Lithium-ion rechargeable battery

Abstract

To provide electrodes and secondary batteries with high capacity density and excellent rapid charging and discharging capabilities. thing. [Solution] The device has a positive electrode and a negative electrode, and the positive electrode has a current collector and a first layer overlapping the current collector. It has a first layer and a second layer that overlaps it, and the first layer has a first active material having a first particle size Furthermore, the second layer has a second active material with a second particle size, and the first particle size is smaller than the second particle size. It is a small battery. The second active material has a surface layer and an interior, and the surface layer is the second active material The region is less than 10 nm from the surface to the interior of the material, and the surface layer and the interior are topotaki It is preferable that it be C.

Description

[Technical Field]

[0001] One aspect of the present invention relates to a secondary battery and a method for manufacturing the same. Related to manufacturing equipment, or related to electronic equipment, energy storage systems, and mobile devices having secondary batteries. do.

[0002] One aspect of the present invention relates to a product, a method, or a method of manufacture; or, the present invention relates to a process , relating to machines, manufacturers, or compositions of matter One aspect of the present invention relates to semiconductor devices, display devices, light-emitting devices, energy storage devices, lighting devices, and electronic devices. , or relating to methods for manufacturing them.

[0003] In this specification, "electronic equipment" refers to all devices that have an energy storage device. Electro-optical devices and information terminal devices with energy storage devices are all electronic devices.

[0004] In this specification, "energy storage device" refers to all elements and devices that have an energy storage function. For example, energy storage devices such as lithium-ion secondary batteries (also known as batteries, secondary batteries, etc.) This includes lithium-ion capacitors and electric double-layer capacitors, among others. [Background technology]

[0005] In recent years, various energy storage technologies have emerged, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. The development of such devices is thriving, particularly lithium-ion batteries, which offer high power output and high energy density. Rechargeable batteries are used in mobile devices such as mobile phones, smartphones, and laptop computers. In addition, portable music players, digital cameras, medical equipment, or hybrid vehicles (HV), electric Next-generation clean energy vehicles such as electric vehicles (EVs) or plug-in hybrid vehicles (PHVs) It is applied to mobile devices such as energy-powered vehicles, and its demand is rapidly expanding in conjunction with the development of the semiconductor industry. Moreover, as a rechargeable energy source, it is indispensable to today's information society. It is.

[0006] Lithium-ion rechargeable batteries use lithium cobalt oxide (LiCoO2), nickel-cobalt oxide, and other materials. Lithium tomanganate (LiNi 1-x-y Co x Mn y O2) or lithium iron phosphate A positive electrode containing positive electrode active material such as LiFePO4, and a black electrode capable of intercalating and releasing lithium. A negative electrode containing a negative electrode active material such as lead or other carbon materials, and ethylene carbonate (EC) or ethylene carbonate (EC) It is composed of electrolytes, including organic solvents such as ethyl carbonate (DEC).

[0007] Furthermore, lithium-ion secondary batteries offer high capacity density, high performance, and suitability for various operating environments. Safety and other factors are required in this regard.

[0008] Patent Document 1 discloses a method for manufacturing electrodes that can increase the capacity density of secondary batteries. It is. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] WO2020 / 128699 pamphlet [Non-patent literature]

[0010] [Non-Patent 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-Patent Literature 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-Patent Literature 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-Patent Literature 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. [Non-Patent Literature 5] A. van de Walle, “Multicomponent multisublattice alloys, nonconfigurational entropy and other additions to the Alloy Theoretic Automated Toolkit”, Calphad Journal 33, 266,(2009). [Non-Patent Document 6] Rasband, WS, ImageJ, US National Institutes of Health, Bethesda, Maryland, USA, http: / / rsb.info.nih.gov / ij / , 1997-2012. [Non-Patent Document 7] Schneider, CA, Rasband, WS, Eliceiri, KW “NIH Image to ImageJ: 25 years of image analysis”. Nature Methods 9, 671-675, 2012. [Non-Patent Document 8] Abramoff, MD, Magelhaes, PJ, Ram, SJ “Image Processing with ImageJ”. Biophotonics International, volume 11, issue 7, pp.36-42, 2004. [Overview of the project] [Problems that the invention aims to solve]

[0011] The objective is to realize a manufacturing method that enables high capacity density of secondary batteries. The objective is to realize a manufacturing method that enables rapid charging and rapid discharging of the pond. Another objective is to provide a method for manufacturing rechargeable batteries that are both durable and reliable.

[0012] The electrodes (positive and negative electrodes) for lithium-ion secondary batteries are slurries containing particulate active material. It is manufactured by applying it to a metal foil called a current collector and drying it. The electrode has an active material layer on the current collector. The active material layer has an active material and voids, and the secondary electric To increase the capacity density of a pond, it is necessary to minimize voids as much as possible. By using electrodes, it is possible to obtain a larger battery capacity even with a secondary battery of the same volume. This makes it possible to improve the capacity density per unit volume. Furthermore, the active material layer with fewer voids The electrodes possessed can be called high-density electrodes, densified electrodes, or electrodes with high membrane density. be.

[0013] The electrodes for lithium-ion secondary batteries have an interface between the current collector and the active material layer, and the active material layer has Therefore, it is desirable to have good electron conduction pathways. Also, in the active material layer, the separator Alternatively, in regions adjacent to the solid electrolyte layer, it is desirable to have good lithium ion conduction pathways. Electrodes with good electron conduction pathways and good lithium ion conduction pathways are suitable for rapid charging. It is an electrode suitable for electric and rapid discharge, and has good electron conduction paths and good lithium ion Electrode structures with conduction pathways and methods for fabricating them are still not sufficiently established. Furthermore, a high-capacity density electrode equipped with good electron conduction pathways and good lithium-ion conduction pathways, Another objective is to provide the structure and method for manufacturing it.

[0014] Furthermore, the description of these problems does not preclude the existence of other problems. One embodiment does not need to solve all of these problems. It is possible to extract other problems from the description of the claims. [Means for solving the problem]

[0015] One aspect of the present invention has a positive electrode and a negative electrode, wherein the positive electrode has a current collector and a first overlapping current collector It has a layer and a second layer that overlaps the first layer, and the first layer is a first active material having a first particle size The first layer has a quality, and the second layer has a second active material which has a second particle size, and the first particle size is the second particle It is a battery that is smaller than its diameter.

[0016] Furthermore, one aspect of the present invention has a positive electrode and a negative electrode, wherein the positive electrode is a current collector and overlaps with the current collector. It has a first layer and a second layer overlapping the first layer, and the first layer has a first particle size. The first layer has an active material, and the second layer has a second active material with a second particle size, and the first particle size is A battery in which the particle size of the second active material is smaller than that of the second active material, and the sphericity of the second active material is between 0.8 and 1.0. .

[0017] Furthermore, one aspect of the present invention has a positive electrode and a negative electrode, wherein the positive electrode is a current collector and overlaps with the current collector. It has a first layer and a second layer overlapping the first layer, and the first layer has a first particle size. The first layer has an active material, and the second layer has a second active material with a second particle size, and the first particle size is The particle size is smaller than that of the second active material, and the second active material has a surface layer and an interior, and the surface layer is the second active This refers to a region of less than 10 nm from the surface of a material towards the interior, and the surface layer and the interior are distinct from each other. It is a topotaxis, a battery.

[0018] Furthermore, one aspect of the present invention has a positive electrode and a negative electrode, wherein the positive electrode is a current collector and overlaps with the current collector. It has a first layer and a second layer overlapping the first layer, and the first layer has a first particle size. The first layer has an active material, and the second layer has a second active material with a second particle size, and the first particle size is The particle size is smaller than that of the second active material, and the second active material has a surface layer and an interior, and the surface layer is the second active This refers to a region of less than 10 nm from the surface of a material towards the interior, and the surface layer and the interior are distinct from each other. It is a topotaxy, and the sphericity of the second active material is between 0.8 and 1.0, and it is a battery. .

[0019] In a battery having a first layer and a second layer as described in any one of the above, on the current collector It is preferable to have a first layer, with a second layer on top of the first layer.

[0020] In the case where there is a first layer on the current collector and a second layer on the first layer, the first layer and the second The first layer has a conductive material, and the mass of the conductive material in the second layer is equal to the quality of the conductive material in the first layer. It is preferable that the quantity be greater than the amount.

[0021] In the case where there is a first layer on the current collector and a second layer on the first layer, the first layer and the second The layers contain a solid electrolyte, and the mass of the solid electrolyte in the first layer is equal to the mass of the solid electrolyte in the second layer. It is preferable that the amount is greater than the mass of body electrolytes.

[0022] A battery as described in any one of the above, wherein the current collector has a second layer, and the second layer has a first It is preferable that it has a layer of [this material].

[0023] In the case where there is a second layer on the current collector and a first layer on the second layer, the first layer and the second The layers contain a conductive material, and the mass of the conductive material in the first layer is equal to the quality of the conductive material in the second layer. It is preferable that the quantity be greater than the amount.

[0024] In the case where there is a second layer on the current collector and a first layer on the second layer, the first layer and the second The first layer has a solid electrolyte, and the mass of the solid electrolyte in the second layer is equal to the mass of the solid electrolyte in the first layer. It is preferable that the amount is greater than the mass of body electrolytes.

[0025] Alternatively, one aspect of the present invention has a positive electrode and a negative electrode, wherein the positive electrode is a current collector and a current collector on the current collector It has a first layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the The first layer has a particle size of 1, and the second layer has a second active material with a particle size of 2. The third layer has a third active material with a third particle size, and the first particle size is smaller than the second particle size. Therefore, the third particle size is smaller than the second particle size, forming a battery.

[0026] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size. The third layer has a third active material with a third particle size, and the first particle size is smaller than the second particle size. Furthermore, the third particle size is smaller than the second particle size, and the sphericity of the second active material is between 0.8 and 1.0. It's below, it's a battery.

[0027] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size and a fourth The third layer has a fourth active material with a particle size of , and the third layer has a third active material with a third particle size. The first particle size is smaller than the second particle size, the third particle size is smaller than the second particle size, and the fourth particle size is smaller than the second particle size. The particle size of the first particle is smaller than that of the second particle; it is a battery.

[0028] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size and a fourth The third layer has a fourth active material with a particle size of , and the third layer has a third active material with a third particle size. The first particle size is smaller than the second particle size, the third particle size is smaller than the second particle size, and the fourth particle size is smaller than the second particle size. The particle size of the first active material is smaller than that of the second active material, and the sphericity of the second active material is between 0.8 and 1.0. It is a battery.

[0029] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size. The third layer has a third active material with a third particle size, and the first and third particle sizes are second The particle size is smaller than that of the second active material, and the second active material has a surface layer and an interior, and the surface layer is the second active material The region is less than 10 nm from the surface to the interior of the material, and the surface layer and the interior are respectively It's a topotaxis, it's a battery.

[0030] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size. The third layer has a third active material with a third particle size, and the first and third particle sizes are second The particle size is smaller than that of the second active material, and the second active material has a surface layer and an interior, and the surface layer is the second active material The region is less than 10 nm from the surface to the interior of the material, and the surface layer and the interior are respectively It is a topotaxis battery in which the sphericity of the second active material is between 0.8 and 1.0.

[0031] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size and a fourth The third layer has a fourth active material with a particle size of , and the third layer has a third active material with a third particle size. Furthermore, the first particle size, the third particle size, and the fourth particle size are smaller than the second particle size, and the second active material is It has a surface layer and an interior, and the surface layer extends 10n from the surface of the second active material toward the interior. It is a cell in a region less than m in size, where the surface and interior are both topotaxi.

[0032] Furthermore, one aspect of the present invention includes a positive electrode and a negative electrode, wherein the positive electrode comprises a current collector and a first on the current collector It has a layer, a second layer on the first layer, and a third layer on the second layer, and the first layer is the first The first active material has a particle size of , and the second layer has a second active material with a second particle size and a fourth The third layer has a fourth active material with a particle size of , and the third layer has a third active material with a third particle size. Furthermore, the first particle size, the third particle size, and the fourth particle size are smaller than the second particle size, and the second active material is It has a surface layer and an interior, and the surface layer extends 10n from the surface of the second active material toward the interior. The region is less than m, and the surface and interior are both topotaxy, and the second active material This is a battery with a sphericity of 0.8 to 1.0.

[0033] A battery having a first layer, a second layer, and a third layer as described in any one of the above, The first layer, the second layer, and the third layer each contain a conductive material, and the mass of the conductive material in the third layer The mass of the conductive material in the second layer is greater than the mass of the conductive material in the first layer. It is preferable that the amount of conductive material in the layer is greater than the mass of the conductive material in the layer.

[0034] A battery having a first layer, a second layer, and a third layer as described in any one of the above, The first layer, the second layer, and the third layer each have a solid electrolyte, and the solid electrolyte of the first layer The mass of the quality is greater than the mass of the solid electrolyte in the second layer, and the solid electrolyte in the second layer Preferably, the mass of the third layer is greater than the mass of the solid electrolyte contained in the third layer.

[0035] In a battery having a solid electrolyte as described in any one of the above, the second active material is the surface layer It has an interior and a surface layer that extends 10 nm from the surface of the second active material inward. The following region, where the surface and interior are both topotaxis, is the second active material. It is preferable that the edge surface has a region in contact with the surface layer and the solid electrolyte.

[0036] One aspect of the present invention is a mobile body having a battery as described in any one of the above.

[0037] One aspect of the present invention is an energy storage system having the battery described in any one of the above.

[0038] One aspect of the present invention is an electronic device having the battery described in any one of the above descriptions. [Effects of the Invention]

[0039] This allows for the provision of secondary batteries capable of high capacity density. Furthermore, it enables rapid charging and rapid discharge. We can provide a rechargeable battery that can generate electricity. Furthermore, a rechargeable battery that is safe and reliable. We can provide this.

[0040] According to one aspect of the present invention, a positive electrode activity in which the decrease in charge / discharge capacity during charge / discharge cycles is suppressed. A material or composite oxide can be provided. Alternatively, the crystal structure can be maintained even after repeated charging and discharging. This can provide a positive electrode active material or composite oxide that is less prone to breakdown. Alternatively, it can provide charge / discharge capacity It is possible to provide a positive electrode active material or composite oxide with a large value. Alternatively, safety or reliability We can provide highly efficient rechargeable batteries.

[0041] This enables the realization of a manufacturing method that allows for high capacity density of secondary batteries. Furthermore, rapid charging is possible. Furthermore, a method for manufacturing secondary batteries capable of rapid discharge can be realized. In addition, safety and A method for manufacturing highly reliable secondary batteries can be provided. Alternatively, a method for manufacturing sufficiently high-density batteries can be provided. This enables the realization of a manufacturing method that can reduce defects occurring in the active material at electrodes. High-density electrodes with fewer defects enable high capacity density, high performance, and various operating environments. This will enable the creation of superior rechargeable batteries that meet safety standards.

[0042] Furthermore, the description of these effects does not preclude the existence of other effects. One embodiment does not need to have all of these effects. Other effects are described in the specification. This will become clear from the description in the drawings, claims, etc., and the specification, drawings, claims From descriptions such as these, it is possible to extract other effects. [Brief explanation of the drawing]

[0043] [Figure 1] Figure 1A shows an example of an electrode illustrating one aspect of the present invention. Figure 1B is a cross-sectional view of the positive electrode active material. [Figure 2] Figures 2A to 2D show partial cross-sectional views of the positive electrode active material. [Figure 3] Figure 3 shows an example of a TEM image where the crystal orientation is roughly consistent. [Figure 4]Figure 4A is an example of a STEM image where the crystal orientation is roughly consistent. Figure 4B is the FFT pattern of the region of the rock salt crystal RS. Figure 4C is the FFT pattern of the region of the layered rock salt crystal LRS. [Figure 5] Figures 5A and 5B show an example of an electrode according to one embodiment of the present invention. [Figure 6] Figures 6A to 6D show examples of electrodes according to one embodiment of the present invention. [Figure 7] Figure 7 shows an example of a method for manufacturing an electrode according to one embodiment of the present invention. [Figure 8] Figures 8A and 8B show an example of a method for manufacturing an electrode according to one embodiment of the present invention. [Figure 9] Figures 9A and 9B show an example of a method for manufacturing an electrode according to one embodiment of the present invention. [Figure 10] Figure 10 shows an example of a method for manufacturing an electrode according to one aspect of the present invention. [Figure 11] Figure 11 shows an example of a calculation relating to an electrode according to one embodiment of the present invention. [Figure 12] Figures 12A to 12F show an example of calculations relating to an electrode according to one embodiment of the present invention. [Figure 13] Figures 13A to 13C show an example of calculations relating to an electrode according to one embodiment of the present invention. [Figure 14] Figures 14A to 14C show an example of calculations relating to an electrode according to one embodiment of the present invention. [Figure 15] Figure 15 shows an example of a calculation relating to an electrode according to one embodiment of the present invention. [Figure 16] Figures 16A and 16B show an example of an electrode according to one embodiment of the present invention. [Figure 17] Figures 17A and 17B show an example of an electrode according to one embodiment of the present invention. [Figure 18] Figures 18A to 18D show an example of an electrode according to one embodiment of the present invention. [Figure 19] Figures 19A and 19B show an example of an electrode according to one embodiment of the present invention. [Figure 20] Figures 20A and 20B show an example of an electrode according to one embodiment of the present invention. [Figure 21]Figures 21A and 21B show an example of an electrode according to one embodiment of the present invention. [Figure 22] Figures 22A and 22B show an example of an electrode according to one embodiment of the present invention. [Figure 23] Figures 23A and 23B show an example of a battery having electrodes according to one embodiment of the present invention. [Figure 24] Figure 24 shows an example of a battery having electrodes according to one embodiment of the present invention. [Figure 25] Figures 25A and 25B show an example of a battery having electrodes according to one embodiment of the present invention. [Figure 26] Figures 26A1 to 26B3 illustrate the crystal structure and calculation results. [Figure 27] Figures 27A1 to 27A3 illustrate the crystal structure. [Figure 28] Figures 28A and 28B illustrate the crystal structure and calculation results. [Figure 29] Figures 29A and 29B illustrate the crystal structure. [Figure 30] Figure 30 illustrates the crystal structure of the positive electrode active material. [Figure 31] Figure 31 illustrates the crystal structure of a conventional positive electrode active material. [Figure 32] Figures 32A and 32B are cross-sectional views of the positive electrode active material, and Figures 32C1 and 32C2 are partial cross-sectional views of the positive electrode active material. [Figure 33] Figure 33 shows the XRD pattern calculated from the crystal structure. [Figure 34] Figure 34 shows the XRD pattern calculated from the crystal structure. [Figure 35] Figure 35 is a cross-sectional view of the positive electrode active material. [Figure 36] Figures 36A to 36C illustrate the method for preparing the positive electrode active material. [Figure 37] Figure 37 shows an example of the production flow of a positive electrode active material, illustrating one aspect of the present invention. [Figure 38] Figure 38 is a cross-sectional view showing a reaction vessel used in one embodiment of the present invention. [Figure 39] Figure 39A is an exploded perspective view of a coin-type rechargeable battery, Figure 39B is a perspective view of a coin-type rechargeable battery, and Figure 39C is a cross-sectional perspective view thereof. [Figure 40] Figure 40A shows an example of a cylindrical secondary battery. Figure 40B shows an example of a cylindrical secondary battery. Figure 40C shows an example of multiple cylindrical secondary batteries. Figure 40D shows an example of an energy storage system with multiple cylindrical secondary batteries. [Figure 41] Figures 41A and 41B illustrate examples of secondary batteries, while Figure 41C shows the inside of a secondary battery. [Figure 42] Figures 42A to 42C illustrate examples of secondary batteries. [Figure 43] Figures 43A and 43B show the external appearance of a secondary battery. [Figure 44] Figures 44A to 44C illustrate the method for manufacturing a secondary battery. [Figure 45] Figures 45A to 45C show examples of battery pack configurations. [Figure 46] Figures 46A to 46C illustrate examples of secondary batteries. [Figure 47] Figures 47A and 47B illustrate an example of a secondary battery. [Figure 48] Figure 48A is a perspective view of a battery pack showing one embodiment of the present invention, Figure 48B is a block diagram of the battery pack, and Figure 48C is a block diagram of a vehicle having a motor. [Figure 49] Figures 49A to 49D illustrate an example of a transport vehicle. Figure 49E illustrates an example of an artificial satellite. [Figure 50] Figures 50A and 50B illustrate an energy storage device according to one embodiment of the present invention. [Figure 51] Figure 51A shows an electric bicycle, Figure 51B shows the secondary battery of an electric bicycle, and Figure 51C is a diagram illustrating an electric motorcycle. [Figure 52] Figures 52A to 52D illustrate an example of an electronic device. [Figure 53] Figure 53A shows an example of a wearable device, Figure 53B shows a perspective view of a wristwatch-type device, and Figure 53C is a diagram illustrating the side view of a wristwatch-type device. Figure 53D is a diagram illustrating an example of wireless earphones. [Figure 54] Figures 54A and 54B are cross-sectional SEM images of the electrodes in the embodiment. [Figure 55] Figures 55A and 55B are cross-sectional SEM images of the electrodes in the example. [Modes for carrying out the invention]

[0044] The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention This is not limited to the description below, and its form and details can be changed in various ways, as is the case for those skilled in the art. This will be easily understood. Furthermore, the present invention shall be interpreted as being limited to the contents of the embodiments described below. It is not something that should be done.

[0045] Furthermore, in the drawings, the size, layer thickness, or area may be exaggerated for clarity. This may be the case. Therefore, it is not necessarily limited to that scale.

[0046] Furthermore, the ordinal numbers used in this specification, etc., as "1st," "2nd," etc., are used for convenience only. It does not indicate the order of processes or stacking order. Therefore, for example, "the first" should be written as "the second". This can be explained by appropriately replacing it with "of" or "the third of," etc. The ordinal numbers described herein do not correspond to the ordinal numbers used to specify one aspect of the present invention. There are cases where this is not the case.

[0047] In this specification, the term "particle" is not limited to spherical (circular cross-section), but also includes individual The cross-sectional shape of each particle can be elliptical, rectangular, trapezoidal, triangular, square with rounded corners, or asymmetrical. Examples include shapes, and individual particles may also have an amorphous shape.

[0048] The particle size can be measured, for example, by laser diffraction particle size distribution measurement, D5 It can be represented as 0. D50 is the cumulative particle amount curve of the particle size distribution measurement result. This is the particle size, or median diameter, when the cumulative amount accounts for 50%. Measurement of particle size This is not limited to laser diffraction particle size distribution measurement, but also the lower limit of measurement for laser diffraction particle size distribution measurement. In the following cases, analysis such as SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope) is performed. The cross-sectional diameter of the particle cross-section may be measured by this method. Particle size when the cross-sectional shape of the particle is not circular. For example, as a measurement method, the area of ​​the particle cross-section is measured using image processing, and the diameter of the circle having that area is measured. The particle size can be calculated as the diameter.

[0049] In this specification, the space group is represented by the international notation (or Hermann-Mauguin notation) S. The notation is written using hort notation. Miller indices are also used to indicate crystal planes and crystals. Direction is indicated. Individual planes indicating crystal planes are indicated using ( ). Space group, crystal plane, and In crystallography, the crystal orientation is indicated by placing a bar above the number, but in this specification, due to formatting constraints... When a bar is placed above a number, instead of placing a bar above it, a minus sign (-) is placed before the number to represent it. There is also [ ] which indicates individual orientations within a crystal, and [ ] which indicates all equivalent orientations. The position is represented by < >, individual planes representing crystal planes are represented by ( ), and sets of planes with equivalent symmetry are represented by {}. Each is expressed separately. Furthermore, the trigonal crystal, represented by the space group R-3m, is easier to understand in terms of its structure. Therefore, it is generally represented as a hexagonal composite hexagonal lattice, and the Miller indices are not only (hkl) but also (h kil) may be used. Here, i is -(h+k).

