of Figure 42B. Figure 43B shows the brightness measurement results for Figure 43A. [Figure 44] Figure 44A is a graph corrected for background noise from Figure 43B. Figure 44B is a bright-field STEM image of the cross-section of the cathode active material. [Figure 45] Figure 45A is a cross-sectional HAADF-STEM image of the positive electrode active material. Figures 45B to 45F show the results of EDX surface analysis. [Figure 46] Figure 46A is a cross-sectional HAADF-STEM image of the positive electrode active material. Figures 46B to 46D show the results of EDX surface analysis. [Figure 47] Figure 47A is a cross-sectional HAADF-STEM image of the positive electrode active material. Figures 47B to 47E are inverted versions of the EDX surface analysis results. [Figure 48] Figure 48 shows a cross-sectional HAADF-STEM image of the positive electrode active material. [Figure 49] Figures 49A and 49B show the results of EDX radiation analysis of the positive electrode active material. [Figure 50] Figures 50A and 50B are SEM images of the positive electrode active material. [Figure 51] Figures 51A and 51B show the grayscale values ​​of the positive electrode active material. [Figure 52] Figures 52A and 52B are luminance histograms of the positive electrode active material. [Figure 53] Figure 53 shows the XRD pattern of the positive electrode active material. [Figure 54]Figures 54A and 54B are enlarged XRD patterns of a portion of Figure 53. [Figure 55] Figure 55 shows the XRD pattern of the positive electrode active material. [Figure 56] Figures 56A and 56B are enlarged XRD patterns of a portion of Figure 55. [Figure 57] Figure 57 shows the XRD pattern of the positive electrode active material. [Figure 58] Figures 58A and 58B are enlarged XRD patterns of a portion of Figure 57. [Figure 59] Figure 59 shows the XRD pattern of the positive electrode active material. [Figure 60] Figures 60A and 60B are enlarged XRD patterns of a portion of Figure 59. [Figure 61] Figures 61A and 61B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 62] Figures 62A and 62B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 63] Figures 63A and 63B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 64] Figures 64A and 64B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 65] Figures 65A and 65B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 66] Figures 66A and 66B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 67] Figures 67A and 67B are graphs showing the cycle characteristics of the positive electrode active material. [Figure 68] Figures 68A and 68B are graphs showing the cycle characteristics of the positive electrode active material. [Modes for carrying out the invention]

[0030] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0031] Furthermore, Miller indices are used to indicate crystal planes and directions in this specification. Individual crystal planes are indicated by parentheses ( ). In crystallography, crystal planes, directions, and space groups are indicated by superscripts above the numbers, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a superscript above it.

[0032] In this specification, segregation refers to the phenomenon in which a certain element (e.g., B) is spatially non-uniformly distributed in a solid composed of multiple elements (e.g., A, B, C).

[0033] Furthermore, the surface of the positive electrode active material refers to the surface of the composite oxide, including the outermost layer and the interior. Therefore, the positive electrode active material does not contain carbon dioxide, hydroxyl groups, etc., that have been chemically adsorbed after fabrication. It also does not contain electrolyte, binder, conductive material, or compounds derived therefrom that are attached to the positive electrode active material. Moreover, the positive electrode active material does not necessarily have to consist entirely of regions containing lithium sites that contribute to charging and discharging.

[0034] In this specification, the layered rock salt crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. It is acceptable for there to be defects such as vacancies in some cations or anions, as long as two-dimensional diffusion of lithium ions is possible. Furthermore, strictly speaking, a layered rock salt crystal structure may have a distorted lattice structure of the rock salt crystal.

[0035] In this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. Some cation or anion deficiencies are acceptable.

[0036] Furthermore, in this specification, a mixture refers to a mixture of multiple materials. A mixture that has undergone mutual diffusion of its elements may be called a composite. A mixture may still be called a composite even if it contains some unreacted materials. The positive electrode active material may also be referred to as a composite, composite oxide, or material.

[0037] Furthermore, in this specification, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all of the insertable and detachable lithium present in the positive electrode active material has been detached. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0038] Furthermore, in this specification, the charging depth when all insertable and detachable lithium is inserted is defined as 0, and the charging depth when all insertable and detachable lithium in the positive electrode active material has been detached is defined as 1.

[0039] In general, in cathode active materials with a layered rock salt-type crystalline structure, the crystalline structure becomes unstable when the lithium between the layered structures composed of transition metals and oxygen decreases. Therefore, in secondary batteries using typical lithium cobalt oxide, charging is limited to a depth of charge of 0.4, a charging voltage of 4.3V (for lithium counter electrodes), and a charging capacity of approximately 160mAh / g.

[0040] In contrast, positive electrode active material with a charging depth of 0.74 to 0.9, or more specifically, a charging depth of 0.8 to 0.83, is considered high-voltage charged positive electrode active material. Therefore, for example, if LiCoO2 is charged to a capacity of 219.2 mAh / g, it is considered high-voltage charged positive electrode active material. Furthermore, in the case of LiCoO2, positive electrode active material that has been charged with a constant current at a charging voltage of 4.525V to 4.7V (in the case of counter electrode lithium) in a 25°C environment, and then charged with a constant voltage until the current value is 0.01C, or approximately 1 / 5 to 1 / 100 of the current value during constant current charging, is also considered high-voltage charged positive electrode active material. Note that C is an abbreviation for Capacity rate, and 1C refers to the magnitude of the current required to fully charge or fully discharge the charge / discharge capacity of a secondary battery in one hour.

[0041] For positive electrode active materials, the insertion of lithium ions is called discharge. Furthermore, positive electrode active materials with a charge depth of 0.06 or less, or positive electrode active materials that have been discharged to 90% or more of their charge capacity from a high-voltage charged state, are considered to be sufficiently discharged positive electrode active materials. For example, in the case of LiCoO2, if the charge capacity is 219.2 mAh / g, it is in a high-voltage charged state, and the positive electrode active material after being discharged to 197.3 mAh / g or more (90% of the charge capacity) is considered to be sufficiently discharged positive electrode active material. In addition, in the case of LiCoO2, positive electrode active material after constant current discharge until the battery voltage is 3V or less (in the case of counter electrode lithium) in a 25°C environment is also considered to be sufficiently discharged positive electrode active material.

[0042] Furthermore, in this specification, an example is shown in which lithium metal is used as the counter electrode in a secondary battery using the positive electrode and positive electrode active material of one aspect of the present invention, but the secondary battery of one aspect of the present invention is not limited to this. Other materials, such as graphite or lithium titanate, may be used for the negative electrode. The properties of the positive electrode and positive electrode active material of one aspect of the present invention, such as resistance to crystal structure collapse even after repeated charging and discharging and obtaining good cycle characteristics, are not affected by the material of the negative electrode. Furthermore, in the case of a secondary battery of one aspect of the present invention, an example is shown in which charging and discharging is performed at a voltage higher than the typical charging voltage of about 4.7V with a lithium counter electrode, but charging and discharging may be performed at a lower voltage. When charging and discharging at a lower voltage, it is expected that the cycle characteristics will be even better than those shown in this specification.

[0043] Furthermore, unless otherwise specified in this specification, the charging and discharging voltages refer to the voltages when the counter electrode is lithium. However, even with the same positive electrode, the charging and discharging voltages of a secondary battery change depending on the material used for the negative electrode. For example, the potential of graphite is approximately 0.1V (vs Li / Li + Therefore, in the case of graphite as the negative electrode, the charge and discharge voltage will be approximately 0.1V lower than in the case of lithium as the counter electrode.

[0044] (Embodiment 1) In this embodiment, a positive electrode active material according to one aspect of the present invention will be described with reference to Figures 1 to 9.

[0045] Figure 1A is a cross-sectional view of a positive electrode active material 100 according to one embodiment of the present invention. Enlarged views of the area around AB in Figure 1A are shown in Figures 1B, 1C1, and 1C2. Enlarged views of the area around CD in Figure 1A are shown in Figures 2A1, 2A2, 2B1, 2B2, 2C1, and 2C2.

[0046] As shown in Figures 1A to 2C2, the positive electrode active material 100 has a surface layer 100a and an interior layer 100b. In these figures, the boundary between the surface layer 100a and the interior layer 100b is indicated by a dashed line. Also in Figure 1A, a dashed line shows a part of the grain boundary. The positive electrode active material 100 also has an outermost layer 100c in a part of the surface layer 100a. In Figure 1B, a dashed line shows the boundary of the outermost layer 100c within the surface layer 100a.

[0047] In this specification, the region extending approximately 10 nm from the surface of the positive electrode active material into the interior is referred to as the surface layer 100a. Surfaces formed by cracks or fissures may also be considered the surface. The surface layer 100a may also be referred to as the near-surface region, near-surface region, or shell. The region deeper than the surface layer 100a of the positive electrode active material is referred to as the interior 100b. The interior 100b may also be referred to as the interior region or core. Furthermore, within the surface layer 100a of the positive electrode active material, the region extending 3 nm from the surface into the interior 100b is referred to as the outermost layer 100c.

[0048] <Each region and lattice constant> In one embodiment of the present invention, the positive electrode active material 100 preferably has a crystalline structure in both the surface layer 100a and the interior 100b. Furthermore, the lattice constant of the a-axis of the crystalline structure of the surface layer 100a is greater than the lattice constant A of the a-axis of the crystalline structure of the interior 100b. core It is preferable that the lattice constant of the b axis of the crystal structure of the surface layer 100a is greater than the lattice constant B of the b axis of the crystal structure of the interior 100b. core It is preferable that the lattice constant of the c-axis of the crystal structure of the surface layer 100a is greater than the lattice constant of the c-axis of the crystal structure of the interior 100b. core It is preferable that it be larger than this.

[0049] Furthermore, it is preferable that the outermost surface layer 100c of the positive electrode active material 100 also has a crystalline structure. Also, the lattice constant A of the a-axis of the crystalline structure of the outermost surface layer 100c. surface This is because the lattice constant of the a-axis of the surface layer 100a and the lattice constant of the a-axis of the interior 100b are different. core It is preferable that it be larger than this. Also, the lattice constant B of the b axis of the crystal structure of the outermost layer 100c. surface The lattice constant of the b axis of the surface layer 100a and the lattice constant of the b axis of the interior 100b are B core It is preferable that it be larger than this. Also, the lattice constant C of the c-axis of the crystal structure of the outermost layer 100c. surface The lattice constant of the c-axis of the surface layer 100a and the lattice constant of the c-axis of the interior 100b are C core It is preferable that it be larger than this.

[0050] Furthermore, the lattice constant A of the a-axis of the outermost layer. surface Therefore, the lattice constant A of the internal a-axis. core The difference after subtracting Δ A Similarly, the lattice constant C of the c-axis of the outermost layer. surface Therefore, the lattice constant C of the internal c-axis. core The difference after subtracting Δ C Let's assume that Δ A Rather than Δ C A larger value is preferable.

[0051] Furthermore, as shown in equations 1 and 2 below, Δ A to A core The value divided by the rate of change R A Let's assume that Δ C to C core The value divided by the rate of change R C Let's assume that.

[0052]

number

[0053]

number

[0054] At this time, the rate of change R A Preferably, it is greater than 0 and 0.12 or less, and more preferably 0.05 or more and 0.07 or less. Or, preferably greater than 0 and 0.07 or less. Or, preferably 0.05 or more and 0.12 or less.

[0055] Also, the rate of change R C Preferably, it is greater than 0 and 0.18 or less, and more preferably 0.09 or more and 0.12 or less. Or, preferably greater than 0 and 0.12 or less. Or, preferably 0.09 or more and 0.18 or less.

[0056] Lattice constants are calculated assuming they belong to the same space group, in order to facilitate comparison between domains.

[0057] For example, it is preferable to use a model in which all regions have the same crystal structure, the same space group, and the same number of atoms per unit cell for calculation. For example, it is not possible to describe the R-3m layered rock salt type with Fm-3m, but it is possible to represent the Fm-3m rock salt type with R-3m. Therefore, for example, if the interior 100b has the characteristics of an R-3m layered rock salt type, and the surface layer 100a and the outermost layer 100c have the characteristics of an Fm-3m rock salt type, then using the crystal structure of the R-3m layered rock salt type as a model for all of them to calculate the lattice constants makes it easy to compare the lattice constants of each region. Note that in the crystal structure of the R-3m layered rock salt type, the lengths of the a axis and the b axis are equal, so in the following, the a axis will be described as representative for the R-3m layered rock salt type.

[0058] Furthermore, even if it is difficult to describe all regions with the same space group, if the anion packing is nearly identical, models with the same number of anions can be said to have equivalent symmetry. In this case, the distance between anions may be used to compare regions instead of the lattice constant. For example, rock salt type, layered rock salt type, and spinel type all have anions in a cubic close-packed structure (ccp arrangement), and can be said to have nearly identical anion packing structures. In such cases, even if the space groups are different, they can be compared as having similar symmetries. The distance between anions can be calculated, for example, from the results of Rietveld analysis of XRD patterns.

[0059] In the following section, we will describe an example of using a layered rock salt crystal structure of space group R-3m as a model for calculating the lattice constants of each region, but this is not the only example. It is preferable to select the optimal structure based on the material of the positive electrode active material 100. For example, it is preferable to adopt the crystal structure that occupies the largest volume among the crystal structures of the positive electrode active material 100. In addition to the layered rock salt type, other crystal structures such as rock salt type, spinel type, and olivine type can be used.

[0060] Whether the surface layer 100a, the interior 100b, and the outermost layer 100c have a crystalline structure can be determined, and if they do, the lattice constants can be determined, for example, by cross-sectional TEM, cross-sectional STEM, and electron diffraction, including limited-field electron diffraction and micro-electron diffraction.

[0061] If a regular arrangement of atoms can be observed in cross-sectional TEM images, cross-sectional STEM images, etc., it can be said that a crystalline structure exists. Similarly, if a diffraction pattern with regular spots can be observed in electron diffraction images, etc., it can be said that a crystalline structure exists.

[0062] Limited-field electron diffraction allows for the analysis of crystal structures in small areas of about 20 nm, and micro-electron diffraction allows for the analysis of even smaller areas of about 1 nm, making them suitable for determining the lattice constants of the surface layer 100a and the outermost layer 100c.

[0063] However, these electron diffraction methods may result in measurement errors due to camera length distortion, etc. Therefore, it is preferable to use two significant figures for the lattice constants obtained by electron diffraction. Alternatively, the lattice constants obtained from these electron diffraction methods may be corrected by referring to lattice constants obtained from powder XRD or literature values, etc.

[0064] For example, in the positive electrode active material 100, the interior 100b occupies most of the volume. Therefore, the lattice constant of the entire positive electrode active material 100, determined by powder XRD, can be considered equal to the lattice constant of the interior 100b, determined by electron diffraction. Thus, the corrected lattice constants of the interior 100a and the outermost layer 100c can be determined from the ratio of the lattice constants of the interior 100b, the surface layer 100a, and the outermost layer 100c obtained from electron diffraction, and the lattice constants obtained from powder XRD.

[0065] It is preferable that the surface layer 100a has a higher concentration of the additive elements described later than the interior layer 100b. It is also preferable that the additives have a concentration gradient. Furthermore, if there are multiple additive elements, it is preferable that the depth of the concentration peaks from the surface differs for each additive element.

[0066] For example, it is preferable that a certain additive element X has a concentration gradient that increases from the interior 100b towards the surface, as shown by the gradient in Figure 1C1. Examples of additive elements X that are preferable to have such a concentration gradient include magnesium, fluorine, titanium, silicon, phosphorus, boron, and calcium.

[0067] Another additive element Y preferably has a concentration gradient, as shown in the gradient in Figure 1C2, and has a concentration peak in a region deeper than that shown in Figure 1C1. The concentration peak may be located in the surface layer 100a or deeper than the surface layer 100a. It is preferable that the concentration peak is in a region other than the outermost surface layer 100c. For example, it is preferable that the peak is in a region from 5 nm to 30 nm from the surface. Examples of additive elements Y that preferably have such a concentration gradient include aluminum and manganese.

[0068] Furthermore, due to the aforementioned concentration gradient of the additive elements, it is preferable that the crystal structure changes continuously from the interior 100b toward the surface layer 100a and the outermost layer 100c.

[0069] Let's consider the case where internal 100b has a layered rock salt crystal structure. One characteristic of the layered rock salt crystal structure is that it has alternating layers of transition metal M and lithium between the cubic close-packed anion structures. Therefore, in internal 100b, layers of transition metal M with high atomic numbers, which are observed with high brightness, and layers of lithium, which are observed with low brightness, are observed alternately using a cross-sectional TEM, etc. The anions oxygen and fluorine both have low atomic numbers, so they are observed with brightness similar to lithium. These elements with low atomic numbers do not appear as distinct bright spots, and in some cases there is only a slight difference in brightness from the background.

[0070] In this specification, a layered rock salt crystal structure is defined as having alternating layers observed with high brightness and layers observed with low brightness in cross-sectional TEM images, etc. This characteristic is observed when viewed from a direction perpendicular to the c-axis in the layered rock salt crystal structure. Even if a layered rock salt crystal structure is present, this characteristic may not be observed when viewed from other directions.

[0071] On the other hand, in the outermost layer 100c, the concentration of additive elements is high, so some of the additive elements are incorporated into the lithium sites. Since lithium sites are surrounded by anions such as oxygen, metallic elements such as magnesium and aluminum are more likely to be incorporated among the additives. In addition, transition metals M, such as cobalt, may be incorporated into some of the lithium sites. Since all of these metals have atomic numbers greater than lithium, they are observed with stronger brightness than lithium in cross-sectional TEM, etc.

[0072] In some cases, additive elements or lithium may be present in part of the transition metal M site. In this case, it will be observed with a weaker brightness than the transition metal M in cross-sectional TEM, etc.

[0073] When many cation substitutions occur in this manner, the crystal structure develops characteristics of a rock salt type, where there is no distinction between lithium sites and transition metal sites. The presence of rock salt type crystal structure characteristics suggests that the additive elements are present at a sufficient concentration. When the additive elements are present at a sufficient concentration, the elution of transition metal M and the departure of oxygen, which can occur when charging at high voltage, can be suppressed. As a result, battery characteristics, especially continuous charging endurance, are improved, and a safe and reliable secondary battery can be produced.

[0074] On the other hand, it is preferable that the outermost layer 100c also possesses the same layered rock salt crystal structure characteristics as the inner layer 100b. This is because if the surface is covered solely with a rock salt crystal structure, the diffusion pathway of lithium may be inhibited, potentially increasing the internal resistance during charging and discharging. For the same reason, it is preferable that the rock salt crystal structure characteristics are limited to approximately 3 nm from the surface.

[0075] Therefore, it is preferable that the outermost layer 100c has both the characteristics of a layered rock salt crystal structure and the characteristics of a rock salt crystal structure. That is, it is preferable that the outermost layer 100c has a layered rock salt crystal structure having alternating layers observed with high brightness and layers observed with low brightness in cross-sectional TEM images, and furthermore, that some of the lithium sites have a metal with an atomic number greater than lithium.

[0076] When additive elements are present at a preferred concentration in a portion of the lithium sites of the outermost layer 100c, the brightness of the lithium site layer in the cross-sectional TEM image will be 3% to 60% of the brightness of the transition metal M site layer. More preferably, it will be 4% to 50%. Even more preferably, it will be 6% to 40%. Or preferably 3% to 50%. Or preferably 3% to 40%. Or preferably 4% to 60%. Or preferably 4% to 40%. Or preferably 6% to 60%. Or preferably 6% to 50%. It is preferable that the lithium site layer and transition metal M site layer used for comparison have a width of 5 nm or more parallel to the arrangement of the transition metal M.

[0077] Brightness in cross-sectional TEM can be calculated, for example, by integrating the brightness of pixels in the dark-field image of the cross-sectional TEM. Similarly, the brightness of the transition metal M-site layer and the lithium-site layer can be calculated by integrating the brightness of pixels parallel to these layers. Specifically, the image can be made grayscale with black representing brightness 0 and white representing brightness 255, and the brightness of each pixel can be integrated in each row. Furthermore, to facilitate the comparison of brightness of metal site layers, a correction may be applied to exclude brightness originating from elements with low atomic numbers, such as oxygen.

[0078] Note that the samples used for cross-sectional TEM and other measurements have a thickness of approximately 20 nm to 200 nm. Therefore, if the surface of the positive electrode active material 100 has irregularities, accurate brightness may not be obtained in the shallower parts from the surface. For this reason, when comparing brightness, it is necessary to compare parts where stable brightness is obtained. For example, if the maximum brightness of the transition metal M-site layer is set to 1, then a transition metal M-site layer with a brightness of 0.7 or higher is considered to have a stable brightness.

[0079] In this specification, the surface of the positive electrode active material 100 in cross-sectional TEM images, cross-sectional STEM images, etc., refers to the surface where a metal element with an atomic number greater than lithium is first observed. More specifically, it refers to the point where the atomic nucleus of a metal element with an atomic number greater than lithium is first observed, i.e., the point where the brightness peak in the cross-sectional TEM image, etc., exists.

[0080] Furthermore, it is sufficient that at least a portion of the outermost layer 100c of the positive electrode active material possesses both the characteristics of a layered rock salt crystal structure and the characteristics of a rock salt crystal structure, as described above. The above characteristics are easily observed if the crystal planes exposed on the surface of the positive electrode active material are roughly parallel to the (001) plane of R-3m, but depending on the crystal plane, these characteristics may not be clearly observed. Therefore, the brightness ratio of the transition metal site layer and the lithium site layer does not necessarily have to be within the above range.