[0050] Further, the theoretical capacity of a positive electrode active material refers to the quantity of electricity when all lithium that can be inserted and desorbed in the positive electrode active material is desorbed. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, and the theoretical capacity of lithium nickelate (LiNiO2) is 275 mAh / g, and the theoretical capacity of lithium manganate ( LiMn2O4) is 148 mAh / g.

[0051] Further, the amount of insertable / desorbable lithium remaining in the positive electrode active material is represented by x in the composition formula, for example, x in Li x CoO2, or x in Li x MO2 (M is a transition metal). x can also be said to be the occupancy of Li at lithium sites. In the case of a positive electrode active material in a secondary battery, x can be defined as (theoretical capacity - charged capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as a positive electrode active material is charged to 219.2 mAh / g, it can be said that Li 0.2 CoO2 has x = 0.2. A small x in Li x CoO2 means, for example, 0. 1 < x ≤ 0.24. The transition metal M can be selected from elements described in groups 4 to 13 of the periodic table, for example, at least one selected from manganese, cobalt, and nickel is used.

[0052] When lithium cobaltate approximately satisfies the stoichiometric ratio, it is LiCoO2 and the occupancy x of Li at lithium sites is 1. A secondary battery that has completed discharge is also LiCoO2, and it can be said that x = 1. The term "completed discharge" as used herein means, for example, discharging at a current of 100 mA / g until the cut-off voltage is reached. This refers to a state where the voltage is 2.5V (vs. counter electrode Li) or lower. Lithium-ion secondary battery In the pond, the lithium occupancy rate of the lithium site becomes x=1, and no more lithium can be added. When this happens, the voltage drops sharply. At this point, it can be said that the discharge has ended. Generally, LiC In lithium-ion secondary batteries using oO2, the discharge voltage reaches 2.5V. Since the voltage drops rapidly, we assume that the discharge has ended under the above conditions.

[0053] Li x The charging and / or discharging capacities used to calculate x in CoO2 are short-circuit and Alternatively, it is preferable to perform the measurement under conditions where the effects of electrolyte decomposition are minimal or nonexistent. For example, data from a secondary battery that experienced a sudden change in capacity, which appears to be due to a short circuit, is used to calculate x. It's preferable not to have it.

[0054] Furthermore, the space group of the crystal structure is identified by methods such as XRD, electron diffraction, and neutron diffraction. Therefore, in this specification, etc., belonging to a certain space group, belonging to a certain space group, To say that something is a space group can be rephrased as being identified as belonging to a certain space group.

[0055] Furthermore, in layered rock salt crystals and rock salt crystals, layers A, B, and C contain anions. However, if the structure is one in which the blocks are stacked with a slight offset from each other, like ABCABC, it is called a cubic close-packed structure. Let's assume that the anions do not have to be strictly cubic in shape. At the same time, real crystals are Because defects are inevitable, the analysis results may not necessarily conform to theory. For example, electron beam In FFT (Fast Fourier Transform) patterns such as folding patterns or TEM images, theoretically The spot may appear in a position slightly different from the theoretical position. For example, the azimuth from the theoretical position may be 5 degrees. If the temperature is below or below 2.5 degrees, it can be said that the structure is cubic close-packed.

[0056] Furthermore, homogeneity refers to a solid composed of multiple elements (e.g., A, B, C) in which one element (e.g., For example, A) refers to the phenomenon where similar characteristics are distributed in a specific region. The elemental concentrations only need to be substantially the same. For example, the difference in elemental concentrations between specific regions should be 10%. It is sufficient if it is within a certain range. Specific areas include, for example, the surface, the top, the protrusions, the recesses, and the interior. It can be listed.

[0057] The electrodes (positive electrode, negative electrode) consist of an active material layer and a current collector. The active material layer is provided on one side of the current collector. An electrode that has been coated on one side is called a single-sided coated electrode, and an electrode in which an active material layer is provided on both sides of the current collector is called a double-sided coated electrode. This is called a coated electrode. One embodiment of the present invention is an electrode and a method for manufacturing the same, which is a single-sided coated electrode and a double-sided coated electrode. This manufacturing method is applicable to any type of electrode.

[0058] Furthermore, positive electrode active materials with added elements are used as composite oxides, positive electrode materials, positive electrode components, and positive electrode materials for secondary batteries. It may be referred to as electrode material, etc. Also, in this specification, etc., positive electrode active material of one aspect of the present invention It is preferable that it has a compound. Also, in this specification, etc., a positive electrode activity of one aspect of the present invention The substance preferably has a composition. Furthermore, in this specification, etc., the correctness of one aspect of the present invention The extremely active material preferably has a complex structure.

[0059] As the charging voltage of a secondary battery increases, the voltage at the positive electrode generally increases. In one aspect of the present invention... The positive electrode active material has a stable crystal structure even at high voltages. The stable crystal structure of the material suppresses the decrease in charge / discharge capacity that occurs with repeated charging and discharging. It is possible.

[0060] (Embodiment 1) This embodiment describes an electrode according to one aspect of the present invention and a method for manufacturing the same.

[0061] [Laminated electrode 1] An electrode according to one aspect of the present invention will be described with reference to Figures 1A to 6D. The electrodes can be used as either the positive or negative electrode, or both. In the case of the positive electrode, active materials In the case of the negative electrode, a positive electrode active material is used as the active material, and in the case of the negative electrode, a negative electrode active material is used as the active material. As an active material used in one embodiment of the electrode, the active material shown in Embodiments 1 to 4 is It can be used.

[0062] Figures 1A, 5A, and 5A show schematic diagrams of electrodes having a laminated structure according to one aspect of the present invention, viewed from the side. This is shown in Figure 5B. Furthermore, the positive electrode active material of the positive electrode having a laminated structure according to one embodiment of the present invention is Particularly preferred examples are illustrated in Figures 1B, 2A to 2D, 3, and 4A to 4C. do.

[0063] As an example of a two-layer electrode according to one aspect of the present invention, electrode 400A is shown in Figure 1A. Electrode 40 0A has an active material layer 414 on the current collector 413, and the active material layer 414 is a first layer 414a The electrode has a two-layer structure, with the first layer 41 and the second layer 414b on the current collector 413. It has 4a, and has a second layer 414b on the first layer 414a. The first layer 414a is The first layer has an active material 411a, and the second layer 414b has a second active material 411b.

[0064] The particle size Ra of the first active material 411a in the first layer 414a is the same as that of the second layer 414b It is preferable that the particle size Rb of the second active material 411b is smaller than the particle size Rb. For example, the particle size is The particle size Ra of the first active material 411a in the first layer 414a is preferably 500 nm or less. The thickness is 5 μm or less, more preferably 1 μm or more and 5 μm or less. The second layer 414b has The particle size Rb of the second active material 411b is preferably 1 μm or more and 35 μm or less, more preferably The particle size is between 5 μm and 25 μm. Note that the particle size of the active material here refers to the particle size of the active material as measured by the aforementioned method. This refers to the median diameter of the active material, which can be measured using one of the following methods.

[0065] Here, the ratio of the sizes of the first active material 411a and the second active material 411b is defined as the particle size. The Rb / particle size Ra is preferably 2 or more and 15 or less, more preferably 3 or more and 10 or less, and further Preferably, it is 4 or more and 8 or less. The first active material 411a and the second active material 411b are on top of each other. Rapid charging and rapid discharging are possible when the relationships described below are met.

[0066] This is because the first active material 411a in the first layer 414a is possessed by the second layer 414b Because the particle size is smaller than that of the second active material 411b, the current collector 413 and the active material layer 414 As the number of contact points increases, the interfacial resistance between the current collector 413 and the active material layer 414 is reduced. Because it is possible to do so.

[0067] Although not shown in Figure 1A, the first layer 414a and the second layer 414b are later The conductive material and binder described above may be included. Or, the first layer 414a, and Layer 414b of layer 2 may contain a conductive material, a binder, and a solid electrolyte, as described later.

[0068] Here, the thickness of the first layer 414a is preferably 1 μm or more and 20 μm or less, more preferably The thickness is between 1 μm and 10 μm. This is because, as a function of the first layer 414a, the interface Reducing resistance is important, but the first active material 411a of the first layer 414a is In the active material layer 414, the particle size of the active material is small, which allows for efficient storage of lithium ions. Since the contribution at this point is low, it is preferable to reduce the thickness of the first layer 414a. That is the case.

[0069] The second active material 411b in the second layer 414b has the most grain size in the active material layer 414. This is a significant factor, and it tends to contribute greatly to the efficient storage of lithium ions. As will be described later in Figure 6, the large particle size active material combines with the small particle size active material and the medium particle size active material. When used together, it enables more efficient storage of lithium ions. The volumetric capacity density of the pole can be increased. Therefore, in the active material layer 414, the second The thickness of layer 414b is preferably 10 μm or more and 200 μm or less, more preferably 20 μm. The thickness is 150 μm or less. In the active material layer 414, the proportion occupied by the second layer 414b is high. To that extent, an electrode with a high volumetric density of 400A can be created.

[0070] In Figure 1A, etc., the first active material 411a and the like in the first layer 414a are shown in cross-section. For ease of understanding, the shape is schematically represented as a circle or a perfect circle. The cross-sectional shape of the active material may be a circle or a shape other than a perfect circle (such as a shape with irregularities, an ellipse, etc.). While this may occur, these shapes are also included in one aspect of the present invention.

[0071] [Positive electrode active material in a layered positive electrode structure] A particularly preferred example of the positive electrode active material in the positive electrode of a laminated structure according to one aspect of the present invention is shown in Figure 1B. The positive electrode active material 100 has a topotaxis region in its surface layer. AB in Figure 1B. Enlarged views of the vicinity are shown in Figures 2A and 2B. An enlarged view of the area around CD in Figure 1B is shown in Figure 2B. This is shown in Figures 2C and 2D. Here, the positive electrode active material 1 has a topotaxis region in its surface layer. Let's explain the example of 00.

[0072] Figure 1B shows the crystal planes parallel to the arrangement of cations, indicated by dotted lines. The arrows indicate lithium during charging and discharging. This indicates the direction of insertion and detachment of the ions. Note that the arrangement of cations referred to here is observed using STEM imaging, etc. This refers to the arrangement of cations other than lithium, which are easily found in transition metals M. A crystal plane parallel to the arrangement of cations is a crystal plane parallel to the direction in which lithium ions can diffuse. This is what is meant. Also, as shown in Figures 2A to 2D, the positive electrode active material 100 has a surface layer 10 It has an outer layer 100a and an inner layer 100b. In these figures, the outer layer 100a and the inner layer 100b are separated by dashed lines. The boundary is shown. Although not shown in the figure, the positive electrode active material 100 may also have grain boundaries.

[0073] In this specification, the surface layer 100a of the positive electrode active material 100 refers, for example, from the surface to the interior. Towards the interior, within 50 nm, more preferably within 35 nm from the surface, and further Preferably within 20 nm from the surface toward the interior, most preferably from the surface toward the interior This refers to an area within 10 nm. Surfaces formed by cracks and / or fissures are also considered surfaces. This is acceptable. The surface layer 100a is synonymous with the vicinity of the surface, the region near the surface, or the shell.

[0074] Furthermore, the region deeper than the surface layer 100a of the positive electrode active material is called the interior 100b. This is synonymous with the internal region or core.

[0075] Furthermore, the surface of the positive electrode active material 100 includes the surface layer 100a, the interior 100b, and the protrusions, etc. This refers to the surface of a composite oxide containing [the specified substance]. Therefore, the positive electrode active material 100 is chemically treated after its manufacture. It is assumed that adsorbed carbonates, hydroxyl groups, etc. are not included. Also, the electrons attached to the positive electrode active material 100 It is assumed that the solution, binder, conductive material, or compounds derived therefrom are not included. Also, cross-sectional STE The surface of the positive electrode active material 100 in M ​​(scanning transmission electron microscope) images, etc., is the electron beam coupling image. The boundary between the region where it is observed and the region where it is not observed, and where the atomic number is greater than lithium. This refers to the outermost region where bright spots originating from the nuclei of metallic elements are observed. (e.g., cross-sectional STEM images) Surfaces in this context can be analyzed using methods with higher spatial resolution, such as electron energy loss spectroscopy (E) Ectron Energy Loss Spectroscopy (EELS), etc. This can be judged in conjunction with the analysis results.

[0076] Furthermore, a grain boundary is, for example, the part where two positive electrode active materials 100 are fixed together, positive electrode active material 1 The part where the crystal orientation changes within 00, that is, the repetition of bright and dark lines in STEM images, etc. This refers to discontinuous areas, areas containing many crystal defects, areas with disordered crystal structures, etc. Crystal defects are defects that can be observed using cross-sectional TEM (transmission electron microscope), cross-sectional STEM images, etc. In other words, it refers to structures where other elements are interposed between the lattice, such as cavities. A grain boundary is a defect. This can be considered one of the pitfalls. Furthermore, the vicinity of a grain boundary refers to the region within 10 nm of the grain boundary. Let's assume that.

[0077] <epitaxy, topotaxy> The positive electrode active material 100 exhibits a continuous change in its crystal structure from the interior 100b toward the surface. Preferably, the crystal orientation of the surface layer 100a and the interior 100b is the same or roughly the same. It is preferable that the crystal orientations match or are roughly matched. The configuration may simply be described as having roughly matching crystal orientations. Or surface layer 10 It is preferable that 0a and internal 100b are topotaxy.

[0078] Topotaxis refers to a three-dimensional structural similarity in which the orientation of the crystals roughly matches. This also refers to having the same crystallographic orientation. Epitaxy is the structure of a two-dimensional interface. This refers to the similarity described above.

[0079] The surface layer 100a and the interior 100b are topotaxis, which causes distortion of the crystal structure, and Alternatively, it can reduce the misalignment of atoms, thereby suppressing the formation of pits. This is possible. Furthermore, because the surface layer 100a has added elements, the transition metal M and acid described later can interact. Suppresses displacement of the layered structure consisting of basic octahedrons, and / or from the positive electrode active material 100 Oxygen desorption can be suppressed. Therefore, charging at high voltage and charging / discharging in high-temperature environments. It is possible to create a positive electrode active material that does not degrade much even when subjected to electricity. In other words, topotaxis is formed in the surface layer. The positive electrode active material 100, having the above properties, does not deteriorate even when charged at high voltage and charged / discharged in high-temperature environments. It can also be described as a positive electrode active material with minimal oxidation. In this specification, a pit refers to a positive electrode active material. This refers to a hole that forms as a defect progresses in quality.

[0080] For example, from the interior 100b of a layered salt mold, a salt mold, or both a salt mold and a layered salt mold. It is preferable that the crystal structure changes continuously toward the characteristic surface and surface layer 100a. It is a rock salt type, or a surface layer 100a having characteristics of both rock salt type and layered rock salt type. It is preferable that the orientation of the layered rock salt-type inner portion 100b substantially matches.

[0081] In the present specification and the like, a composite oxide containing lithium and a transition metal M including cobalt has a layered rock salt-type crystal structure belonging to the space group R-3m, which refers to a crystal structure having a rock salt-type ion arrangement in which cations and anions are alternately arranged, wherein the transition metal M and lithium are each regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies of cations or anions may be present. Further, strictly speaking, the layered rock salt-type crystal structure may in some cases be a structure in which the lattice of a rock salt-type crystal is distorted.

[0082] Further, the rock salt-type crystal structure refers to a crystal structure having a cubic crystal system including the space group Fm-3m in which cations and anions are alternately arranged. Vacancies of cations or anions may be present.

[0083] Further, having both the characteristics of the layered rock salt-type and rock salt-type crystal structures can be determined by electron diffraction, TEM images, cross-sectional STEM images, and the like.

[0084] In the rock salt-type structure, there is no distinction between cation sites, whereas in the layered rock salt-type structure, there are two types of cation sites in the crystal structure: one is mostly occupied by lithium, and the other is occupied by the transition metal M. The laminated structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt-type and the layered rock salt-type. Among the bright spots in an electron diffraction pattern corresponding to the crystal plane forming this two-dimensional plane, when the central spot (transmitted spot) is taken as the origin 000, the bright spot closest to the central spot is for example, the (111) plane in an ideal rock salt-type structure, and for example, the (003) plane in an ideal layered rock salt-type structure. It forms a plane. For example, when comparing electron diffraction patterns of rock-salt-type MgO and layered rock-salt-type LiCoO2 , the bright spot on the (003) plane of LiCoO2 is observed at approximately half the distance of the bright spot on the (111) plane of MgO. Therefore, when the analysis region includes, for example, two phases of rock-salt-type MgO and layered rock-salt-type LiCoO2, in the electron diffraction pattern, there exists a plane orientation where high-intensity bright spots and low-intensity bright spots are alternately arranged. Bright spots common to both the rock-salt type and the layered rock-salt type have high intensity , while bright spots that only occur in the layered rock-salt type have low intensity.

[0085] In addition, in a cross-sectional STEM image or the like, when the crystal structure of the layered rock-salt type is observed from a direction perpendicular to the c-axis , layers observed with high intensity and layers observed with low intensity are alternately observed. The rock-salt type does not exhibit such characteristics because there is no distinction between cation sites. In the case of a crystal structure having characteristics of both the rock-salt type and the layered rock-salt type, when observed from a specific crystal orientation, in a cross-sectional STEM image or the like , layers observed with high intensity and layers observed with low intensity are alternately observed, and further, in the low-intensity layer, that is, a part of the lithium layer, a metal having an atomic number larger than that of lithium is present.

[0086] Anions in layered rock-salt-type crystals and rock-salt-type crystals have a cubic close-packed structure (face-centered cubic lattice structure ). It is presumed that the anions of the O3'-type crystal described later also have a cubic close-packed structure. Therefore, when a layered rock-salt-type crystal and a rock-salt-type crystal are in contact with each other, there exists a crystal plane in which the orientation of the cubic close-packed structure constituted by anions is aligned.

[0087] Alternatively, it can also be explained as follows. Anions on the {111} plane of a cubic crystal structure have a triangular lattice. The layered rock-salt type belongs to the space group R-3m and has a rhombohedral structure However, to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and is of the layered rock salt type (00 01) The plane has a hexagonal lattice. The triangular lattice of the cubic {111} plane is of the layered rock salt type (000 1) It has an atomic arrangement similar to the hexagonal lattice of the plane. The consistency between the two lattices is called the cubic lattice. It can be said that the orientation of the densely packed structure is aligned.

[0088] However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, and the space group of rock salt crystals is R-3m. Since it is different from the space group Fm-3m (the space group of typical rock salt crystals), it satisfies the above conditions. The Miller indices of the crystal planes differ between layered rock salt crystals and O3'-type crystals, and between rock salt crystals. The specification describes layered rock salt crystals, O3' type, and rock salt crystals as being composed of anions. When the orientations of the cubic close-packed structures are aligned, the crystal orientations are approximately the same, or topotaki When saying it is topotaxy or epitaxy There is a match. Furthermore, the crystal orientation is roughly consistent in the combination of the layered rock salt type and the rock salt type described above. This is not limited to that. It also applies to combinations with other crystal structures such as spinel and perovskite types. However, when the orientation of the cubic close-packed structure composed of anions is aligned, the crystal orientation is approximately one It can be said that it will be done.

[0089] The approximate agreement of the crystal orientations in the two regions is indicated by TEM (Transmission). Electron Microscope, Transmission Electron Microscope) image, STEM (Scann ing Transmission Electron Microscope, Scanning Transmission HAADF-STEM (High-angle Annular D High-angle scattering annular dark-field scanning transmission electron microscope (TEM) ) image, ABF-STEM (Annular Bright-Field Scanni ng Transmission Electron Microscope, annular bright-field scanni ng transmission electron microscope) images, electron diffraction patterns, FFT patterns of TEM images, STEM images and the like can be used for the judgment. XRD (X-ray Diffraction, X -ray diffraction), electron diffraction, neutron diffraction and the like can also be used as materials for the judgment.

[0090] FIG. 3 shows an example of a TEM image in which the orientations of a layered rock salt-type crystal LRS and a rock salt-type crystal RS substantially match . In a TEM image, STEM image, HAADF-STEM image, ABF-STEM image or the like , an image reflecting the crystal structure can be obtained.

[0091] For example, in a high-resolution TEM image or the like, contrast derived from crystal planes can be obtained. By means of electron beam diffraction and interference, for example, when an electron beam is incident perpendicularly to the c-axis of a composite hexagonal lattice of layered rock salt type , contrast derived from the (0003) plane is obtained as repetition of bright bands (bright strips ) and dark bands (dark strips). Therefore, repetition of bright lines and dark lines is observed in a TEM image, and when the angle between bright lines (for example, between L shown in FIG. 3 and L RS and L LRS ) is 0° or more and 5° or less, or 0° or more and 2.5° or less, it can be determined that the crystal planes substantially match , that is, the crystal orientations substantially match. Similarly, even when the angle between dark lines is 5° or less, or 2.5° or less, it can be determined that the crystal orientations substantially match . It is generally difficult to clearly distinguish the difference between "match" and "substantially match". Therefore, in the present specification, the term "match" refers to a case of complete matching . This includes cases where the angle between bright fringes is 0 degrees (for example) and cases where they are roughly the same. Let's assume that.

[0092] Furthermore, HAADF-STEM images provide contrast proportional to the atomic number, Elements with higher magnitudes appear brighter. For example, layered rock salts belonging to space group R-3m are observed brighter. In the case of lithium baltate, cobalt (atomic number 27) has the largest atomic number, therefore, The electron beam is strongly scattered at the position of the cobalt atom, and the arrangement of cobalt atoms becomes a bright fringe or a highly luminous fringe. It is observed as an array of points. Therefore, lithium cobaltate has a layered rock salt type crystal structure. When observed perpendicular to the c-axis, the arrangement of cobalt atoms perpendicular to the c-axis is either a bright line or a strong brightness. Observed as an array of dots, the arrangement of lithium atoms and oxygen atoms is seen as dark lines or areas of low brightness. It is observed as a region. Fluorine (atomic number 9) is used as an additive element in lithium cobalt oxide. The same applies when magnesium (atomic number 12) is present.

[0093] Therefore, in the HAADF-STEM image, bright and dark lines appear in two regions with different crystal structures. If the repetition of the above is observed, and the angle between bright fringes is 5 degrees or less, or 2.5 degrees or less, then the original The arrangement of the particles is roughly consistent, that is, the orientation of the crystals is roughly consistent. Yes, it is possible. Similarly, if the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, the crystal is also possible. It can be concluded that the orientations are roughly consistent.

[0094] In ABF-STEM, elements with smaller atomic numbers appear brighter, but the atomic number... Since it is similar to HAADF-STEM in that it can obtain appropriate contrast, HAAD The orientation of the crystal can be determined in the same way as with F-STEM images.

[0095] Figure 4A shows a STEM image where the orientations of layered rock salt crystals (LRS) and rock salt crystals (RS) are roughly consistent. An example is shown. The FFT of the region of rock salt crystal RS is shown in Figure 4B, and the FFT of the region of layered rock salt crystal LRS is shown. The FFT is shown in Figure 4C. The composition and JCPDS (Joint Co) are shown to the left in Figures 4B and 4C. mmittee on Powder Diffraction Standard) The card number, along with the calculated d-value and angle, are shown. The actual measured values ​​are shown on the right. Spots marked with O represent zero-order diffraction, and the center position of these spots is marked with X.

[0096] In Figure 4B, the spot labeled A originates from the 11-1 reflection of the cubic crystal. In Figure 4C, The spots marked A originate from layered salt deposits and 0003 reflection. Figures 4B and Figure From 4C, the orientation of 11-1 reflection for cubic crystals and the orientation of 0003 reflection for layered rock salt are roughly... It can be seen that they match. That is, the line passing through AO in Figure 4B and the line passing through AO in Figure 4C It can be seen that the line and are roughly parallel. Here, approximate coincidence and approximate parallelism mean that the angles are This refers to a temperature between 0 and 5 degrees Celsius, or between 0 and 2.5 degrees Celsius.

[0097] Thus, in FFT and electron diffraction, the orientation of layered rock salt crystals and rock salt crystals is roughly one When doing so, the layered rock salt type has a <0003> orientation and the rock salt type has a <11-1> orientation, roughly They may coincide. In this case, these reciprocal lattice points are spot-like, that is, other It is preferable that the reciprocal lattice points are not continuous with other reciprocal lattice points. The fact that it is not continuous means that it has high crystallinity.

[0098] Furthermore, as mentioned above, the 11-1 reflection orientation of cubic crystals and the 0003 reflection orientation of layered rock salt types If these roughly coincide, depending on the direction of incidence of the electron beam, layered rock salt type 0003 reflection may occur. Spots not originating from layered salt-type 0003 reflections can be observed in a reciprocal lattice space that differs from the orientation of layered salt rock. It can be measured. For example, the spot marked B in Figure 4C is a layered salt-type 10¹⁴ reflector. This originates from the reciprocal lattice point (A in Figure 4C) of the layered salt rock type 0003 reflection. The angle from the direction of ) is between 52° and 56° (i.e., ∠AOB is between 52° and 56°). (It is less than or equal to °), and d may be observed in locations between 0.19 nm and 0.21 nm. Note that this index is just one example and does not necessarily have to match it. For example, each Equivalent reciprocal lattice points in this location are also acceptable.

[0099] Similarly, in a different reciprocal space from the spot where cubic 11-1 reflections were observed, cubic 11-1 Spots that are not of the origin of reflection may be observed. For example, in Figure 4B, the spot labeled B The spot originates from the 200 reflection of the cubic crystal. This is due to the 11-1 of the cubic crystal. The angle from the direction of the previous reflection (A in Figure 4B) is between 54° and 56° (i.e., ∠A Diffraction spots may be observed at locations where the out-of-bounds (OB) angle is between 54° and 56°. This Miller index is just an example and does not necessarily have to match it. For example, each Equivalent reciprocal lattice points in this location are also acceptable.

[0100] Furthermore, layered rock salt type cathode active materials, including lithium cobalt oxide, have a (0003) face. And the equivalent plane thereof, as well as the (10-14) plane and its equivalent plane, appear as crystal planes. It is known to be prone to deformation. Therefore, the shape of the positive electrode active material should be carefully observed using an SEM or similar device. Therefore, in order to make the (0003) plane easier to observe, for example, an electron beam is used in a TEM, etc. [12- 10] It is possible to thin-section the observation sample using FIB or similar methods so that it becomes the incident light. If you want to determine the consistency of the orientation, the (0003) plane of layered rock salt is easy to observe. It is preferable to thin it into flakes.

[0101] The electrode 400A shown in Figure 1A is a positive electrode active material 1 having a topotaxis region in its surface layer. It is preferable to have 00. That is, the first active material 411a and the second active material 411 b, either one or both, is a positive electrode active material 100 having a topotaxis region in its surface layer. It is preferable that it has

[0102] As described above, the positive electrode having a laminated structure according to one aspect of the present invention has a topotaxis region in the surface layer. It is preferable to have a positive electrode active material 100 having a region. For example, a composite oxide having additive elements can be used as the positive electrode active material 100. Details of the composite oxide having additive elements will be described in Embodiment 2. This section provides an overview of composite oxides containing additive elements and explains their use as positive electrodes in multilayer structures. do.

[0103] Composite oxides having additive elements obtained by the manufacturing methods shown in Embodiments 2 and 3 It has crystals with a hexagonal layered structure, and the crystals are not limited to single crystals (also called crystallites). In the case of polycrystalline materials, several crystallites come together to form primary particles. Primary particles are, This refers to a particle that is recognized as a single particle during SEM observation. Furthermore, a secondary particle is a primary particle. This refers to a clump of particles that have aggregated. The aggregation of primary particles does not depend on the binding forces acting between multiple primary particles. No. Covalent bonds, ionic bonds, hydrophobic interactions, van der Waals forces, and other intermolecular forces. It could be any one interaction, or multiple binding forces could be at work.

[0104] When producing a composite oxide using the manufacturing method shown in Embodiment 2, a non-aggregating primary oxide is produced. Although they often form particles, secondary particles have a small number of primary particles (e.g., fewer than 10). This may be formed. As shown in Figures 2A to 2D, the manufacturing method shown in Embodiment 2 The composite oxide produced using this method preferably has additive elements in its surface layer. The additive elements in the surface layer include nickel, cobalt, magnesium, calcium, Chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium Um, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron One or more of the following can be used: , and arsenic. Also, as additive elements It is preferable that it has one or more selected from bromine and beryllium. However, Bromine and beryllium are elements that are toxic to living organisms, as mentioned earlier. It is preferable to use additive elements.

[0105] As a composite oxide having additive elements, for example, lithium cobalt oxide containing magnesium. , lithium cobalt oxide containing magnesium and fluorine, magnesium and aluminum Lithium cobalt oxide, magnesium, aluminum, and fluorine are cobalt having Lithium cobalt oxide having lithium oxide, magnesium, aluminum, and nickel, lithium cobalt oxide containing magnesium, aluminum, nickel and fluorine, lithium cobalt oxide containing magnesi um, aluminum, nickel and barium, and lithium cobalt oxide containing magn esium, aluminum, nickel, barium and fluorine, and the like, the composite oxide shown in Embodiment 2 can be used.

[0106] When a composite oxide is produced by the coprecipitation method shown in Embodiment 3, secondary particles having a large number (for example, 10 or more) of primary particles may be formed.

[0107] The crystal having the above hexagonal layered structure contains a first transition metal, a second transition metal and a third one or more selected from among transition metals. Specifically, the first transition metal is nicke l, the second transition metal is cobalt, the third transition metal is manganese, and LiN i x Co y Mn z O₂ (x>0, y>0, 0.8<x+y+z<1.2) represented Ni CoMn system (also referred to as NCM) can be used. Specifically, for example, 0.1x<y <8x and 0.1x<z<8x are preferably satisfied. As an example, x, y and z preferably satisfy x:y:z=1:1:1 or a value in the vicinity thereof. Alternatively, as an example , x, y and z preferably satisfy x:y:z=5:2:3 or a value in the vicinity thereof. Alternatively, as an example, x, y and z preferably satisfy x:y:z=8:1:1 or a value in the vicinity thereof. Alternatively, as an example, x, y and z satisfy x:y:z=9:0 .5:0.5 or a value in the vicinity thereof is preferably satisfied. Alternatively, as an example, x, y and It is preferable that x:y:z = 6:2:2 or a value in its vicinity. For example, x, y, and z satisfy the value x:y:z=1:4:1 or a value in its vicinity. This is preferable.

[0108] Furthermore, the composite oxide having the additive elements obtained by the above method is a first transition metal, a second transition metal In addition to transition metals and third transition metals, magnesium, aluminum, and calcium may be used as needed. Zium, zirconium, vanadium, chromium, iron, copper, zinc, gallium, germanium, It consists of strontium, yttrium, niobium, molybdenum, tin, barium, and lanthanum. The group may include one or more selected elements. Charging and discharging of a secondary battery using the above positive electrode active material. From the standpoint of improving the capacity retention rate after the electric cycle, magnesium, calcium, aluminum, and It is preferable to include one or more elements selected from among zirconium.

[0109] Next, another example of an electrode having a laminated structure according to one aspect of the present invention will be described. In Figure 1A, As an example of an electrode having a laminated structure according to one aspect of the present invention, a two-layer electrode is shown. As another example of an electrode having a laminated structure according to one aspect of the present invention, a three-layer electrode is provided in the lateral direction A schematic diagram is shown in Figure 5A. The electrode 400B with a three-layer structure according to one aspect of the present invention is a current collector 41 3 has an active material layer 414 on top, and the active material layer 414 is a first layer 414a, a second layer 414b The active material layer 414 has a first layer 414a and a third layer 414c. A second layer 414b is located on 414a, and a third layer 414c is located on the second layer 414b. The first layer 414a has the first active material 411a, and the second layer 414b has the second active material 4 The electrode shown in Figure 1A has 11b, and the third layer 414c has the third active material 411c. Similar to 400A, electrode 400B shown in Figure 5A has a topotaxis region in its surface layer. It is preferable to have a positive electrode active material 100. That is, a first active material 411a, a second active One or more of substance 411b and the third active material 411c are topotaxis in the surface layer It is preferable to have a positive electrode active material 100 having a certain region.

[0110] The particle size Ra of the first active material 411a in the first layer 414a is the same as that of the second layer 414b It is preferable that the particle size Rb of the second active material 411b is smaller than the particle size Rb of the third layer 41 The particle size Rc of the third active material 411c possessed by 4c is the same as the second active material possessed by the second layer 414b. It is preferable that the particle size Rb of quality 411b is smaller. For example, the particle size of the first layer 414 The particle size Ra of the first active material 411a possessed by a is preferably 500 nm or more and 5 μm or less. More preferably, it is 1 μm or more and 5 μm or less. The second active material 4 of the second layer 414b The particle size Rb of 11b is preferably 1 μm or more and 35 μm or less, more preferably 5 μm or more. It is 5 μm or less. The particle size Rc of the third active material 411c in the third layer 414c is preferred. More preferably, it is between 500 nm and 5 μm, and more preferably between 1 μm and 5 μm. Here, the particle size of the active material is the particle size that can be measured using any of the measurement methods described above. This refers to the median diameter of a substance.

[0111] Here, the ratio of the sizes of the first active material 411a and the second active material 411b is defined as the particle size. The Rb / particle size Ra is preferably 2 or more and 15 or less, more preferably 3 or more and 10 or less, and further Preferably, it is between 4 and 8. Also, the third active material 411c and the second active material 411b As the size ratio, particle size Rb / particle size Rc is preferably 2 or more and 10 or less, more preferably The value is between 3 and 5.

[0112] Although not shown in Figure 5A, the first layer 414a, the second layer 414b, and the third layer 4 14c may include a conductive material and a binder, as described later. Or, the first layer 41 4a, the second layer 414b, and the third layer 414c are conductive materials, binders, and, as described later, It may contain a solid electrolyte.

[0113] The first active material 411a is present in the first layer 414a, and the second active material is present in the second layer 414b The substance 411b and the third active material 411c of the third layer 414c are related as shown above. If the conditions are met, rapid charging and rapid discharging become possible.

[0114] This is because the first active material 411a in the first layer 414a is possessed by the second layer 414b Because the particle size is smaller than that of the second active material 411b, the current collector 413 and the active material layer 414 As the number of contact points increases, the interfacial resistance between the current collector 413 and the active material layer 414 is reduced. Because it is possible to do so.

[0115] Here, the thickness of the first layer 414a is preferably 1 μm or more and 20 μm or less, more preferably The thickness is preferably 1 μm or more and 10 μm or less. This is because the first layer 414a As a function, it is important to reduce the interfacial resistance, but the first active of the first layer 414a In substance 411a, the particle size of the active material is small in the active material layer 414, and the lithium ion efficiency is Since its contribution to storage is low, the thickness of the first layer 414a is reduced. This is because it is preferable.

[0116] In addition, Figure 5A, etc., shows a cross-section of the first active material 411a, etc., of the first layer 414a. For ease of understanding, the shape is schematically represented as a circle or a perfect circle. The cross-sectional shape of the active material may be a circle or a shape other than a perfect circle (such as a shape with irregularities, an ellipse, etc.). While this may occur, these shapes are also included in one aspect of the present invention.

[0117] Next, we will explain the relationship between the second layer 414b and the third layer 414c. c is farther from the current collector 413 than the first layer 414a and the second layer 414b. Therefore, the electronic resistance is high, the relative potential becomes low, and the rate of the battery reaction tends to decrease. For example, unlike the electrode structure of one aspect of the present invention, the third active material 4 of the third layer 414c If 11c and the second active material 411b of the second layer 414b have similar particle sizes, In the case of a region far from the current collector 413 (a position corresponding to the third layer 414c), This slows down the battery reaction, causing uneven reaction in the active material layer 414, and as a result, rapid charging... Furthermore, rapid discharge can reduce the charge and discharge capacity.

[0118] Here, in the electrode structure of one aspect of the present invention described above, the third layer 414c has The third active material 411c has a particle size that is larger than the second active material 411b in the second layer 414b. Because it is small, the rate of the battery reaction in the third layer 414c is lower than the rate of the battery reaction in the second layer 414b. The rate of the battery reaction increases during rapid charging and rapid discharging. This makes it possible to reduce reaction unevenness in layer 414, and as a result, rapid charging and Even when rapid discharge is performed, the reduction in the chargeable and dischargeable capacity is suppressed. This becomes possible.

[0119] The second active material 411b in the second layer 414b has the most grain size in the active material layer 414. This is a significant factor, and it tends to contribute greatly to the efficient storage of lithium ions. As will be described later in Figure 6, the large particle size active material combines with the small particle size active material and the medium particle size active material. When used together, it enables more efficient storage of lithium ions. The volumetric capacity density of the pole can be increased. Therefore, in the active material layer 414, the second The thickness of layer 414b is preferably 10 μm or more and 200 μm or less, more preferably 20 μm. Preferably, the thickness is 150 μm or less. In the active material layer 414, the second layer 414b The higher the proportion of this component, the higher the volumetric density of the electrode 400B can be.

[0120] The presence of a third layer 414c reduces unevenness in the battery reaction in the active material layer 414. This enables rapid charging and rapid discharging. At this time, the thickness of the third layer 414c Furthermore, preferably 1 μm to 20 μm, more preferably 1 μm to 10 μm. That is the case.

[0121] As described above, in Figure 5A, the first layer 414a, the second layer 414b, and the third layer 4 An electrode 400B having a 3-layer laminated structure of 14c is shown. A third aspect of the present invention is shown. The structure of the electrode having layer 414c is not limited to the three-layer structure described above. For example, see Figure 5B. As shown, a two-layer laminated structure having a second layer 414b and a third layer 414c It may also be an electrode 400C. Even with electrode 400C, with respect to electrode 400B As explained above, the relationship between the second layer 414b and the third layer 414c enables rapid charging, and Rapid discharge becomes possible.

[0122] Next, regarding the second active material 411b of the second layer 414b, see Figures 6A to 6D. I will use it to explain.

[0123] The second active material 411b in the second layer 414b has the most grain size in the active material layer 414. This is significant and contributes greatly to the efficient storage of lithium ions. Here, the second is Ideally, layer 414b should have a dense structure, as shown in Figure 6A. However, in reality, the structure often has gaps, as shown in Figure 6B. Therefore, Figure 6 As shown in C, in addition to the large particle size second active material 411b, there is a small particle size fourth active material 411 If d is present, a structure is formed in which the fourth active material 411d is between the particles of the second active material 411b. It is easy to remove, and as a result the density of the second layer 414b increases. Also, as shown in Figure 6D, In addition to the second active material 411b of particle size, there is a fourth active material 411d of small particle size, and a medium particle size If a fifth active material 411e is present, the fourth active material 4 A structure having 11d and the fifth active material 411e is easily formed, resulting in the second layer 414b The density will increase.

[0124] Here, by pressing the second layer 414b-2 shown in Figure 6B, the density becomes higher than that of Figure 6B. It is possible to make the second layer 414b with high strength, but it is possible to exceed the strength of the second active material 411b. There is a problem that the second active material 411b cracks when excessive pressure is applied. Therefore, if the sphericity of the second active material 411b is high, even if pressed with higher pressure, the second active Material 411b is resistant to cracking. In other words, it is easy to obtain a high-density second layer 414b. Therefore It is preferable that the second active material 411b has a high degree of sphericity.

[0125] <Sphericity> The sphericity of the active material refers to the sphericity of the active material particles, that is, how perfectly spherical the shape of the active material particles is. This is a numerical value that indicates how close it is to the actual sphericity. For example, the median diameter D50±50% is used to determine sphericity. After processing for cross-sectional observation, particles having a particle size of L are subjected to cross-sectional observation, and the perimeter length L of the particle cross-section is measured. By measuring the area S of the particle cross-section, the sphericity (SP) can be calculated using the following formula. can.

[0126]

number

[0127] Spheres of the first active material 411a, the second active material 411b, and the third active material 411c Preferably, the degree is 0.6 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less. Most preferably, it is between 0.9 and 1.0.

[0128] Furthermore, as shown in Figures 6C and 6D, along with the large-particle second active material 411b , using a fourth active material 411d with a small particle size and / or a fifth active material 411e with a medium particle size In the second active material 411b, pressing further increases the density of the second layer 414b. This becomes possible. In this case as well, as mentioned above, the active material has high sphericity. It is preferable that the fourth active material 411d has a small particle size, and the fifth active material has a medium particle size. The sphericity of quality 411e is preferably 0.6 or more and 1.0 or less, more preferably 0.8. The value is 1.0 or less, most preferably 0.9 or more and 1.0 or less.

[0129] <Particle size> In the second layer 414b, the particle size of the second active material 411b is greater than that of the fifth active material 411e. It is preferable that the particle size of the fifth active material 411e is larger than that of the fourth active material 411d. i. The particle size of the active material in the second layer 414b is, for example, the particle size of the second active material 411b. As mentioned above, the diameter is preferably 1 μm or more and 35 μm or less, more preferably 5 μm or more and 25 μm or less. The particle size of the fourth active material 411d in the second layer 414b is preferably μm or less. The second is 500 nm to 5 μm, more preferably 1 μm to 5 μm. The particle size of the fifth active material 411e in layer 414b is preferably 1 μm or more and 20 μm or less. More preferably, the particle size is between 5 μm and 15 μm.

[0130] The second layer 414b consists of a second active material 411b (large particle size) and a fourth active material 411d (small particle size). If the diameter is such that the ratio of the mass of the second active material 411b and the fourth active material 411d is If we express the ratio of the second active material 411b to the fourth active material 411d as 1:Ma, then Ma is preferably The second layer is 0.05 or more and 0.5 or less, more preferably 0.1 or more and 0.4 or less. 414b is composed of the second active material 411b (large particle size) and the fourth active material 411d (small particle size). When a fifth active material 411e (medium particle size) is present, the second active material 411b and the fourth active material The ratio of mass between substance 411d and the fifth active substance 411e is the ratio of mass between the second active substance 411b and the fourth active substance If we represent substance 411d as the fifth active material 411e = 1:Mb:Mc, then Mb is greater than or equal to 0.1. It is preferably 5 or less, and Mc is between 0.1 and 0.5.

[0131] The above examples show electrodes with a two-layer structure and electrodes with a three-layer structure, but what about four or more layers? It may also be an electrode having small particle size active A layer containing material (first layer 414a) and a layer containing large-particle active material (second layer 414b) ) and a layer having a medium-particle active material may be provided between them. Also, the three-layer structure shown in Figure 5A In the electrode, a layer having a small particle size active material (first layer 414a) and a layer having a large particle size active material It has a layer (second layer 414b) and a layer between it that has medium-sized active material, and a large-sized active material A layer containing material (second layer 414b) and a layer containing small particle size active material (third layer 414c The electrode may have a five-layer structure, with a layer containing a medium-particle active material between the two layers.

[0132] When a composite oxide having the above-mentioned additive elements is used as the positive electrode of a laminated structure according to one aspect of the present invention In this, the first active material 411a is present in the first layer 414a, and the second layer 414b is present in The second active material 411b and the third active material 411c contained in the third layer 414c They may have the same type (and combination) of additive elements, but they may also be different. i. Also, the first active material 411a in the first layer 414a and the second active material 414b in the second layer 414b The second active material 411b and the third active material 411c contained in the third layer 414c These may have the same concentration of additive elements, or they may be different.

[0133] For example, the second active material 411b of the second layer 414b contains magnesium, aluminum Using lithium cobalt oxide having um and nickel, the third layer 414c has the third The active material 411c is lithium cobalt oxide containing magnesium, and the structure is as follows: It is possible.

[0134] Furthermore, for example, the first active material 411a and the third layer 414c of the first layer 414a The concentration of the additive element in the third active material 411c possessed by the second layer 414b is the same as the concentration of the additive element in the third active material 411c possessed by the second layer 414b The concentration can be higher than that of the additive elements present in the active material 411b of 2.

[0135] In the example above, the active material in the active material layer 414 was described, but the active material layer 414 is later It may have one or more of the conductive materials, binders, and solid electrolytes described below. Furthermore, the active material of the active material layer 414 is the positive electrode described in Embodiments 2 to 4. An active material and a negative electrode active material can be used.

[0136] [Method for fabricating a layered electrode 1] An example of a method for manufacturing electrodes according to one aspect of the present invention will be explained with reference to Figures 7 to 10.

[0137] In Figure 7, the first layer 414a is fabricated in steps S11 to S21. In steps S21 to S31, a second layer 414b is fabricated, and in step S3 An example of an electrode fabrication method is shown, in which a third layer 414c is fabricated in steps 1 to S41. In Figure 7, the mixture 501 prepared in step S12 and the mixture prepared in step S22 As a method for preparing mixture 502 and mixture 503 prepared in step S32, see Figure 8B. Any of the manufacturing methods shown in Figures 9A, 9B, and 10 can be used, and multiple manufacturing methods can be used. It is also possible to use a combination of laws.

[0138] In step S11 of Figure 7, the current collector is prepared. Also, in step S12, Prepare the 501 blend.

[0139] Next, in step S13 of Figure 7, the mixture 501 is applied to the current collector. For example, metals such as stainless steel, gold, platinum, aluminum, titanium, and their alloys, Highly conductive materials can be used. Also, the material used for the positive electrode current collector is at the positive electrode potential. It is preferable that it does not leach. As for the coating method in step S13, a slot die method, Labia, blade, and combinations thereof can be used. A continuous coating machine may be used for coating. Following step S13, in step S14... Then, the mixture 501 applied to the current collector is dried. As a drying method, for example, hot water Batch-type dryers such as plate dryers, drying ovens, forced-air dryers, and vacuum dryers, as well as hot-air dryers. Continuous systems, such as those combining infrared drying with a continuous coating machine, can be used. After that, the coated electrode 511 of step S21 is obtained.

[0140] Here, as shown in Figure 7, after drying in step S14, pressing takes place as step S15. This can be done. Pressing methods include flat plate pressing, hydrostatic pressing, and roll pressing. Any pressing method can be used. When using a roll press, for example, the active material layer The temperature is set to between 10°C and 200°C, preferably between 80°C and 150°C. It is preferable that the temperature of the water is regulated.

[0141] Next, in step S22 of Figure 7, the mixture 502 is prepared.