[0081] Furthermore, electron diffraction can also be used to analyze the characteristics of layered rock salt crystal structures and rock salt crystal structures.

[0082] Rock salt deposits have one type of cation and exhibit high symmetry. Layered rock salt deposits, on the other hand, have two types of cations arranged in a regular pattern, resulting in lower symmetry than rock salt deposits. Consequently, they have twice as many bright spots corresponding to specific surface orientations as rock salt deposits.

[0083] Furthermore, in the case of a crystal structure that possesses characteristics of both rock salt type and layered rock salt type, the diffraction pattern will show a plane orientation in which bright spots of high and low brightness are arranged alternately. Bright spots common to both rock salt type and layered rock salt type will have high brightness, while bright spots occurring only in layered rock salt type will have low brightness.

[0084] It is preferable that the transition metal M, particularly cobalt and nickel, is uniformly dissolved in the entire positive electrode active material 100. However, if the concentration of some transition metals M, such as nickel, is low, it may fall below the detection limit in analyses such as XPS.

[0085] For example, if the number of nickel atoms is 2 atomic percent or less compared to the number of cobalt atoms, then the nickel content in the lithium composite oxide will be 0.5 atomic percent or less. On the other hand, the detection limit for XPS and EDX is generally around 1 atomic percent. Therefore, if nickel is uniformly dissolved throughout the positive electrode active material 100, it may be detected below the detection limit by analytical methods such as XPS and EDX. In this case, being detected below the detection limit suggests that the nickel concentration is 1 atomic percent or less and that it is uniformly dissolved throughout the positive electrode active material 100.

[0086] On the other hand, using ICP-MS or similar methods, it is possible to quantify transition metals even at concentrations of 1 atomic percent or less.

[0087] The positive electrode active material 100 may also contain additive elements that are widely dissolved in the interior 100b and do not have a concentration gradient. Alternatively, a portion of the transition metal M present in the positive electrode active material 100, such as manganese, may have a concentration gradient that increases from the interior 100b towards the surface.

[0088] <Contained elements> The positive electrode active material 100 comprises lithium, a transition metal M, oxygen, and an additive element. The positive electrode active material 100 can also be described as a composite oxide represented by LiMO2 with the additive element added. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented by LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2.

[0089] The transition metal M in the positive electrode active material 100 is preferably a metal that can form a layered rock salt type composite oxide belonging to space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, the transition metal in the positive electrode active material 100 may be cobalt only, nickel only, two types of cobalt and manganese, two types of cobalt and nickel, or three types of cobalt, manganese, and nickel. In other words, the positive electrode active material 100 can have composite oxides containing lithium and a transition metal M, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is substituted with manganese, lithium cobalt oxide in which part of the cobalt is substituted with nickel, and nickel-manganese-lithium cobalt oxide.

[0090] In particular, using cobalt as the transition metal M in the positive electrode active material 100 in an amount of 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics. Furthermore, if nickel is included in addition to cobalt within the above range as the transition metal M, the displacement of the layered structure consisting of octahedra of cobalt and oxygen may be suppressed. Therefore, the crystal structure may become more stable, especially in the charged state at high temperatures, which is preferable.

[0091] Furthermore, the transition metal M does not necessarily have to contain manganese. By using a cathode active material 100 that is substantially free of manganese, the above advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics may be even greater. The weight of manganese contained in the cathode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0092] On the other hand, if nickel is used as the transition metal M in the positive electrode active material 100 in an amount of 33 atomic percent or more, preferably 60 atomic percent or more, and more preferably 80 atomic percent or more, the raw materials may be cheaper compared to the case where cobalt is abundant, and the charge / discharge capacity per unit weight may increase, which is preferable.

[0093] Note that the transition metal M does not necessarily have to include nickel.

[0094] It is preferable to use at least one of the following as additive elements in the positive electrode active material 100: magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. These additive elements may further stabilize the crystal structure of the positive electrode active material 100, as will be described later. In other words, the positive electrode active material 100 can include lithium cobalt oxide with magnesium and fluorine, lithium cobalt oxide with magnesium, fluorine, and titanium, lithium nickel-cobalt oxide with magnesium and fluorine, lithium cobalt-aluminate with magnesium and fluorine, lithium nickel-cobalt-aluminate with magnesium and fluorine, lithium nickel-manganese-cobalt oxide with magnesium and fluorine, etc. In this specification, additive elements may also be referred to as mixtures, part of raw materials, or impurity elements.

[0095] Furthermore, the additive elements do not necessarily have to include magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, or boron.

[0096] In one embodiment of the present invention, the positive electrode active material 100 is reinforced by a surface layer 100a, i.e., the outer periphery of the particles, which has a high concentration of additives, so that even if lithium is removed from the positive electrode active material 100 due to charging, the layered structure consisting of octahedrons of cobalt and oxygen does not break down.

[0097] Furthermore, it is preferable that the concentration gradient of the additive elements be similar throughout the entire surface layer 100a of the positive electrode active material 100. It can also be said that it is preferable that the reinforcement resulting from the high concentration of impurities is uniformly present in 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 particles, defects such as cracks may occur from there, which may lead to cracking of the positive electrode active material and a decrease in charge / discharge capacity.

[0098] In this specification, homogeneity refers to the phenomenon in which, in a solid composed of multiple elements (e.g., A, B, C), a certain element (e.g., A) is distributed in a specific region with similar characteristics. It is sufficient that the elemental concentrations in the specific regions are substantially the same. For example, the difference in elemental concentrations between specific regions should be within 10%. Examples of specific regions include the surface, surface layer, convex areas, concave areas, and interior.

[0099] However, the concentration gradient of all additive elements does not necessarily have to be homogeneous across the entire surface layer 100a of the positive electrode active material 100. Examples of the distribution of additive element X near CD in Figure 1A are shown in Figures 2A1, 2B1, and 2C1. Examples of the distribution of additive element Y near CD are shown in Figures 2A2, 2B2, and 2C2.

[0100] For example, as shown in Figures 2A1 and 2A2, there may be a region in the surface layer 100a where neither additive element X nor additive element Y is present. Also, as shown in Figures 2B1 and 2B2, there may be a region where additive element X is present but additive element Y is not. Furthermore, as shown in Figures 2C1 and 2C2, there may be a region where additive element X is not present but additive element Y is present. In Figure 2C2, it is preferable that additive element Y has a peak in a region other than the outermost layer, similar to Figure 1C2. For example, it is preferable that the peak is in a region from 3 nm to 30 nm from the surface.

[0101] Furthermore, the positive electrode active material 100 may have a recessed portion 102 and a protruding portion 103 as shown in Figure 1A. Additive elements may be present in the recessed portion 102 and the protruding portion 103 at a higher concentration than in the interior 100b or the surface layer 100a.

[0102] The positive electrode active material 100 may have depressions, cracks, pits, or V-shaped cross-sections. These are defects, and repeated charging and discharging may lead to the leaching of transition metal M, collapse of the crystal structure, cracking of the main body, and oxygen detachment. However, if there are embedded portions 102 that fill these defects, the leaching of transition metal M and other defects can be suppressed. Therefore, a positive electrode active material 100 with excellent reliability and cycle characteristics can be obtained.

[0103] Furthermore, the positive electrode active material 100 may have protrusions 103 as regions where the additive elements are unevenly distributed.

[0104] As mentioned above, if the additive elements in the positive electrode active material 100 are in excess, they may adversely affect lithium insertion and removal. Furthermore, when used in a secondary battery, they may lead to increased internal resistance and decreased charge / discharge capacity. On the other hand, if there are insufficient elements, they may not be distributed throughout the entire surface layer 100a, resulting in insufficient suppression of crystal structure degradation. Thus, impurity elements (also called additive elements) in the positive electrode active material 100 need to be at an appropriate concentration, but adjusting this concentration is not easy.

[0105] Therefore, if the positive electrode active material 100 has regions where impurity elements are unevenly distributed, some of the excess impurities are removed from the interior 100b of the positive electrode active material 100, allowing for an appropriate impurity concentration in the interior 100b. This suppresses the increase in internal resistance and the decrease in charge / discharge capacity when used as a secondary battery. The ability to suppress the increase in the internal resistance of a secondary battery is an extremely desirable characteristic, especially at high charge / discharge rates, such as 2C or higher.

[0106] Furthermore, in positive electrode active material 100 having regions where impurity elements are unevenly distributed, it is permissible to mix in a certain excess of impurities during the manufacturing process. This is preferable because it widens the margin in production.

[0107] In this specification, "non-uniformity" refers to a situation where the concentration of one element differs from that of others. Other terms that may be used include segregation, precipitation, heterogeneity, bias, high concentration, or low concentration.

[0108] Magnesium, one of the additive elements X, is divalent and is more stable in lithium sites than transition metal sites in the layered rock salt crystal structure, thus easily occupying lithium sites. The presence of magnesium at an appropriate concentration in the lithium sites of the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. Furthermore, the presence of magnesium can suppress the release of oxygen around the magnesium during high-voltage charging. Magnesium is preferable as it does not adversely affect lithium insertion and removal during charging and discharging when present at an appropriate concentration. However, excessive magnesium may adversely affect lithium insertion and removal. Therefore, as will be described later, it is preferable that the surface layer 100a has a higher concentration of transition metal M than magnesium, for example.

[0109] Aluminum, one of the additive elements Y, is trivalent and can exist at transition metal sites in the layered rock salt crystal structure. Aluminum can suppress the leaching of surrounding cobalt. Furthermore, because aluminum has a strong bonding force with oxygen, it can suppress the departure of oxygen from around the aluminum. Therefore, by including aluminum as an additive element, it is possible to create a positive electrode active material 100 whose crystal structure is less likely to collapse even after repeated charging and discharging.

[0110] Fluorine is a monovalent anion, and if some of the oxygen in the surface layer 100a is replaced by fluorine, the lithium release energy decreases. This is because the change in the valence of cobalt ions accompanying lithium release 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 100 is replaced by fluorine, the release and insertion of lithium ions near the fluorine can occur more smoothly. This is preferable because it improves charge-discharge characteristics, rate characteristics, etc., when used in a secondary battery.

[0111] Titanium oxide is known to be superhydrophilic. Therefore, by using a positive electrode active material 100 having titanium oxide in its surface layer 100a, it is possible that wettability with highly polar solvents will be improved. When used in a secondary battery, good contact at the interface between the positive electrode active material 100 and the highly polar electrolyte may be achieved, potentially suppressing an increase in internal resistance.

[0112] As the charging voltage of a secondary battery increases, the voltage at the positive electrode generally rises. The positive electrode active material according to one aspect of the present invention has a stable crystal structure even at high voltages. The stability of the crystal structure of the positive electrode active material in the charged state suppresses the decrease in charge / discharge capacity that occurs with repeated charging and discharging.

[0113] Furthermore, a short circuit in a secondary battery can not only cause malfunctions in the charging and discharging operations of the secondary battery, but also lead to overheating and ignition. To realize a safe secondary battery, it is preferable that the short-circuit current is suppressed even at high charging voltages. The positive electrode active material 100 in one aspect of the present invention suppresses the short-circuit current even at high charging voltages. Therefore, it is possible to create a secondary battery that achieves both high charge / discharge capacity and safety.

[0114] The concentration gradient of additive elements can be evaluated using methods such as energy-dispersive X-ray spectroscopy (EDX) and electron probe microanalysis (EPMA). EDX measurements that scan within a region to evaluate it in two dimensions are called EDX surface analysis. Measurements that scan linearly to evaluate the distribution of atomic concentrations within positive electrode active material particles are called line analysis. Furthermore, sometimes line analysis refers to data extracted from linear regions using EDX surface analysis. Measurements taken without scanning within a region are called point analysis.

[0115] EDX surface analysis (e.g., elemental mapping) allows for the quantitative analysis of the concentrations of additive elements in the surface layer 100a, interior 100b, and near grain boundaries of the positive electrode active material 100, including the outermost surface layer 100c. Furthermore, EDX radiation analysis allows for the analysis of the concentration distribution and maximum values ​​of the additive elements.

[0116] When EDX radiation analysis is performed on a positive electrode active material 100 having magnesium as an additive element, the magnesium concentration peak in the surface layer 100a is preferably located in the outermost layer 100c, extending from the surface of the positive electrode active material 100 toward the center to a depth of 3 nm, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0117] Furthermore, in a positive electrode active material 100 having magnesium and fluorine as additive elements, it is preferable that the distribution of fluorine overlaps with the distribution of magnesium. Therefore, when EDX radiation analysis is performed, the peak of fluorine concentration in the surface layer 100a is preferably located in the outermost layer 100c, extending from the surface of the positive electrode active material 100 toward the center to a depth of 3 nm, more preferably to a depth of 1 nm, and even more preferably to a depth of 0.5 nm.

[0118] It should be noted that not all additive elements have the same concentration distribution. For example, if the positive electrode active material 100 contains aluminum as an additive element, it is preferable that its distribution is slightly different from that of magnesium and fluorine, as described above. For example, when EDX radiation analysis is performed, it is preferable that the peak of magnesium concentration is closer to the surface than the peak of aluminum concentration in the surface layer 100a. For example, it is preferable that the peak of aluminum concentration is located at a depth of 0.5 nm to 50 nm from the surface toward the center of the positive electrode active material 100, and more preferably at a depth of 5 nm to 30 nm. Or it is preferable that it is located at 0.5 nm to 30 nm. Or it is preferable that it is located at 5 nm to 50 nm.

[0119] Furthermore, when the positive electrode active material 100 is subjected to line analysis or surface analysis, the ratio of the number of atoms of impurity element I to the transition metal M in the surface layer 100a (I / M) is preferably 0.05 or more and 1.00 or less. Moreover, if the impurity element is titanium, the ratio of the number of atoms of titanium to the transition metal M (Ti / M) is preferably 0.05 or more and 0.4 or less, and more preferably 0.1 or more and 0.3 or less. If the impurity element is magnesium, the ratio of the number of atoms of magnesium to the transition metal M (Mg / M) is preferably 0.4 or more and 1.5 or less, and more preferably 0.45 or more and 1.00 or less. Moreover, if the impurity element is fluorine, the ratio of the number of atoms of fluorine to the transition metal M (F / M) is preferably 0.05 or more and 1.5 or less, and more preferably 0.3 or more and 1.00 or less.

[0120] Furthermore, the surface of the positive electrode active material 100 in the EDX radiation analysis results can be estimated as follows: For elements uniformly present in the interior 100b of the positive electrode active material 100, such as oxygen or transition metals M such as cobalt, the point where the detected amount in the interior 100b becomes half is defined as the surface.

[0121] Since the positive electrode active material 100 is a composite oxide, it is preferable to estimate the surface using the detected amount of oxygen. Specifically, first, the average value of the oxygen concentration is obtained from the region where the detected amount of oxygen in the interior 100b is stable. aveWe will determine the oxygen O2 that is thought to be present outside the surface due to chemiadsorption or background. background If detected, O background Subtracting this gives the average oxygen concentration O ave This can be done. This average value O ave Half of that value, that is, 1 / 2O ave The measurement point that shows the closest measurement value can be estimated to be the surface of the positive electrode active material.

[0122] The surface can also be estimated using the transition metal M present in the positive electrode active material 100. For example, if more than 95% of the transition metal M is cobalt, the surface can be estimated in the same way as above using the detected amount of cobalt. Alternatively, the surface can be estimated in the same way using the sum of the detected amounts of multiple transition metals M. The detected amount of transition metal M is suitable for surface estimation because it is less affected by chemiadsorption.

[0123] Furthermore, when line analysis or surface analysis is performed on the positive electrode active material 100, the ratio of additive element I to transition metal M (I / M) near the grain boundaries is preferably 0.020 or more and 0.50 or less. More preferably 0.025 or more and 0.30 or less. More preferably 0.030 or more and 0.20 or less. Or preferably 0.20 or more and 0.30 or less. Or preferably 0.20 or more and 0.20 or less. Or preferably 0.25 or more and 0.50 or less. Or preferably 0.030 or more and 0.50 or less. Or preferably 0.030 or more and 0.30 or less.

[0124] For example, when the additive element is magnesium and the transition metal M is cobalt, the ratio of the number of magnesium atoms to cobalt atoms (Mg / Co) is preferably 0.020 or more and 0.50 or less. Furthermore, 0.025 or more and 0.30 or less is preferred. Furthermore, 0.030 or more and 0.20 or less is preferred. Or 0.020 or more and 0.30 or less is preferred. Or 0.020 or more and 0.20 or less is preferred. Or 0.025 or more and 0.50 or less is preferred. Or 0.030 or more and 0.50 or less is preferred. Or 0.030 or more and 0.30 or less is preferred.

[0125] Furthermore, the positive electrode active material 100 may have a coating on at least a portion of its surface. Figure 3 shows an example of a positive electrode active material 100 having a coating 104.

[0126] Preferably, the coating 104 is formed by the accumulation of decomposition products of the electrolyte during charging and discharging. In particular, when high-voltage charging is repeated, it is expected that the charge-discharge cycle characteristics will be improved by having a coating derived from the electrolyte on the surface of the positive electrode active material 100. This is because it suppresses the increase in impedance on the surface of the positive electrode active material or suppresses the elution of the transition metal M. Preferably, the coating 104 contains carbon, oxygen, and fluorine. Furthermore, if LiBOB and / or SUN (suberonitrile) is used as part of the electrolyte, a good quality coating is more likely to be obtained. Therefore, it is more preferable if the coating 104 contains boron and / or nitrogen, as this tends to result in a good quality coating. Also, the coating 104 does not need to cover the entire positive electrode active material 100.

[0127] <Crystal structure> Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiMO2.

[0128] It is known that the Jahn-Teller effect in transition metal compounds differs in strength depending on the number of electrons in the d orbitals of the transition metal.

[0129] In nickel-containing compounds, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the effect of the Jahn-Teller effect is suggested to be smaller, and it may have better resistance when charged at high voltages, making it preferable.

[0130] The positive electrode active material will be explained using Figures 4 to 7. Figures 4 to 7 describe the case where cobalt is used as the transition metal M in the positive electrode active material.

[0131] <Conventional positive electrode active material> The positive electrode active material shown in Figure 6 is lithium cobalt oxide (LiCoO2) without the addition of fluorine and magnesium, as described later in the manufacturing method. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Figure 6 changes depending on the depth of charge.

[0132] As shown in Figure 6, lithium cobalt oxide at charge depth 0 (discharge state) has a region with a crystal structure of space group R-3m, where lithium occupies octahedral sites, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called the O3 type crystal structure. The CoO2 layer refers to a structure in which octahedral structures, in which oxygen atoms are 6-coordinated to cobalt, are continuous in a plane with shared edges.

[0133] Furthermore, at a charge depth of 1, it has a crystal structure of space group P-3m1, with one CoO2 layer present in the unit cell. For this reason, this crystal structure is sometimes called an O1 type crystal structure.

[0134] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.8 has a crystal structure with space group R-3m. This structure can be described as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) 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 6, the c-axis of the H1-3 type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0135] As an example, the H1-3 type crystal structure can be represented as follows, as described in Non-Patent Literature 3: the coordinates of cobalt and oxygen in the unit cell are 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. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygen atoms. On the other hand, as will be described later, the O3' type crystal structure in one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' structure and the H1-3 type structure, and that the O3' structure shows less variation from the O3 structure compared to the H1-3 type structure. The choice of which unit cell is preferable to represent the crystal structure of the positive electrode active material can be made, for example, in Rietveld analysis using XRD, by selecting the one that results in the smallest GOF (goodness of fit) value.

[0136] When high-voltage charging occurs, such as when the charging voltage is 4.6V or higher relative to the oxidation-reduction potential of lithium metal, or when deep charging occurs, such as when the charging depth is 0.8 or higher, and when this charging and discharging cycle is repeated, 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.

[0137] However, these two crystal structures exhibit a significant displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 6, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m(O3). Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0138] Furthermore, the volume difference is also significant. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

[0139] In addition, the H1-3 type crystal structure, which consists of continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0140] Therefore, repeated high-voltage charging and discharging causes the crystal structure of lithium cobalt oxide 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.

[0141] <Positive electrode active material according to one aspect of the present invention> ≪Crystal structure≫ The positive electrode active material 100 according to one aspect of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charging and discharging. Furthermore, it can reduce the change in volume. Therefore, the positive electrode active material according to one aspect of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material according to one aspect of the present invention can adopt a stable crystal structure in a high-voltage charged state. Therefore, the positive electrode active material according to one aspect of the present invention may be less prone to short circuits when a high-voltage charged state is maintained. In such cases, safety is further improved, which is preferable.

[0142] In one embodiment of the present invention, the change in crystal structure and the difference in volume per unit of the same number of transition metal M atoms are small between a fully discharged state and a high-voltage charged state.

[0143] Figure 4 shows the crystal structure of the positive electrode active material 100 before and after charging and discharging. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal M, and oxygen. In addition to the above, it is preferable to have magnesium as an additive. It is also preferable to have fluorine as an additive.

[0144] The crystal structure at charge depth 0 (discharge state) in Figure 4 is R-3m(O3), the same as in Figure 6. On the other hand, when the positive electrode active material 100 is fully charged, it has a crystal structure different from the H1-3 type crystal structure. This structure has a space group R-3m and is not a spinel type crystal structure, but ions such as cobalt and magnesium occupy the oxygen 6 coordination positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Furthermore, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, in this specification, this structure is referred to as the O3' type crystal structure or the pseudo-spinel type crystal structure. Accordingly, the O3' type crystal structure may be rephrased as the pseudo-spinel type crystal structure. In both the O3 type crystal structure and the O3' type crystal structure, it is preferable that dilute magnesium is present between the CoO2 layers, i.e., at the lithium sites. It is also preferable that fluorine is present randomly and dilutely at the oxygen sites.

[0145] In addition, in the O3' type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate position, and in this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0146] Furthermore, although Figure 4 shows lithium present at all lithium sites with equal probability, the positive electrode active material 100 in one embodiment of the present invention is not limited to this. It may be present preferentially at some lithium sites. For example, Li belonging to space group P2 / m 0.5 Similar to CoO2, lithium may be present at a specific, aligned lithium site. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0147] Furthermore, the O3' type crystal structure can be said to be similar to the CdCl2 type crystal structure, although it has Li randomly between the layers. This CdCl2 type-like crystal structure is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0148] In one embodiment of the present invention, the change in crystal structure when charged at high voltage and a large amount of lithium is released is suppressed compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 4, there is almost no displacement of the CoO2 layer in these crystal structures.

[0149] More specifically, the positive electrode active material 100 according to one embodiment of the present invention exhibits high crystal structure stability even at high charging voltages. For example, in conventional positive electrode active materials, there is a region of charging voltage at which the R-3m(O3) crystal structure can be maintained even at a charging voltage of approximately 4.6V relative to the potential of lithium metal, which results in an H1-3 type crystal structure. Furthermore, there is a region where an O3' type crystal structure can be adopted even at higher charging voltages, such as 4.65V to 4.7V relative to the potential of lithium metal. Only when the charging voltage is increased even further may an H1-3 type crystal be observed. Moreover, even at lower charging voltages (for example, when the charging voltage is 4.5V or higher and less than 4.6V relative to the potential of lithium metal), the positive electrode active material 100 according to one embodiment of the present invention may be able to adopt an O3' type crystal structure.

[0150] Therefore, in the positive electrode active material 100 of one aspect of the present invention, the crystal structure is less likely to collapse even when repeatedly charged and discharged at high voltage.

[0151] Furthermore, in the case of a secondary battery, if graphite is used as the negative electrode active material, 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, for example, even when the voltage of a secondary battery using graphite as the negative electrode active material is between 4.3V and 4.5V, the positive electrode active material 100 of one embodiment of the present invention can maintain the R-3m(O3) crystal structure, and can also adopt the O3' type crystal structure in regions with higher charging voltages, for example, when the secondary battery voltage is above 4.5V and below 4.6V. Moreover, even at lower charging voltages, for example, when the secondary battery voltage is between 4.2V and 4.3V, the positive electrode active material 100 of one embodiment of the present invention may adopt the O3' type crystal structure.

[0152] Furthermore, the O3' type crystal structure can be represented by showing the coordinates of cobalt and oxygen in the unit cell as follows: Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25.

[0153] Additives such as magnesium, which are randomly and dilutely present between CoO2 layers, i.e., at lithium sites, have the effect of suppressing the displacement of the CoO2 layers when charged at high voltage. Therefore, when magnesium is present between CoO2 layers, an O3' type crystal structure is more likely to be formed. For this reason, it is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100 according to one embodiment of the present invention. Furthermore, in order to distribute magnesium throughout the particles, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 100 according to one embodiment of the present invention.

[0154] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the likelihood that additives, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site does not help maintain the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation of lithium.

[0155] Therefore, it is preferable to add a fluorine compound to lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. Adding a fluorine compound lowers the melting point of lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute magnesium throughout the particles at a temperature where cation mixing is less likely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0156] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of transition metal M atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably around 0.02. Alternatively, 0.001 times or more and less than 0.04 is preferred, or 0.01 or more and 0.1 or less is preferred. The magnesium concentration shown here may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material blend during the process of manufacturing the positive electrode active material.

[0157] Lithium cobalt oxide may be mixed with one or more metals other than cobalt (hereinafter referred to as metal Z), such as nickel, aluminum, manganese, titanium, vanadium, and chromium, and it is particularly preferable to add nickel and one or more aluminum. Manganese, titanium, vanadium, and chromium may be more readily stable in the tetravalent state and may contribute significantly to structural stability. By adding metal Z, the crystal structure of the positive electrode active material in one embodiment of the present invention may become more stable, for example, in a high-voltage charged state. Here, in the positive electrode active material in one embodiment of the present invention, it is preferable that metal Z is added at a concentration that does not significantly change the crystallinity of lithium cobalt oxide. For example, it is preferable that the amount is such that the aforementioned Jahn-Teller effect does not occur.

[0158] As shown in the legend in Figure 4, transition metals such as nickel and manganese, and aluminum are preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0159] In one embodiment of the present invention, the charge-discharge capacity of the positive electrode active material may decrease as the magnesium concentration increases. One reason for this is that the amount of lithium contributing to charge-discharge decreases due to the presence of magnesium at the lithium sites. In addition, excess magnesium may generate magnesium compounds that do not contribute to charge-discharge. In one embodiment of the present invention, the charge-discharge capacity per unit weight and per unit volume may be increased by including nickel as metal Z in addition to magnesium. In another embodiment of the present invention, the charge-discharge capacity per unit weight and per unit volume may be increased by including aluminum as metal Z in addition to magnesium. In yet another embodiment of the present invention, the charge-discharge capacity per unit weight and per unit volume may be increased by including nickel and aluminum in addition to magnesium.

[0160] The concentrations of elements such as magnesium and metal Z in the positive electrode active material according to one embodiment of the present invention are expressed below in terms of the number of atoms.

[0161] The number of nickel atoms in the positive electrode active material 100 according to one aspect of the present invention 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 preferably more than 0% and 4% or less. Alternatively, it is preferably more than 0% and 2% or less. Alternatively, it is preferably 0.05% to 7.5% or less. Alternatively, it is preferably 0.05% to 2% or less. Alternatively, it is preferably 0.1% to 7.5% or less. Alternatively, it is preferably 0.1% to 4% or less. The nickel concentration shown herein may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material 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.

[0162] Nickel present at the above concentrations readily dissolves uniformly throughout the positive electrode active material 100, thus contributing particularly to the stabilization of the crystal structure of the interior 100b. Furthermore, the presence of divalent nickel in the interior 100b may allow divalent additive elements, such as magnesium, which are randomly and dilutely present at lithium sites nearby, to exist more stably. As a result, the leaching of magnesium may be suppressed even after high-voltage charging and discharging. This can improve the charge-discharge cycle characteristics. Thus, combining the effects of nickel in the interior 100b with the effects of magnesium, aluminum, titanium, fluorine, etc., in the surface layer 100a is extremely effective in stabilizing the crystal structure during high-voltage charging.

[0163] The number of aluminum atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferred, or 0.1% to 4% is preferred. The aluminum concentration shown here may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material 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.

[0164] In one embodiment of the present invention, the positive electrode active material preferably contains the element W, and more preferably phosphorus as the element W. Furthermore, in one embodiment of the present invention, the positive electrode active material more preferably contains a compound containing phosphorus and oxygen.

[0165] In one embodiment of the present invention, the positive electrode active material contains a compound with element W, which may suppress short circuits when a high-voltage charge state is maintained.

[0166] In one embodiment of the present invention, if the positive electrode active material contains phosphorus as element X, the hydrogen fluoride generated by the decomposition of the electrolyte may react with the phosphorus, potentially reducing the concentration of hydrogen fluoride in the electrolyte.

[0167] When the electrolyte contains LiPF6, hydrolysis may generate hydrogen fluoride. Hydrogen fluoride may also be generated by the reaction between PVDF, used as a component of the positive electrode, and alkali. Reducing the hydrogen fluoride concentration in the charging solution may suppress corrosion and peeling of the coating on the current collector. Furthermore, it may suppress the decrease in adhesion due to gelation or insolubilization of PVDF.

[0168] In one embodiment of the present invention, when the positive electrode active material contains magnesium in addition to element X, the stability in a high-voltage charged state is extremely high. When element X is phosphorus, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. Or preferably 1% to 10%. Or preferably 1% to 8%. Or preferably 2% to 20%. Or preferably 2% to 8%. Or preferably 3% to 20%. Or preferably 3% to 10%. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. Or preferably 0.1% to 5%. Or preferably 0.1% to 4%. Or preferably 0.5% to 10%. Or preferably 0.5% to 4%. Or preferably 0.7% to 10%. Alternatively, a concentration of 0.7% to 5% is preferred. The concentrations of phosphorus and magnesium shown herein may be, for example, values ​​obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or they may be based on the values ​​of the raw material formulation during the manufacturing process of the positive electrode active material.

[0169] The positive electrode active material may have cracks. The presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, within the positive electrode active material with cracks on its surface may suppress the propagation of these cracks.

[0170] ≪Surface layer≫ It is preferable that magnesium is distributed throughout the particles of the positive electrode active material 100 according to one embodiment of the present invention, but in addition, it is preferable that the magnesium concentration in the surface layer 100a is higher than the average of the entire particle. Alternatively, it is preferable that the magnesium concentration in the surface layer 100a is higher than the concentration in the interior 100b. For example, it is preferable that the magnesium concentration in the surface layer 100a measured by XPS, etc., is higher than the average magnesium concentration of the entire particle measured by ICP-MS, etc. Alternatively, it is preferable that the magnesium concentration in the surface layer 100a measured by EDX surface analysis, etc., is higher than the magnesium concentration in the interior 100b.

[0171] Furthermore, in one embodiment of the present invention, when the positive electrode active material 100 contains one or more metals other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal in the surface layer 100a is higher than the average concentration of the entire particle. Alternatively, it is preferable that the concentration of the metal in the surface layer 100a is higher than the concentration in the interior 100b. For example, it is preferable that the concentration of elements other than cobalt in the surface layer 100a, as measured by XPS, is higher than the average concentration of the elements in the entire particle, as measured by ICP-MS. Alternatively, it is preferable that the concentration of elements other than cobalt in the surface layer 100a, as measured by EDX surface analysis, is higher than the concentration of elements other than cobalt in the interior 100b.

[0172] Unlike the interior of the crystal, the surface layer has broken bonds, and during charging, lithium escapes from the surface, making it a region where the lithium concentration tends to be lower than in the interior. Therefore, it is a region that is prone to instability and the crystal structure is easily disrupted. A higher magnesium concentration in the surface layer 100a can more effectively suppress changes in the crystal structure. Furthermore, a higher magnesium concentration in the surface layer 100a can also be expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0173] Furthermore, it is preferable that the concentration of fluorine in the surface layer 100a of the positive electrode active material 100 in one embodiment of the present invention is higher than the average concentration of fluorine throughout the entire particle. Alternatively, it is preferable that the fluorine concentration in the surface layer 100a is higher than the concentration in the interior 100b. The presence of fluorine in the surface layer 100a, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0174] Thus, it is preferable that the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention has a different composition from the interior 100b, with higher concentrations of additive elements, such as magnesium and fluorine. Furthermore, it is preferable that the surface layer has a crystalline structure that is stable at room temperature (25°C). For this reason, the surface layer 100a may have a different crystalline structure from the interior 100b. For example, at least a portion of the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention may have a rock salt-type crystalline structure. Also, if the surface layer 100a and the interior 100b have different crystalline structures, it is preferable that the crystal orientations of the surface layer 100a and the interior 100b are roughly the same.

[0175] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0176] That the crystal orientations of the two regions substantially match can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, and the like. X-ray diffraction (XRD), electron diffraction, neutron diffraction and the like can also be used as materials for the determination. In a TEM image or the like, the arrangement of cations and anions can be observed as a repetition of bright lines and dark lines. When the orientation of the cubic close-packed structure is aligned between the layered rock salt-type crystal and the rock salt-type crystal, it can be observed that the angle formed by the repetition of bright lines and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that light elements such as oxygen and fluorine may not be clearly observable in a TEM image or the like; in such cases, the matching of orientations can be determined based on the arrangement of metal elements.

[0177] However, if the surface layer portion 100a consists only of MgO or only of a structure in which MgO and CoO(II) form a solid solution, insertion and desorption of lithium becomes difficult. Therefore, it is necessary that the surface layer portion 100a contains at least cobalt, also contains lithium in a discharged state, and has a path for insertion and desorption of lithium. It is also preferable that the concentration of cobalt is higher than that of magnesium.

[0178] It is also preferable that the additive element X is located in the surface layer portion 100a of the particles of the positive electrode active material 100 according to one embodiment of the present invention. For example, the positive electrode active material 100 according to one embodiment of the present invention may be covered with a coating containing the additive element X.

[0179] <<Grain Boundaries>> It is more preferable that, in addition to the distribution described above, a part of the additive element contained in the positive electrode active material 100 according to one embodiment of the present invention is segregated at the grain boundaries 101 as shown in FIG. 1A.

[0180] More specifically, it is preferable that the magnesium concentration at and near the grain boundaries 101 of the positive electrode active material 100 is higher than that in other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries 101 is also higher than that in other regions of the interior 100b.

[0181] The grain boundary 101 is a type of surface defect. Therefore, like the grain surface, it is prone to instability, and changes in the crystal structure are likely to begin. For this reason, if the magnesium concentration at and near the grain boundary 101 is high, changes in the crystal structure can be suppressed more effectively.

[0182] Furthermore, if the magnesium and fluorine concentrations are high at and near the grain boundaries, even if cracks occur along the grain boundaries 101 of the particles of the positive electrode active material 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 after cracks have occurred.

[0183] In this specification, the vicinity of grain boundary 101 refers to the region extending approximately 10 nm from the grain boundary. A grain boundary is a plane where the arrangement of atoms changes and can be observed in an electron microscope image. Specifically, it refers to a region in an electron microscope image where the angle between the repetition of bright and dark lines exceeds 5 degrees.

[0184] ≪Particle size≫ In one embodiment of the present invention, if the particle size of the positive electrode active material 100 is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if it is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte. Therefore, the median diameter (D50) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. Or preferably 1 μm or more and 40 μm or less. Or preferably 1 μm or more and 30 μm or less. Or preferably 2 μm or more and 100 μm or less. Or preferably 2 μm or more and 30 μm or less. Or preferably 5 μm or more and 100 μm or less. Or preferably 5 μm or more and 40 μm or less.

[0185] <Analysis method> Whether a certain positive electrode active material is a positive electrode active material 100 according to one embodiment of the present invention that exhibits an O3' type crystal structure when charged with a high voltage can be determined by analyzing the positive electrode charged with a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material 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 a positive electrode obtained by disassembling a secondary battery.

[0186] One aspect of the present invention, the positive electrode active material 100, is characterized by minimal change in its crystal structure between the high-voltage charged state and the discharged state, as described above. Materials in which the crystal structure that changes significantly from the discharged state accounts for 50 wt% or more when charged at high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that simply adding additive elements may not result in the desired crystal structure. For example, even if both materials are lithium cobalt oxide containing magnesium and fluorine, there are cases where the O3' type crystal structure accounts for 60 wt% or more when charged at high voltage, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a predetermined voltage, the O3' type crystal structure may account for almost 100 wt%, and if the predetermined voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, to determine whether or not a material is the positive electrode active material 100 of one aspect of the present invention, analysis of the crystal structure, including XRD, is necessary.

[0187] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they may change from an O3' type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0188] ≪Charging method≫ High-voltage charging to determine whether a certain composite oxide is the positive electrode active material 100 according to one aspect of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) with lithium as the counter electrode and then charging it.

[0189] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry of a mixture of positive electrode active material, conductive additive, and binder.

[0190] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode will differ. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0191] The electrolyte in the electrolyte solution may be 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7, and vinylene carbonate (VC) at 2 wt%.

[0192] Polypropylene with a thickness of 25 μm can be used for the separator.

[0193] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0194] The coin cell prepared under the above conditions is charged with a constant current of 0.5C at an arbitrary voltage (e.g., 4.6V, 4.65V, or 4.7V), and then charged with a constant voltage until the current value becomes 0.01C. Note that 1C can be 137mA / g or 200mA / g. The temperature is 25°C. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere, and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When performing various analyses thereafter, it is preferable to seal it under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing it in a sealed container under an argon atmosphere.

[0195] ≪XRD≫ There are no particular limitations on the apparatus and conditions for XRD measurement. For example, measurement can be performed using the following apparatus and conditions. XRD apparatus: D8 ADVANCE, manufactured by Bruker AXS X-ray source: CuKα radiation Output: 40 KV, 40 mA Slit system: Div. Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scanning Measurement range (2θ): 15° (degrees) or more and 90° or less Step width (2θ): set to 0.01° Counting time: 1 second per step Sample stage rotation: 15 rpm

[0196] When the measurement sample is a powder, it can be set by a method such as placing it in a glass sample holder, or sprinkling the sample onto a silicon non-reflective plate coated with grease. When the measurement sample 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 to align with the measurement surface required by the apparatus.

[0197] Ideal powder XRD patterns obtained using CuKα1 radiation, calculated from models of the O3'-type crystal structure and the H1-3-type crystal structure, are shown in FIG. 5 and FIG. 7. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2 (O3) at a depth of charge of 0 and CoO2 (O1) at a depth of charge of 1 are also shown. The patterns for LiCoO2 (O3) and CoO2 (O1) were created from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 4) using Reflex Powder Diffraction, which is one of the modules of Materials Studio (BIOVIA). The 2θ range was set to 15° to 75°, Step size=0.01, wavelength λ1=1.540562×10 -10m and λ2 were not set, and the Monochromator was set to single. The H1-3 type crystal structure pattern was similarly created from the crystal structure information described in Non-Patent Literature 3. For the O3' type crystal structure pattern, the crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0198] As shown in Figure 5, 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°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 7, these peaks do not appear in the H1-3 type crystal structure and CoO2 (P-3m1, O1). Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° when charged at high voltage is a characteristic feature of the positive electrode active material 100 in one embodiment of the present invention.

[0199] This can also be described as the position where the XRD diffraction peaks appear being close between the crystal structure at a charging depth of 0 and the crystal structure after high-voltage charging. More specifically, it can be said that for two or more, more preferably three or more, of the main diffraction peaks of the two, the difference in the position where the peaks appear is 2θ = 0.7 or less, and more preferably 2θ = 0.5 or less.

[0200] In one embodiment of the present invention, the positive electrode active material 100 has an O3' type crystal structure when charged with a high voltage, but not all particles have to have an O3' type crystal structure. Other crystal structures may be included, or some 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 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3' type crystal structure accounts for 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be obtained.

[0201] Furthermore, even after more than 100 charge-discharge cycles from the start of measurement, it is preferable that the O3' type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more when Rietveld analysis is performed.

[0202] Furthermore, the crystallite size of the O3'-type crystal structure possessed by the particles of the positive electrode active material decreases to only about 1 / 10th of that of LiCoO2(O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3'-type crystal structure can be confirmed after high-voltage charging. On the other hand, in simple LiCoO2, even if some parts can adopt a structure similar to the O3'-type crystal structure, the crystallite size becomes smaller, and the peak becomes broad and small. The crystallite size can be determined from the full width at half maximum of the XRD peak.

[0203] In one embodiment of the present invention, the positive electrode active material preferably has a small effect of the Jahn-Teller effect, as described above. The positive electrode active material in one embodiment of the present invention preferably has a layered rock salt type crystal structure and mainly contains cobalt as a transition metal. In addition, in one embodiment of the present invention, the positive electrode active material may contain metal Z as described above, in addition to cobalt, as long as the effect of the Jahn-Teller effect is small.

[0204] In the cathode active material, we will use XRD analysis to investigate the range of lattice constants in which the Jahn-Teller effect is presumed to be small.

[0205] Figure 8 shows the results of calculating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material of one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and nickel. Figure 8A shows the results for the a-axis, and Figure 8B shows the results for the c-axis. Note that the XRD patterns used for these calculations are from the powder after synthesis of the positive electrode active material, before it is incorporated into the positive electrode. The nickel concentration on the horizontal axis represents the nickel concentration when the sum of the number of cobalt and nickel atoms is taken as 100%. The positive electrode active material was prepared in the same manner as the preparation method shown in Figure 11, which will be described later, except that an aluminum source was not used. The nickel concentration represents the nickel concentration in the positive electrode active material when the sum of the number of cobalt and nickel atoms is taken as 100%.

[0206] Figure 9 shows the results of estimating the lattice constants on the a-axis and c-axis using XRD when the positive electrode active material according to one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and manganese. Figure 9A shows the results for the a-axis, and Figure 9B shows the results for the c-axis. Note that the lattice constants shown in Figure 9 are for the powder after synthesis of the positive electrode active material and were measured by XRD before being incorporated into the positive electrode. The manganese concentration on the horizontal axis represents the manganese concentration when the sum of the number of cobalt and manganese atoms is taken as 100%. The positive electrode active material was prepared according to the manufacturing method shown in Figure 11, which will be described later, except that a manganese source was used instead of a nickel source, and an aluminum source was not used. The manganese concentration represents the manganese concentration when the sum of the number of cobalt and manganese atoms is taken as 100% in step S21.

[0207] Figure 8C shows the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 8A and 8B. Figure 9C shows the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 9A and 9B.

[0208] Figure 8C shows a significant change in the a-axis / c-axis at nickel concentrations of 5% and 7.5%, with a larger strain on the a-axis. This strain may be Jahn-Teller strain. This suggests that a superior cathode active material with low Jahn-Teller strain can be obtained at nickel concentrations below 7.5%.

[0209] Next, Figure 9A suggests that when the manganese concentration is 5% or higher, the behavior of the lattice constant changes is different and does not follow Vegard's law. Therefore, it is suggested that the crystal structure is different when the manganese concentration is 5% or higher. Thus, a manganese concentration of, for example, 4% or less is preferable.