[0142] Next, in step S23 of Figure 7, the mixture 502 is applied to the coating electrode 511, and then In step S24, the mixture 502 applied to the coated electrode 511 is dried. Therefore, the application method in step S23 is the method described in the explanation of step S13. Yes, it is possible. Furthermore, the drying method in step S24 may be the method described in the explanation of step S14. It can be there. After drying, the coated electrode 512 of step S31 is obtained.

[0143] Here, as shown in Figure 7, after drying in step S24, pressing is performed as step S25. This can be done. As a pressing method, use the method described in the explanation of step S15. It is possible.

[0144] Next, in step S32 of Figure 7, the mixture 503 is prepared.

[0145] Next, in step S33 of Figure 7, the mixture 503 is applied to the coating electrode 512, and then In step S34, the mixture 503 applied to the coated electrode 512 is dried. Therefore, the application method in step S33 is the method described in the explanation of step S13. Yes, it is possible. Furthermore, the drying method in step S34 may be the method described in the explanation of step S14. It can be done. After drying, the coated electrode 513 of step S41 is obtained.

[0146] Here, as shown in Figure 7, after drying in step S34, pressing is performed as step S35. This can be done. As a pressing method, use the method described in the explanation of step S15. It is possible to perform all of steps S15, S25, and S35. It is preferable that, for example, one of steps S15, S25, and S35 Alternatively, if the density of the active material layer 414 can be increased without performing step S15, step S Step 25 and one or two of step S35 may be omitted.

[0147] The manufacturing process described above produces the first layer 414a, the second layer 414b, and the third layer An electrode 400B having layer 414c can be fabricated. In the manufacturing method, by completing the electrode fabrication in step S31, the first layer 414a, and electrode 400A having a second layer 414b, and the second layer 414b, and third An electrode 400C having a layer 414c can be fabricated.

[0148] In Figures 8 to 10, mixture 501, mixture 502, and mixture 501, as shown in Figure 7, are shown in Figure 7. A method for preparing a mixture that can be used as 03 is shown.

[0149] As step S101 in Figure 8A, prepare the binder 110, and as step S102 Prepare the dispersion medium 120.

[0150] For example, as binder 110, polystyrene, methyl polyacrylate, polymethacrylate Methyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polymethyl Nyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide Polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene Pyrene, polyisobutylene, polyethylene terephthalate, nylon, polyvinyl fluoride Den (PVDF), polyacrylonitrile (PAN), ethylene propylene diem polymer - Use one or more of the following materials: polyvinyl acetate, nitrocellulose, etc. This can be done. For example, the dispersion medium 120 can be water, methanol, ethanol, acetone, tetraethanol. Lahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone ( One or more of the following: NMP and dimethyl sulfoxide (DMSO) A suitable combination of the binder 110 and the dispersion medium 120 is: A combination of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) It is preferable to use a binder. Details of the binder will be described later.

[0151] Next, in step S103, the binder 110 and the dispersion medium 120 are mixed, and step A binder mixture 1001 of p S104 is obtained. As a mixing method, for example, a propeller type mixing A mixing device, a planetary rotating mixing device, or a thin-film swirling mixing device can be used. The binder mixture 1001 is in a state in which the binder 110 is well dispersed in the dispersion medium 120. It is desirable that this be the case.

[0152] As step S111 in Figure 8B, prepare the binder mixture 1001, and step S11 2. Prepare conductive material 1002. This will be used to knead the mixture in a later step. The amount of binder mixture 1001 prepared in step S111 is such that it forms the positive electrode active material layer. By preparing a smaller amount than the total amount needed, it is possible to achieve a mixing ratio suitable for solid kneading. In this case, any deficiency in binder mixture 1001 can be added in the step after the kneading stage. Furthermore, "solid kneading" refers to mixing using a high viscosity.

[0153] Examples of conductive material 1002 include acetylene black and furnace black. Graphite such as carbon black, artificial graphite, and natural graphite, carbon nanofibers, etc. One of the following: carbon fibers such as carbon nanotubes, or graphene compounds. Alternatively, two or more types may be used. Details of conductive materials will be described later.

[0154] In this specification, graphene compounds refer to multilayer graphene, multigraphene, and oxidized graphene. Graphene, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, Includes reduced multilayer graphene oxide, reduced multilayer graphene oxide, etc. Graphene A compound is a compound that contains carbon, has a shape such as a flat plate or sheet, and is formed by a 6-membered carbon ring. This refers to a structure having a dimensional structure. A bent shape is also preferable. The carbon 6-membered The two-dimensional structure formed by the ring can be called a carbon sheet. Graphene compounds have functional groups. It is preferable to have it. Also, the graphene compound rolls up like carbon nanofibers. It may be as follows. Details of the graphene compound will be described later.

[0155] Next, in step S121, the binder mixture 1001 and the conductive material 1002 are Mix to obtain mixture 1010 of step S122. As a method of mixing, for example, propeller Mixing devices such as a type-based mixing device, a planetary rotating mixing device, or a thin-film swirling mixing device may be used. can.

[0156] Next, in step S123 of Figure 8B, the active material 10 is prepared. For example, in Figure 8B When the mixture 1030 to be prepared is used to prepare the first layer 414a, the active material 10 is the The active material 411a is used. Also, the mixture 1030 prepared in Figure 8B is the second When used to fabricate layer 414b, the second active material 411b is used as the active material 10. When the mixture 1030 prepared in Figure 8B is used to prepare the third layer 414c, The third active material 411c is used as material 10.

[0157] Next, in step S131, the mixture 1010 and the active material 10 are mixed, and in step S A mixture of 132 and 1020 is obtained. As a mixing method, for example, a propeller-type mixing device, a planetary mixing device, etc. A rotary mixing device or a thin-film swirling mixing device can be used. Step S In the mixing of 131, it is preferable to perform kneading at high viscosity (sometimes called solid kneading). By mixing with high viscosity, the aggregation of powders such as active materials can be undone.

[0158] Next, prepare the binder mixture 1001 in step S133 and disperse it in step S134. Prepare the medium 1003. In step S111, the total amount necessary to form the active material layer If you have prepared a smaller amount of binder mixture 1001 than the total volume, then in step S132 The deficiency of the binder mixture 1001 can then be added. If the entire amount of the necessary binder mixture 1001 was prepared in step S111, then step It is not necessary to prepare the binder mixture 1001 in step S133. As the dispersion medium 1003, see Figure 8. A dispersion medium similar to that used in step S102 of A can be used. The amount of dispersion medium 1003 is... It is desirable to adjust the amount prepared so that it has the appropriate viscosity for application in step A.

[0159] Next, in step S141, the mixture 1020 from step S132 and step S 134 dispersion medium 1003 and the binder mixture 1001 prepared in step S133, Mixing is performed to obtain the mixture 1030 of step S142. The mixture 1030 is sometimes called the positive electrode slurry. Also, the negative electrode active material is used as the active material. When used, mixture 1030 is sometimes referred to as the negative electrode slurry.

[0160] In Figure 9A, the electrode fabrication method is simplified, and the binder mixture 1001 and conductive material 1002 are used. The example shows the mixing of the active material 10 and the active material 10 all at once in step S121. Figure 9A shows the step Depending on the mixing method of step S121, the mixing method of step S131, and the amount of dispersion medium 1003 For steps such as adjusting the viscosity of mixture 1031, use the method described in the explanation of Figure 8B. It is possible.

[0161] Figure 9B shows an example of a method for preparing a mixture 1032 having two types of active materials 10. In step S123, the active material 10a is prepared, and in step S124, the active material 10b is prepared Prepare, and in step S131, mix 1010, active material 10a, and active material 10b Mixture 1032 is prepared in the same manner as shown in Figure 8B, except for the mixing step. This can be done. Figure 9B shows an example using two types of active material 10, but the active material 10a is It is also acceptable to use three types, including active material 10c in addition to active material 10b. Furthermore, four or more types are also acceptable. It may contain an active material.

[0162] In Figure 9B, the mixture 1010, active material 10a, and active material 10b are added in step S131. In the example shown, mixing was done at once, but as shown in Figure 10, active material 10a and active material 10 You may mix b and beforehand.

[0163] [Calculations regarding electrode 1 in a layered structure] A calculation relating to an example of an electrode according to one aspect of the present invention will be explained with reference to Figures 11 to 15. ru.

[0164] Figure 11 shows a schematic diagram of the structural model used in the calculations. Figure 11 contains a collection of diagrams for clarity. The term "current collector" is used, but the calculation does not include the current collector. Furthermore, the experiment was conducted using structures in the range of d=0μm to d=120μm. Note that d is positive The electrode current collector (current collector 1) and the positive electrode active material layer (positiv From the interface with the e electrode active material layer This indicates the distance in the direction of the negative electrode current collector (current collector 2). The interface between the positive electrode current collector and the positive electrode active material layer is d=0μm, and the positive electrode active material layer and the separator The interface position with the separator is d=50μm, and the separator and the negative electrode active material layer (negative electrode active material lay The interface position with r) is d = 70 μm, and the interface position between the negative electrode active material layer and the negative electrode current collector is d =120μm. Here, from d=0μm to d=50μm, the particle size, void ratio, Figures 12A to 12A show the calculation settings profile for Model A, where the volume ratio of the active material is kept constant. This is shown in 12C. Also, Model B has a three-layer structure from d=0μm to d=50μm. The calculation settings profiles are shown in Figures 12D to 12F.

[0165] In Model A, the particle size of the active material in the positive electrode active material layer was kept constant at 20 μm. In Model B, It was made into a three-layer structure. In Model B, from d=0μm to d=120μm, the first The layers are arranged in the order of the first layer, the second layer, and the third layer, with the particle size of the active material in the first layer being 5 μm, and the particle size of the active material in the second layer being 5 μm. The particle size was set to 20 μm, and the particle size of the third layer was set to 5 μm. The separator film thickness was 20 μm. The negative electrode active material layer was subjected to the same conditions in Model A and Model B (film thickness 50 μm, active material). A particle size of 1 μm was used. The calculation conditions for charge and discharge current were 0.1C, 1C, 2C, and 3C. The calculations were performed using 4C and 5C.

[0166] In the computational structure model shown in Figures 11 and 12A to 12F, charging and discharging We performed calculations on the voltage-capacitance curve. The calculations for the charge-discharge simulation were performed as follows: The calculation was performed using PyBaMM (version 0.4.0). The DFN (Doyle-Fuller-Newman) model included with M was used. The dataset used is a modified version of Marquis2019, which is included with PyBaMM. Ta.

[0167] As a result of the charge-discharge simulation, the calculated discharge curves are shown in Figures 13A to 14C. Figure 13A shows the discharge curve at 0.1C, and Figure 13B shows the discharge curve at 1C. Figure 13C shows the discharge curve at 2C, and Figure 14A shows the discharge curve at 3C. Figure 14B shows the discharge curve at 4C, and Figure 14C shows the discharge curve at 5C. - It is. In the calculation under these conditions, as shown in Figure 13A, the discharge rate is low. Under certain conditions (low discharge current), the capacity of Model A is greater than that of Model B, which has a three-layer structure. Despite the high results, the discharge rate shown in Figure 14C is high under the conditions (high discharge current). Under certain conditions, the relationship is reversed, and the capacity of the three-layer structure of Model B is greater than that of Model A. The calculation result showed that the quantity was higher. Figure 15 shows the discharge energy for these results. The relationship between - and C rate is summarized below. As shown in the above calculations, one aspect of the present invention The electrode with the layered structure described above is expected to be suitable for rapid charging and rapid discharging.

[0168] [Laminated electrode structure 2] Another embodiment of the electrode according to the present invention will be described with reference to Figures 16 to 21.

[0169] Figure 16A shows the three-layer electrode 400B shown in Figure 5A, with the conductive material 415 evenly distributed on it. This is a schematic diagram showing electrode 400D in the case of [the specified configuration]. Also, Figure 16B shows the three-layer structure shown in Figure 5A. Electrode 4 when conductive material 415 and solid electrolyte 421 are evenly distributed on electrode 400B This is a schematic diagram showing 00E. Electrode 400D is suitable in a battery using a liquid electrolyte. This is an electrode structure. Furthermore, electrode 400E is used in all-solid-state batteries and semi-solid-state batteries using solid electrolyte 421. This electrode structure is suitable for batteries.

[0170] A positive electrode according to one aspect of the present invention is a positive electrode active material 10 having a topotaxis region in its surface layer. It is preferable to have 0. That is, the first active material 411a, the second active material 411b, the Any one of the third active material 411c, the fourth active material 411d, and the fifth active material 411e Alternatively, it is preferable to have a positive electrode active material 100 having a topotaxis region in its surface layer. It seems so.

[0171] Here, the electrode 400E is provided with a positive electrode active material 100 having a topotaxis region in its surface layer. The preferred structure for use will be explained using Figures 17A and 17B. Similarly, in Figures 17A and 17B, the dotted lines indicate crystal planes parallel to the arrangement of cations. The arrows also indicate the direction of lithium (Li) insertion and removal during charging and discharging. In other words, the positive electrode active material. In the 100, lithium can be inserted and removed at the ends of the cation arrangement. On the particle surface of the active material 100, the surface where the ends of the arrangement of cations are exposed is called the edge. It can be called a surface.

[0172] In an electrode having a solid electrolyte 421, such as electrode 400E, as shown in the schematic diagram in Figure 17A The solid electrolyte 421 is positioned in the direction of lithium insertion and deinsertion in the positive electrode active material 100. It is preferable to do so. In other words, on the edge surface of the positive electrode active material 100, the positive electrode active material 1 It is preferable that the surface layer of 00 and the solid electrolyte 421 are in contact. Here, solid The surface layer of the positive electrode active material 100 in contact with the electrolyte 421 is topotak In the case of C, lithium io in the contact region between the positive electrode active material 100 and the solid electrolyte 421 This is particularly preferable because it allows for smooth movement of the particles.

[0173] Furthermore, when the two positive electrode active materials 100 are in contact via the solid electrolyte 421, as shown in Figure 17A. Thus, each of the two positive electrode active materials 100 has lithium in the positive electrode active material 100 It is preferable that the solid electrolyte 421 is in contact with the insertion and removal direction. In other words, In each of the two positive electrode active materials 100, the edge surface and the solid electrolyte 421 are in contact. It is preferable to have a region. In the example of Figure 17A, two positive electrode active materials 100 and 1 Although an example was shown where three solid electrolytes 421 are in contact, this example is not limited to this case, and three positive electrode active materials 100 One solid electrolyte 421 may be in contact with the two positive electrode active materials 100 and the two solid electrolytes. 421 may be in contact with the electrode, and there are no particular restrictions on the number of positive electrode active materials 100 and the number of solid electrolytes 421. .

[0174] An example in which the solid electrolyte 421 is in the direction of lithium insertion and deinsertion in the positive electrode active material 100. A schematic diagram of a particularly preferred structure is shown in Figure 17B. In Figure 17B, the number on the current collector 413 A first layer 414a, a second layer 414b on the first layer 414a, and a solid electrolyte 421, The electrode is shown, and the first layer 414a has a positive region that is topotaxis in the surface layer. The first layer 414b has an extremely active material 411Ta, and the second layer 414b has a topotaxis region in its surface area. It has positive electrode active material 411Tb. Thus, positive electrode active material 411Ta and positive electrode active material 411 Tb preferably has a region that is in contact with the solid electrolyte 421. Here, the first The multiple positive electrode active materials 411Ta in layer 414a are, as shown in Figure 17B, positive electrode active materials The second layer 414b is positioned at the end of the direction of lithium insertion and deinsertion in 411Ta. It is preferable that such a feature be provided. Similarly, the plurality of positive electrode active materials in the second layer 414b 411Tb is the first layer ahead of the direction of lithium insertion and deinsertion in the positive electrode active material 411Tb. It is preferable that it be positioned such that 414a is located. That is, positive electrode active material 411Ta The direction of lithium insertion and deinsertion in the positive electrode active material 411Tb It is preferable that the direction of separation and the direction are roughly parallel.

[0175] In this case, the rate of lithium migration from the first layer 414a to the second layer 414b is improved. This can be achieved by improving the rate at which lithium moves from the first layer 414a toward the negative electrode. This structure allows for rapid charging and charging in low-temperature environments. This is possible. Also, similar to charging, discharging (the transfer of lithium from the negative electrode side towards the first layer 414a) In terms of operation, it can be said that the structure is advantageous for rapid discharge and discharge in low-temperature environments.

[0176] In this embodiment, a high capacity density and suitable for rapid charging and rapid discharging are shown in Figures 16A and 16A. An example of an electrode structure that further develops the electrode structure shown in 16B will be described.

[0177] The first active material 411a is present in the first layer 414a, and the second active material is present in the second layer 414b Each of the material 411b and the third active material 411c of the third layer 414c is above As explained in the notes, the distance from the current collector 413 is different. Also, as shown in Figure 23A... It could also be said that the distance from the sea urchin separator 440 is different. Or, as shown in Figure 23B In other words, the distance from the solid electrolyte layer 420 is different.

[0178] Now, let's consider the third layer 414c, which is relatively far from the current collector 413. In the third layer 414c, due to the distance from the current collector 413, within the active material layer 414 In this region, electron transfer resistance is high (also called a region of low electron mobility). As shown, the second layer 414b has higher electron transfer resistance compared to the first layer 414a. The structure for reducing the difference in movement resistance is shown in Figures 18A and 18B. Figure 18B is the same as Figure 18. This figure shows the profile of the conductive material ratio between A1 and A2 in A. (See Figure 18B) Thus, the proportion of conductive material in the second layer 414b is greater than the proportion of conductive material in the first layer 414a. The proportion of the material is larger, and the proportion of conductive material in the third layer 414 is greater than that of the second layer 414b. By creating a structure (electrode 400F) in which the proportion of conductive material in c is larger, the first layer 41 Reduce the difference in electron transfer resistance between layer 4a, the second layer 414b, and the third layer 414c. This becomes possible. In other words, the mass of the conductive material in the third layer 414c is equal to the mass of the second layer The mass of the conductive material in the second layer 414b is greater than the mass of the conductive material in layer 414b, and the mass of the conductive material in the second layer 414b is greater than the mass of the conductive material in layer 414b. It is preferable that the mass of conductive material in layer 414a is greater than the mass of conductive material in layer 1. This allows for rapid charging and Furthermore, it is possible to reduce the unevenness of the battery reaction in the active material layer 414 during rapid discharge. Yes.

[0179] Here, we consider the first layer 414a, which is relatively far from the solid electrolyte layer 420. In the first layer 414a, due to the distance from the solid electrolyte layer 420, the active material A region within layer 414 with high ion transport resistance (also known as a region with low ionic conductivity). Similarly, the second layer 414b has a lower ion transfer resistance compared to the third layer 414c. The resistance is high. A structure to reduce this difference in ion transfer resistance is shown in Figures 18C and 18D. Figure 18D shows the profile of the solid electrolyte ratio between B1 and B2 in Figure 18C. This is a diagram. As shown in Figure 18D, the proportion of solid electrolyte in the third layer 414c is greater than the proportion of solid electrolyte in the third layer 414c. The proportion of solid electrolyte in the second layer 414b is larger, and the solid electrolyte in the second layer 414b A structure in which the proportion of solid electrolytes in the first layer 414a is greater than the proportion of body electrolytes. By using an electrode of 400G, the first layer 414a, the second layer 414b, and the third layer 4 This makes it possible to reduce the difference in ion transfer resistance at 14c. In other words, the first The mass of the solid electrolyte in layer 414a is less than the mass of the solid electrolyte in the second layer 414b. There is also a large amount of solid electrolyte, and the mass of the solid electrolyte in the second layer 414b is equal to the mass of the solid electrolyte in the third layer 414c. It is preferable that the amount is greater than the mass of the body electrolyte. This is because in rapid charging and rapid discharging This makes it possible to reduce the unevenness of the battery reaction in the active material layer 414.

[0180] Figures 19A and 19B show the conductive material ratio profiles shown in Figures 18A and 18B, and The profiles of solid electrolyte ratios shown in Figures 18C and 18D, and the electrical activity when superimposed on them. The electrode structure (electrode 400H) is shown. Figure 19B shows the conductive material between C1 and C2 in Figure 19A. This figure shows the proportion profile and the solid electrolyte proportion profile. All-solid-state batteries When electrode 400H is present, the difference in electron transfer resistance in the active material layer 414 is reduced. By reducing the difference in ion transfer resistance in the active material layer 414, faster charging is achieved. This enables the realization of all-solid-state batteries suitable for rapid discharge.

[0181] The conductive material ratio profile and solid electrolyte ratio are shown in Figures 18 and 19. Here is an example of applying the profile to a two-layer electrode structure (electrode 400I and electrode 400J). This is shown in Figures 20 and 21. In the two-layer electrode structure as described above, the active material To reduce the difference in electron transfer resistance in layer 414 and to reduce ion transfer in the active material layer 414 By reducing the difference in dynamic resistance, all-solid-state batteries suitable for faster charging and discharging can be developed. It becomes Noh.

[0182] Next, we will discuss the positive electrode, negative electrode, current collector, conductive material, binder, and graphite as explained so far. Regarding the compound, separator, electrolyte, and outer casing, further details will be added in the descriptions of each item below. I will now provide an explanation of the additional information.

[0183] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material. It may also have the conductive material 415 and binder described later. The structure of the positive electrode active material layer is as follows: It is preferable to have the following layered structure.

[0184] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material. It may also have the conductive material 415 and binder described later. The structure of the negative electrode active material layer is as follows: It is preferable to have the following layered structure.

[0185] Another form of negative electrode is one that does not have negative electrode active material at the end of battery manufacturing. This may also be the case. As a negative electrode without negative electrode active material, for example, at the end of battery manufacturing A negative electrode having only a negative electrode current collector, wherein lithium is detached from the positive electrode active material by battery charging. Um ions are deposited as lithium metal on the negative electrode current collector, forming a negative electrode active material layer. This can be done. A battery using such a negative electrode is a negative electrode-free (anode-free) battery. It is sometimes called a pond, anode-less battery, etc.

[0186] When using a negative electrode without negative electrode active material, the deposition of lithium on the negative electrode current collector is made uniform. It may have a film for this purpose. For example, a film for homogenizing lithium deposition may be lithium A solid electrolyte having ionic conductivity can be used. As the solid electrolyte, a sulfide granular solid electrolyte can be used. Solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. However, polymer-based solid electrolytes can be relatively easily used to form a uniform film on the negative electrode current collector. Therefore, it is suitable as a film for homogenizing the deposition of lithium. For homogenization, for example, a metal film that forms an alloy with lithium can be used. For example, a magnesium metal film can be used as the metal film that forms the alloy with lithium. Yes, it is possible. Lithium and magnesium form a solid solution over a wide range of compositions, therefore, It is suitable as a film for homogenizing the precipitation of um.

[0187] Further, in the case of using a negative electrode that does not include a negative electrode active material, using a negative electrode current collector having irregularities is possible. When a negative electrode current collector having irregularities is used, the recesses of the negative electrode current collector form cavities in which lithium contained in the negative electrode current collector is likely to precipitate, so that dendritic morphology can be suppressed when lithium precipitates.

[0188] [Current Collector] As the positive electrode current collector and the negative electrode current collector, stainless steel, gold, platinum, zinc, iron, copper, aluminu m, titanium and other metals, as well as alloys thereof, may be used, which are materials having high conductivity and not alloying with carrier ions such as lithium. The current collector may be appropriately used in shapes such as a sheet shape, a mesh shape, a punching metal shape, and an expanded metal shape. It is preferable to use a current collector having a thickness of 10 μm or more and 30 μm or less.

[0189] It is preferable that the negative electrode current collector is made of a material that does not alloy with carrier ions such as lithium.

[0190] As the current collector, a titanium compound may be provided by laminating it on the metal shown above. As the titanium compou nd, for example, titanium nitride, titanium oxide, titanium nitride in which part of nitrogen is substituted with oxygen , titanium oxynitride (TiO x N y , 0<x<2, 0<y<1), and titanium oxide in which part of oxygen is substituted with nitrogen may be used, and one or more selected from the above may be used by mixing or laminating. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxygen diffusion. For example, by providing the titanium compound on the surface of the current collector, on the current collector The reaction between the material and the metal in the active material layer formed therein is suppressed. The active material layer contains oxygen. When a compound is included, the oxidation reaction between the metal element and oxygen can be suppressed. Aluminum is used as the current collector, and the active material layer is formed using graphene oxide, which will be described later. In such cases, there is concern about the oxidation reaction between the oxygen present in graphene oxide and aluminum. In such cases, by providing a titanium compound on aluminum, This can suppress the oxidation reaction between the current collector and graphene oxide.

[0191] [Conductive material] Conductive materials, also called conductivity imparters or conductivity enhancers, are made of carbon materials. By attaching a conductive material between the active materials, multiple active materials are electrically connected to each other, increasing conductivity. Note that "adhesion" refers only to the physical close contact between the active material and the conductive material. There is no covalent bond, and when bonding occurs, when bonding occurs by van der Waals forces, the surface of the active material When a conductive material covers a portion of a surface, when the conductive material fits into the surface irregularities of the active material, when they come into contact with each other This concept includes cases where devices are electrically connected even if they are not physically connected.

[0192] The active material layers, such as the positive electrode active material layer and the negative electrode active material layer, preferably contain a conductive material.

[0193] Examples of conductive materials include acetylene black and furnace black. Graphite such as Bombrak, artificial graphite, and natural graphite, carbon nanofibers, and Carbon fibers such as carbon nanotubes, and graphene compounds, or one of these or Two or more types can be used.

[0194] Examples of carbon fibers include mesophase pitch carbon fibers and isotropic pitch carbon fibers. Carbon fibers can be used. In addition, carbon nanofibers or Carbon nanotubes can be used, for example, in the gas phase. It can be produced using growth methods, etc.

[0195] Furthermore, the active material layer contains metal powders such as copper, nickel, aluminum, silver, and gold as conductive materials. It may have metal fibers, conductive ceramic materials, etc.

[0196] The content of conductive material relative to the total amount of active material layer is preferably 1 wt% to 10 wt%, A concentration of 1 wt% to 5 wt% is more preferable.

[0197] Unlike granular conductive materials such as carbon black that make point contact with the active material, graphene compounds Because it enables surface contact with low contact resistance, it requires less granular active material than ordinary conductive materials. The electrical conductivity between the material and the graphene compound can be improved. Therefore, the active material The ratio in the material layer can be increased. This increases the discharge capacity of the secondary battery. It can be made to happen.

[0198] Particulate carbon-containing compounds such as carbon black and graphite, or carbon nanotubes Fibrous carbon-containing compounds such as these can easily enter tiny spaces. These tiny spaces are, for example, multiple spaces. This refers to the regions between active materials. Carbon-containing compounds that easily enter minute spaces and multiple particles By combining sheet-like carbon-containing compounds such as graphene, which can impart conductivity, By using this method, the electrode density can be increased, and a superior conductive path can be formed. A secondary battery obtained by the manufacturing method of one aspect of the invention has high capacity density and stability. It can do this and is effective as a secondary battery for use in vehicles.

[0199] [Binder] The active material layer preferably has a binder. The binder may be, for example, an electrolyte and an active material. To bind or fix. Also, the binder consists of an electrolyte and a carbon-based material, an active material and a carbon-based material, and multiple Multiple active materials, multiple carbon-based materials, etc., can be bound or fixed together.

[0200] As a binder, polystyrene, methyl polyacrylate, polymethyl methacrylate ( Methyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol Polyethylene oxide (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide Polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, poly Isobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVD) F) Polyacrylonitrile (PAN), ethylene propylene diene polymer, polyacetic acid It is preferable to use materials such as vinyl or nitrocellulose.

[0201] Polyimides possess excellent thermal, mechanical, and chemical stability.

[0202] Fluorine-containing polymer materials, specifically polyvinylidene fluoride ( Materials such as PVDF can be used. PVDF has a melting point in the range of 134°C to 169°C. It is a resin with excellent thermal stability.

[0203] Also, as a binder, styrene-butadiene rubber (SBR), styrene-isoprene- Styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propion It is preferable to use rubber materials such as lendiene copolymers. Also, as a binder, Fluorocarbon rubber can be used.

[0204] Furthermore, it is preferable to use a water-soluble polymer as the binder. As molecules, for example, polysaccharides can be used. As for polysaccharides, carboxymethyl Cholecellulose (CMC), methylcellulose, ethylcellulose, hydroxypropyl Cellulose derivatives such as cellulose, diacetylcellulose, and regenerated cellulose, or syrup Powders and other forms can be used. Furthermore, these water-soluble polymers can be used in combination with the aforementioned rubber materials. It is even preferable to use it in this way.

[0205] You may use a combination of several of the binders mentioned above.

[0206] [Graphene compounds] In this specification, graphene compounds refer to graphene, multilayer graphene, and multi-graphene. Fen, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced oxide Graphene, reduced multilayer graphene oxide, reduced multilayer graphene oxide, graph Includes graphene quantum dots, etc. Graphene compounds are compounds that have carbon atoms and are in the form of flat plates, sheets, etc. It refers to a structure that has a shape and is formed by a two-dimensional structure made of a six-membered carbon ring. The resulting two-dimensional structure can be described as a carbon sheet. The graphene compound has functional groups. It is also preferable that the graphene compound has a bent shape. The compound may be rolled up into a form resembling carbon nanofibers.

[0207] In this specification, graphene oxide refers to, for example, a material having carbon and oxygen, and in a sheet-like form. It refers to a substance that has functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups. .

[0208] In this specification, reduced graphene oxide refers to, for example, a substance having carbon and oxygen, and This refers to a structure that has a T-shape and a two-dimensional structure formed from a six-membered carbon ring. It could be said that a single reduced graphene oxide sheet functions, but multiple sheets are stacked together. It may be reduced graphene oxide has a carbon concentration greater than 80 atomic%. The material has a portion where the oxygen concentration is between 2 atomic% and 15 atomic%. This is preferable. By using such carbon and oxygen concentrations, a small amount of conductive material can be used. It can function as an electrical material. Furthermore, reduced graphene oxide exhibits a Raman spectrum. It is preferable that the intensity ratio of the G band to the D band, G / D, is 1 or greater. Reduced graphene oxide, which has a high strength ratio, functions as a highly conductive material even in small amounts. It is possible.

[0209] By reducing graphene oxide, pores can be created in graphene compounds. There is a match.

[0210] Alternatively, a material in which the ends of graphene are terminated with fluorine may be used.

[0211] In the longitudinal section of the active material layer, a sheet-like gradient is found in the internal region of the active material layer, which is roughly uniform. The graphene compounds are dispersed. Multiple graphene compounds are shown in Figures 22A and 22B. The granular active material is partially covered by the granular active material, or spread on the surface of the granular active material. Because they are formed to adhere to each other, they are in surface contact with one another.

[0212] Here, multiple graphene compounds bond together to form a network of graphene compounds. Forming a material sheet (hereinafter referred to as graphene compound net or graphene net) This is possible. When the active material is covered with a graphene net, the graphene net interacts with the active material. It can also function as a binder to combine them. Therefore, the amount of binder can be reduced. Because it is possible or not to use, the active material in the electrode volume or electrode weight The ratio of quality can be improved. In other words, the charge and discharge capacity of the secondary battery can be increased. It is possible.

[0213] Here, graphene oxide is used as the graphene compound and mixed with the active material to form an active material layer. It is preferable to form a layer and then reduce it. In other words, the completed active material layer is a reduced oxide. It is preferable that the graphene compound has dispersibility in polar solvents. By using extremely high-quality graphene oxide, the graphene compound is incorporated into the internal region of the active material layer. It can be dispersed in a generally uniform manner. Contains uniformly dispersed graphene oxide. The solvent is volatilized and removed from the dispersion medium, and the graphene oxide is reduced, so that the graphene oxide remaining in the active material layer The phen compounds are dispersed to the extent that they partially overlap and are in surface contact with each other, thus creating a three-dimensional structure. A conductive path can be formed. Note that the reduction of graphene oxide can be performed, for example, by heat treatment. This can be done by hand, or by using a reducing agent.

[0214] Furthermore, by using a spray drying device beforehand, the entire surface of the active material is covered with conductive material. A graphene compound is formed as a coating, and then the active materials are electrically bonded together with the graphene compound. It is also possible to connect them electrically and form a conductive path.

[0215] Furthermore, along with the graphene compound, the materials used in forming the graphene compound are mixed. It may also be used in the active material layer. For example, as a catalyst when forming graphene compounds. The child may be mixed with the graphene compound. The catalyst used when forming the graphene compound and For example, silicon dioxide (SiO2, SiO x (x<2), aluminum oxide, iron Examples include particles containing nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles are preferably such that the D50 is 1 μm or less, and 100 nm or less. More preferable.

[0216] [Separator] A separator is placed between the positive and negative electrodes. Examples of separators include paper. Fibers, nonwoven fabrics, glass fibers, ceramics, or nylon (polycellulose) containing cellulose. Riamide, Vinylon (polyvinyl alcohol-based fiber), Polyester, Acrylic, Poly Synthetic fibers made from olefins, polyurethanes, etc., can be used. The separator is processed into a bag shape and positioned to enclose either the positive or negative electrode. preferable.

[0217] The separator is a porous material having pores with a diameter of at least 2 nm. It is preferable that the pores have a size of 6.5 nm or larger, and that the pores have a size of about 20 nm. It is more preferable to have it. In the case of the semi-solid secondary battery described above, the separator can be omitted. It can also be done this way.

[0218] The separator may have a multilayer structure. For example, an organic material such as polypropylene or polyethylene. The material film contains ceramic-based materials, fluorine-based materials, polyamide-based materials, or a combination thereof. Mixtures and other materials can be coated onto it. Examples of ceramic materials include aluminum oxide. Aluminum particles, silicon oxide particles, etc. can be used. Examples of fluorine-based materials include PVDF, polytetrafluoroethylene, etc. can be used. Polyamide materials and For example, nylon, aramid (meta-aramid, para-aramid), etc. can be used. It is possible.

[0219] Coating with ceramic materials improves oxidation resistance, thus preventing separation during high-voltage charging and discharging. This can suppress the degradation of the data and improve the reliability of secondary batteries. Furthermore, fluorine-based materials... Coating the electrode makes it easier for the separator and electrode to adhere to each other, which can improve the output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, thus improving the heat resistance of secondary batteries. Safety can be improved.

[0220] For example, a mixture of aluminum oxide and aramid material is applied to both sides of a polypropylene film. It may also be done by applying aluminum oxide to the surface of the polypropylene film that is in contact with the positive electrode. A mixed material of um and aramid may be coated, and a fluorine-based material may be coated on the surface in contact with the negative electrode. .

[0221] Using a multilayer separator ensures the safety of secondary batteries even with a thin overall separator. Because this can be maintained, the capacity per unit volume of the secondary battery can be increased.

[0222] [Electrolyte] The solid electrolyte 421 in the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte. Oxide-based solid electrolytes, halide-based solid electrolytes, etc., can be used.

[0223] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 G e 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S・30P2S5, 30Li 2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57 Li2S・38SiS2・5Li4SiO4, 50Li2S・50GeS2, etc.), sulfides Crystallized glass (Li7P3S 11 Li 3.25 P 0.95 Contains sulfides (S4, etc.). Solid electrolytes have materials with high conductivity, can be synthesized at low temperatures, and are relatively soft. Because it is soft, it has advantages such as the conductivity path being easily maintained even after charging and discharging.

[0224] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x L i 3x Materials having a NASICON-type crystal structure (Li 1-Y Al Y Ti2 -Y (PO4)3 etc.) Materials having a garnet-type crystal structure (Li7La3Zr2O 12 Materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 etc.), LLZ O(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50 Li4SiO4·50Li3BO3 etc.), oxide crystallized glass (Li 1.07 Al0.6 9Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) include . Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0225] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiC l, LiBr, LiI, and the like. Composite materials obtained by filling these halide-based solid electrolytes into the pores of porous aluminum oxide or porous silica can also be used as solid electro lytes.

[0226] Alternatively, different solid electrolytes may be mixed and used.

[0227] Among these, Li having 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 according to one embodiment of the present invention, so a synergistic effect on improving cycle characteristics can be expected, which is preferable. In addition, improvement in productivity through process reduction can also be expected. In this specification and the like, the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition meta l, X: S, P, As, Mo, W, etc.), in which a structure where MO6 octahedra and XO4 tetrahedra share vertices and are arranged three-dimensionally.

[0228] When a liquid electrolyte 576 is used in a secondary battery, for example, ethylene car bonate (EC), propylene carbonate (PC), butylene carbonate, chloro ​Ethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone Dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl 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, sulfol One of the following, such as sultone, or any combination and ratio of two or more of these. It can be used as a percentage.

[0229] Furthermore, as the solvent for electrolyte 576, an ionic liquid (molten at room temperature) that is flame-retardant and non-volatile is used. By using one or more salts, internal short circuits or overcharging of the secondary battery can occur. Even if the temperature in a certain region rises, it can prevent the secondary battery from rupturing or catching fire. The body consists of cations and anions, and includes organic cations and anions. Organic cations and And, quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium Aliphatic onium cations such as cations, as well as imidazolium cations, and pyridium Aromatic cations such as nium cations are examples. Also, monovalent amides can be used as anions. Anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroal chlorosulfonate anion, tetrafluoroborate anion, perfluoroalkylborate Perfluorophosphonate anions, hexafluorophosphate anions, or perfluoroalkyl phosphates Examples include fate anions.

[0230] In particular, in a secondary battery according to one aspect of the present invention, silicon is used as the active material of the negative electrode. In such cases, it is preferable to use a liquid electrolyte 576 that contains an ionic liquid.

[0231] A secondary battery according to one aspect of the present invention is, for example, a lithium ion, sodium ion, potassium ion Alkali metal ions such as ions, calcium ions, strontium ions, barium ions Alkaline earth metal ions such as ions, beryllium ions, and magnesium ions serve as carriers. It exists as an ion.

[0232] When lithium ions are used as carrier ions, for example, the electrolyte is a lithium salt. Includes lithium salts such as LiPF6, LiClO4, LiAsF6, and LiBF4. , LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl1 0, Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3S O2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9 SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used.

[0233] Furthermore, the electrolyte preferably contains fluorine. For example, a fluorine-containing electrolyte is fluorine An electrolyte comprising one or more cyclic carbonates and lithium ions is used. It is possible. Fluorinated cyclic carbonates improve flammability and lithium ion secondary This can improve battery safety.

[0234] As a fluorinated cyclic carbonate, fluorinated ethylene carbonate, for example, monofluorinated ethylene carbonate, Fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene Lentinum carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3E C) Tetrafluoroethylene carbonate (F4EC), etc., can be used. Oh, DFEC has isomers such as cis-4,5 and trans-4,5. , lithium ions are solvated using one or more fluorinated cyclic carbonates. Therefore, transporting the electrolyte within the electrodes during charging and discharging is important for operation at low temperatures. Therefore, fluorinated cyclic carbonate is not used as a small amount of additive, but rather during the charging and discharging of lithium. By contributing to ion transport, operation at low temperatures becomes possible. Lithium ions in secondary batteries ON moves in clusters of several to several dozen units.

[0235] By using fluorinated cyclic carbonates as the electrolyte, the solvent within the electrolyte contained in the electrode The energy required for desolvation when the lithium ions in the mixture enter the active material particles is reduced. This desolvation energy can be reduced, allowing lithium to operate even in the low-temperature range. The ON ions become easier to insert into or detach from the active material particles. Note that lithium ions are in a solvated state. While they may move in their original state, a hopping phenomenon occurs where the coordinating solvent molecules are replaced. In some cases, lithium ions become more easily desolvated, and their movement due to the hopping phenomenon occurs. This can make it cheaper and easier for lithium ions to move. The decomposition products of the electrolyte adhere to the surface of the active material, causing degradation of the secondary battery. There is a concern about this. However, if the electrolyte contains fluorine, the electrolyte will be fluid. Therefore, the decomposition products of the electrolyte become less likely to adhere to the surface of the active material. This reduces the degradation of the secondary battery. It can be suppressed.

[0236] Solvated lithium ions form clusters in the electrolyte, and in the negative electrode, positive It may move between the polarity and the negative polarity, within the positive polarity, etc.

[0237] In this specification, electrolytes include solid electrolytes, liquid electrolytes, or semi-solid electrolytes. It is a general term that includes [the following].

[0238] Degradation is likely to occur at interfaces within secondary batteries, such as the interface between the active material and the electrolyte. In one embodiment of a secondary battery, by having an electrolyte containing fluorine, the active material and the electrolyte To prevent degradation that can occur at the interface with the substance, typically the alteration of the electrolyte or the increase in the viscosity of the electrolyte. This can be done. In addition, for electrolytes containing fluorine, a binder or graphene compound can be used. The configuration may be such that it clings to or holds the electric It is possible to maintain a state in which the viscosity of the dissolved substance is reduced, or in other words, to maintain a fluid state of the electrolyte. This improves the reliability of secondary batteries. DFE has two fluorine atoms bonded together. F4EC, which has four C atoms bonded to it, has a higher viscosity compared to FEC, which has one fluorine atom bonded to it. The viscosity is low, the material is fluid, and the coordination bond with lithium is weak. Therefore, the viscosity of the active material particles is low. This can reduce the adhesion of highly viscous decomposition products to the active material particles. When lithium ions adhere to or cling to the active material particles, it becomes difficult for them to move at the interface between the particles. Electrolytes containing fluorine can be solvated to form an active material (positive electrode active material or negative electrode active material). It reduces the formation of decomposition products that adhere to the surface. Also, by using an electrolyte containing fluorine, By preventing the adhesion of decomposed material, the formation and growth of dendrites can be prevented. .

[0239] Another characteristic is that it uses electrolytes containing fluorine as its main component. The electrolyte content is 5% by volume or more, 10% by volume or more, preferably 30% by volume or more, up to 100 volumes. It should be less than or equal to %.

[0240] In this specification, the main component of the electrolyte is defined as 5% or more by volume of the total electrolyte of the secondary battery. This refers to the fact that... Also, the term "more than 5 volume percent of the total electrolyte of the secondary battery" here refers to the secondary battery... This refers to the proportion of the total electrolyte measured during manufacturing. It also refers to the proportion of the electrolyte after the secondary battery is manufactured. When decomposing the electrolyte, quantify the proportion of each type of electrolyte present. It is difficult to determine whether a particular organic compound makes up 5% or more of the total electrolyte by volume. It can be determined.

[0241] By using an electrolyte containing fluorine, a wide temperature range is achieved, specifically, from -40°C upwards to 15°C. It is possible to realize a secondary battery that can operate at temperatures below 0°C, preferably between -40°C and 85°C. Cut.

[0242] Furthermore, the electrolytes include vinylene carbonate, propanesultone (PS), and tert-butyl. Benzene (TBB), lithium bis(oxalate)borate (LiBOB), and also sucrose Additives such as dinitrile compounds like cinonitrile and adiponitrile may be added. The concentration of the additive should be, for example, 0.1% by volume or more and less than 5% by volume relative to the total electrolyte.

[0243] In addition to the above, electrolytes include γ-butyrolactone, acetonitrile, dimethoxyethane, It may contain one or more aprotic organic solvents such as tetrahydrofuran.

[0244] Furthermore, the presence of a polymer material in which the electrolyte gels enhances safety against leakage, etc. Okay. Typical examples of polymer materials that gel include silicone gel, acrylic gel, and acrylic gel. Lilonitrile gel, polyethylene oxide gel, polypropylene oxide gel, Examples include gels made from fluorine-based polymers.

[0245] Examples of polymer materials include polyalkylenes such as polyethylene oxide (PEO). Polymers having an oxide structure, PVDF, and polyacrylonitrile, etc., and the Copolymers containing these can be used. For example, PVDF and hexafluoropropylene PVDF-HFP, a copolymer of (HFP), can be used. The polymer may have a porous structure.

[0246] Furthermore, the above configuration is an example of a secondary battery using a liquid electrolyte, but it is not particularly limited to such configurations. For example, semi-solid-state batteries and all-solid-state batteries can also be fabricated.

[0247] In this specification, the positive electrode applies to both secondary batteries using a liquid electrolyte and semi-solid batteries. The layer placed between the negative electrode and the negative electrode will be called the electrolyte layer. The electrolyte layer of a semi-solid battery is formed by film deposition. This can be described as a formed layer, and can be distinguished from a liquid electrolyte layer.

[0248] Furthermore, in this specification, a semi-solid battery means that at least one of the electrolyte layer, positive electrode, and negative electrode is This refers to a battery containing semi-solid materials. Here, "semi-solid" means that the ratio of solid material to solid material is 50%. That is not what it means. A semi-solid is a solid that possesses the properties of a solid, such as having little volume change, but is flexible. This means that it also possesses some properties similar to those of a liquid, such as being liquid. For example, a single material or multiple materials can be used. It may also be a substance that has been impregnated into the body material.

[0249] Furthermore, in this specification, a polymer electrolyte secondary battery is defined as having an electrolyte layer between the positive and negative electrodes. This refers to a secondary battery containing a polymer. Polymer electrolyte secondary batteries are dry (or intrinsic) polymer batteries. This includes polymer electrolyte batteries and polymer gel electrolyte batteries.

[0250] Electrolyte 576 comprises a lithium-ion conductive polymer and a lithium salt.

[0251] In this specification, a lithium-ion conductive polymer refers to a cation conductive polymer such as lithium. It is a polymer that has properties. More specifically, it is a polymer having polar groups to which cations can coordinate. It is a compound. Polar groups include ether groups, ester groups, nitrile groups, and carbonyl groups. It is preferable that the material contains siloxanes, etc.

[0252] Examples of lithium-ion conductive polymers include polyethylene oxide (PEO), Derivatives having polyethylene oxide as the main chain, polypropylene oxide, polyacrylic Polymethacrylates, polysyl esters, polysiloxanes, polyphosphazenes, etc. are used. It is possible to be there.

[0253] The lithium-ion conductive polymer may be branched or crosslinked. It may also be a polymer. The molecular weight is preferably, for example, 10,000 or more, and preferably 100,000 or more. It is preferable to have a certain state.

[0254] Lithium-ion conductive polymers exhibit partial motion (also called segmental motion) of polymer chains. Lithium ions move while changing the polar groups with which they interact. For example, PEO Then, the lithium ions change the oxygen they interact with through the segmental motion of the ether chain. It moves. The temperature is close to the melting or softening point of the lithium-ion conductive polymer, or When the temperature is high, the crystalline region dissolves and the amorphous region increases, and the movement of the ether chains becomes more active. Therefore, the ionic conductivity increases. For this reason, PEO is used as a lithium ion conductive polymer. When using this product, it is preferable to perform charging and discharging at temperatures above 60°C.