[0210] It should be noted that the above-mentioned ranges for nickel and manganese concentrations do not necessarily apply to the surface layer 100a. In other words, higher concentrations may be acceptable in the surface layer 100a.

[0211] Based on the above considerations regarding the preferred range of lattice constants, in a positive electrode active material according to one embodiment of the present invention, the layered rock salt type crystal structure of the particles of the positive electrode active material in a non-charged or discharged state, as estimated from the XRD pattern, has a lattice constant of 2.814 × 10⁻¹⁴ in the a-axis. -10 Larger than m, 2.817 × 10 -10 It is smaller than m, and the lattice constant of the c axis is 14.05 × 10⁻¹⁰. -10 Larger than m, 14.07 × 10 -10 It was found that a value smaller than m is preferable. The state without charging and discharging may, for example, be the powder state before the positive electrode of the secondary battery is manufactured.

[0212] Alternatively, in the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, it is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is greater than 0.20000 and less than 0.20049.

[0213] Alternatively, when XRD analysis is performed on the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, a first peak may be observed when 2θ is between 18.50° and 19.30°, and a second peak may be observed when 2θ is between 38.00° and 38.80°.

[0214] The peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100. The crystal structures of the surface layer 100a, the outermost layer 100c, etc., can be analyzed by electron diffraction of the cross-section of the positive electrode active material 100.

[0215] ≪XPS≫ X-ray photoelectron spectroscopy (XPS) allows for analysis of regions from the surface to a depth of approximately 2 to 8 nm (usually less than 5 nm), enabling quantitative analysis of the concentration of each element in about half of the surface layer 100a. Furthermore, narrow-scan analysis allows for the analysis of the bonding state of elements. The quantitative accuracy of XPS is generally around ±1 atomic percent, and the detection limit is approximately 1 atomic percent, although this varies depending on the element.

[0216] When XPS analysis is performed on the positive electrode active material 100 according to one embodiment of the present invention, the number of atoms of the additive element is preferably 1.6 to 6.0 times the number of atoms of the transition metal M, and more preferably 1.8 to less than 4.0 times. When the additive is magnesium and the transition metal M is cobalt, the number of magnesium atoms is preferably 1.6 to 6.0 times the number of cobalt atoms, and more preferably 1.8 to less than 4.0 times. Furthermore, the number of halogen atoms such as fluorine is preferably 0.2 to 6.0 times the number of atoms of the transition metal M, and more preferably 1.2 to 4.0 times.

[0217] For XPS analysis, monochromatic aluminum can be used as the X-ray source, for example. The extraction angle can be set to, for example, 45°. Measurements can be performed using, for example, the following equipment and conditions. Measurement device: PHI QuanteraII X-ray source: Monochromatic Al (1486.6 eV) Detection area: 100 μmφ Detection depth: Approximately 4-5 nm (extraction angle 45°) Measurement spectrum: Wide scan, narrow scan of each detected element

[0218] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably around 684.3 eV. This value is different from both the bond energy of lithium fluoride, which is 685 eV, and the bond energy of magnesium fluoride, which is 686 eV. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains fluorine, it is preferable that the bond is with something other than lithium fluoride and magnesium fluoride.

[0219] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably around 1303 eV. This value is different from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains magnesium, it is preferable that the bond is with an element other than magnesium fluoride.

[0220] It is preferable that additive elements, such as magnesium and aluminum, which are more abundant in the surface layer 100a, have concentrations measured by XPS or the like that are higher than concentrations measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0221] When magnesium and aluminum are processed to expose their cross-sections and analyzed using TEM-EDX, it is preferable that the concentration in the surface layer 100a is higher than the concentration in the interior 100b. Processing can be carried out, for example, by FIB (Focused Ion Beam).

[0222] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms. On the other hand, the ratio of magnesium atoms (Mg / Co) determined by ICP-MS analysis is preferably 0.001 to 0.06.

[0223] On the other hand, it is preferable that the nickel contained in the transition metal M is not concentrated in the surface layer 100a but is distributed throughout the entire positive electrode active material 100. However, this does not apply if there are regions where the aforementioned additive elements are concentrated.

[0224] ≪ESR≫ As described above, in one embodiment of the present invention, the positive electrode active material preferably has cobalt and nickel as transition metals and magnesium as an additive element. As a result, some Co 3+ Ni 2+ It is replaced by, and also some Li + is Mg 2+ It is preferable that it be replaced with Li. + is Mg 2+ As a result of being replaced by, the Ni 2+ It is reduced to Ni 3+ This can sometimes happen. Also, some Li + is Mg 2+ It is replaced by and consequently the neighboring Co 3+ It is reduced to Co 2+ This can happen. Also, some Co 3+ is Mg 2+ It is replaced by and consequently the neighboring Co 3+ It is oxidized to Co 4+ This can happen.

[0225] Therefore, in one aspect of the present invention, the positive electrode active material is Ni 2+, Ni 3+ , Co 2+ and Co 4+ It is preferable to contain one or more of any of the above. Further, the spin density attributable to one or more of Ni, Ni, Co and Co per weight of the positive electrode active material is preferably not less than 2.0×10 2+ , Ni 3+ , Co 2+ and Co 4+ spins / g and not more than 1.0×10 17 spins / g and not more than 1.0×10 21 spins / g. Using a positive electrode active material having the aforementioned spin density is preferable because it stabilizes the crystal structure particularly in a charged state. Note that if the magnesium concentration is too high, the spin density attributable to one or more of Ni, Ni, Co and Co may decrease in some cases. 2+ , Ni 3+ , Co 2+ and Co 4+ のいずれか一以上に起因するスピン密度が低くなる場合がある。

[0226] The spin density in the positive electrode active material can be analyzed using, for example, electron spin resonance (ESR: Electron Spin Resonance).

[0227] ≪EPMA≫ EPMA (Electron Probe Microanalysis) enables quantitative determination of elements. In the case of area analysis, the distribution of each element can be analyzed.

[0228] EPMA analyzes a region from the surface to a depth of about 1 μm. Therefore, the concentration of each element may differ from measurement results obtained using other analysis methods. For example, when surface analysis is performed on the positive electrode active material 100, the concentration of additives present in the surface layer may be lower than the result obtained by XPS. Further, the concentration of additives present in the surface layer may be higher than the result obtained by ICP-MS or the blending value of raw materials in the process of producing the positive electrode active material.

[0229] When an EPMA surface analysis is performed on a cross-section of the positive electrode active material 100 according to one embodiment of the present invention, it is preferable that the concentration of the additive elements has a concentration gradient that increases from the interior to the surface. More specifically, as shown in Figure 1C1, it is preferable that magnesium, fluorine, titanium, and silicon have a concentration gradient that increases from the interior to the surface. Also, as shown in Figure 2C2, it is preferable that aluminum has a concentration peak in a region deeper than the concentration peaks of the above elements. The aluminum concentration peak may be located at the surface or deeper than the surface.

[0230] Furthermore, the surface and surface layer of the positive electrode active material in one embodiment of the present invention do not contain carbon dioxide, hydroxyl groups, etc., that have been chemically adsorbed after the positive electrode active material has been manufactured. It also does not contain electrolyte, binder, conductive material, or compounds derived therefrom that have adhered to the surface of the positive electrode active material. Therefore, when quantifying the elements present in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc., that can be detected by surface analysis, including XPS and EPMA.

[0231] ≪Surface roughness and specific surface area≫ In one embodiment of the present invention, the positive electrode active material 100 preferably has a smooth surface with few irregularities. A smooth surface with few irregularities is one factor indicating that the distribution of additive elements in the surface layer 100a is good.

[0232] The smoothness and minimal irregularities of the surface can be determined, for example, from a cross-sectional SEM image or TEM image of the positive electrode active material 100, or from the specific surface area of ​​the positive electrode active material 100.

[0233] For example, the surface smoothness of the positive electrode active material 100 can be quantified from a cross-sectional SEM image as shown below.

[0234] First, the positive electrode active material 100 is processed using FIB or the like to expose its cross-section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, protective agent, etc. Next, an SEM image of the interface between the protective film, etc. and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image using image processing software. For example, Gaussian blurring (σ=2) is performed, followed by binarization. Interface extraction is then performed using image processing software. Furthermore, the interface line between the protective film, etc. and the positive electrode active material 100 is selected using an automatic selection tool, etc., and the data is extracted into spreadsheet software, etc. Using the functions of the spreadsheet software, correction is performed from the regression curve (quadratic regression), and parameters for roughness calculation are obtained from the slope-corrected data, and the root mean square surface roughness (RMS) is calculated by calculating the standard deviation. In addition, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm from the outer circumference of the particle.

[0235] In this embodiment, the particle surface of the positive electrode active material 100 preferably has a roughness index, namely, root mean square surface roughness (RMS), which is less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0236] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited, but for example, "ImageJ" can be used. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

[0237] For example, the actual specific surface area A measured by the gas adsorption method using the constant-volume method. R And the ideal specific surface area A i The surface smoothness of the positive electrode active material 100 can also be quantified from this ratio.

[0238] Ideal specific surface area A i This is calculated by assuming that all particles have the same diameter as D50, the same weight, and are ideal spheres.

[0239] The median diameter D50 can be measured using a particle size analyzer that employs laser diffraction and scattering methods. The specific surface area can be measured using a specific surface area measuring device that employs a gas adsorption method based on constant volume, for example.

[0240] In one embodiment of the present invention, the positive electrode active material 100 has an ideal specific surface area A determined from the median diameter D50. i And the actual specific surface area A R Ratio A R / A i It is preferable that the value is 2.1 or less.

[0241] This embodiment can be used in combination with other embodiments.

[0242] (Embodiment 2) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figures 10 to 14.

[0243] <Step S11> As step S11 in Figure 10, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen.

[0244] For example, lithium carbonate, lithium fluoride, lithium hydroxide, lithium oxide, etc., can be used as lithium sources.

[0245] As the transition metal M, it is preferable to use a metal that can form a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, as the transition metal M source, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used.

[0246] When using metals capable of forming layered rock salt-type composite oxides, it is preferable to use a mixing ratio of cobalt, manganese, and nickel within a range that allows for a layered rock salt-type crystalline structure. Furthermore, aluminum may be added to these transition metals within a range that allows for a layered rock salt-type crystalline structure.

[0247] As the transition metal M source, oxides, hydroxides, etc. of the above-mentioned metals exemplified as transition metal M can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. As the manganese source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0248] <Step S12> Next, in step S12, the lithium source and the transition metal M source are mixed. The mixing can be done dry or wet. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0249] <Step S13> Next, in step S13, the mixed material is heated. This step may be called firing or first heating to distinguish it from later heating steps. Heating is preferably carried out at 800°C or higher but less than 1100°C, more preferably at 900°C or higher but less than 1000°C, and even more preferably at around 950°C. Alternatively, 800°C or higher but less than 1000°C is preferable. Alternatively, 900°C or higher but less than 1100°C is preferable. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal responsible for the oxidation-reduction reaction used as the transition metal M, or evaporation of lithium. For example, if cobalt is used as the transition metal M, a defect in which cobalt becomes divalent may occur.

[0250] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Alternatively, 1 hour to 20 hours is preferable. Alternatively, 2 hours to 100 hours is preferable. A shorter heating time is more productive and preferable. Firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or lower, more preferably -100°C or lower). For example, heating at 1000°C for 10 hours is preferable, with a heating rate of 200°C / h and a flow rate of 10 L / min of the dry atmosphere. The heated material can then be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably 10 hours to 50 hours.

[0251] However, cooling to room temperature in step S13 is not mandatory. If there are no problems in carrying out the subsequent steps S41 to S44, the cooling may be extended to a temperature higher than room temperature.

[0252] <Step S14> Next, in step S14, the calcined material is recovered to obtain a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. Specifically, lithium cobaltate, lithium manganeseate, lithium nickelate, lithium cobaltate in which some of the cobalt is replaced by manganese, lithium cobaltate in which some of the cobalt is replaced by nickel, or nickel-manganese-lithium cobaltate are obtained.

[0253] Alternatively, a pre-synthesized composite oxide containing lithium, a transition metal M, and oxygen may be used as step S14. In this case, steps S11 to S13 can be omitted.

[0254] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industrial Co., Ltd. can be used as a pre-synthesized composite oxide. This lithium cobalt oxide has a median diameter (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0255] Alternatively, lithium cobalt oxide particles manufactured by Nippon Chemical Industrial Co., Ltd. (product name: Cellseed C-5H) can be used. These are lithium cobalt oxide particles with a median diameter (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0256] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) are used.

[0257] <Step S21> Next, in step S21, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. It is also preferable to prepare a lithium source.

[0258] Examples of fluorine sources that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). Furthermore, the fluorine source is not limited to a solid; for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc., may be used and mixed in the atmosphere during the heating process described later. Multiple fluorine sources may also be used in combination. Among these, lithium fluoride is preferred because, among solid fluorine sources, it has a relatively low melting point of 848°C and is easily melted during the annealing process described later.

[0259] For example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc., can be used as magnesium sources.

[0260] For example, lithium fluoride and lithium carbonate can be used as lithium sources. In other words, lithium fluoride can be used as both a lithium source and a fluorine source. Similarly, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0261] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The effect of lowering the melting point is maximized when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. 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 (LiF) and magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (x = around 0.33). In this specification, "around" means a value greater than 0.9 times and less than 1.1 times the value.

[0262] Furthermore, if the following mixing and grinding steps are carried out wet, a solvent should be prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers such as diethyl ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, acetone will be used.

[0263] <Step S22> Next, in step S22, the materials of the above mixture 902 are mixed and pulverized. Mixing can be done dry or wet, but wet mixing is preferred because it allows for finer pulverization. For example, a ball mill or a bead mill can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the pulverizing media. It is preferable to carry out this mixing and pulverization process thoroughly to finely pulverize the mixture 902.

[0264] <Step S23> Next, in step S23, the materials mixed and pulverized above are recovered to obtain mixture 902. The mixture 902 preferably has a median diameter (D50) of 600 nm to 20 μm, more preferably 1 μm to 10 μm, or 600 nm to 10 μm, or 1 μm to 20 μm. This finely pulverized mixture 902 makes it easier to uniformly adhere the mixture 902 to the surface of the composite oxide particles when mixed with lithium, a transition metal M, and oxygen in a later step. Uniform adhesion of the mixture 902 to the surface of the composite oxide particles is preferable because it facilitates the distribution of halogens and magnesium throughout the surface layer of the composite oxide particles after heating. If there are regions in the surface layer that do not contain halogens and magnesium, it may be difficult to form the O3' type crystal structure described later in the charged state.

[0265] <Step S41> Next, in step S41, the LiMO2 obtained in step S14 is mixed with the mixture 902. The ratio of the number of transition metal atoms M in the composite oxide having lithium, a transition metal, and oxygen to the number of magnesium atoms Mg in the mixture 902 is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0266] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter mixing time than in step S12. Also, dry mixing is less likely to destroy particles 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 zirconia balls as the grinding medium.

[0267] <Step S42> Next, in step S42, the materials mixed above are collected to obtain mixture 903.

[0268] In this embodiment, a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities is described, but the present invention is not limited to this. Instead of the mixture 903 in step S42, a starting material of lithium cobalt oxide to which a magnesium source and a fluorine source have been added and calcined may be used. In this case, it is not necessary to separate the processes in steps S11 to S14 and steps S21 to S23, making it simpler and more productive.

[0269] Alternatively, lithium cobalt oxide with magnesium and fluorine added beforehand may be used. Using lithium cobalt oxide with magnesium and fluorine added makes the process up to step S42 easier to complete.

[0270] Furthermore, magnesium sources and fluorine sources may be added to lithium cobalt oxide that has already been treated with magnesium and fluorine.

[0271] <Step S43> Next, in step S43, the mixture 903 is heated in an oxygen-containing atmosphere. It is more preferable that this heating is carried out in a way that inhibits adhesion so that the particles of the mixture 903 do not stick together. This step is sometimes called annealing to distinguish it from the previous heating step.

[0272] Examples of heating methods that have an anti-adhesion effect include heating while stirring the mixture 903, and heating while vibrating the container containing the mixture 903.

[0273] The heating temperature in step S43 must be above the temperature at which the reaction between LiMO2 and mixture 902 proceeds. The temperature at which the reaction proceeds is simply the temperature at which the elemental interdiffusion between LiMO2 and mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in oxides, the melting temperature T m 0.757 times (Tammann temperature T) dSolid-phase diffusion occurs from this point. For example, if LiMO2 is LiCoO2, since the melting point of LiCoO2 is 1130°C, the temperature in step S43 should be 500°C or higher.

[0274] However, it is preferable that the annealing temperature be above the melting temperature of at least a portion of mixture 903, as this facilitates the reaction. Therefore, it is preferable that the annealing temperature be above the eutectic point of mixture 902. If mixture 902 contains LiF and MgF2, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable that the temperature in step S43 be 742°C or higher.

[0275] Furthermore, when mixture 903 is prepared by mixing LiCoO2:LiF:MgF2 in a molar ratio of 100:0.33:1, an endothermic peak is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, an annealing temperature of 830°C or higher is more preferable.

[0276] A higher annealing temperature is preferable because it facilitates the reaction, shortens the annealing time, and increases productivity.

[0277] However, the annealing temperature must be below the decomposition temperature of LiMO2 (1130°C in the case of LiCoO2). Furthermore, at temperatures near the decomposition temperature, there is a concern that a small amount of LiMO2 may decompose. For this reason, the annealing temperature is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0278] Therefore, the annealing temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 830°C to 1130°C is preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0279] Furthermore, when heating mixture 903, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere to an appropriate range.

[0280] In the manufacturing method described in this embodiment, some materials, such as lithium fluoride which is a fluorine source, function as a flux. This function allows the annealing temperature to be lowered to below the decomposition temperature of LiMO2, for example, between 742°C and 950°C, enabling the distribution of additives such as magnesium to the surface layer and the production of a positive electrode active material with good properties.

[0281] However, since gaseous lithium fluoride is lighter than oxygen, heating causes lithium fluoride to volatilize, reducing the amount of lithium fluoride in mixture 903. This weakens its function as a flux. Therefore, heating is necessary while suppressing the volatilization of lithium fluoride. Even if lithium fluoride is not used as a fluorine source, lithium fluoride may still be produced and volatilize from the reaction of Li and F on the surface of LiMO2. Therefore, even if a fluoride with a higher melting point than lithium fluoride is used, the same need to suppress volatilization is required.

[0282] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing lithium fluoride, that is, to heat the mixture 903 while the partial pressure of lithium fluoride in the heating furnace is high. Such heating can suppress the volatilization of lithium fluoride in the mixture 903.

[0283] Annealing is preferably carried out for an appropriate amount of time. The appropriate annealing time varies depending on conditions such as the annealing temperature, the size and composition of the LiMO2 particles in step S14, etc. When the particles are small, a lower temperature or shorter time may be preferable than when the particles are large.

[0284] For example, if the median diameter (D50) of the particles in step S14 is about 12 μm, the annealing temperature is preferably between 600°C and 950°C. The annealing time is preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0285] On the other hand, if the median diameter (D50) of the particles in step S24 is about 5 μm, the annealing temperature is preferably, for example, 600°C to 950°C. The annealing time is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours.

[0286] The cooling time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0287] <Step S44> Next, in step S44, the annealed material can be recovered to produce the positive electrode active material 100. At this time, it is preferable to further sift the recovered particles. Sifting can dislodge any adhesion between the positive electrode active material 100 particles.

[0288] Next, we will explain a different manufacturing method from that shown in Figure 10 using Figures 11 to 14. Since there are many similarities with Figure 10, we will mainly explain the differences. For the similarities, please refer to the explanation for Figure 10.

[0289] Figure 10 illustrates a method for preparing the LiMO2 obtained in step S14 and the mixture 902 in step S41, but the present invention is not limited to this. As shown in steps S31 and S32 of Figures 11 to 14, other additive elements may be added.

[0290] As additive elements, one or more can be selected from, for example, nickel, aluminum, manganese, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. Figures 11 to 14 show examples in which two types of additive elements are used: a nickel source in step S31 and an aluminum source in step S32.

[0291] These additive elements are preferably used in the form of oxides, hydroxides, fluorides, etc., of each element, which have been pulverized. Pulverization can be carried out, for example, by a wet process.

[0292] As shown in Figure 11, the nickel source and aluminum source can be mixed simultaneously with the mixture 902 in step S42. This method is preferable because it is more productive due to the fewer annealing steps required.

[0293] As shown in Figure 12, multiple additive sources may be mixed in different steps. For example, a nickel source can be mixed in step S61-1, and an aluminum source in step S61-2. When additive sources are mixed in multiple steps in this way, the mixing method can be changed. For example, in step S61-1, nickel hydroxide can be used as the nickel source and mixed using a solid-phase method, and in step S61-2, aluminum alkoxide can be used as the aluminum source and mixed using a sol-gel method. By going through such a process, it may be possible to improve the distribution of additive elements.

[0294] The sol-gel method can be performed, for example, as follows:

[0295] First, the alkoxide additive is dissolved in the alcohol. The alkoxy group of the alkoxide additive preferably has 1 to 18 carbon atoms, and the carbon atoms may be substituted or unsubstituted.

[0296] For example, aluminum isopropoxide, aluminum butoxide, aluminum ethoxide, etc., can be used as aluminum alkoxides.

[0297] For example, methanol, ethanol, propanol, 2-propanol, butanol, and 2-butanol can be used as the solvent alcohol. It is preferable to use an alcohol of the same type as the alkoxy group of the additive element. The amount of water in the solvent is preferably 3% by volume or less, and more preferably 0.3% by volume or less. By using an alcohol as the solvent, the degradation of LiMO2 during the manufacturing process can be suppressed more effectively than when water is used.

[0298] Next, the material to be treated is mixed with an alcohol solution of the additive element alkoxide and stirred in an atmosphere containing water vapor.

[0299] By placing the material in an atmosphere containing H2O, hydrolysis of the alkoxide of the additive element occurs. Subsequently, dehydration condensation occurs between the products. Repeated hydrolysis and condensation reactions generate a sol of oxide of the additive element. This reaction also occurs on the material being treated, forming a layer containing the additive element on the surface. After that, the material is recovered, and the alcohol is vaporized to obtain mixture 903.

[0300] As shown in Figure 13, annealing may be performed multiple times as steps S53 and S55, with the adhesion suppression operation step S54 being performed in between. The annealing conditions for steps S53 and S55 can be considered in reference to the description in step S43. Examples of adhesion suppression operations include crushing with a pestle, mixing using a ball mill, mixing using a rotary-orbit mixer, sieving, and vibrating the container containing the complex oxide.

[0301] Alternatively, as shown in Figure 14, LiMO2 and mixture 902 may be mixed in step S41, annealed, and then the nickel source and aluminum source may be mixed in step S61. This will be mixture 904. Mixture 904 is annealed again in step S63. The annealing conditions can be considered in reference to the description in step S43.

[0302] Furthermore, the step of introducing additive elements may be replaced. For example, as shown in Figure 15, a mixture 901 having a nickel source and an aluminum source may first be mixed with LiMO2, annealed in step S43, and then mixed with a mixture 902 having a magnesium source and a fluorine source.

[0303] Thus, by separating the processes for introducing the transition metal M and the additives, it is sometimes possible to change the depth profile of each element. For example, the concentration of the additive element can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of the additive element to this reference can be made higher in the surface layer than in the interior.

[0304] This embodiment can be used in combination with other embodiments.

[0305] (Embodiment 3) In this embodiment, an example of a secondary battery according to one aspect of the present invention will be described using Figures 16 to 19.

[0306] <Example of a secondary battery configuration 1> The following explanation uses a secondary battery, in which the positive electrode, negative electrode, and electrolyte are enclosed in an outer casing, as an example.

[0307] [Positive electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may also contain a conductive material and a binder. The positive electrode active material used is a positive electrode active material manufactured using the manufacturing method described in the previous embodiment.

[0308] The positive electrode active material described in the foregoing embodiment may also be used as a mixture with another positive electrode active material.

[0309] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. Examples thereof include compounds such as LiFePO₄, LiFeO₂, LiNiO₂, LiMn₂O₄, V₂O₅, Cr₂O₅, and MnO₂.

[0310] Further, as another positive electrode active material, it is preferable to mix lithium nickelate (LiNiO₂ or LiNi 1-x M x O₂ (0 < x < 1) (M = Co, Al, etc.)) with a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn₂O₄. With this configuration, the characteristics of the secondary battery can be improved.

[0311] Further, as another positive electrode active material, a composition formula Li a Mn b M c O dA lithium manganese composite oxide can be used, which can be represented as follows: Here, element M is preferably a metallic element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particle of lithium manganese composite oxide, <a / (b+c)<2、かつc>it is preferable that the discharge is 0 0 and 0.26 ≤ (b+c) / d < 0.5. The composition of metals, silicon, phosphorus, etc., of the entire particle of lithium manganese composite oxide can be measured, for example, using ICP-MS (inductively coupled plasma mass spectrometer). The oxygen composition of the entire particle of lithium manganese composite oxide can be measured, for example, using EDX (energy dispersive X-ray spectrometry). It can also be determined by using valence evaluation of molten gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. Lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may also contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0312] The following describes an example of a cross-sectional configuration when graphene or a graphene compound is used as the conductive material in the active material layer 200.

[0313] Figure 16A shows a longitudinal cross-sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 100, graphene or graphene compound 201 as a conductive material, and a binder (not shown).

[0314] ​In this specification, graphene compound 201 includes 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 a material having carbon, having a plate-like or sheet-like shape, and having a two-dimensional structure formed by a six-membered carbon ring. The two-dimensional structure formed by the 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. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0315] In this specification, graphene oxide refers to a material having carbon and oxygen, having a sheet-like structure, and possessing functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0316] In this specification, reduced graphene oxide refers to a material having carbon and oxygen, having a sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. It may also be called a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be laminated together. It is preferable that reduced graphene oxide has a portion where the carbon concentration is greater than 80 atomic%, and the oxygen concentration is between 2 atomic% and 15 atomic%. By having such carbon and oxygen concentrations, it can function as a highly conductive material even in small quantities. It is also preferable that reduced graphene oxide has a G / D intensity ratio of 1 or more in the Raman spectrum. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small quantities.

[0317] Graphene compounds may possess excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Furthermore, graphene compounds may have a sheet-like shape. Graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. They may also exhibit very high conductivity even when thin, allowing for the efficient formation of conductive paths within the active material layer with a small amount. Therefore, using graphene compounds as a conductive material can increase the contact area between the active material and the conductive material. It is preferable that the graphene compound adheres to at least a portion of the active material particles. It is also preferable that the graphene compound overlaps at least a portion of the active material particles. Furthermore, it is preferable that the shape of the graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the irregularities of a single active material particle or the irregularities formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a portion of the active material particles. Additionally, the graphene compound may have holes.

[0318] When using active material particles with small particle sizes, such as 1 μm or less, the specific surface area of ​​the active material particles is large, and more conductive paths are required to connect the active material particles. In such cases, it is preferable to use a graphene compound that can efficiently form conductive paths even in small amounts.

[0319] Due to the properties described above, graphene compounds are particularly effective as conductive materials in secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles, and secondary batteries for drones, may require rapid charging and rapid discharging characteristics. Mobile electronic devices may also require rapid charging characteristics. Rapid charging and rapid discharging can also be described as high-rate charging and high-rate discharging. For example, this refers to charging and discharging at 1C, 2C, or 5C or higher.

[0320] In the longitudinal section of the active material layer 200, as shown in Figure 16B, sheet-like graphene or graphene compound 201 is dispersed approximately uniformly within the active material layer 200. In Figure 16B, graphene or graphene compound 201 is schematically represented by thick lines, but in reality, it is a thin film having a single or multilayer thickness of carbon molecules. Multiple layers of graphene or graphene compound 201 are formed to partially cover multiple granular positive electrode active materials 100, or to adhere to the surface of multiple granular positive electrode active materials 100, and are therefore in surface contact with each other.

[0321] Here, multiple graphenes or graphene compounds can bond together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or eliminated, thereby improving the ratio of active material to electrode volume and electrode weight. In other words, the charge and discharge capacity of the secondary battery can be increased.

[0322] Here, it is preferable to use graphene oxide as graphene or graphene compound 201, mix it with the active material to form a layer that becomes the active material layer 200, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in polar solvents, for the formation of graphene or graphene compound 201, the graphene or graphene compound 201 can be dispersed approximately uniformly within the active material layer 200. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene or graphene compound 201 remaining in the active material layer 200 partially overlaps and is dispersed to the extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent.

[0323] Therefore, unlike granular conductive materials such as acetylene black, which make point contact with the active material, graphene or graphene compound 201 enables surface contact with low contact resistance. As a result, the electrical conductivity between the granular positive electrode active material 100 and graphene or graphene compound 201 can be improved with a smaller amount than with conventional conductive materials. Consequently, the ratio of positive electrode active material 100 in the active material layer 200 can be increased. This allows for an increase in the discharge capacity of the secondary battery.

[0324] Furthermore, by using a spray-drying device beforehand, it is possible to cover the entire surface of the active material with a graphene compound, which is a conductive material, as a coating, and to further form conductive paths between the active materials using the graphene compound.

[0325] Alternatively, the active material layer 200 may be made by mixing the graphene compound with the material used to form the graphene compound. For example, particles used as a catalyst when forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used when forming the graphene compound include silicon dioxide (SiO2, SiO2). x Examples of particles include those having (x<2), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. Preferably, the D50 of the particles is 1 μm or less, and more preferably 100 nm or less.

[0326] [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.

[0327] 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, as well as starch. It is even preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0328] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, 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.

[0329] You may use a combination of several of the binders mentioned above.

[0330] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials, while possessing excellent adhesive and elastic properties, can be difficult to adjust in viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. Suitable materials with particularly excellent viscosity-modifying properties include, for example, water-soluble polymers. Suitable water-soluble polymers with particularly excellent viscosity-modifying properties include the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, as well as cellulose derivatives such as regenerated cellulose, and starch.

[0331] Furthermore, cellulose derivatives such as carboxymethylcellulose can be made more effective as viscosity modifiers by increasing their solubility, for example, by using salts such as sodium salts or ammonium salts of carboxymethylcellulose. Increased solubility also improves the dispersibility of the active material and other components when preparing electrode slurries. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0332] Water-soluble polymers stabilize viscosity by dissolving in water and can stably disperse active materials and other materials used as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, because they possess functional groups, they are expected to be easily and stably adsorbed onto the surface of the active material. Additionally, cellulose derivatives such as carboxymethylcellulose often contain functional groups such as hydroxyl groups and carboxyl groups. Because of these functional groups, the polymers interact with each other and are expected to broadly cover the surface of the active material.

[0333] 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.

[0334] [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 positive electrode potential. Aluminum alloys with added elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. Alternatively, it may be formed from a metallic element that reacts with silicon to form a silicide. Examples of 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. The current collector should preferably have a thickness of 5 μm to 30 μm.

[0335] [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 conductive material and a binder.

[0336] [Negative electrode active material] For example, alloy materials or carbon-based materials can be used as the negative electrode active material.

[0337] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have larger charge-discharge capacities than carbon, and silicon in particular has a large 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. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. In this context, 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.

[0338] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO refers to SiO x It can also be expressed as follows: Here, it is preferable that x has one neighboring value. For example, x is preferably between 0.2 and 1.5, and more preferably between 0.3 and 1.2. Or preferably between 0.2 and 1.2. Or preferably between 0.3 and 1.5.

[0339] Suitable carbon-based materials include graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0340] 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. Also, it is relatively easy to reduce the surface area of ​​MCMB, which may be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0341] When lithium ions are inserted into graphite (during the formation of lithium-graphite intercalation compounds), graphite exhibits a potential as low as that of lithium metal (0.05V to 0.3V vs. Li / Li). + This allows lithium-ion secondary batteries to exhibit a high operating voltage. Furthermore, graphite is preferred because it has advantages such as a relatively high charge / discharge capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0342] Furthermore, titanium dioxide (TiO2) and lithium titanium oxide (Li4Ti5O2) are used as negative electrode active materials. 12 ), lithium-graphite intercalation compound (Li x Oxides such as C6, niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.

[0343] Furthermore, as the negative electrode active material, a Li3N type structure is used, which is a lithium and transition metal binitride. 3-x M x N(M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 The N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm²). 3 ) indicates a preference.

[0344] Using a lithium-transition metal complex nitride is preferable because it contains lithium ions in the negative electrode active material, allowing it to be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode active material. Even when using a lithium-ion-containing material as the positive electrode active material, the lithium-transition metal complex nitride can be used as the negative electrode active material by pre-desorbing the lithium ions contained in the positive electrode active material.

[0345] 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. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 This can also occur with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0346] 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.

[0347] [Negative electrode current collector] The negative electrode current collector can be made of the same material as the positive electrode current collector. However, it is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0348] [Electrolyte] The electrolyte contains a solvent and an electrolyte. The solvent for the electrolyte is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio.

[0349] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from rupturing or catching fire even if the internal temperature rises due to internal short circuits or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0350] Furthermore, examples of electrolytes to be dissolved in the above solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10 Cl 10 Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), and LiN(C2F5SO2)2 can be used individually or in any combination and ratio of two or more of these salts.

[0351] For secondary batteries, it is preferable to use a highly purified electrolyte with a low content of particulate matter and elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0352] Furthermore, additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the added material should be, for example, 0.1 wt% to 5 wt% relative to the total solvent. VC or LiBOB are particularly preferred because they readily form a good coating.

[0353] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0354] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0355] 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.

[0356] 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.

[0357] Furthermore, instead of an electrolyte, solid electrolytes containing inorganic materials such as sulfides or oxides, or solid electrolytes containing polymer materials such as PEO (polyethylene oxide), can be used. When using a solid electrolyte, the installation of separators and spacers becomes unnecessary. In addition, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0358] [Separator] Furthermore, secondary batteries preferably have a separator. As the separator, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers made of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane can be used. It is preferable that the separator is processed into an envelope shape and arranged to enclose either the positive or negative electrode.

[0359] 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, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0360] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging, and thus improving the reliability of secondary batteries. Coating with fluorine-based materials improves adhesion between the separator and electrodes, thereby improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thus enhancing the safety of secondary batteries.

[0361] 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.

[0362] By using a multilayer separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the charge / discharge capacity per unit volume of the secondary battery.

[0363] [Exterior] The outer casing of a secondary battery can be made of metal materials such as aluminum or resin materials. A film-like outer casing can also be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing.

[0364] <Example of a secondary battery configuration 2> The following describes the configuration of a secondary battery using a solid electrolyte layer as an example of a secondary battery configuration.

[0365] As shown in Figure 17A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0366] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is a positive electrode active material manufactured using the manufacturing method described in the previous embodiment. The positive electrode active material layer 414 may also have a conductive additive and a binder.

[0367] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0368] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 17B. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0369] As the solid electrolyte 421 in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halogen-based solid electrolyte, etc., can be used.

[0370] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 Li 3.25 P 0.95It contains S4, etc. Sulfide-based solid electrolytes have advantages such as the availability of materials with high conductivity, the ability to be synthesized at low temperatures, and their relatively soft nature which helps maintain conductive paths even after charging and discharging.

[0371] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x Materials having a NASICON-type crystal structure (Li 1-X Al X Ti 2-X (PO4)3 etc.) Materials having a garnet-type crystal structure (Li7La3Zr2O 12 Materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glass (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc. are included. Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0372] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, and LiI. Furthermore, composite materials in which these halide-based solid electrolytes are packed into the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0373] Alternatively, different solid electrolytes may be mixed and used.

[0374] In particular, Li has a NASICON-type crystal structure. 1+x Al x Ti 2-x(PO4)3 (0<x<1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that may be included in the positive electrode active material used in the secondary battery 400 according to one embodiment of the present invention, so a synergistic effect on improving cycle characteristics can be expected, which is preferable. Improvements in productivity through process reduction can also be expected. Note that in this specification and the like, the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0375] [Exterior Body and Shape of Secondary Battery] Materials of various materials and shapes can be used for the exterior body of the secondary battery 400 according to one embodiment of the present invention, and it is preferable that the exterior body has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0376] For example, FIG. 18 illustrates an example of a cell for evaluating materials of an all-solid-state battery.

[0377] FIG. 18A is a schematic cross-sectional view of an evaluation cell. The evaluation cell includes a lower member 761, an upper member 762, a fixing screw and a wing nut 764 for fixing them, and the evaluation material is fixed by pressing an electrode plate 753 through rotating a pressing screw 763. An insulator 766 is provided between the lower member 761 made of a stainless steel material and the upper member 762. An O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0378] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and pressed by an electrode plate 753 from above. FIG. 18B is an enlarged perspective view of the periphery of this evaluation material.

[0379] As the evaluation material, an example of a stacked body of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view thereof is shown in FIG. 18C. Note that the same reference numerals are used for the same portions in FIGS. 18A, 18B, and 18C.

[0380] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be considered to correspond to the positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be considered to correspond to the negative electrode terminal. Electrical resistance and other parameters can be measured while applying pressure to the evaluation material via the electrode plates 751 and 753.

[0381] Furthermore, it is preferable to use a package with excellent airtightness for the outer casing of a secondary battery according to one embodiment of the present invention. For example, a ceramic package or a resin package can be used. Also, when sealing the outer casing, it is preferable to block out the outside air and perform the sealing in a sealed atmosphere, for example, inside a glove box.

[0382] Figure 19A shows a perspective view of a secondary battery according to one embodiment of the present invention, having a different exterior and shape from that shown in Figure 18. The secondary battery in Figure 19A has external electrodes 771 and 772 and is sealed with an exterior having a plurality of package members.

[0383] Figure 19B shows an example of a cross-section cut along the dashed line in Figure 19A. The laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a with an electrode layer 773a provided on a flat plate, a frame-shaped package member 770b, and a package member 770c with an electrode layer 773b provided on a flat plate. Insulating materials such as resin or ceramic can be used for the package members 770a, 770b, and 770c.

[0384] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. The external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0385] This embodiment can be used in appropriate combination with other embodiments.

[0386] (Embodiment 4) This embodiment describes an example of the shape of a secondary battery having a positive electrode, as described in the previous embodiment. The materials used in the secondary battery described in this embodiment can be referenced to those described in the previous embodiment.

[0387] <Coin-type rechargeable battery> First, let's describe an example of a coin-type rechargeable battery. Figure 20A is an external view of a coin-type (single-layer flat type) rechargeable battery, and Figure 20B is a cross-sectional view thereof.

[0388] 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, both 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.

[0389] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0390] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, which are corrosion-resistant to the electrolyte, or alloys thereof or alloys of these with other metals (e.g., stainless steel). Furthermore, it is preferable to coat them with nickel, aluminum, or the like to prevent corrosion 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.

[0391] The negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in Figure 20B, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 at the bottom, and the positive electrode can 301 and negative electrode can 302 are pressed together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0392] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0393] Here, Figure 20C is used to explain the current flow during charging of a secondary battery. When a lithium-ion secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In a lithium-ion secondary battery, the anode and cathode are reversed during charging and discharging, and the oxidation and reduction reactions are reversed. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Accordingly, in this specification, whether charging or discharging, whether a reverse pulse current is flowing or a charging current is flowing, the positive electrode will be called the "positive electrode" or "+ electrode (positive electrode)," and the negative electrode will be called the "negative electrode" or "- electrode (negative electrode)." Using the terms anode (positive electrode) and cathode (negative electrode), which are related to oxidation and reduction reactions, would be reversed during charging and discharging, potentially causing confusion. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode and cathode are used, it should be specified whether they refer to the charging or discharging phase, and whether they correspond to the positive or negative electrode.

[0394] A charger is connected to the two terminals shown in Figure 20C, and the secondary battery 300 is charged. As the secondary battery 300 charges, the potential difference between the electrodes increases.

[0395] <Cylindrical rechargeable battery> Next, an example of a cylindrical secondary battery will be described with reference to Figure 21. Figure 21A shows an external view of a cylindrical secondary battery 600. Figure 21B is a schematic cross-section of the cylindrical secondary battery 600. As shown in Figure 21B, the cylindrical secondary battery 600 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. These positive electrode cap and battery casing (outer casing) 602 are insulated by a gasket (insulating packing) 610.

[0396] Inside the hollow cylindrical battery casing 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 center pin. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of a metal such as nickel, aluminum, or titanium, which is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (for example, stainless steel). Furthermore, it is preferable to coat the battery casing 602 with nickel, aluminum, or the like to prevent corrosion by the electrolyte. Inside the battery casing 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 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0397] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active material on both sides of the current collector. 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. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 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. Furthermore, the PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the current amount through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0398] Alternatively, as shown in Figure 21C, a module 615 may be constructed by sandwiching multiple secondary batteries 600 between conductive plates 613 and 614. The multiple secondary batteries 600 may be connected in parallel, in series, or connected in parallel and then in series. By constructing a module 615 with multiple secondary batteries 600, a large amount of power can be extracted.

[0399] Figure 21D is a top view of module 615. For clarity, the conductive plate 613 is shown with a dotted line. As shown in Figure 21D, module 615 may have conductors 616 that electrically connect a plurality of secondary batteries 600. A conductive plate can be superimposed on the conductors 616. A temperature control device 617 may also be provided between the plurality of secondary batteries 600. When a secondary battery 600 is overheated, it can be cooled by the temperature control device 617, and when a secondary battery 600 is too cold, it can be heated by the temperature control device 617. This makes the performance of module 615 less susceptible to the ambient temperature. The heat transfer medium in the temperature control device 617 is preferably insulating and non-flammable.

[0400] By using the positive electrode active material described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0401] <Example of a secondary battery structure> Another example of a secondary battery structure will be explained using Figures 22 to 26.

[0402] Figures 22A and 22B show the external view of the battery pack. The battery pack includes a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to the antenna 914 via the circuit board 900. A label 910 is attached to the secondary battery 913. Furthermore, as shown in Figure 22B, the secondary battery 913 is connected to terminals 951 and 952. The circuit board 900 is secured with a seal 915.

[0403] The circuit board 900 has terminal 911 and circuit 912. Terminal 911 is connected to terminal 951, terminal 952, antenna 914, and circuit 912. Multiple terminals 911 may be provided, and each of the multiple terminals 911 may be used as a control signal input terminal, a power supply terminal, etc.

[0404] The circuit 912 may be provided on the back surface of the circuit board 900. The antenna 914 is not limited to a coil shape, but may be, for example, linear or plate-shaped. Alternatively, antennas such as a planar antenna, aperture antenna, traveling wave antenna, EH antenna, magnetic field antenna, or dielectric antenna may be used. Or, the antenna 914 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 may function as one of the two conductors of the capacitor. This makes it possible to exchange power not only through electromagnetic and magnetic fields, but also through electric fields.