[0255] Shannon's ionic radius (Shannon et al., Acta A 32(19) According to 76) 751.), the radius of a monovalent lithium ion is 0.590 × when it is 4-coordinate. 10 -1 nm, 0.76 × 10 for 6-coordinate -1 nm, 0.92 × 10 for 8-coordinate. -1 It is in nm. The radius of a divalent oxygen ion is 1.35 × 10⁻⁶ when it is two-coordinate. -1 nm, 3 1.36 × 10 -1 nm, 1.38 × 10 for 4-coordinate. -1 nm, 6-coordinate 1.40 × 10 -1 nm, 1.42 × 10 for 8-coordinate. -1 It is nm. Adjacent Lith The distance between polar groups in a um ion conductive polymer chain maintains the ionic radius as described above. In this state, the lithium ion and the anions of the polar group can exist stably at a distance greater than that. It is preferable that the distance is such that sufficient interaction occurs between the lithium ion and the polar group. This is preferable. However, as mentioned above, segmental motion occurs, so a constant distance is always maintained. It doesn't need to be maintained. It just needs to be an appropriate distance for lithium ions to pass through.

[0256] Furthermore, lithium salts include, for example, lithium along with phosphorus, fluorine, nitrogen, sulfur, oxygen, Having at least one of chlorine, arsenic, boron, aluminum, bromine, and iodine. Compounds can be used. For example, LiPF6, LiN(FSO2)2(lithium bicarbonate). (fluorosulfonyl)imide, LiFSI, LiN(SO2CF3)2(lithium) Bis(trifluoromethanesulfonyl)amide, LiTFSA), LiClO4, LiA sF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 Li2B 12 Cl 12 LiCF3SO3, LiC4F9SO3 , LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2 LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, Lithium One type of lithium salt such as bis(oxalate)borate (LiBOB), or one of these. Two or more of these can be used in any combination and ratio.

[0257] In particular, using LiFSI is preferable because it provides good low-temperature characteristics. TFSA is less reactive with water compared to LiPF6, etc. Therefore, LiFSI is used in electrolysis. This facilitates control of the dew point when fabricating the electrode and electrolyte layers. For example, by minimizing moisture content. In addition to dry rooms with inert atmospheres such as argon and controlled dew points, as well as ordinary large It can be handled even in an air-filled environment. Therefore, productivity is improved, which is desirable. Also, LiFSI Furthermore, using a highly dissociative and plasticizing Li salt such as LiTFSA is preferable to using ether. When using lithium conduction that utilizes the segmental motion of the chain, it can be used over a wide temperature range. It is particularly preferable.

[0258] By having little to no organic solvents, secondary batteries can be made less likely to ignite or burn. This is preferable as it improves safety. Also, electrolyte 576 is free of organic solvents or non-organic solvents. If the electrolyte layer is always small, it has sufficient strength even without a separator, and the positive and negative electrodes It is possible to electrically insulate it. Since a separator is not required, it is highly productive. It can be used as a next-generation battery. If the electrolyte layer has electrolyte 576 and an inorganic filler, This further increases the strength, making it possible to create a rechargeable battery with higher safety.

[0259] [Exterior] The outer casing of a secondary battery can be made of, for example, metal materials such as aluminum and resin materials. A film-like outer covering can be used. For example, polyethylene, polypropylene, polycarbonate, ionomer, polya On a film made of materials such as mid, aluminum, stainless steel, copper, nickel, etc., which have excellent flexibility A thin metal film is provided, and a polyamide resin is used as the outer surface of the exterior body on top of the thin metal film. A three-layer film with an insulating synthetic resin film, such as an ester resin, can be used. Furthermore, it is preferable to use a fluororesin film as the film. Mu has high stability against acids, alkalis, organic solvents, etc., and is not associated with side effects from reactions in secondary batteries, etc. By suppressing corrosion and other issues, a superior secondary battery can be realized. Fluororesin film and PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkaldehyde) (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FE P(perfluoroethylenepropene copolymer: tetrafluoroethylene and hexafluoroethylene) Polypropylene copolymer, ETFE (ethylene tetrafluoroethylene copolymer: tetrafluoroethylene copolymer) Examples include copolymers of trafluoroethylene and ethylene.

[0260] [Internal structure of the battery] A battery having electrodes according to one embodiment of the present invention will be described with reference to Figures 23 and 24.

[0261] As shown in Figure 23A, a secondary battery according to one aspect of the present invention has a positive electrode 410 and a separator 440 and has a negative electrode 430. The positive electrode 410 in Figure 23A has the electrode structure shown in Figure 18A above. This is a positive electrode using the positive electrode active material described in Embodiments 2 and 3. Any one or more of the substances can be used. The secondary battery shown in Figure 23A is a liquid battery. The solution 576 is contained in the space between particles of the layered structure of the positive electrode 410. It is preferable that the following conditions be met.

[0262] As shown in Figures 23B and 24, a secondary battery according to one aspect of the present invention has a positive electrode 410 and a solid-state battery. It has a decomposed layer 420 and a negative electrode 430. The positive electrode 410 shown in Figures 23B and 24 is the previous The positive electrode uses the electrode structure shown in Figure 19A described above, and the positive electrode active material is the same as in Embodiment 2. Any one or more of the positive electrode active materials described in Embodiment 3 can be used. The active material layer 414 of the positive electrode may have the aforementioned conductive material and binder.

[0263] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 has a positive electrode 410. This region is located between the positive electrode 410 and the negative electrode 430, and does not contain either the positive electrode 410 or the negative electrode 430. .

[0264] As shown in Figure 24, 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 active material layer 434 may have a conductive material and a binder. When using metallic lithium, there is no need to make it into particles, so as shown in Figure 23B, it is a solid. The negative electrode 430 can be made without the electrolyte 421. Metallic lithium can be used for the negative electrode 430. Having this feature is preferable because it can improve the energy density of the secondary battery.

[0265] The solid electrolyte 421 in the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte. Oxide-based solid electrolytes, halide-based solid electrolytes, etc., can be used.

[0266] Furthermore, Figure 25 shows a modified example of a battery having a solid electrolyte 421, as shown in Figures 23B and 24. This is shown in Figures A and 25B. The batteries shown in Figures 25A and 25B consist not only of a solid electrolyte 421. These batteries have a liquid electrolyte 576. For this reason, it is sometimes called a semi-solid battery. In a semi-solid battery, the advantages of the solid electrolyte 421 are It has flame retardancy and the advantage of liquid electrolyte 576, which is the increased contact interface between the active material and the electrolyte. This results in a battery that combines the advantages of both. In this case, as the liquid electrolyte 576, an ionic liquid is used. Using an electrolyte containing this material results in a flame-retardant battery, which is particularly preferable.

[0267] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0268] (Embodiment 2) In this embodiment, a positive electrode active material 100 that can be used in a secondary battery according to one aspect of the present invention As an example, Figures 26A to 36 show the positive electrode active material 100A and its manufacturing method. I will explain.

[0269] [Cathode active material] Figure 1B is a cross-sectional view of a positive electrode active material 100A that can be used in a secondary battery according to one embodiment of the present invention. Figures 2A and 2B show enlarged views of the area around AB in Figure 1B. Figures 2C and 2D show enlarged views of the area around -D.

[0270] As shown in Figures 1B and 2A to 2D, the positive electrode active material 100A has a surface layer 100a And it has an interior 100b. In these figures, the boundary between the surface layer 100a and the interior 100b is shown by a dashed line. This indicates.

[0271] <Elements present in the positive electrode active material> The positive electrode active material 100A comprises lithium, a transition metal M, oxygen, and an additive element A. Alternatively, the positive electrode active material 100A is a composite oxide (LiMO2) having lithium and a transition metal M. It may have a compound to which additive element A is added. However, the composition of the composite oxide is strictly Li:M:O is not limited to 1:1:2. Also, the positive electrode with added element A. The active material is sometimes also referred to as a complex oxide.

[0272] The positive electrode active material of a lithium-ion secondary battery maintains charge neutrality even when lithium ions are inserted and removed. To maintain this, it is necessary to have a transition metal that can undergo oxidation and reduction. A positive electrode active material according to one aspect of the present invention For quality 100A, it is preferable to use cobalt as the transition metal M responsible for the redox reaction. In addition to cobalt, at least one or two selected from nickel and manganese are used. It is also acceptable if, among the transition metals M present in the positive electrode active material 100A, cobalt is present in an amount of 75 atomic percent or more. Preferably, the concentration is 90 atomic percent or more, and more preferably 95 atomic percent or more, as this allows for relatively easy synthesis. It is desirable because it has many advantages, such as being easy to handle, having excellent cycle characteristics, and being easy to manage.

[0273] Furthermore, of the transition metal M in the positive electrode active material 100A, cobalt should be 75 atomic percent or more, preferably 9 atomic percent. If the amount is 0 atomic percent or more, and more preferably 95 atomic percent or more, then lithium nickelate (LiN Compared to composite oxides such as iO2, where nickel accounts for the majority of the transition metal M, Li x CoO2 exhibits better stability when x is small. This is true for cobalt rather than nickel. However, this is thought to be because the effect of strain due to the Jahn-Teller effect is small. The strength of the Jahn-Teller effect varies depending on the number of electrons in the d orbitals of the transition metal. Yes. Low-spin nickel(III) with octahedral coordination, such as lithium nickelate, accounts for the majority. Such layered rock salt-type complex oxides are greatly influenced by the Jahn-Teller effect, and nickel and oxygen The octahedron layer is prone to distortion. Therefore, the crystal structure collapses during the charge-discharge cycle. Concerns are growing that this will occur. Also, nickel ions are larger than cobalt ions, and lithium It is close in size to a um ion. Therefore, like lithium nickelate, nickel makes up the majority. In layered rock salt-type composite oxides, cation mixing of nickel and lithium occurs. There is a problem called "sui".

[0274] On the other hand, the transition metal M in the positive electrode active material 100A preferably contains nickel in an amount of 33 atomic percent or more. If 60 atomic percent or more, and more preferably 80 atomic percent or more is used, when there is a lot of cobalt... Compared to that, the raw materials may be cheaper, and the charge / discharge capacity per unit weight may increase. It is preferable.

[0275] The additive element A in the positive electrode active material 100A is magnesium, fluorine, nickel, Aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, rhodium One or two selected from ion, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium. It is preferable to use the above. Furthermore, the sum of the transition metals among the added element A should be less than 25 atomic percent. Preferably, less than 10 atomic percent, more preferably less than 5 atomic percent.

[0276] In other words, the positive electrode active material 100A is a cobalt oxide lithium with magnesium and fluorine added. Lithium cobalt oxide with added um, magnesium, fluorine, and titanium, magnesium Lithium cobalt oxide, magnesium, and fluorine, with added fluorine and aluminum. and nickel-added lithium cobaltate, magnesium, fluorine, nickel and It may contain lithium cobalt oxide with added aluminum, etc.

[0277] These additive elements A make the crystal structure of the positive electrode active material 100A more stable, as will be described later. To stabilize. In this specification, additive element A is synonymous with a mixture or part of the raw materials.

[0278] Note that the additive element A is not necessarily magnesium, fluorine, nickel, aluminum, or thi. Tan, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon It does not have to contain sulfur, phosphorus, boron, bromine, or beryllium.

[0279] For example, if we consider a positive electrode active material 100A that is substantially free of manganese, its synthesis is relatively easy. The advantages mentioned above, such as ease of handling and excellent cycle characteristics, become even more pronounced. The weight of manganese contained in the positive electrode active material 100A is, for example, 600 ppm or less, more preferably. It is preferable that the concentration be 100 ppm or less. The weight of manganese is determined, for example, by GD-MS. It can be analyzed.

[0280] Next, using Figures 26 to 29, we will examine the surface layer with and without added elements. I will now explain the results of the crystal structure calculation.

[0281] In particular, in the surface layer of lithium cobalt oxide that does not contain additive elements, cobalt oxide is present. There is a possibility of cobalt oxide containing metal defects. Figure 26A1 shows lithium cobaltate. Figure 26A2 shows the crystal structure of um (LCO) and the crystal structure of cobalt oxide (CoO). As shown in Figures 26A1 and 26A2, {110} of LCO and {110} of CoO The crystal orientations are roughly consistent, but the interplanes of {001}, which is perpendicular to {110} of LCO, are different. The gap is 1.405 nm, and the plane perpendicular to {110} of CoO is 6 times {1-11}. There is a 5.1% difference between this and the interplanar spacing of 1.477 nm.

[0282] Figure 26B1 shows lithium cobalt oxide (LCO) with cobalt oxide (CoO) in the surface layer. This is a schematic diagram. An enlarged view of the surface layer is shown in Figure 26B2. The surface layer contains LCO and CoO. Figure 26B3 shows the results of calculations using classical molecular dynamics for a portion of the LCO. The interplanar spacing of {001}, which is the plane perpendicular to {0}, and the plane of {110} of CoO, which is perpendicular to {1 Because there is a difference of more than 5% in the interplanar spacing which is 6 times that of {-11}, it is circled with a dashed line in Figure 26B3. As shown in the example, multiple shifts in the atomic arrangement occur. Such unstable areas are cobalt It is thought that oxygen is more easily released, which can lead to the formation of pits.

[0283] Furthermore, even in the case of lithium cobalt oxide containing additive elements, cobalt oxide is present in the surface layer. This can happen. Figure 27A1 shows the crystal structure of lithium cobalt oxide (LCO), and Figure 27A2 The crystal structure of cobalt oxide (CoO) is shown in the figure, assuming magnesium is used as an additive element. Figure 27A3 shows the crystal structure of magnesium oxide (MgO). Figures 27A1 to 27A3 show... As shown, the {110} of LCO and the {110} of CoO and MgO have matching oxygen sequences. It is topotaxis. Also, the plane {1-11} perpendicular to {110} of MgO A 6x interplanar spacing is 1.461 nm, which is the interplanar spacing of {001} in LCO, which is 1.405 nm. It is longer than m and shorter than 1.477 nm, which is six times the interplanar spacing of {1-11} in CoO. Therefore, the case where LCO and MgO are in contact is more lattice-dependent than the case where LCO and CoO are in contact. It is thought that there is little alignment and little distortion.

[0284] Next, we will examine whether CoO and MgO form a solid solution. (1-x) Mg x Formation of O Energy is described in Non-Patent Document 5 as ATAT (Alloy Theoretic Auto The analysis is performed using the MATED Toolkit software. ATAT stands for First Principles Mechanism. This software combines arithmetic and cluster expansion methods to efficiently advance structure exploration. Yes, there is. As for first-principles calculation software, there is VASP (Vienna Ab init Using the io Simulation Package, the calculation conditions are as shown in Table 1. I did. Using ATAT, Co (1-x) Mg x x in O is 0.125, 0.143. Figure 28A shows the results of exploring the placement for the cases of 0.250, 0.500, and 0.833. The gray parallelogram in Figure 28A represents an Mg-O octahedron (MgO6) with Mg at its center. This shows that the black parallelogram is a Co-O octahedron (CoO6) with Co at its center. This is what it demonstrates.

[0285] [Table 1]

[0286] As shown in Figure 28A, Co (1-x) Mg x The graph of the formation energy of O is convex downwards. Therefore, since solid solution is more stable, it is suggested that CoO and MgO can be dissolved in solid solution. It is also suggested that Co and Mg are dispersed in the solid solution state.

[0287] Co in a solid solution state (1-x) Mg x O has anisotropy in interplanar spacing, and LC in any crystal orientation It is difficult to determine whether it can become O and topotaxy. Therefore, the volume of the structural model for each proportion is The volume per metal atom, divided by the number of metal atoms in the structural model (10 -3 nm 3 )of Figure 28B shows the results of calculating the trend of changes in interplanar spacing. From Figure 28B, solid solution fracture of Mg. As the combination increases, (1-x) Mg xThe volume of O tends to decrease and approach that of MgO. This suggests that LCO and Co (1-x) Mg x On the surface in contact with O, L The discrepancy between the plane spacing of {001} in CO is expected to decrease.

[0288] Therefore, it is thought that CoO and MgO readily form a solid solution. When heated, CoO and MgO form a solid solution. As the dissolution progresses, the surface layer 100 of the positive electrode active material 100A changes from Figure 29A to Figure 29B. a contains solid solution Co (1-x) Mg x It is thought that O can be formed. (1-x) Mg x O has less lattice mismatch with LCO than CoO. Therefore, Co (1-x) Mg x O The surface layer 100a having this property is more likely to become topotaxis with the LCO in the interior 100b. Furthermore, as indicated by the length of the white arrows in Figures 29A and 29B, the stress decreases.

[0289] Thus, even when cobalt oxide is present on the surface of lithium cobalt oxide, By adding the additive elements and heating, the surface layer 100a is made of cobalt oxide and acid containing the additive elements. It can be formed into a solid solution of the ion. Therefore, the surface layer 100a of the positive electrode active material 100A and the inner Part 100b is prone to topotaxy. Therefore, the positive electrode activity is less likely to form pits. It can be made of substance 100A.

[0290] <Crystal structure> ≪Li x When x in CoO2 is 1 >> In one aspect of the present invention, the positive electrode active material 100A is in a discharge state, i.e., Li x In CoO2, x=1 In some cases, it is preferable to have a layered rock salt type crystal structure belonging to space group R-3m. Rock salt-type composite oxides have high discharge capacity and possess a two-dimensional lithium ion diffusion pathway. It is suitable for thium ion insertion / desorption reactions and is excellent as a positive electrode active material for secondary batteries. Therefore, in particular, the interior 100b, which accounts for most of the volume of the positive electrode active material 100A, has a layered rock salt type crystalline structure. It is preferable to have a structure. Figure 30 shows a layered rock salt type crystal structure with R-3m O3 attached. vinegar.

[0291] On the other hand, the surface layer 100a of the positive electrode active material 100A in one aspect of the present invention becomes positive electrode active material upon charging Even if lithium is removed from quality 100A, the internal 100b will still consist of an octahedron of transition metal M and oxygen. It is preferable that the layered structure has a function to reinforce it so that it does not break. Alternatively, the surface layer 100a It is preferable that it functions as a barrier film for the positive electrode active material 100A. Alternatively, the positive electrode active material 100 It is preferable that the outer surface portion 100a of A reinforces the positive electrode active material 100A. The reinforcement referred to here includes the removal of oxygen and other processes affecting the surface layer 100a of the positive electrode active material 100A. To suppress structural changes in the internal 100b, and / or the electrolyte of the positive electrode active material 100A This refers to suppressing oxidative decomposition on the surface.

[0292] Therefore, it is preferable that the surface layer 100a has a different crystal structure from the interior 100b. Furthermore, the surface layer 100a has a more stable composition and crystal structure at room temperature (25°C) than the interior layer 100b. It is preferable that it be a structure. For example, the surface layer 10 of the positive electrode active material 100A in one aspect of the present invention Preferably, at least a portion of 0a has a rock salt-type crystalline structure. Or the surface layer 10 It is preferable that 0a has both layered rock salt type and rock salt type crystal structures. Alternatively, the surface layer 100a preferably has characteristics of both layered rock salt type and rock salt type crystalline structures. It seems so.

[0293] The surface layer 100a is the region where lithium ions first desorb during charging, and the interior 100b This is a region where the lithium concentration tends to be lower than that. Also, the positive electrode active material of the surface layer 100a The atoms on the surface of material 100A can be described as having some of their bonds broken. Therefore, the surface layer 1 00a is prone to instability and is a region where degradation of the crystal structure is likely to begin. On the other hand, the surface layer If part 100a can be made sufficiently stable, Li x Even when x in CoO2 is small, for example, Even if x is less than or equal to 0.24, the layered structure consisting of an octahedron of the transition metal M and oxygen in the interior 100b can be broken. It can be made more difficult. Furthermore, it consists of an octahedron of the transition metal M and oxygen in the interior 100b. This can suppress the shifting of layers.

[0294] In order to give the surface layer 100a a stable composition and crystal structure, the surface layer 100a contains added elements. It is preferable to have A, and more preferable to have multiple additive elements A. Also, the surface layer 1 00a has a higher concentration of one or more selected elements A than the internal 100b. Preferred. Also, one or more elements selected from the additive elements A present in the positive electrode active material 100A are concentrated. It is preferable that it has a degree gradient. Furthermore, the positive electrode active material 100A is distributed by the added element A. It is more preferable that they are different. For example, due to the addition of element A, the concentration peaks are different from the surface. It is preferable that the depths differ. The concentration peak referred to here is the surface layer 100a Alternatively, it refers to the maximum concentration value at a depth of 50 nm or less from the surface.

[0295] For example, some of the additive elements A include magnesium, fluorine, nickel, titanium, silicon, and phosphorus. Boron, calcium, etc., are present from the interior 100b to the surface, as indicated by the density of the hatches in Figure 2A. It is preferable to have a concentration gradient that increases towards the end. Let's call this added element X.

[0296] Other additive elements A, such as aluminum and manganese, are shown in Figure 2B by the density of the hatches. It is preferable that the mixture has a concentration gradient and a concentration peak in a region deeper than that shown in Figure 2A. The concentration peak may be located in the surface layer 100a, or it may be located deeper than the surface layer 100a. For example, having a peak in the region between 5 nm and 30 nm from the surface towards the interior. This is preferable. An element having such a concentration gradient will be referred to as additive element Y.

[0297] For example, magnesium, one of the additive elements X, is divalent, and magnesium ions are found in layered rocks. In salt-type crystal structures, the lithium site is more stable than the transition metal M site. Therefore, it easily enters the lithium site. Magnesium is in the lithium site of the surface layer 100a. By being present at an appropriate concentration, it is possible to easily maintain the layered rock salt type crystalline structure. The magnesium present in the thium site functions as a pillar supporting the CoO2 layers. It is presumed that the presence of magnesium means that Li x For example, if x in CoO2 is 0 At a temperature of 0.24 or lower, the desorption of oxygen around magnesium can be suppressed. The presence of magnesium is expected to increase the density of the positive electrode active material 100A. Furthermore, if the magnesium concentration in the surface layer 100a is high, the hydrofluoric acid produced by the decomposition of the electrolyte will be affected. It can also be expected that the corrosion resistance will improve.

[0298] Magnesium, at appropriate concentrations, negatively affects the insertion and removal of lithium during charging and discharging. The above benefits can be enjoyed without affecting lithium. However, if magnesium is in excess, lithium This may adversely affect insertion and deinsertion. Furthermore, it may reduce the effect on stabilizing the crystal structure. This can happen. This is because magnesium, in addition to lithium sites, is a transition metal M-site. This is thought to be because it will also be able to enter the to Unwanted magnesium compounds (oxides and fluorides, etc.) that are not substituted are present in the positive electrode active material. It may segregate on surfaces and become a resistive component in secondary batteries. Also, magnesium in the positive electrode active material. As the concentration increases, the discharge capacity of the positive electrode active material may decrease. This is due to lithium This is thought to be because too much magnesium is present at the site, reducing the amount of lithium that contributes to charging and discharging. It can be done.

[0299] Therefore, it is preferable that the total amount of magnesium in the positive electrode active material 100A is appropriate. For example, the positive electrode active material 100A of one aspect of the present invention has a ratio of the sum of the transition metals M The magnesium ratio (Mg / M) is preferably 0.25% to 5%, and preferably 0.5% to 2%. A percentage of % or less is more preferable, and about 1% is even more preferable. This refers to the entire positive electrode active material 100A. The amount of magnesium present is, for example, determined by GD-MS, ICP-MS, etc., using the positive electrode active material. This could be the value obtained from the overall elemental analysis of 100A, or the value obtained from the process of preparing the positive electrode active material 100A. It may also be based on the values ​​of the raw material blend at a given time.