[0405] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has the function of shielding, for example, the electromagnetic field from the secondary battery 913. For the layer 916, a magnetic material can be used, for example.

[0406] Note that the structure of the battery pack is not limited to that shown in Figure 22.

[0407] For example, as shown in Figures 23A and 23B, antennas may be provided on each of the opposing pairs of faces of the secondary battery 913 shown in Figures 22A and 22B. Figure 23A is an external view showing one of the pair of faces, and Figure 23B is an external view showing the other of the pair of faces. For parts that are the same as those of the secondary battery shown in Figures 22A and 22B, the explanation of the secondary battery shown in Figures 22A and 22B can be appropriately referred to.

[0408] As shown in Figure 23A, an antenna 914 is provided on one of the pair of surfaces of the secondary battery 913 with a layer 916 in between, and as shown in Figure 23B, an antenna 918 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 in between. The layer 917 has the function of shielding the electromagnetic field from, for example, the secondary battery 913. For the layer 917, a magnetic material can be used, for example.

[0409] By adopting the above structure, the size of both antenna 914 and antenna 918 can be increased. Antenna 918 has a function that allows for data communication with external devices, for example. Antenna 918 can be fitted with an antenna of a shape that is applicable to antenna 914, for example. As a communication method between the secondary battery and other devices via antenna 918, response methods that can be used between the secondary battery and other devices, such as NFC (Near Field Communication), can be applied.

[0410] Alternatively, as shown in Figure 23C, a display device 920 may be provided on the secondary battery 913 shown in Figures 22A and 22B. The display device 920 is electrically connected to terminal 911. Note that a label 910 does not need to be provided on the part where the display device 920 is provided. Note that for the same parts as the secondary battery shown in Figures 22A and 22B, the explanation of the secondary battery shown in Figures 22A and 22B can be appropriately applied.

[0411] The display device 920 may display, for example, an image indicating whether or not it is charging, or an image indicating the amount of stored power. The display device 920 can be, for example, electronic paper, liquid crystal display, or electroluminescent (EL) display. For example, using electronic paper can reduce the power consumption of the display device 920.

[0412] Alternatively, as shown in Figure 23D, a sensor 921 may be provided on the secondary battery 913 shown in Figures 22A and 22B. The sensor 921 is electrically connected to terminal 911 via terminal 922. For parts that are the same as those of the secondary battery shown in Figures 22A and 22B, the explanation of the secondary battery shown in Figures 22A and 22B can be appropriately applied.

[0413] The sensor 921 may have the function of measuring, for example, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared radiation. By providing the sensor 921, for example, data indicating the environment in which the secondary battery is placed (such as temperature) can be detected and stored in the memory of the circuit 912.

[0414] Furthermore, an example of the structure of the secondary battery 913 will be explained using Figures 24 and 25.

[0415] The secondary battery 913 shown in Figure 24A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is impregnated with 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 24A, 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) or a resin material.

[0416] Furthermore, as shown in Figure 24B, the housing 930 shown in Figure 24A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 24B, 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.

[0417] For the housing 930a, an insulating material such as organic resin can be used. 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, an antenna such as antenna 914 may be provided inside the housing 930a. For the housing 930b, for example, a metal material can be used.

[0418] Furthermore, the structure of the wound body 950 is shown in Figure 25. 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.

[0419] The negative terminal 931 is connected to terminal 911 shown in Figure 22 via one of terminals 951 and 952. The positive terminal 932 is connected to terminal 911 shown in Figure 22 via the other of terminals 951 and 952.

[0420] By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0421] <Laminated rechargeable battery> Next, an example of a laminated secondary battery will be described with reference to Figures 26 to 36. If a laminated secondary battery has a flexible structure, it can be mounted on an electronic device that has at least a part of a flexible component, and the secondary battery can be bent in accordance with the deformation of the electronic device.

[0422] A laminated secondary battery 980 will be described using Figure 26. The laminated secondary battery 980 has a wound body 993 as shown in Figure 26A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950 described in Figure 25, the wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 with the separator 996 in between, and then winding the stacked sheet.

[0423] The number of layers in the stack consisting of the negative electrode 994, positive electrode 995, and separator 996 can be appropriately designed according to the required charge / discharge capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0424] As shown in Figure 26B, a secondary battery 980 can be manufactured as shown in Figure 26C by housing the aforementioned wound body 993 in a space formed by bonding a film 981, which serves as the outer casing, and a film 982, which has a recess, together by thermocompression or the like. The wound body 993 has lead electrodes 997 and 998 and is impregnated with an electrolyte solution inside the film 981 and the film 982, which has a recess.

[0425] The film 981 and the film 982 having recesses can be made of metal materials such as aluminum or resin materials. If resin materials are used for the film 981 and the film 982 having recesses, the film 981 and the film 982 having recesses can be deformed when an external force is applied, making it possible to create a flexible storage battery.

[0426] Furthermore, although Figures 26B and 26C show an example using two films, a space may be formed by folding a single film, and the aforementioned wound body 993 may be housed in that space.

[0427] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0428] Furthermore, while Figure 26 illustrates an example of a secondary battery 980 having a wound body in a space formed by a film that serves as the outer casing, a secondary battery having multiple strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film that serves as the outer casing may also be used, for example, as shown in Figure 27.

[0429] The laminate-type secondary battery 500 shown in Figure 27A comprises a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte 508, and an outer casing 509. The separator 507 is installed between the positive electrode 503 and the negative electrode 506, which are located inside the outer casing 509. The outer casing 509 is filled with the electrolyte 508. The electrolyte 508 can be the electrolyte shown in Embodiment 3.

[0430] In the laminate-type secondary battery 500 shown in Figure 27A, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, parts of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged to be exposed to the outside from the outer casing 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the outer casing 509, and instead, lead electrodes may be used to ultrasonically bond the lead electrodes to the positive electrode current collector 501 or the negative electrode current collector 504, thereby exposing the lead electrodes to the outside.

[0431] In a laminate-type secondary battery 500, the outer casing 509 can be made of a laminate film with a three-layer structure, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing.

[0432] Furthermore, an example of the cross-sectional structure of the laminate-type secondary battery 500 is shown in Figure 27B. For simplicity, Figure 27A shows an example consisting of two current collectors, but in reality, it is composed of multiple electrode layers as shown in Figure 27B.

[0433] Figure 27B shows an example where the number of electrode layers is 16. Even with 16 electrode layers, the secondary battery 500 retains its flexibility. Figure 27B shows a structure with a total of 16 layers: 8 layers of negative electrode current collectors 504 and 8 layers of positive electrode current collectors 501. Figure 27B also shows a cross-section of the negative electrode extraction section, where the 8 layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16; it can be more or fewer. A larger number of electrode layers allows for a secondary battery with greater charge and discharge capacity. Conversely, a smaller number of electrode layers allows for a thinner design and a secondary battery with superior flexibility.

[0434] Here, an example of the external view of a laminate-type secondary battery 500 is shown in Figures 28 and 29. Figures 28 and 29 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.

[0435] Figure 30A 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. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 30A.

[0436] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 28, will be explained using Figures 30B and 30C.

[0437] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 30B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. 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, ultrasonic welding, for example, can 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.

[0438] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0439] Next, as shown in Figure 30C, 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 the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte 508 can be added later.

[0440] Next, the electrolyte 508 (not shown) 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 508 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.

[0441] By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery 500 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0442] In all-solid-state batteries, applying a predetermined pressure in the stacking direction of the stacked positive and negative electrodes can maintain good contact conditions at the internal interfaces. Applying a predetermined pressure in the stacking direction of the positive and negative electrodes can suppress expansion in the stacking direction due to charging and discharging of the all-solid-state battery, thereby improving the reliability of the all-solid-state battery.

[0443] This embodiment can be used in appropriate combination with other embodiments.

[0444] (Embodiment 5) This embodiment describes an example of mounting a secondary battery, which is one aspect of the present invention, into an electronic device.

[0445] First, Figures 31A to 31G show examples of mounting the bendable secondary battery described in the previous embodiment into an electronic device. Examples of electronic devices to which the bendable secondary battery is applied 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.

[0446] Furthermore, rechargeable batteries with flexible shapes can be incorporated into the interior or exterior walls of houses and buildings, or into the curved surfaces of the interior or exterior of automobiles.

[0447] Figure 31A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into the housing 7401, as well as operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 also has a secondary battery 7407. By using a secondary battery according to one embodiment of the present invention for the above secondary battery 7407, a lightweight and long-lasting mobile phone can be provided.

[0448] Figure 31B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and the entire device is bent, the secondary battery 7407 located inside is also bent. Figure 31C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in the bent state. The secondary battery 7407 has lead electrodes that are electrically connected to a current collector. For example, the current collector is made of copper foil, and a portion of it is alloyed with gallium to improve the adhesion with the active material layer that is in contact with the current collector, resulting in a configuration that ensures high reliability of the secondary battery 7407 when it is bent.

[0449] Figure 31D shows an example of a bangle-type display device. The portable display device 7100 comprises a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Figure 31E shows the state of the secondary battery 7104 when bent. When the secondary battery 7104 is worn on the user's arm in a bent state, the housing deforms, and the curvature of part or all of the secondary battery 7104 changes. The degree of curvature at any point in the curve is expressed as the radius of the corresponding circle, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or secondary battery 7104 changes within the range of a radius of curvature of 40 mm to 150 mm. High reliability can be maintained as long as the radius of curvature on the main surface of the secondary battery 7104 is within the range of 40 mm to 150 mm. By using a secondary battery according to one embodiment of the present invention for the secondary battery 7104 described above, a lightweight and long-life portable display device can be provided.

[0450] Figure 31F shows an example of a wristwatch-type personal information terminal. The personal information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0451] The 7200 personal digital assistant (PDCA) can run various applications such as mobile phone calls, email, document viewing and creation, music playback, internet communication, and computer games.

[0452] The display unit 7202 has a curved display surface, allowing it to display information along the curved surface. Furthermore, the display unit 7202 is equipped with a touch sensor, allowing it to be operated by touching the screen with a finger or stylus. For example, touching the icon 7207 displayed on the display unit 7202 can launch an application.

[0453] The operation button 7205 can be assigned various functions, including time setting, power on / off, wireless communication on / off, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the functions of the operation button 7205 can be freely configured by the operating system built into the personal digital assistant 7200.

[0454] Furthermore, the 7200 portable information terminal is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless-enabled headset to enable hands-free calling.

[0455] Furthermore, the portable information terminal 7200 is equipped with an input / output terminal 7206, allowing it to directly exchange data with other information terminals via a connector. It can also be charged via the input / output terminal 7206. Note that charging may also be performed wirelessly without using the input / output terminal 7206.

[0456] The display unit 7202 of the portable information terminal 7200 has a secondary battery according to one aspect of the present invention. By using a secondary battery according to one aspect of the present invention, a lightweight and long-lasting portable information terminal can be provided. For example, the secondary battery 7104 shown in Figure 31E can be incorporated inside the housing 7201 in a curved state, or inside the band 7203 in a bendable state.

[0457] The portable information terminal 7200 preferably has sensors. For example, it is preferable that the sensor includes human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, as well as touch sensors, pressure sensors, and acceleration sensors.

[0458] Figure 31G shows an example of an armband-type display device. The display device 7300 has a display unit 7304 and a secondary battery according to one embodiment of the present invention. The display device 7300 may also be equipped with a touch sensor on the display unit 7304 and can also function as a portable information terminal.

[0459] The display unit 7304 has a curved display surface, allowing it to display information along the curved surface. Furthermore, the display device 7300 can change its display status via standardized short-range wireless communication.

[0460] Furthermore, the display device 7300 is equipped with input / output terminals, allowing it to directly exchange data with other information terminals via connectors. It can also be charged via the input / output terminals. Note that charging may also be performed wirelessly without using the input / output terminals.

[0461] By using a secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0462] Furthermore, an example of mounting the secondary battery with good cycle characteristics shown in the previous embodiment into an electronic device will be explained using Figures 31H, 32, and 33.

[0463] By using a secondary battery according to one embodiment of the present invention as a secondary battery in everyday electronic devices, it is possible to provide lightweight and long-lasting products. Examples of everyday electronic devices include electric toothbrushes, electric shavers, and electric beauty devices. For the secondary batteries in these products, there is a need for a stick-shaped battery that is easy for the user to hold, is small, lightweight, and has a large charge / discharge capacity.

[0464] Figure 31H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In Figure 31H, the electronic cigarette 7500 consists of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle and sensors. To enhance safety, a protection circuit to prevent overcharging and over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in Figure 31H has external terminals so that it can be connected to a charging device. Since the secondary battery 7504 is the tip when held, it is desirable that its total length is short and its weight is light. A secondary battery according to one aspect of the present invention has a high charge / discharge capacity and good cycle characteristics, so it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period of time.

[0465] Next, Figures 32A and 32B show an example of a foldable tablet terminal. The tablet terminal 9600 shown in Figures 32A and 32B includes a housing 9630a, a housing 9630b, a movable part 9640 connecting housings 9630a and 9630b, a display unit 9631 having display units 9631a and 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, a tablet terminal with a larger display area can be created. Figure 32A shows the tablet terminal 9600 in an open state, and Figure 32B shows the tablet terminal 9600 in a closed state.

[0466] Furthermore, the tablet terminal 9600 has a power storage unit 9635 inside the housing 9630a and housing 9630b. The power storage unit 9635 is provided across housing 9630a and housing 9630b, passing through the movable part 9640.

[0467] The display unit 9631 can have all or part of its area designated as a touch panel area, and data can be entered by touching images, characters, input forms, etc., including icons, displayed in that area. For example, keyboard buttons may be displayed on the entire surface of the display unit 9631a on the housing 9630a side, and information such as characters and images may be displayed on the display unit 9631b on the housing 9630b side.

[0468] Alternatively, the display unit 9631b on the housing 9630b may be used to display a keyboard, while the display unit 9631a on the housing 9630a may be used to display information such as characters and images. Alternatively, the display unit 9631 may be used to display a touch panel keyboard display switching button, so that the keyboard is displayed on the display unit 9631 when the button is touched with a finger or stylus.

[0469] Furthermore, it is possible to simultaneously input touch input to the touch panel area of ​​the display unit 9631a on the housing 9630a side and the touch panel area of ​​the display unit 9631b on the housing 9630b side.

[0470] Furthermore, switches 9625 to 9627 may not only serve as an interface for operating the tablet terminal 9600, but also as an interface for switching various functions. For example, at least one of switches 9625 to 9627 may function as a switch to turn the tablet terminal 9600 on and off. Also, for example, at least one of switches 9625 to 9627 may have a function to switch the display orientation, such as portrait or landscape, or a function to switch between monochrome and color display. Also, for example, at least one of switches 9625 to 9627 may have a function to adjust the brightness of the display unit 9631. The brightness of the display unit 9631 can be optimized according to the amount of ambient light during use, as detected by the light sensor built into the tablet terminal 9600. Note that the tablet terminal may incorporate other detection devices in addition to the light sensor, such as a gyroscope, an accelerometer, or other sensors that detect tilt.

[0471] Furthermore, while Figure 32A shows an example where the display area of ​​the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side are approximately the same, the display areas of the display units 9631a and 9631b are not particularly limited, and the size of one may differ from the other, and the display quality may also differ. For example, one display panel may be capable of displaying a higher resolution than the other.

[0472] Figure 32B shows the tablet terminal 9600 in a folded state. The tablet terminal 9600 includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. Furthermore, an energy storage body according to one embodiment of the present invention is used as the energy storage body 9635.

[0473] As mentioned above, the tablet terminal 9600 is foldable, so when not in use, the casings 9630a and 9630b can be folded together. Folding protects the display unit 9631, thereby increasing the durability of the tablet terminal 9600. Furthermore, the energy storage unit 9635 using a secondary battery according to one aspect of the present invention has a high charge / discharge capacity and good cycle characteristics, thus providing a tablet terminal 9600 that can be used for long periods of time over an extended period.

[0474] Furthermore, the tablet terminal 9600 shown in Figures 32A and 32B may also have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date, or time on the display unit, a touch input function for touch input operation or editing of information displayed on the display unit, and a function for controlling processing by various software (programs).

[0475] The solar cell 9633 mounted on the surface of the tablet terminal 9600 can supply power to the touch panel, display unit, or video signal processing unit, etc. The solar cell 9633 can be installed on one or both sides of the housing 9630, allowing for an efficient configuration of charging the energy storage unit 9635. Using a lithium-ion battery as the energy storage unit 9635 offers advantages such as miniaturization.

[0476] Furthermore, the configuration and operation of the charge / discharge control circuit 9634 shown in Figure 32B will be explained with a block diagram in Figure 32C. Figure 32C shows the solar cell 9633, energy storage unit 9635, DC-DC converter 9636, converter 9637, switches SW1 to SW3, and display unit 9631, with the energy storage unit 9635, DC-DC converter 9636, converter 9637, and switches SW1 to SW3 corresponding to the charge / discharge control circuit 9634 shown in Figure 32B.

[0477] First, let's explain an example of operation when electricity is generated by the solar cell 9633 using ambient light. The power generated by the solar cell is boosted or stepped down by the DC-DC converter 9636 to obtain a voltage suitable for charging the energy storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, switch SW1 is turned on, and the converter 9637 boosts or steps down the voltage to the voltage required by the display unit 9631. When the display unit 9631 is not being used, SW1 is turned off and SW2 is turned on to charge the energy storage unit 9635.

[0478] The solar cell 9633 is shown as an example of a power generation method, but it is not particularly limited, and the energy storage unit 9635 may be charged by other power generation methods such as piezoelectric elements or thermoelectric elements (Peltier elements). For example, a contactless power transmission module that transmits and receives power wirelessly (non-contact) to charge the energy storage unit may be used, or a combination of other charging methods may be used.

[0479] Figure 33 shows an example of another electronic device. In Figure 33, the display device 8000 is an example of an electronic device using a secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and has a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, etc. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or it can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power source.

[0480] The display unit 8002 can use semiconductor display devices such as liquid crystal displays, light-emitting devices equipped with light-emitting elements such as organic EL elements in each pixel, electrophoretic displays, DMDs (Digital Micromirror Devices), PDPs (Plasma Display Panels), and FEDs (Field Emission Displays).

[0481] Furthermore, the term "display device" includes all information display devices, such as those for receiving TV broadcasts, personal computers, and advertising displays.

[0482] In Figure 33, the fixed-type lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, etc. In Figure 33, the case in which the secondary battery 8103 is installed inside the ceiling 8104 on which the housing 8101 and light source 8102 are installed is illustrated, but the secondary battery 8103 may also be installed inside the housing 8101. The lighting device 8100 can receive power from a commercial power source, or it can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power source.

[0483] Although Figure 33 illustrates a fixed lighting device 8100 installed on the ceiling 8104, the secondary battery according to one aspect of the present invention can also be used in fixed lighting devices installed on surfaces other than the ceiling 8104, such as the side wall 8105, floor 8106, window 8107, etc., or in tabletop lighting devices, etc.

[0484] Furthermore, the light source 8102 can be an artificial light source that artificially generates light using electricity. Specifically, examples of the above artificial light sources include incandescent light bulbs, discharge lamps such as fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0485] In Figure 33, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, etc. In Figure 33, the case in which the secondary battery 8203 is provided in the indoor unit 8200 is illustrated, but the secondary battery 8203 may also be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source, or it can use power stored in the secondary battery 8203. In particular, when both the indoor unit 8200 and the outdoor unit 8204 are equipped with secondary batteries 8203, even when power cannot be supplied from the commercial power source due to a power outage or the like, the air conditioner can be used by using the secondary battery 8203 according to one aspect of the present invention as an uninterruptible power supply.

[0486] Although Figure 33 illustrates a separate-type air conditioner consisting of an indoor unit and an outdoor unit, the secondary battery according to one aspect of the present invention can also be used in an integrated-type air conditioner that has the functions of both the indoor and outdoor units in a single housing.

[0487] In Figure 33, the electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one aspect of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, etc. In Figure 33, the secondary battery 8304 is installed inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source, or it can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one aspect of the present invention as an uninterruptible power source.

[0488] Furthermore, among the electronic devices mentioned above, high-frequency heating devices such as microwave ovens and electric rice cookers require high power in a short period of time. Therefore, by using a secondary battery according to one aspect of the present invention as an auxiliary power source to supplement the power that cannot be supplied by the commercial power supply, it is possible to prevent the commercial power supply circuit breaker from tripping when the electronic device is in use.

[0489] Furthermore, by storing power in the secondary battery during periods when electronic devices are not in use, particularly during periods when the proportion of the total amount of power supplied by the commercial power source that is actually used (referred to as the power usage rate) is low, it is possible to suppress the increase in the power usage rate outside of these periods. For example, in the case of the electric refrigerator-freezer 8300, power is stored in the secondary battery 8304 at night when the temperature is low and the refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature is high and the refrigerator door 8302 and freezer door 8303 are opened and closed, the secondary battery 8304 can be used as an auxiliary power source, thereby keeping the daytime power usage rate low.

[0490] According to one aspect of the present invention, the cycle characteristics of a secondary battery can be improved, thereby enhancing its reliability. Furthermore, according to one aspect of the present invention, a secondary battery with a high charge / discharge capacity can be created, thereby improving the characteristics of the secondary battery and thus making the secondary battery itself smaller and lighter. Therefore, by incorporating a secondary battery according to one aspect of the present invention into the electronic device described in this embodiment, it is possible to create an electronic device that has a longer lifespan and is lighter.

[0491] This embodiment can be implemented in appropriate combination with other embodiments.

[0492] (Embodiment 6) In this embodiment, an example of an electronic device using a secondary battery, as described in the previous embodiment, will be explained with reference to Figures 34A to 35C.

[0493] Figure 34A 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.

[0494] For example, a secondary battery according to one aspect of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 34A. 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 achieved. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0495] 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. A secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0496] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided within the thin housing 4002a of the device 4002. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0497] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on the device 4003, which can be attached to clothing. The secondary battery 4003b can be provided within the thin housing 4003a of the device 4003. By incorporating the secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0498] Furthermore, a secondary battery according to one aspect 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 inside the belt portion 4006a. By incorporating a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0499] Furthermore, a secondary battery according to one aspect 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 strap unit 4005b, and a secondary battery can be provided in either the display unit 4005a or the strap unit 4005b. By providing a secondary battery according to one aspect of the present invention, a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0500] The display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0501] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, allowing for health management.

[0502] Figure 34B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0503] A side view is also shown in Figure 34C. Figure 34C shows the internal structure with the secondary battery 913. The secondary battery 913 is the same secondary battery as shown in Embodiment 4. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, and is small and lightweight.

[0504] Figure 34D shows an example of wireless earphones. Here, wireless earphones with a pair of main units 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0505] The main units 4100a and 4100b include a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. Preferably, they also have a circuit board with a wireless IC or the like, charging terminals, etc. They may also have a microphone.

[0506] The case 4110 contains a secondary battery 4111. Preferably, it also has a circuit board on which wireless ICs, charge control ICs, and other circuits are mounted, as well as charging terminals. It may also have a display unit, buttons, etc.

[0507] The main units 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. This allows them to play audio data sent from other electronic devices. Furthermore, if the main units 4100a and 4100b have microphones, they can send sound acquired by the microphones to other electronic devices, process the audio data, and then send it back to the main units 4100a and 4100b for playback. This allows them to be used, for example, as a translation device.

[0508] Furthermore, the secondary battery 4103 in the main unit 4100a can be charged from the secondary battery 4111 in the case 4100. The coin-type secondary battery, cylindrical secondary battery, etc., from the previous embodiment can be used as the secondary battery 4111 and secondary battery 4103. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 as the positive electrode has a high energy density, and by using it in the secondary battery 4103 and secondary battery 4111, a configuration that can accommodate space saving due to the miniaturization of wireless earphones can be realized.

[0509] Figure 35A 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.

[0510] For example, 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 could 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 aspect of the present invention and a semiconductor device or electronic components. By using the secondary battery 6306 according to one aspect of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be made into a highly reliable electronic device with a long operating time.

[0511] Figure 35B shows an example of a robot. The robot 6400 shown in Figure 35B 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.

[0512] 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.

[0513] 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.

[0514] The upper camera 6403 and 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, lower camera 6406 and obstacle sensor 6407.

[0515] 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 inside. By using the secondary battery according to one aspect of the present invention in the robot 6400, the robot 6400 can be made into an electronic device with a long operating time and high reliability.

[0516] Figure 35C shows an example of an aircraft. The aircraft 6500 shown in Figure 35C has a propeller 6501, a camera 6502, and a secondary battery 6503, and is capable of autonomous flight.

[0517] For example, image data captured by camera 6502 is stored in electronic component 6504. Electronic component 6504 can analyze the image data and detect the presence or absence of obstacles during movement. Furthermore, electronic component 6504 can estimate the remaining battery level from the change in the storage capacity of secondary battery 6503. The aircraft 6500 is equipped with a secondary battery 6503 according to one aspect of the present invention. By using a secondary battery according to one aspect of the present invention in the aircraft 6500, the aircraft 6500 can be made into an electronic device with a long operating time and high reliability.

[0518] This embodiment can be implemented in appropriate combination with other embodiments.

[0519] (Embodiment 7) This embodiment shows an example in which a secondary battery, according to one aspect of the present invention, is mounted on a vehicle.

[0520] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized.

[0521] Figure 36 illustrates a vehicle using a secondary battery, which is one embodiment of the present invention. The automobile 8400 shown in Figure 36A 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. By using one embodiment of the present invention, a vehicle with a long driving range can be realized. The automobile 8400 also has a secondary battery. The secondary battery can be used by arranging the secondary battery modules shown in Figures 21C and 21D on the floor of the vehicle. Alternatively, a battery pack combining multiple secondary batteries as shown in Figure 24 may be installed on the floor of the vehicle. The secondary battery can not only drive the electric motor 8406 but also supply power to light-emitting devices such as headlights 8401 and room lights (not shown).

[0522] Furthermore, the secondary battery can supply power to display devices such as the speedometer and tachometer of the 8400 automobile. The secondary battery can also supply power to semiconductor devices such as the navigation system of the 8400 automobile.

[0523] The automobile 8500 shown in Figure 36B can be charged by receiving power from an external charging facility via a plug-in method or contactless power supply method to the secondary battery of the automobile 8500. Figure 36B shows the state in which the secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. When charging, the charging method and connector specifications can be carried out as appropriate using a prescribed method such as CHAdeMO® or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power supply. For example, the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0524] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless 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 wireless power supply method can be used to transmit and receive power between 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. Electromagnetic induction or magnetic resonance methods can be used for this wireless power supply.

[0525] Furthermore, Figure 36C shows an example of a two-wheeled vehicle using a secondary battery according to one embodiment of the present invention. The scooter 8600 shown in Figure 36C is equipped with a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0526] Furthermore, the scooter 8600 shown in Figure 36C can accommodate the secondary battery 8602 in the under-seat storage compartment 8604. The secondary battery 8602 can be stored in the under-seat storage compartment 8604 even if the compartment is small. The secondary battery 8602 is removable, so when charging, it can be carried indoors, charged, and then stored back in before riding.

[0527] According to one aspect of the present invention, the cycle characteristics of the secondary battery are improved, and the charge and discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to the weight reduction of the vehicle, and thus the driving range can be improved. In addition, the secondary battery installed in the vehicle can be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using commercial power during peak power demand. By avoiding the use of commercial power during peak power demand, it is possible to contribute to energy saving and the reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, so the amount of rare metals such as cobalt can be reduced.

[0528] This embodiment can be implemented in appropriate combination with other embodiments. [Examples]

[0529] In this example, a positive electrode active material 100 according to one embodiment of the present invention was prepared, and its characteristics were analyzed.

[0530] <Fabrication of positive electrode active material> The sample prepared in this embodiment will be described with reference to the manufacturing method shown in Figure 14.

[0531] For step S14, a commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) was prepared as LiMO2, containing cobalt as the transition metal M and no particular additive elements. Lithium fluoride and magnesium fluoride were mixed to this by solid-phase method, similar to steps S21 to S23, S41 and S42. When the number of cobalt atoms is set to 100, the number of lithium fluoride molecules is 0.33 and the number of magnesium fluoride molecules is 1. This was designated as mixture 903.

[0532] Next, the mixture was annealed in the same manner as in step S43. 30g of mixture 903 was placed in a rectangular alumina container, a lid was placed on, and it was heated in a muffle furnace. The furnace was purged and oxygen gas was introduced, and there was no flow during heating. The annealing temperature was 900°C and the annealing time was 20 hours.

[0533] Nickel hydroxide and aluminum hydroxide were added to the heated composite oxide and mixed in the same manner as in steps S31, S32, S61, and S62. The addition was done so that, when the number of cobalt atoms was set to 100, the number of nickel atoms was 0.5 and the number of aluminum atoms was 0.5. This was designated as mixture 904.

[0534] Next, the mixture was annealed in the same manner as in step S63. 100g of mixture 904 was placed in a rectangular alumina container, a lid was placed on top, and it was heated in a muffle furnace. The oxygen gas flow rate during heating was 10 L / min. The annealing temperature was 850°C and the annealing time was 10 hours. The cathode active material prepared in this manner was designated as Sample 1-1 (step S66).

[0535] Next, sample 1-2 was prepared in the same manner as sample 1-1, except that step S43 (annealing) was performed at 850°C for 60 hours with an oxygen gas flow rate of 10 L / min during heating, and step S63 (annealing) was performed at 850°C for 2 hours.

[0536] Next, as shown in the preparation method in Figure 11, a nickel source and an aluminum source were mixed together with a magnesium source and a fluorine source, and the annealing in step S43 was performed at 850°C for 60 hours with an oxygen gas flow rate of 10 L / min during heating. This mixture was prepared in the same manner as Sample 1-1 and designated as Sample 1-3.

[0537] Next, as shown in the preparation method in Figure 15, lithium cobalt oxide was first mixed with a nickel source and an aluminum source, and after annealing in step S43 (850°C, 2 hours, oxygen gas flow rate of 10 L / min during heating), a magnesium source and a fluorine source were mixed in, and annealing in step S63 (850°C, 2 hours) was performed. The result was prepared in the same manner as Sample 1-1, and was designated as Sample 1-4.

[0538] Next, as shown in the preparation method in Figure 12, aluminum isopropoxide (Al(Oi-Pr)3) was used as the aluminum source and mixed in a different process than that used for the nickel source to prepare samples 1-5. Isopropanol was used as the solvent for the Al isopropoxide. The mixture obtained in step S61-1 and the Al isopropoxide were reacted with water in the atmosphere for 17 hours while stirring, then dried to dryness in a forced-air drying oven at 80°C for 3 hours, and then annealed in step S63 (850°C, 2 hours). Other conditions were the same as for samples 1-2.

[0539] Next, with the number of cobalt atoms set to 100, lithium fluoride molecules were added to a ratio of 0.66 and magnesium fluoride molecules to a ratio of 2, while all other conditions were the same as for Samples 1-5. This mixture was designated as Sample 1-6.

[0540] Next, as shown in Figure 13, samples 1-7 were prepared by repeating annealing and adhesion suppression operations multiple times. In this case, the first and second annealing were performed at 900°C for 10 hours, and the third annealing was performed at 920°C for 10 hours. As an adhesion suppression operation during annealing, the composite oxide was placed in a mortar and crushed with a pestle. Other conditions were the same as for samples 1-3.

[0541] Next, sample 1-8 was prepared in the same manner as sample 1-7, except that the third annealing temperature was set to 900°C.

[0542] As a comparative example, we used lithium cobalt oxide (manufactured by Nippon Chemical Industrial Co., Ltd., Cellseed C-10N), which contains cobalt as a transition metal and does not contain any additive elements, as Sample 2.

[0543] Sample 3 was prepared in the same manner as Samples 1-3, except that it did not use a nickel or aluminum source.

[0544] Sample 4 was prepared in the same manner as Samples 1-5, except that it did not use a nickel or aluminum source.

[0545] Sample 5 was prepared in the same manner as Samples 1-5, except that it did not use an aluminum source.

[0546] Sample 6 was prepared in the same manner as Samples 1-5, except that a nickel source was not used.

[0547] Sample 7 was prepared in the same manner as Sample 3, except that when the number of cobalt atoms was set to 100, the number of lithium fluoride molecules was 0.17 and the number of magnesium fluoride molecules was 0.5.

[0548] Furthermore, when the number of cobalt atoms was set to 100, lithium fluoride molecules were added in such a way that the number of molecules was 0.17 and magnesium fluoride molecules were added in such a way that the number of molecules was 0.5. The annealing temperature in step S43 was set to 900°C for 20 hours, and a titanium source was used instead of an aluminum source, with titanium isopropoxide (TTIP) being used as the titanium source. Sample 8 was prepared in the same manner as Sample 6, except that the preparation was the same.

[0549] Table 1 shows the preparation conditions for Samples 1-1 through 8. As is clear from Table 1, Samples 1-1 through 1-8 all share the common characteristic of being prepared by adding magnesium, fluorine, nickel, and aluminum sources to LiCoO2 without any particular additive elements, and then annealing them. Therefore, to distinguish them from samples that do not share this characteristic, they can all be referred to as Sample 1.

[0550] Table 1

[0551] <sem> Figure 37A shows the surface SEM image of sample 1-2, Figure 37B shows the surface SEM image of sample 1-3, Figure 37C shows the surface SEM image of sample 1-4, and Figure 37D shows the surface SEM image of sample 2. Samples 1-2 through 1-4, which were annealed with additives, were observed to have rounded corners, few irregularities, and a smooth surface. On the other hand, sample 2, which was not annealed, was observed to have relatively sharp corners, many irregularities, and a rough surface.

[0552] <Electron diffraction> The results of cross-sectional TEM and electron diffraction analysis of the positive electrode active material of sample 1-1 prepared as described above are shown in Figures 38 to 41.

[0553] Figure 38A is a cross-sectional TEM image of the positive electrode active material from the surface to a depth of approximately 3 μm. The selected-field electron diffraction image of area 1, indicated by the white circle in Figure 38A, is shown in Figure 38B. Some of the bright spots in Figure 38B are labeled 1, 2, 3, and O, as shown in Figure 38C. O is transmitted light, and 1, 2, and 3 are diffraction spots.

[0554] Area 1 is located at a depth of 50 nm or more from the surface and is inside the positive electrode active material. The measured values ​​of the restricted field diffraction patterns inside were d=0.144 nm for area 1, d=0.138 nm for area 2, and d=0.479 nm for area 3. The plane angles were ∠1O2=17°, ∠1O3=90°, and ∠2O3=74°.

[0555] These results confirmed that the interior of the positive electrode active material has a layered rock salt-type crystalline structure. The lattice constant of the a-axis was 2.88 Å, and the lattice constant of the c-axis was 14.37 Å. Note that 1 Å is equal to 10⁻¹⁰ Å. -10 It is m.

[0556] The literature values ​​for layered rock salt-type LiCoO2 are d=0.141nm for 1, d=0.135nm for 2, and d=0.468nm for 3, with surface angles of ∠1O2=17°, ∠1O3=90°, and ∠2O3=73°. The difference from the literature values ​​is considered to be measurement error.

[0557] Figure 39A shows the micro-electron diffraction pattern inside the positive electrode active material. Some of the bright spots in Figure 39A are labeled 1, 2, 3, and O, as shown in Figure 39B.

[0558] The measured values ​​of the micro-electron diffraction patterns inside were d=0.142nm for 1, d=0.122nm for 2, and d=0.240nm for 3. The plane angles were ∠1O2=30°, ∠1O3=90°, and ∠2O3=59°.

[0559] These results also confirmed that the interior of the positive electrode active material has a layered rock salt type crystalline structure. Lattice constant A of the a-axis. core The lattice constant of the c-axis is 2.84 Å, and the lattice constant of the c- core It was 14.4 Å.

[0560] Figure 40A is a cross-sectional TEM image of the positive electrode active material from the surface to a depth of approximately 40 nm. The micro-electron diffraction pattern of point 2, indicated by * in Figure 40A, is shown in Figure 40B. Some of the bright spots in Figure 40B are labeled 1, 2, 3, and O, as shown in Figure 40C.

[0561] Point 2 is approximately 13 nm deep from the surface and is a region within the cathode active material where the aluminum concentration is high, as shown in the linear EDX beam analysis described later. The measured values ​​of the micro-electron diffraction patterns in this region were d=0.143 nm for point 1, d=0.122 nm for point 2, and d=0.240 nm for point 3. The plane angles were ∠1O2=31°, ∠1O3=89°, and ∠2O3=59°.

[0562] These results also confirmed that the interior of the positive electrode active material has a layered rock salt-type crystalline structure. The lattice constant of the a-axis was 2.86 Å, and the lattice constant of the c-axis was 14.4 Å. These values ​​are close to those calculated from Figures 39A and 39B, indicating that there is no significant difference in the lattice constant even in regions with high aluminum concentration.

[0563] Figure 41A is a cross-sectional TEM image of the positive electrode active material from the surface to a depth of approximately 30 nm. The micro-electron diffraction pattern of point 1, indicated by * in Figure 41A, is shown in Figure 41B. Some of the bright spots in Figure 41B are labeled 1, 2, 3, and O, as shown in Figure 41C.

[0564] Point 1 is the outermost layer of the surface of the positive electrode active material. The measured values ​​of the micro-electron diffraction patterns of the outermost layer were d=0.151nm for point 1, d=0.128nm for point 2, and d=0.266nm for point 3. The surface angles were ∠1O2=31°, ∠1O3=90°, and ∠2O3=59°.

[0565] As shown in Figure 41B, the micro-electron diffraction pattern of the outermost layer showed alternating arrangements of bright spots with high brightness and bright spots with low brightness, as indicated by the arrows. When focusing on the arrangement of bright spots including the low brightness, the crystal structure identified from such a diffraction pattern is that of layered rock salt. However, when only the bright spots with high brightness are extracted, it can be determined that the crystal structure is close to that of rock salt. Therefore, it can be said that the outermost layer from which this diffraction pattern was obtained has characteristics of a layered rock salt crystal structure, but also some characteristics of a rock salt crystal structure. The difference in brightness in this diffraction pattern corresponds to the difference in brightness in TEM images, such as those shown in Figure 43B.

[0566] Lattice constant A of the a-axis surface The lattice constant of the c-axis is 3.02 Å. surface The value was 15.96 Å.

[0567] The lattice constants of the interior and outermost layer, determined above, are shown in Table 2. For comparison, literature values ​​are also shown.

[0568] [Table 2]

[0569] As shown in Table 2, in the positive electrode active material according to one embodiment of the present invention, the lattice constant A of the a-axis of the outermost layer, which is a part of the surface layer, is calculated by microelectron diffraction. surface The value is 3.02 Å, and the lattice constant A of the internal a-axis is calculated by microelectron diffraction. core It was larger than 2.84 Å. Similarly, the lattice constant C of the c-axis of the outermost layer. surface This is 15.96 Å, and the internal c-axis lattice constant C is calculated by micro-electron diffraction. core It was larger than 14.4 Å.

[0570] Table 3 shows the difference and rate of change of lattice constants between the interior and outermost layer, as determined by micro-electron diffraction.

[0571] [Table 3]

[0572] As shown in Table 3, the lattice constant A of the a-axis of the outermost layer surface And the lattice constant A of the internal a-axis. core The difference Δ A The lattice constant C of the outermost layer's c-axis is greater than 0.18 Å. surface And the lattice constant C of the internal c-axis. core The difference Δ C The value of 1.56 Å was larger.

[0573] Furthermore, the lattice constant A of the a-axis of the outermost layer. surface And the lattice constant A of the internal a-axis. core The rate of change R A The value was 0.063. Also, the lattice constant C of the c-axis of the outermost layer. surface And the lattice constant C of the internal c-axis. core The rate of change R C The value was 0.108.

[0574] These findings reveal that the change in lattice constants between the interior and outermost layer is greater in the c-axis direction than in the a-axis direction.

[0575] <Cross-sectional STEM and Brightness> Cross-sectional STEM images of the positive electrode active material of sample 1-1 prepared as described above are shown in Figures 42A to 42C. Figure 42A is a cross-sectional STEM image of the positive electrode active material from the surface to a depth of approximately 15 nm. Figure 42B is a cross-sectional STEM image of the positive electrode active material in a region with a depth of approximately 6 nm and a width of approximately 8 nm from the surface. Figure 42C is a cross-sectional STEM image from the surface to a depth of approximately 3.5 nm. These are dark-field images.

[0576] As shown in Figure 42A, within the positive electrode active material, layers of transition metal M were observed as a series of strong white bright spots, exhibiting a layered rock salt-type crystal structure and high crystallinity. Furthermore, the surface of the positive electrode active material was roughly parallel to the (001) plane of the layered rock salt-type crystal structure. The lithium layer between the transition metal M layers was only slightly gray, with almost no bright spots observed. The same was true for oxygen, which forms an octahedron around the transition metal M. This cross-sectional STEM image clearly shows that elements with low atomic numbers, such as lithium and oxygen, do not produce distinct bright spots.

[0577] On the other hand, as shown in Figures 42B and 42C, weak bright spots were observed at the lithium sites in the outermost layer. Since their brightness is higher than that of lithium and oxygen, they are considered to be elements with a larger atomic number than lithium. Furthermore, since these elements are present at the lithium sites, they are considered to be elements that can form cations, and therefore they are metallic elements with a larger atomic number than lithium. In other words, they are transition metals M or metallic elements among the additive elements. Of the additive elements present in Sample 1-1, magnesium and aluminum are metallic. Therefore, the weak bright spots present at the lithium sites in the outermost layer are considered to be cobalt, magnesium, or aluminum.

[0578] Figures 43A to 44B show a comparison of the brightness of the transition metal M-site layer and the lithium-site layer using the cross-sectional STEM image in Figure 42B. Figure 43A is a 90° rotation of Figure 42B. For the image in Figure 43A, the brightness was integrated parallel to the transition metal M-site layer. Figure 43B shows the brightness of each pixel row graphically.

[0579] Next, in order to facilitate comparison of the luminance of metal elements, the luminance derived from anions such as oxygen atoms was corrected as background. Specifically, correction was performed by approximating a straight line between the vertices of the valleys of each peak. The background is shown by a dotted line in FIG. 43B.

[0580] FIG. 44A shows a graph after correction. The horizontal axis represents the depth from the surface. The peak of luminance of the first metal element was taken as the surface. The vertical axis represents intensity, which was normalized by setting the maximum value of the number of white pixels up to a depth of 6 nm as 1. FIG. 44B shows the diagram of FIG. 43A with brightness inversion to improve visibility.