[0300] Furthermore, nickel, one of the additive elements X, is either a transition metal M site or a lithium site. It can also be present. When present at the transition metal M site, the redox potential is different compared to cobalt. This is desirable because it leads to an increase in discharge capacity due to the lower value.

[0301] Furthermore, when nickel is present at the lithium site, it forms a layer consisting of an octahedron of transition metal M and oxygen. The displacement of the structural components can be suppressed. Furthermore, changes in volume associated with charging and discharging can be suppressed. Also, the elastic modulus... It gets bigger, meaning it becomes harder. This is because the nickel present in the lithium site also becomes harder. It is presumed that this is because they function as pillars supporting the layers together. Therefore, they are particularly vulnerable to high temperatures, such as 45°C. It is preferable that the crystal structure becomes more stable in the above charging state.

[0302] On the other hand, an excess of nickel may increase the distortion caused by the Jahn-Teller effect. Furthermore, an excess of nickel may adversely affect the insertion and removal of lithium. .

[0303] Therefore, it is preferable that the total amount of nickel contained in the positive electrode active material 100A is appropriate. For example, the number of nickel atoms in positive electrode active material 100A exceeds 0% of the number of cobalt atoms. Preferably 7.5% or less, preferably 0.05% to 4%, and preferably 0.1% to 2%. The lower end is preferable, and 0.2% to 1% is more preferable. Or, greater than 0% and 4% or less is preferable. It is preferable that it is greater than 0% and less than or equal to 2%. Or that it is between 0.05% and 7.5%. Preferred. Or, 0.05% to 2% is preferred. Or, 0.1% to 7.5% is preferred. Preferably, 0.1% to 4%. The amount of nickel shown here is, for example, These are values ​​obtained by performing an overall elemental analysis of the positive electrode active material using GD-MS, ICP-MS, etc. Alternatively, it may be based on the values ​​of the raw material composition during the process of manufacturing the positive electrode active material.

[0304] Furthermore, aluminum, one of the additive elements Y, is a transition metal M in the layered rock salt crystal structure. It can be present on the site. Aluminum is a trivalent typical element and its valence does not change, therefore it is charged Even during electricity generation, lithium around aluminum is difficult to move. Therefore, aluminum and its surroundings The lithium acts as a pillar, which can suppress changes in the crystal structure. Also, the surrounding aluminum It has the effect of suppressing the elution of transition metal M and improving continuous charging resistance. Also, the Al-O bond Because it is stronger than the Co-O bond, it can suppress the elimination of oxygen around the aluminum. These effects improve thermal stability. Therefore, aluminum is used as the additive element Y. Having this feature improves safety when used in secondary batteries. Furthermore, crystals can be maintained even after repeated charging and discharging. This allows for the creation of a positive electrode active material 100A that is less prone to structural collapse.

[0305] On the other hand, an excess of aluminum may negatively affect the insertion and removal of lithium. ru.

[0306] Therefore, it is preferable that the total amount of aluminum in the positive electrode active material 100A is appropriate. For example, the total number of aluminum atoms in the positive electrode active material 100A is equal to the number of cobalt atoms. Preferably, the number of offspring is 0.05% to 4%, preferably 0.1% to 2%, and 0.3%. A concentration of 1.5% or less is more preferable. Or a concentration of 0.05% to 2% is preferable. Or 0 0.1% to 4% is preferred. The amount referred to here in relation to the entire positive electrode active material 100A is... For example, elemental analysis of the entire positive electrode active material 100A is performed using GD-MS, ICP-MS, etc. It may be any value, or it may be based on the raw material composition value in the process of manufacturing the positive electrode active material 100A. It's okay to be there.

[0307] Furthermore, fluorine, one of the added elements X, is a monovalent anion, and in the surface layer 100a When some of the oxygen is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of the cobalt ion associated with lithium desorption differs depending on the presence or absence of fluorine. For example, if it does not contain fluorine, it is trivalent to tetravalent, and if it contains fluorine, it is divalent to trivalent. This is due to the different oxidation-reduction potentials of the balt ions. Therefore, the surface layer of the positive electrode active material 100A If some of the oxygen in 100a is replaced by fluorine, then lithium ions near the fluorine... It can be said that the detachment and insertion of the battery occur smoothly. Therefore, when used in a secondary battery, Discharge characteristics, current characteristics, etc. can be improved. Also, the surface that comes into contact with the electrolyte The presence of fluorine in the surface layer 100a effectively improves corrosion resistance to hydrofluoric acid. It can be made possible. Also, as will be described in later embodiments, lithium fluoride and other fluoride If the melting point of the phosphate is lower than the melting point of the other additive element A source, the melting point of the other additive element A source is... It can function as a fluxing agent (also called a deconforming agent).

[0308] Furthermore, titanium oxide, one of the additive elements X, is known to be superhydrophilic. Therefore, by using a positive electrode active material 100A having titanium oxide in the surface layer 100a, the electrode It may improve wettability with highly solvent-resistant solvents. (Positive electrode active material when used in a secondary battery) The 100A resistor and the highly polar electrolyte interface have good contact, which suppresses the increase in internal resistance. There is a possibility that this will happen.

[0309] Furthermore, if phosphorus, one of the additive elements X, is present in the surface layer 100a, Li x x during CoO2 When the value is kept low, it is preferable that a short circuit can be suppressed. For example, it is preferable that the compound containing phosphorus and oxygen exists in the surface layer 100a.

[0310] If the positive electrode active material 100A contains phosphorus, hydrogen fluoride is generated by the decomposition of the electrolyte. The reaction with phosphorus may potentially lower the hydrogen fluoride concentration in the electrolyte, which is preferable.

[0311] If the electrolyte contains LiPF6, hydrolysis may generate hydrogen fluoride. Furthermore, polyvinylidene fluoride (PVDF) and alkali are used as components of the positive electrode. This reaction may generate hydrogen fluoride, which could lead to a decrease in the hydrogen fluoride concentration in the electrolyte. This may help suppress corrosion and / or peeling of the coating on the current collector. This may help suppress the decrease in adhesiveness due to gelation and / or insolubilization of PVDF.

[0312] If the positive electrode active material 100A contains phosphorus along with magnesium, Li x Small x in CoO2 The stability in the refractory state is extremely high, which is desirable. The positive electrode active material 100A contains phosphorus. In this case, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, and preferably 2% to 1%. 0% or less is more preferable, and 3% to 8% is even more preferable. Or 1% to 10% or less. The lower is preferable. Or 1% to 8% is preferable. Or 2% to 20% is preferable. i. Or preferably 2% to 8%. Or preferably 3% to 20%. Or Preferably, the amount is between 3% and 10%. In addition, the number of magnesium atoms is equal to the number of cobalt atoms. Preferably between 0.1% and 10%, more preferably between 0.5% and 5%, and 0.7% or more. 4% or less is more preferable. Or 0.1% to 5% is preferable. Or 0.1% or more. Preferably 4% or less. Or preferably 0.5% to 10%. Or preferably 0.5% to 4%. Preferably less than %. Or preferably 0.7% to 10%. Or 0.7% to 5%. The following is preferable. The phosphorus and magnesium concentrations shown here are, for example, determined by GC-MS, IC50. The values ​​may also be those obtained by performing an overall elemental analysis of the positive electrode active material 100A using P-MS, etc. This may also be based on the raw material composition values ​​during the manufacturing process of the positive electrode active material 100A.

[0313] Furthermore, if the positive electrode active material 100A has cracks, the positive electrode active material with the cracks on its surface Inside, for example in the embedded part, there is phosphorus, or more specifically, a compound containing phosphorus and oxygen. This can help suppress the progression of cracks.

[0314] Furthermore, if the surface layer 100a contains both magnesium and nickel, divalent nickel Near Li, divalent magnesium may be able to exist more stably. x C Even when x in oO2 is small, magnesium elution can be suppressed. Therefore, the surface layer 10 This could contribute to the stabilization of 0a.

[0315] Furthermore, if you have both additive elements X and Y, which have different distributions of additive element A, then It is preferable that the crystal structure can be stabilized over a wide range. For example, the positive electrode active material 100A is of the added element X Magnesium and nickel, which are part of the composition, and aluminum, which is one of the additive elements Y, together Having this results in a wider range of crystal structures than when only one of the additive elements X or Y is present. This can stabilize the positive electrode active material 100A, which contains both additive element X and additive element Y. In this case, surface stabilization can be adequately achieved by additive element X such as magnesium, Additive elements Y, such as luminium, are not essential on the surface. Rather, aluminum is used in deeper regions. For example, a wider distribution in the region between 5 nm and 50 nm from the surface is more advantageous. This is preferable because it stabilizes the crystal structure in the region.

[0316] As described above, when there are multiple additive elements A, the effects of each additive element A synergistically affect the surface. This can contribute to further stabilization of part 100a. In particular, magnesium, nickel and aluminum The presence of um is highly desirable as it provides a stable composition and crystal structure.

[0317] However, if the surface layer 100a is occupied only by a compound of additive element A and oxygen, lithium insertion This is undesirable because it makes ingress and detachment difficult. For example, if the surface layer 100a is MgO, M Structures in which gO and NiO(II) are in solid solution, and / or MgO and CoO(II) are in solid solution. It is undesirable for the structure to consist solely of this. Therefore, the surface layer 100a must contain at least cobalt It has a lithium element, and in the discharged state, it also has lithium, and has a path for lithium insertion and removal. It is necessary.

[0318] To ensure sufficient pathways for lithium insertion and removal, the surface layer 100a is made of magnesium. A higher cobalt concentration is preferable. For example, the number of magnesium atoms (Mg) and cobalt. The ratio of Co atoms to Mg / Co is preferably 0.62 or higher. Also, the surface layer 100 It is preferable that the concentration of cobalt in a is higher than that of nickel. Also, the surface layer 100a is aluminum. It is preferable that the concentration of cobalt is higher than that of nium. Also, the surface layer 100a is preferable to fluorine. A high cobalt concentration is preferable.

[0319] Furthermore, too much nickel may inhibit lithium diffusion, therefore the surface layer 100 It is preferable that the concentration of magnesium in a is higher than that of nickel. For example, nickel atoms The number is preferably 1 / 6 or less of the number of magnesium atoms.

[0320] Furthermore, some of the additive element A, particularly magnesium, nickel, and aluminum, are internally 10 Although it is preferable that the concentration in the surface layer 100a is higher than that in the interior 100b, It is preferable that magnesium and aluminum be present in a dilute state. When present at the lithium site at an appropriate concentration, it maintains a layered rock salt-type crystalline structure, similar to the above. It has the effect of making it easier. Also, nickel is present in the internal 100b at an appropriate concentration. This can suppress the displacement of the layered structure consisting of octahedra of the transition metal M and oxygen, similar to the above. Furthermore, when magnesium and nickel are present together, divalent magnesium is present near divalent nickel. A phase that suppresses magnesium leaching, as magnesium may be able to exist more stably. A multiplicative effect can be expected.

[0321] ≪Li x When x is small during CoO2≫ In one aspect of the present invention, the positive electrode active material 100A has the above-mentioned additive element A in the discharge state. Due to having a distribution and / or crystal structure, Li x When x is small in CoO2 The crystal structure in this state differs from that of conventional positive electrode active materials. Here, x being small means 0.1 <x This means ≤ 0.24.

[0322] Using Figures 30 to 34, Li x Regarding the change in crystal structure associated with the change in x in CoO2 Next, we will explain this while comparing a conventional positive electrode active material with a positive electrode active material 100A according to one embodiment of the present invention.

[0323] Figure 31 shows the changes in the crystal structure of a conventional positive electrode active material. The conventional positive electrode active material shown in Figure 31 is In particular, lithium cobalt oxide (LiCoO2) that does not contain additive element A. Changes in the crystal structure of lithium cobalt oxide without A are described in Non-Patent Documents 1 to 3, etc. It is stated.

[0324] Figure 31 shows Li with R-3m O3 attached. x Lithium cobalt oxide with x=1 exists in CoO2 It shows the following crystal structure. In this crystal structure, lithium is at the octahedral site. It occupies the space, and there are three CoO2 layers in the unit cell. Therefore, this crystal structure is O3 type It is sometimes called a crystal structure. The CoO2 layer is an octahedral structure in which oxygen atoms are coordinated to cobalt in a 6-coordinate manner. A structure is defined as a continuous structure on a plane with shared edges. This is defined as a cobalt and oxygen 8 It can also be described as a layer made up of faces.

[0325] Furthermore, in conventional lithium cobalt oxide, the symmetry of lithium increases when x = approximately 0.5. It is known to have a crystal structure that belongs to the monoclinic space group P2 / m. A single CoO2 layer exists within the unit cell. Therefore, it is called O1 type, or monoclinic O1 type. There are cases where this happens.

[0326] Furthermore, the positive electrode active material at x=0 has a crystal structure of the trigonal space group P-3m1, and A single CoO2 layer exists within the beam unit cell. Therefore, this crystal structure is called O1 type, may sometimes be referred to as trigonal O1 type. Further, a trigonal crystal can be converted into a composite hexagonal lattice, and the hexagonal O1 type is also sometimes used for reference.

[0327] In addition, conventional lithium cobaltate when x is approximately 0.12 has a crystal structure of space group R-3m. This structure can also be described as a structure in which a CoO2 structure like the trigonal O1 type and a LiCoO2 structure like R-3m O3 are alternately stacked. For this reason, this crystal structure is sometimes referred to as the H1-3 type crystal structure. Note that unevenness can actually occur in the intercalation and deintercalation of lithium,[{END]] so experimentally the H1-3 type crystal structure is observed from when x is approximately 0.25. Further , in actuality, the number of cobalt atoms per unit cell in the H1-3 type crystal structure is twice that in other structures. However, for ease of comparison with other crystal structures in the present specification including FIG. 31, the c-axis of the H1-3 type crystal structure is illustrated as being 1 / 2 that of the unit cell.

[0328] As an example, the H1-3 type crystal structure is described in Non-Patent Document 3, wherein the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), O2(0, 0, 0.11535±0. 00045). O1 and O2 are each an oxygen atom. Regarding which unit cell should be used to represent the crystal structure of the positive electrode active material , this can be determined, for example, by Rietveld analysis of an XRD pattern. In this case, a unit cell that gives a small GOF (goodness of fit) value may be adopted.

[0329] Li x When charging that causes x in LixCoO2 to be 0.24 or less and discharging are repeated, conventional​​ Lithium cobalt oxide has an H1-3 type crystal structure and a R-3m O3 structure in the discharged state. During this process, changes in the crystal structure (i.e., non-equilibrium phase transitions) occur repeatedly.

[0330] However, these two crystal structures show a large displacement of the CoO2 layer. (See dotted line in Figure 31) And as indicated by the arrows, in the H1-3 type crystal structure, the CoO2 layer is in a discharged state R-3m It deviates significantly from O3. Such dynamic structural changes affect the stability of the crystal structure. It could have negative effects.

[0331] Furthermore, these two crystal structures also differ significantly in volume. (Comparison based on the same number of cobalt atoms) In this case, the volume difference between the H1-3 type crystal structure and the R-3m O3 type crystal structure in the discharged state is 3. It exceeds 5%, typically 3.9% or higher.

[0332] In addition, the H1-3 type crystal structure has a continuous structure of CoO2 layers, similar to the trigonal O1 type. The structure is likely to be unstable.

[0333] Therefore, if you repeatedly perform charge-discharge cycles such that x becomes 0.24 or less, the conventional lithium cobalt oxide The crystal structure of the material breaks down. This breakdown of the crystal structure causes a deterioration in cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also the lithium This is because it becomes difficult to insert and remove the um.

[0334] On the other hand, in the positive electrode active material 100A of one embodiment of the present invention shown in Figure 30, Li x x in CoO2 The change in crystal structure between discharge state 1 and the state where x is 0.24 or less is different from that of conventional positive electrode active materials. The difference is small. More specifically, the CoO in the state where x is 1 and the state where x is 0.24 or less. The displacement between the two layers can be reduced. Also, the volume when compared per cobalt atom The change can be minimized. Therefore, in one embodiment of the present invention, the positive electrode active material 100A is such that x The crystal structure is resistant to breakdown even after repeated charging and discharging that results in a voltage of 0.24 or less, resulting in excellent cycle performance. The characteristics can be realized. Furthermore, the positive electrode active material 100A in one aspect of the present invention is Li x C In a state where x in oO2 is 0.24 or less, a more stable crystal structure than that of conventional positive electrode active materials is obtained. Therefore, the positive electrode active material 100A in one embodiment of the present invention is Li x x in CoO2 is 0. When the state is maintained at 24 or less, a short circuit is unlikely to occur. In such cases, two The next battery will have improved safety, which is preferable.

[0335] Li x When x in CoO2 is approximately 1 and 0.2, the inside of the positive electrode active material 100A The crystal structure of b is shown in Figure 30. The interior 100b occupies most of the volume of the positive electrode active material 100A. Because it occupies a large portion and contributes significantly to charging and discharging, the displacement and volume changes of the CoO2 layer are the most important factors. This can also be considered a problematic aspect.

[0336] When x=1, the positive electrode active material 100A exhibits the same R-3m O3 properties as conventional lithium cobalt oxide. It has the following crystal structure.

[0337] However, the positive electrode active material 100A is different from conventional lithium cobalt oxide, which has an H1-3 type crystal structure. When x is 0.24 or less, for example, around 0.2 and around 0.15, it is different from this. It has a crystalline structure.

[0338] When x = approximately 0.2, the positive electrode active material 100A of one embodiment of the present invention has a trigonal space group R has a crystal structure belonging to -3m. The symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is referred to as an O3'-type crystal structure. In FIG. 30, R-3m O3' is marked to show this crystal structure.

[0339] In the O3'-type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be represented as Co(0,0, 0.5), O(0,0,x), where x is within the range of 0.20≦x≦0.25. Regarding the lattice constant of the unit cell, for the a-axis, 2.797≦a≦2.837 (×10 -1 nm) is preferable, 2.807≦a≦2.827 (×10 -1 nm) is more preferable, and representatively a=2.817 (×10 -1 nm). For the c-axis, 13.681≦c≦13.881 ( ×10 -1 nm) is preferable, 13.751≦c≦13.811 is more preferable, and representatively c=13.781 (×10 -1 nm).

[0340] In the O3'-type crystal structure, ions such as cobalt, nickel, and magnesium occupy 6-coordination oxygen positions . Light elements such as lithium may occupy 4-coordination oxygen positions.

[0341] As indicated by the dotted line in FIG. 30, between R-3m O3 in a discharged state and the O3'-type crystal structure there is almost no shift in the CoO2 layer.

[0342] Furthermore, the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0343] As described above, in the positive electrode active material 100A according to one aspect of the present invention, Li xThe x in CoO2 is small. At that time, that is, when a lot of lithium is desorbed, the change in crystal structure is greater than that of conventional cathode active materials. This is also suppressed. Furthermore, the change in volume when comparing per the same number of cobalt atoms is also suppressed. Therefore, the positive electrode active material 100A undergoes repeated charging and discharging such that x becomes 0.24 or less. Even when reversed, the crystal structure is less likely to collapse. Therefore, the positive electrode active material 100A is suitable for charge-discharge cycles. The decrease in charge / discharge capacity is suppressed. In addition, more lithium can be stably used than in conventional positive electrode active materials. Because it can be used in this way, the positive electrode active material 100A has a large discharge capacity per unit weight and per unit volume. Therefore, by using positive electrode active material 100A, the discharge capacity per unit weight and per unit volume is increased. It is possible to manufacture large quantities of rechargeable batteries.

[0344] The positive electrode active material 100A is Li x When x in CoO2 is between 0.15 and 0.24 It has been confirmed that it may have an O3' type crystal structure, and x is greater than 0.24 and greater than 0.27. It is also presumed to have an O3' type crystal structure below. However, the crystal structure is Li x OO Because it is affected not only by x in 2, but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc. It is not necessarily limited to the above range of x.

[0345] Therefore, the positive electrode active material 100A is Li x In CoO2, x is greater than 0.1 and less than or equal to 0.24. In this case, it is not necessary for all of the interior 100b of the positive electrode active material 100A to have an O3' type crystal structure. It may contain other crystalline structures, or it may be partially amorphous.

[0346] Also Li x To make x in CoO2 small, it is generally necessary to charge with a high charging voltage. Therefore, Li x When x in CoO2 is small, it is charged with a high charging voltage. This can be rephrased as "state." For example, using the potential of lithium metal as a reference, it would be 4.6V or higher. When CC / CV charging is performed at this voltage in a 25°C environment, conventional positive electrode active materials produce H1-3 type crystals. The structure becomes apparent. Therefore, a charging voltage of 4.6V or higher, based on the potential of lithium metal, is considered high. This can be called the charging voltage. Furthermore, unless otherwise specified in this specification, the term "charging voltage" is used. This is expressed using the potential of lithium metal as the reference.

[0347] Therefore, the positive electrode active material 100A in one aspect of the present invention can be used at high charging voltages, for example, at 25°C. Even when charged at a voltage of 4.6V or higher, it maintains a crystal structure with the symmetry of R-3mO3. This can be rephrased as "it is preferable because it allows for higher charging voltages, for example, 25°C." When charged with a voltage of 4.65V to 4.7V, it can adopt an O3' type crystal structure. This can be rephrased as "it is preferable for that reason."

[0348] Even with a positive electrode active material of 100A, the H1-3 type crystal was only observed when the charging voltage was further increased. This may occur. Also, as mentioned above, the crystal structure is related to the number of charge / discharge cycles, charge / discharge current, and electrolyte. Because it is affected by factors such as the following, if the charging voltage is lower, for example, if the charging voltage is 4 at 25°C Even at voltages between 0.5V and 4.6V, the positive electrode active material 100A of one embodiment of the present invention has an O3' type crystal structure. There are cases where this is possible.

[0349] Furthermore, when graphite is used as the negative electrode active material in a secondary battery, for example, the graphite is more than described above. The voltage of the secondary battery decreases by the amount of the potential difference. The potential of graphite is based on the potential of lithium metal. It is approximately 0.05V to 0.2V. Therefore, secondary batteries using graphite as the negative electrode active material In this case, the same crystal structure is observed when the voltage obtained by subtracting the potential of graphite from the above voltage.

[0350] Furthermore, in O3' shown in Figure 30, lithium is present at all lithium sites with equal probability. As shown, but not limited to this, they may be concentrated in certain lithium sites, or For example, the monoclinic O1(Li) shown in Figure 31. 0.5 It may have symmetries like CoO2. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0351] Furthermore, the O3' type crystal structure has lithium randomly between the layers, but it is similar to the CdCl2 type. It can also be said that it is a crystal structure similar to the crystal structure. The crystal structure is lithium nickelate Li 0.06 The crystal structure when charged to NiO2 is similar However, the cathode active material is either pure lithium cobaltate or a layered rock salt type containing a large amount of cobalt. It is known that it does not usually adopt a CdCl2-type crystal structure.

[0352] Furthermore, the concentration gradient of additive element A is obtained at multiple locations on the surface layer 100a of the positive electrode active material 100A. It is preferable that the gradient is similar. In other words, the reinforcement originating from the added element A is in the surface layer 10 It is preferable that it is present homogeneously in 0a. Even if there is reinforcement in a part of the surface layer 100a, the reinforcement If there are missing parts, there is a risk of stress concentrating in those missing parts. When stress concentrates in a particular area, defects such as cracks can form, leading to cracking and discharge of the positive electrode active material. This could lead to a decrease in capacity.