[0581] As shown in FIG. 44A, in a region where the depth from the surface is deeper than 3 nm, transition metal M-site layers were present with high luminance. No peak was present in the lithium site layers between the transition metal M-site layers.

[0582] On the other hand, at a depth of less than about 0.8 nm from the surface, the peaks were low in both the transition metal M-site layers and the lithium site layers, and sufficient intensity could not be obtained. This may be an error derived from the unevenness of the positive electrode active material. However, at a depth of 0.8 nm or more from the surface, the luminance of the transition metal M-site layers reached 0.7 or more of the maximum value, and sufficient intensity was obtained.

[0583] In the region from about 0.8 nm to 3 nm in depth from the surface, a peak lower than that of the transition metal M-site layers was observed in the lithium site layers (dotted arrow in FIG. 44A). This low peak is considered to indicate that an additive metal element or transition metal M is present in the lithium site layers. The peak of this lithium site layer was 3% or more and 60% or less of the maximum value, more specifically 4% or more and 50% or less, and even more specifically 6% or more and 40% or less. Further, as compared with the intensity of the first transition metal site layer having sufficient intensity, it was 5% or more and 65% or less, more specifically 8% or more and 50% or less.

[0584] <EDX line area analysis> The results of EDX area analysis performed on the surface layer portion of the cross section of the positive electrode active material of Sample 1-1 produced above are shown in FIGS. 45A to 47E.

[0585] For ease of comparison, the same cross-sectional HAADF-STEM images covering the surface and interior of the positive electrode active material are shown in Figures 45A, 46A and 47A. Figure 45B is a mapping image of fluorine in the same region as the HAADF-STEM image, Figure 45C is that of carbon, Figure 45D is that of magnesium, Figure 45E is that of oxygen, and Figure 45F is that of aluminum. Figure 46B is a mapping image of nickel in the same region as the HAADF-STEM image, Figure 46C is that of silicon, and Figure 46D is that of cobalt. To improve visibility, brightness-inverted mapping images of some elements are shown in Figures 47B to 47E. Figure 47B is a brightness-inverted mapping image of fluorine, Figure 47C is that of magnesium, Figure 47D is that of aluminum, and Figure 47E is that of nickel.

[0586] From Figures 45 to 47, it was revealed that oxygen and cobalt are distributed throughout the entire positive electrode active material. In addition, magnesium and fluorine had higher concentrations in the surface layer, particularly in the outermost surface layer. It was observed that aluminum is broadly distributed up to approximately 30 nm from the surface. Nickel was considered to have a concentration equal to or below the background level.

[0587] <EDX line analysis> Next, EDX line analysis was performed on the surface layer portion of the positive electrode active material of Sample 1-1. Figure 48 is a cross-sectional STEM image covering the surface and interior of the positive electrode active material. The region surrounded by the white line in Figure 48 is the measurement region. As indicated by the white arrow in the figure, the analysis was performed from the outside to the inside of the positive electrode active material 100. The results are shown in Figures 49A and 49B. The horizontal axis represents the distance from the measurement start point (Distance), and the vertical axis represents atomic percent (Atomic%). Note that the detection limit of EDX line analysis is approximately 1 atomic percent, depending on the element.

[0588] Figure 49B is an enlarged view of a part of Figure 49A. From Figures 49A and 49B, it was confirmed that magnesium and fluorine exist in the outermost surface layer and have a concentration gradient in which the concentration increases from the interior toward the surface. The concentration was highest at the surface, forming a sharp peak. The distribution of silicon showed the same tendency.

[0589] The peak for magnesium concentration was at 4.0 atomic percent, measured at a distance of 4.6 nm. The peak for fluorine concentration was at 4.0 atomic percent, measured at a distance of 4.4 nm.

[0590] The aluminum concentration peak was located deeper than the magnesium and fluorine peaks and was broadly distributed over distances of more than 20 nm. The aluminum concentration peak was measured at 3.9 atomic percent at a distance of 16.1 nm.

[0591] Nickel was below the detection limit, i.e., less than 1 atomic percent, at all measurement points.

[0592] Oxygen was detected from outside the surface of the positive electrode active material. This is thought to be due to the influence of carbon dioxide and hydroxyl groups chemically adsorbed onto the surface after the positive electrode active material was fabricated, or as background noise.

[0593] A protective carbon film was formed when the cross-sectional STEM sample was prepared using FIB, resulting in a high concentration of carbon detected outside the surface of the positive electrode active material. Carbon inside the surface is considered background noise.

[0594] The surface was estimated from the detected oxygen levels as follows. First, the 20-40 nm range indicated by the arrow in Figure 49A was considered a region where the atomic percentage of oxygen was stable. The average atomic percentage of oxygen in this region was 54.4%. Furthermore, the 0-3 nm range was considered a region where the atomic percentage of background or chemiadsorbed oxygen was stable. The average O in this region was... background It was 11.8%. ave From O background The result of subtracting 42.6% is the average O of the corrected oxygen. ave Therefore, 1 / 2O ave The oxygen concentration was 21.3%. The closest measurement point for oxygen was at a distance of 4.4 nm. Therefore, in this example, we estimated the surface at a distance of 4.4 nm. This was the same measurement point as the peak of fluorine concentration.

[0595] Furthermore, when estimating the surface from the detected amount of cobalt, the following method is used. The range of 20-40 nm was defined as the region where the atomic percentage of cobalt is stable. The average Co in this region is... ave It was 37.8 atomic percent. Therefore, 1 / 2 Co ave The concentration was 18.9 atomic percent. The closest cobalt measurement point was at a distance of 4.6 nm.

[0596] Thus, whether using oxygen or cobalt, the measurement points at almost the same distance are estimated to be the surface. From these results, it can be said that both of the above methods are valid for estimating the surface.

[0597] Thus, EDX surface analysis and line analysis confirmed that the positive electrode active material of one embodiment of the present invention is a positive electrode active material 100 having magnesium and fluorine in the surface layer, particularly the outermost layer, and having a concentration gradient from the interior to the surface. It was also confirmed that the concentration peak of aluminum is located at a deeper position than the concentrations of magnesium and fluorine.

[0598] Assuming a surface depth of 4.4 nm, based on the oxygen detection level, the magnesium concentration peak was at a depth of 0.2 nm. The fluorine concentration peak was at a depth of 0 nm. The aluminum concentration peak was at a depth of 11.7 nm.

[0599] <Surface irregularities of the active material> Next, the surface smoothness of the positive electrode active material prepared as described above was evaluated by measuring the surface irregularities of Sample 1-1 and Sample 2 using the following method.

[0600] First, SEM images were acquired for sample 1-1 and sample 2. The SEM measurement conditions were the same for both sample 1-1 and sample 2. Measurement conditions include acceleration voltage and magnification. In this example, a conductive coating was applied to sample 1-1 and sample 2 as a pretreatment before observation. Specifically, platinum sputtering was performed for 20 seconds. Observation was performed using a Hitachi High-Tech scanning electron microscope SU8030. The measurement conditions were an acceleration voltage of 5kV and a magnification of 5000x. Other measurement conditions such as a working distance of 5.0mm, emission current of 9~10.5μA, extraction voltage of 5.8V, SEU mode (Upper secondary-electron detector), and ABC mode (Auto Brightness Contrast Control) were also kept the same, and observation was performed with autofocus.

[0601] Figure 50A shows the SEM image of sample 1-1, and Figure 50B shows the SEM image of sample 2. Sample 1-1, which was heated after the addition of additive elements, was observed to have a smoother surface than sample 2. In each figure, the area to be analyzed next is indicated by a rectangle. The area of ​​the area to be analyzed was 4 μm × 4 μm, and this area was the same for all samples. The area within the area to be used as a horizontal SEM observation surface was ensured.

[0602] Here, the inventors focused on the fact that the surface state of the positive electrode active material is captured with changes in brightness in the images shown in Figures 50A and 50B. They considered whether it might be possible to quantify information about the surface irregularities through image analysis by utilizing changes in brightness.

[0603] Therefore, in this embodiment, we attempted to quantify the surface smoothness of the positive electrode active material by analyzing the images shown in Figures 50A and 50B using the image processing software "ImageJ". Note that "ImageJ" is merely an example of the image processing software used for this analysis, and the method is not limited to "ImageJ".

[0604] First, using "ImageJ," we obtain 8-bit versions of the images shown in Figures 50A and 50B (these are called grayscale images). A grayscale image represents each pixel with 8 bits and includes luminance (brightness information). For example, an 8-bit grayscale image can represent luminance with 2 to the power of 8 = 256 gradations. Darker areas have fewer gradations, while brighter areas have more. We attempted to quantify the change in luminance in relation to the number of gradations. This numerical value is called the grayscale value. By obtaining the grayscale value, it becomes possible to numerically evaluate the unevenness of the positive electrode active material.

[0605] Furthermore, it becomes possible to represent the brightness changes of the target area using a histogram. A histogram is a three-dimensional representation of the grayscale distribution in a target area, and is also called a brightness histogram. By obtaining a brightness histogram, it becomes possible to visually evaluate the unevenness of the positive electrode active material in an easy-to-understand manner.

[0606] Following the above procedure, 8-bit grayscale images were obtained from the images of Sample 1-1 and Sample 2, and the grayscale values ​​and luminance histograms were also obtained.

[0607] Figure 51A shows the grayscale values ​​for sample 1-1, and Figure 51B shows the grayscale values ​​for sample 2. The x-axis represents the grayscale value, and the y-axis represents the count, which corresponds to the proportion of the grayscale value shown on the x-axis. The count is shown on a logarithmic scale (log count). Figures 52A and 52B show the luminance histograms for sample 1-1 and sample 2, respectively.

[0608] The graphs in Figures 51A and 51B show the ranges containing the minimum and maximum values ​​of the grayscale. It was found that the maximum and minimum values ​​for Sample 1-1 are between 96 and 206, while for Sample 2 they are between 82 and 206. Table 4 below shows the minimum value, maximum value, the difference between the maximum and minimum values ​​(maximum value - minimum value), and the standard deviation.

[0609] [Table 4]

[0610] As shown in Table 4, sample 1-1, with its smooth surface, had a difference of 120 or less between its maximum and minimum values. It also exhibited a smaller standard deviation and less variability.

[0611] Furthermore, for Sample 1-1 and Sample 2, eight other samples prepared under the same conditions were selected, and image analysis was performed in the same manner as in this embodiment. The same trend was observed when these eight samples were examined.

[0612] This image analysis allowed us to quantitatively confirm the smoothness of the surface. It was found that the positive electrode active material, when heated with magnesium, fluorine, nickel, and aluminum added, had fewer irregularities on its surface and was smooth.

[0613] <Electrode density> Next, using Sample 1-1, positive electrodes were fabricated with varying conductive material and pressing conditions, and the electrode density was evaluated.

[0614] First, a slurry was prepared by mixing the positive electrode active material, conductive material, and PVDF, and this slurry was coated onto an aluminum current collector. The conductive material used was AB alone, a mixture of AB and graphene (AB:graphene = 8:2 by weight), or a mixture of AB and VGCF (registered trademark) (manufactured by Showa Denko K.K.) (AB:VGCF = 8:2 by weight). NMP was used as the solvent for the slurry.

[0615] After drying, the positive electrode was subjected to 0 to 5 light presses and 0 or 1 strong press. The light press was 210 kN / m and the strong press was 1467 kN / m. A calender roll was used for both presses.

[0616] Table 5 shows the mixing ratio, pressing conditions, conductive material, and electrode density (g / cc).

[0617] [Table 5]

[0618] As shown in Table 5, it was found that using a mixture of AB and graphene as the conductive material resulted in a higher electrode density after pressing than using AB alone. Furthermore, when a mixture of AB and graphene was used, with a conductive material content of 1 wt%, and weak pressing was performed two or more times, the electrode density was 3.72 g / cc or higher.

[0619] <xrd> For samples 1-7 and sample 2 prepared as described above, secondary batteries with lithium counter electrodes were fabricated, and their crystal structures after charging were analyzed by XRD.

[0620] First, a slurry was prepared by mixing the positive electrode active material, AB, and PVDF in a weight ratio of active material:AB:PVDF = 95:3:2, and this slurry was coated onto an aluminum current collector. NMP was used as the solvent for the slurry.

[0621] No pressure was applied during the manufacturing process of the positive electrode.

[0622] Using the fabricated positive electrode, a coin-shaped battery cell of the CR2032 type (20 mm in diameter, 3.2 mm in height) was created.

[0623] Lithium metal was used for the counter electrode.

[0624] The electrolyte in the electrolyte solution was 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution itself was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7.

[0625] A 25 μm thick polypropylene was used for the separator.

[0626] The positive and negative electrode cans were made of stainless steel (SUS).

[0627] For the secondary batteries fabricated as described above, the structure after the initial charge was measured. The charging voltage was 4.65V or 4.7V. The charging temperature was 25℃ or 45℃. The charging method was CC / CV (0.5C, each voltage, 0.05C cut). In this embodiment and other measurements of the crystal structure after charging, 1C was defined as 200mA / g. The charging capacity is shown in Table 6.

[0628] [Table 6]

[0629] The charged secondary battery was then disassembled in a glove box under an argon atmosphere, the positive electrode was removed, and the electrolyte was removed by cleaning it with DMC (dimethyl carbonate). The removed positive electrode was attached to a flat substrate with double-sided tape and sealed in a dedicated cell under an argon atmosphere. The positive electrode active material layer was set to match the measurement surface required by the device. Regardless of the charging temperature, the XRD measurement was performed at room temperature.

[0630] The equipment and conditions for XRD measurement were as follows: XRD system: Bruker AXS D8 ADVANCE X-ray source:CuKα ray Output: 40KV, 40mA Slit type: Div.Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scan Measurement range (2θ): 15° to 75° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0631] Figure 53 shows the XRD patterns of samples 1-7 and 2 at various voltages and temperatures after charging. Figure 54A shows an enlarged pattern for 18°≦2θ≦21.5°, and Figure 54B shows an enlarged pattern for 36°≦2θ=47°. For comparison, the XRD patterns of O1, H1-3, and O3' are also shown.

[0632] Figures 53 to 54B clearly show that samples 1-7 possessed an O3' type crystal structure under all conditions: 4.65V at 25°C, 4.65V at 45°C, 4.7V at 25°C, and 4.7C at 45°C. Furthermore, at 4.7C at 45°C, in addition to the O3' type, H1-3 type and O1 type crystal structures were also present. The best crystallinity of the O3' type was observed under the condition of 4.65V at 45°C.

[0633] Furthermore, it was revealed that sample 2, both at 4.7V25℃ and 4.7C45℃, primarily possessed an H1-3 type crystal structure. Almost no peaks originating from an O3' type crystal structure were observed.

[0634] Next, for samples 1-7, the charging temperature was set to 0°C, 25°C, 45°C, 65°C, or 85°C, and the structure after the second charge was measured. The charging method was CC / CV (0.5C, 4.7V, 0.05C cut), and the discharging method was CC (0.5C, 2.5V cut). The charge and discharge capacities are shown in Table 7.

[0635] [Table 7]

[0636] Then, as described above, the positive electrode was removed from the secondary battery and XRD measurements were performed.

[0637] Figure 55 shows the XRD patterns at various temperatures after charging. Figure 56A shows an enlarged pattern for 18°≦2θ≦21.5°, and Figure 56B shows an enlarged pattern for 36°≦2θ=47°. For comparison, the XRD patterns of O1, H1-3, O3', and R-3m(LiCoO2) before charging are also shown.

[0638] Similar to the initial charge, the second charge also revealed the presence of an O3'-type crystal structure under the conditions of 4.7V 25℃ and 4.7V 45℃. At 4.7V 45℃, in addition to the O3'-type, an O1-type crystal structure was also present. Under the conditions of 4.7V 65℃ and 4.7V 85℃, the crystallinity was low, suggesting that the crystal structure was different from O1, H1-3, and O3'.

[0639] Next, the structure of samples 1-7 was measured after the first charge / discharge cycle, the 30th charge / discharge cycle, and the 50th charge / discharge cycle at a charging temperature of 25°C. The charging method was CC / CV (0.5C, 4.7V, 0.05C cut), and the discharging method was CC (0.5C, 2.5V cut). The charge / discharge capacities are shown in Table 8.

[0640] [Table 8]

[0641] Then, as described above, the positive electrode was removed from the secondary battery and XRD measurements were performed.

[0642] Figure 57 shows the XRD patterns after each charge and discharge cycle. Figure 58A shows an enlarged pattern for 18°≦2θ≦21.5°, and Figure 58B shows an enlarged pattern for 36°≦2θ=47°. For comparison, the XRD patterns of O1, H1-3, O3', and R-3m(LiCoO2) before charging are also shown.

[0643] In all three cycles—the first, 30th, and 50th—the R-3m(LiCoO2) crystal structure was confirmed after discharge. As the number of charge-discharge cycles increased, the peak, especially during charging, tended to broaden, and the crystallinity decreased.

[0644] Furthermore, while the device possesses an O3'-type crystal structure during the initial charge, it was inferred that it would have an H1-3-type crystal structure after the 30th and 50th charges. It was also inferred that an R-3m(LiCoO2) crystal structure would be present after the 50th charge. This is thought to be because the surface layer of the positive electrode active material deteriorates, and some of the lithium remains within the positive electrode active material even after charging. On the other hand, the fact that it maintains a discharge capacity exceeding 160 mAh / g even after 50 cycles indicates that the positive electrode active material is sufficiently resistant to degradation.

[0645] Next, the structure of samples 1-7 was measured after the first charge / discharge cycle, the 10th charge / discharge cycle, and the 50th charge / discharge cycle at a charge / discharge temperature of 45°C. The charging method was CC / CV (0.5C, 4.7V, 0.05C cut), and the discharging method was CC (0.5C, 2.5V cut). The charge / discharge capacities are shown in Table 9.

[0646] [Table 9]

[0647] Figure 59 shows the XRD patterns after each charge and discharge cycle. Figure 60A shows an enlarged pattern for 18°≦2θ≦21.5°, and Figure 60B shows an enlarged pattern for 36°≦2θ=47°. For comparison, the XRD patterns of O1, H1-3, O3', and R-3m(LiCoO2) before charging are also shown.

[0648] It was confirmed that the crystal structure was O3' type during the initial charge and R-3m(LiCoO2) during the initial discharge. After that, degradation progressed faster than the charge-discharge cycle at 25°C, and after 50 cycles, the change in crystal structure between charge and discharge was small, suggesting that the lithium insertion-deletion reaction had decreased.

[0649] <Half-cell charge / discharge cycle characteristics> A secondary battery with a lithium counter electrode was fabricated using the positive electrode active material of Sample 1-1 and Sample 2, and its charge-discharge cycle characteristics were evaluated.

[0650] First, a slurry was prepared by mixing the positive electrode active material, AB, and PVDF in a weight ratio of active material:AB:PVDF = 95:3:2, and this slurry was coated onto an aluminum current collector. NMP was used as the solvent for the slurry.

[0651] After coating the current collector with slurry, the solvent was evaporated. Then, pressurization was applied at 210 kN / m, followed by further pressurization at 1467 kN / m. The positive electrode was obtained through these steps. The loading weight of the positive electrode was approximately 7 mg / cm³. 2 The density was 3.8 g / cc or higher.

[0652] Using the fabricated positive electrode, a coin-shaped battery cell of the CR2032 type (20 mm in diameter, 3.2 mm in height) was created.

[0653] Lithium metal was used for the counter electrode.

[0654] The electrolyte in the electrolyte solution was 1 mol / L lithium hexafluoride phosphate (LiPF6). The electrolyte solution consisted of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, to which 2 wt% vinylene carbonate (VC) was added.

[0655] A 25 μm thick polypropylene was used for the separator.

[0656] The positive and negative electrode cans were made of stainless steel (SUS).

[0657] In evaluating the charge-discharge cycle characteristics, the charging voltage was set to 4.4V, 4.5V, or 4.6V. The measurement temperatures were 25°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 85°C. Charging was performed using CC / CV ...

Claims

1. A positive electrode active material having lithium, cobalt, nickel, magnesium, aluminum, oxygen, and fluorine, The outermost surface layer of the positive electrode active material has regions in which bright spots indicating a rock salt type crystal structure belonging to space group Fm-3m or Fd-3m are observed in the micro-electron diffraction pattern, and bright spots indicating a layered rock salt type crystal structure belonging to space group R-3m are observed. The interior of the positive electrode active material has regions in which bright spots exhibiting a layered rock salt type crystal structure belonging to space group R-3m are observed in the micro-electron diffraction pattern. The lattice constant of the c-axis of the outermost layer is greater than the lattice constant of the c-axis of the interior. When the positive electrode active material was subjected to EDX radiation analysis, the peaks in magnesium concentration and fluorine concentration were present within a depth of 3 nm from the surface toward the center of the positive electrode active material. A positive electrode active material in which, when the positive electrode active material is subjected to EDX radiation analysis, the peak of the aluminum concentration is located deeper than the peaks of the magnesium concentration and the peaks of the fluorine concentration.

2. In claim 1, The nickel concentration in the outermost layer is 1 atomic percent or less. The nickel in the positive electrode active material is solid-dissolved throughout the positive electrode active material.

3. In claim 1 or claim 2, In the cross-sectional TEM image of the positive electrode active material, when the brightness originating from anions is corrected as background and the maximum brightness from the surface to a depth of 6 nm in the cross-sectional TEM image is normalized to 1, the peak of the lithium site layer from the surface to a depth of 0.8 nm to 3 nm in the cross-sectional TEM image is 3% to 60% of the maximum value.

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