[0353] However, the doped element A is not necessarily the same throughout the entire surface layer 100a of the positive electrode active material 100A. It is not necessary to have such a concentration gradient. An example of the distribution of additive element X near CD in Figure 1B is shown below. Figure 2C shows an example of the distribution of additive element Y near CD, as shown in Figure 2D.

[0354] Here, we assume that the surface near CD is parallel to the arrangement of cations. The distribution of additive element A on the row surface may differ from that of the other surfaces. For example, cation ion The surface parallel to the arrangement of elements and its surface layer 100a are selected from additive elements X and Y. The distribution of one or more concentration peaks is limited to the shallower portion from the surface compared to other orientations. It may be defined as follows: Alternatively, the surface parallel to the arrangement of cations and its surface layer 100a may be Compared to other orientations, the concentrations of one or more selected elements X and Y are It may be low. Alternatively, the surface parallel to the arrangement of cations and its surface layer 100a may contain the added element. One or more elements selected from X and the additive element Y may be below the detection limit.

[0355] In the layered rock salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This is a structure in which CoO2 layers and lithium layers are alternately stacked parallel to the (001) plane. Therefore, it can be said that the lithium ion diffusion pathway also exists parallel to the (001) plane. do.

[0356] Since the CoO2 layer is relatively stable, the surface on which the CoO2 layer exists is relatively stable. The main diffusion pathways of lithium ions during charging and discharging are not exposed on this surface.

[0357] On the other hand, on the plane not parallel to the arrangement of cations, that is, on the plane not parallel to the CoO2 layer, lithium The ion diffusion pathways are exposed. Therefore, the surface and surface layer are not parallel to the arrangement of cations. Section 100a is an important region for maintaining the lithium ion diffusion pathway, and at the same time, This region is prone to instability because it is the first region where the um ion is released. Reinforcing the non-parallel surfaces and surface layers 100a of the positive electrode active material 100A It is extremely important for maintaining the crystal structure.

[0358] Therefore, in the positive electrode active material 100A of another aspect of the present invention, the arrangement of cations is not parallel. The distribution of additive element A on the surface and its surface layer 100a is as shown in Figures 2A and 2B. It is important that they are present at a desirable depth, rather than being distributed only in the layer. On the other hand, positive ions As described above, the concentration of additive element A is low in the plane parallel to the arrangement of elements and in its surface layer 100a. It may be included, or it may not be included.

[0359] After preparing high-purity LiCoO2 as described in a later embodiment, the additive element A is added later. The manufacturing method, which involves mixing and heating, primarily involves the diffusion of lithium ions through which the added element A is absorbed. It spreads. Therefore, the added element A on the surface that is not parallel to the arrangement of cations and on its surface layer 100a This makes it easier to set the distribution within a favorable range.

[0360] Furthermore, it is preferable that the surface of the positive electrode active material 100A is smooth and has few irregularities, but it is not always necessary. However, not all of the positive electrode active material 100A is like that. Layered rock salt type crystal structure of R-3m The composite oxide having the following characteristics is formed on a plane parallel to the arrangement of cations, for example, on the plane where lithium is arranged. This makes slippage more likely. For example, there is a surface where lithium is arranged as shown in Figure 32A. In this case, the lithium is arranged as shown by the arrows in Figure 32B through processes such as pressing. Slippage can occur parallel to the surface, potentially causing deformation.

[0361] In this case, the newly formed surface and its surface layer 100a as a result of the slip are supplied with the additive. Element A may not exist or may be below the detection limit. EF in Figure 32B slips. This is an example of a newly formed surface and its surface layer 100a. A magnified view of the area near EF. Figures 32C1 and 32C2 show this. In Figures 32C1 and 32C2, Figures 2A to Figure Unlike 2D, the additive elements X and Y are not distributed.

[0362] However, slip tends to occur parallel to the arrangement of cations, so the newly formed surface and The surface layer 100a tends to be parallel to the lithium diffusion pathway. In this case, lithium ions Because the diffusion pathway is not exposed and it is relatively stable, additive element A is either absent or below the detection limit. Even so, there are hardly any problems.

[0363] As mentioned above, it has a layered rock salt type with a composition of LiCoO2 and a crystal structure of R-3m. In the composite oxide, cobalt and lithium are arranged parallel to the (001) plane. Also, HAAD In F-STEM images, cobalt, which has the highest atomic number in LiCoO2, shows the highest brightness. Therefore, in HAADF-STEM images, the arrangement of high-luminosity atoms is cobalt. This can be considered an array. The repetition of this high-luminosity array is synonymous with crystal fringes or lattice fringes. .

[0364] ≪Grain Boundaries≫ In addition to the distribution described above, the additive element A in the positive electrode active material 100A of one aspect of the present invention is It is more preferable that at least a portion of the particles are concentrated at or near the grain boundaries.

[0365] In this specification, etc., "uneven distribution" refers to a situation where the concentration of an element in one region differs from that in other regions. This refers to segregation, precipitation, heterogeneity, unevenness, or a mixture of areas with high and low concentrations. It is synonymous with "to do".

[0366] For example, the magnesium concentration at and near the grain boundaries of the positive electrode active material 100A is internally 1 It is preferable that the fluorine concentration in and near the grain boundaries is higher than in other regions of 00b. It is also preferable that the internal 100b region is higher than other regions. It is also preferable that the Kell concentration is higher than in other regions of the interior 100b. It is preferable that the aluminum concentration in the surrounding area is also higher than in other areas of the interior 100b.

[0367] Grain boundaries are a type of surface defect. Therefore, like surfaces, they tend to be unstable and can alter the crystal structure. Chemical reaction is likely to begin. Therefore, if the concentration of additive element A is high at and near the grain boundaries, This allows for more effective suppression of changes in the crystal structure.

[0368] Furthermore, if the magnesium and fluorine concentrations are high at and near the grain boundaries, this will occur Even if a crack occurs along the grain boundary of the positive electrode active material 100A in one aspect of the clarity, Magnesium and fluorine concentrations increase near the surface created by the process. This method can improve the corrosion resistance of the positive electrode active material to hydrofluoric acid even after rack formation.

[0369] <Particle size> In one embodiment of the present invention, the particle size of the positive electrode active material 100A is such that if it is too large, lithium diffusion becomes difficult. However, there are problems such as the surface of the active material layer becoming too rough when it is coated onto the current collector. If it is too small, it becomes difficult to support the active material layer when coating the current collector, and the reaction with the electrolyte becomes excessive. Problems such as excessive propagation also arise. Therefore, the median diameter (D50) should be 1 μm or more. It is preferable that the particle size is 2 μm or less, more preferably 2 μm or more and 40 μm or less, and 5 μm or more and 3 μm or less. 0 μm or less is more preferable. Or 1 μm to 40 μm is preferable. Or 1 μm Preferably, the particle size is 30 μm or less. Or, preferably, 2 μm or more and 100 μm or less. Or, 2 μ m to 30 μm is preferred. Or 5 μm to 100 μm is preferred. Or 5 A particle size of 40 μm or more is preferred.

[0370] <Analysis method> A certain positive electrode active material is Li x When x in CoO2 is small, it has a crystal structure of the O3' type. Whether or not it is a positive electrode active material 100A according to one aspect of the invention depends on Li x The positive electrode with a small x in CoO2 The positive electrode containing the active material is subjected to XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), This can be determined by analyzing it using methods such as nuclear magnetic resonance (NMR).

[0371] In particular, XRD can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution. It is possible to compare the crystallinity and crystal orientation, the periodic strain of the lattice and crystallites. Even if the positive electrode obtained by disassembling a secondary battery is measured directly, the size can be analyzed, and sufficient accuracy can be achieved. It is preferable in that it can be obtained, etc. Among XRDs, in powder XRDs, the positive electrode active material 100A Diffraction peaks reflecting the crystal structure of internal 100b of positive electrode active material 100A, which occupies the majority of the volume. You can obtain this.

[0372] The positive electrode active material 100A in one aspect of the present invention is Li x x during CoO2 A characteristic feature is that there is little change in the crystal structure when the value is 1 and when it is 0.24 or less. High voltage When charged, materials in which the crystal structure changes significantly and where the crystal structure accounts for more than 50% are subjected to high voltage. This is undesirable because it cannot withstand the charging and discharging cycles.

[0373] Also, note that simply adding element A may not result in the formation of an O3' type crystal structure. Caution is necessary. For example, lithium cobalt oxide containing magnesium and fluorine, or They share the common characteristic of being lithium cobalt oxide containing magnesium and aluminum. However, depending on the concentration and distribution of additive element A, Li x If x in CoO2 is 0.24 or less, then O3' When the H1-type crystal structure accounts for more than 60%, and when the H1-3 type crystal structure accounts for more than 50%. And, there is.

[0374] Furthermore, even with the positive electrode active material 100A of one embodiment of the present invention, if x is too small, such as 0.1 or less, Alternatively, under conditions where the charging voltage exceeds 4.9V, H1-3 type or trigonal O1 type crystals may be used. A structure may also be formed. Therefore, whether or not it is positive electrode active material 100A according to one embodiment of the present invention To determine this, analysis of the crystal structure, including XRD, and charging capacity or charging Voltage and other information are required.

[0375] However, in cases where x is small, the positive electrode active material may undergo a change in its crystal structure when exposed to the atmosphere. There are cases where the crystal structure changes from an O3' type to an H1-3 type. Therefore, all samples used for crystal structure analysis are handled in an inert atmosphere such as an argon atmosphere. It is preferable to drink.

[0376] Furthermore, is the distribution of additive element A in a certain positive electrode active material in the state described above? Whether or not this is the case can be determined, for example, by XPS, energy-dispersive X-ray spectroscopy (EDX). Persistive X-ray Spectroscopy, EPMA (Electron Probe Microscopic Analysis) This can be determined by analyzing the data using methods such as small-scale analysis.

[0377] Furthermore, the crystal structure of the surface layer 100a, grain boundaries, etc., is determined by the electron beam temperature of the cross-section of the positive electrode active material 100A. It can be analyzed by folding, etc.

[0378] ≪Charging method≫ Whether a certain composite oxide is the positive electrode active material 100A of one aspect of the present invention is determined by high-voltage charging This can be determined by performing the following: For example, if the composite oxide is used as the positive electrode and lithium is used as the counter electrode. Using this material, a coin cell (CR2032 type, 20mm in diameter and 3.2mm in height) was fabricated. High-voltage charging is the solution.

[0379] More specifically, the positive electrode is made of a slurry containing a positive electrode active material, a conductive material, and a binder. Alternatively, a positive electrode current collector made of aluminum foil coated with aluminum foil can be used.

[0380] Lithium metal can be used as the counter electrode. However, if a material other than lithium metal is used as the counter electrode... When this occurs, the potential of the secondary battery and the potential of the positive electrode are different. Voltage and potential in this specification, etc. Unless otherwise specified, this represents the potential of the positive electrode.

[0381] The electrolyte in the electrolyte solution contains 1 mol / L lithium hexafluoride phosphate (LiPF6). The electrolyte used is ethylene carbonate (EC) and diethyl carbonate (DEC). EC:DEC = 3:7 (volume ratio), vinylene carbonate (VC) is mixed at 2 wt%. You can use the one that you have.

[0382] A 25 μm thick porous polypropylene film can be used as the separator.

[0383] The positive electrode and negative electrode cans can be made of stainless steel (SUS). Cut.

[0384] The coin cell fabricated under the above conditions can be subjected to any voltage (for example, 4.5V, 4.55V, 4.5V, 4.5V). Up to 6V, 4.65V, 4.7V, 4.75V, or 4.8V, with a current of 10mA / g Constant current charging is performed. In order to observe the phase change of the positive electrode active material, charging with such a small current value is necessary. It is desirable to charge it. The temperature should be 25°C or 45°C. After charging in this way If you disassemble the coin cell in a glove box under an argon atmosphere and take out the positive electrode, A positive electrode active material with a desired charging capacity can be obtained. When performing various analyses afterward, the reaction with external components can be observed. To suppress this, it is preferable to seal it in an argon atmosphere. For example, XRD is sealed in an argon atmosphere. This can be done by sealing the device in an airtight container. Also, after charging is complete, the positive electrode can be removed promptly. It is preferable to subject it to analysis. Specifically, it is preferable to do so within 1 hour after charging is complete, and within 30 minutes. The inside is preferable.

[0385] Furthermore, when analyzing the crystal structure of the charged state after multiple charge-discharge cycles, the conditions of those multiple charge-discharge cycles are considered. The charging conditions may differ from those described above. For example, charging may be performed at any voltage (e.g., 4.6V). Up to 4.65V, 4.7V, 4.75V, or 4.8V, with a current value of 100mA / g. Charge with current, then charge with constant voltage until the current value reaches 10mA / g, and discharge at 2.5V, 1 Constant current discharge can be achieved at 00mA / g.

[0386] Furthermore, when analyzing the crystal structure of the discharged state after multiple charge-discharge cycles, for example, 2.5V A constant current discharge can be achieved with a current value of 100 mA / g.

[0387] ≪XRD≫ The equipment and conditions for XRD measurement are not particularly limited. For example, the following equipment and conditions It can be measured in units. XRD system: Bruker AXS D8 ADVANCE X-ray source:CuKα1 ray Output: 40KV, 40mA Slit width: Div.Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0388] If the sample to be measured is a powder, place it in a glass sample holder or grease Setting up can be done by methods such as sprinkling the sample onto a silicone anti-reflective plate coated with a special coating. Yes, it is possible. If the measurement sample is the positive electrode, attach the positive electrode to the substrate with double-sided tape, and then measure the positive electrode active material. The layers can be set to match the measurement surface required by the device.

[0389] The CuKα1 line, calculated from the O3' type crystal structure and the H1-3 type crystal structure model, The ideal powder XRD patterns are shown in Figures 33 and 34. In Figure 34, for comparison, Therefore Li x LiCoO2O3 at x=1 in CoO2, H1-3 type, and three at x=0 The ideal XRD pattern calculated from the crystal structure of gonal O1 is also shown. The patterns of (O3) and CoO2(O1) are ICSD (Inorganic Crysts) Results obtained from the tal Structure Database (see Non-Patent Document 4) From crystal structure information, one of the modules in Materials Studio (BIOVIA) This was created using Reflex Powder Diffraction. 2θ The range is 15° to 75°, with a step size of 0.01 and a wavelength of λ1 = 1.540. 562×10 -10 m, λ2 are not set, Monochromator is single and The H1-3 type crystal structure pattern was similarly created from the crystal structure information described in Non-Patent Document 3. Success. The O3' type crystal structure pattern is the XRD pattern of the positive electrode active material according to one embodiment of the present invention. The crystal structure was estimated from this, and TOPAS ver.3 (crystal structure analysis software manufactured by Bruker) was used. The garment was fitted, and an XRD pattern was created as with the others.

[0390] As shown in Figure 33, in the O3' type crystal structure, 2θ = 19.25 ± 0.12° (19 (0.13° or more and less than 19.37°), and 2θ = 45.47 ± 0.10° (45.37° Diffraction peaks appear at angles greater than or equal to 45.57°.

[0391] However, as shown in Figure 34, in the H1-3 type crystal structure and trigonal O1, these positions No peak appears. Therefore, Li x When x is small in CoO2, 2θ = 19.25 ±0.12° (19.13° or greater and less than 19.37°), and 2θ = 45.47 ± 0.1 The appearance of a diffraction peak at 0° (45.37° or more and less than 45.57°) is one of the characteristics of this invention. This can be considered a characteristic of the positive electrode active material 100A.

[0392] This is the position where the XRD diffraction peak appears in the crystal structure for x=1 and x≦0.24. It can also be said that they are close. More specifically, the main crystal structures for x=1 and x≦0.24 For the peaks among the folded peaks where 2θ is between 42° and 46°, the difference in 2θ is 0 It can be said that the angle is 0.7° or less, and more preferably 0.5° or less.

[0393] In one embodiment of the present invention, the positive electrode active material 100A is Li x When x in CoO2 is small, O3 It has a crystal structure of type ', but not all of them have to be of type O3'. Other crystal structures It may contain or be partially amorphous. However, regarding the XRD pattern... When Rietveld analysis is performed, it is preferable that the O3' type crystal structure accounts for 50% or more. It is more preferable that it be 60% or more, and even more preferable that it be 66% or more. O3 'The crystal structure of type ' accounts for 50% or more, more preferably 60% or more, and even more preferably 66% or more. If present, it can be used to create a cathode active material with sufficiently excellent cycle characteristics.

[0394] Furthermore, Rietveld analysis was performed even after more than 100 charge-discharge cycles from the start of measurement. When this occurs, it is preferable that the O3' type crystal structure accounts for 35% or more, and preferably 40% or more. Preferably, it is 43% or more, and even more preferably 43% or more.

[0395] Furthermore, the sharpness of the diffraction peaks in the XRD pattern indicates high crystallinity. The subsequent diffraction peaks should be sharp, i.e., have a narrow full width at half maximum (FMAX). FMAX is important for the same crystalline phase. The resulting peaks also differ depending on the XRD measurement conditions and the value of 2θ. In the case of the conditions, for peaks observed where 2θ = 43° or more and 46° or less, the full width at half maximum is, for example... Preferably, it is 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. It seems that not all peaks necessarily need to meet this requirement. Some peaks If this requirement is met, it can be said that the crystal phase has high crystallinity. This contributes to the stabilization of the crystal structure after sufficient charging.

[0396] Furthermore, the crystallite size of the O3' type crystal structure of the positive electrode active material 100A is determined by the discharge state. It only drops to about 1 / 20th of LiCoO2(O3). Therefore, the positive electrode before charging and discharging and Even under the same XRD measurement conditions, Li x When x in CoO2 is small, a clear O3' type is observed. The peaks of the crystal structure can be observed. On the other hand, in conventional LiCoO2, a portion of the crystal structure is of the O3' type. Even if a structure similar to the original can be adopted, the crystallite size will be smaller, and the peaks will be broad and small. The crystallite size can be determined from the full width at half maximum of the XRD peak.

[0397] ≪XPS≫ In X-ray photoelectron spectroscopy (XPS), in the case of inorganic oxides, monochromatic aluminum is used as the X-ray source. Using the Kα rays of the genus Mu, the depth from the surface is approximately 2 nm to 8 nm (typically less than 5 nm). Since analysis of the region up to that point is possible, approximately half of the region relative to the depth of the surface layer 100a is analyzed. This allows for the quantitative analysis of the concentration of each element. Furthermore, by performing narrow scan analysis... It can analyze the bonding state of elements. Note that the quantitative accuracy of XPS is typically ±1 atomic percent. The detection limit varies depending on the element, but it is approximately 1 atomic percent.

[0398] The positive electrode active material 100A in one aspect of the present invention is one or more concentrated elements selected from additive element A. It is preferable that the degree is higher in the surface layer 100a than in the interior 100b. The concentration of one or more elements selected from the additive element A in 0a is the total concentration of the positive electrode active material 100A. This is equivalent to saying that it is preferable for the result to be higher than the average. For example, if measured by XPS, The concentration of one or more additive elements A selected from the surface layer 100a is determined by ICP-MS ( Measured by inductively coupled plasma mass spectrometry (GD-MS) or glow discharge mass spectrometry (GD-MS), etc. It is preferable that the concentration of additive element A is higher than the average concentration of the entire positive electrode active material 100A. This can be done. For example, at least a portion of the surface layer 100a measured by XPS, etc. It is preferable that the magnesium concentration is higher than the total magnesium concentration in the positive electrode active material 100A. Furthermore, the nickel concentration in at least a portion of the surface layer 100a is the same as that of the entire positive electrode active material 100A. It is preferable that the nickel concentration is higher than that. Also, at least a portion of the surface layer 100a It is preferable that the aluminum concentration is higher than the total aluminum concentration of the positive electrode active material 100A. Furthermore, the fluorine concentration in at least a portion of the surface layer 100a is equal to the concentration of fluorine in the entire positive electrode active material 100A. It is preferable that the concentration is higher than that of fluorine.

[0399] Furthermore, the surface and surface layer 100a of the positive electrode active material 100A in one aspect of the present invention are positive electrode active material It is assumed that the carbonates, hydroxyl groups, etc., that were chemically adsorbed after the preparation of quality 100A do not contain any other components. Also, the positive electrode activity Electrolytes, binders, conductive materials, or compounds derived therefrom that adhere to the surface of substance 100A It is assumed that it is not included. Therefore, when quantifying the elements contained in the positive electrode active material, XPS and other methods are used. A correction is applied to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that may be detected in the surface analysis. It is also possible to do so. For example, in XPS, it is possible to separate the types of bonds through analysis, A correction may be made to exclude CF bonds originating from the diaphytic compound.

[0400] Furthermore, before subjecting the positive electrode active material to various analyses, the electrolyte, binder, and conductive material adhering to its surface must be examined. or to remove compounds derived therefrom, the sample such as the positive electrode active material and positive electrode active material layer is treated Washing may be performed. In this case, lithium may dissolve into the solvent used for washing. However, even in that case, the added element A is not easily dissolved, so the atoms of added element A It does not affect numerical ratios.

[0401] The concentration of additive element A may also be compared in ratio to cobalt. This allows for comparison while reducing the influence of carbon dioxide and other substances chemically adsorbed after the positive electrode active material has been fabricated. It is preferable. For example, the ratio of magnesium to cobalt atoms (Mg / C) determined by XPS analysis. o is preferably between 0.4 and 1.5. On the other hand, Mg by analysis using ICP-MS The value of / Co is preferably between 0.001 and 0.06.

[0402] Similarly, the positive electrode active material 100A is designed to ensure sufficient lithium insertion and removal pathways. It is preferable that the concentrations of lithium and cobalt in layer 100a are higher than those of each additive element A. It seems so. This is a selection of additive elements A present in the surface layer 100a, as measured by XPS, etc. Or, the concentration of lithium and cobalt in the surface layer 100a is higher than the concentration of each of the two or more added element A. It can be said that a higher concentration is preferable. For example, the surface layer measured by XPS, etc. The magnesium concentration in at least a portion of 100a is higher than that of the surface layer 1 measured by XPS, etc. It is preferable that the concentration of at least some of the cobalt in 00a is high. Similarly, magnesium It is preferable that the lithium concentration is higher than the nickel concentration. A high concentration of lithium is preferable. Similarly, a higher concentration of lithium is preferable to a higher concentration of nickel. It is preferable that the concentration of cobalt is higher than that of aluminum. Similarly, It is preferable that the lithium concentration is higher than the luminium concentration. Also, it is preferable that the fluorine concentration is higher. A high concentration of lithium is preferable. Similarly, a higher concentration of lithium than fluorine is preferable. It's nice.

[0403] Furthermore, additive elements Y, including aluminum, can reach deeper regions, for example, at depths from the surface. It is more preferable that the distribution is broad in the region between 5 nm and 50 nm. Therefore, ICP-M Analysis of the entire cathode active material 100A using S, GD-MS, etc. revealed that aluminum and other components were present. Although the additive element Y is detected, if it is below the detection limit in XPS, etc., it is preferable. It's nice.

[0404] Furthermore, when XPS analysis was performed on the positive electrode active material 100A according to one embodiment of the present invention, cobalt The number of magnesium atoms is preferably 0.4 to 1.2 times the number of atoms of the other atoms, and 0. A ratio of 65 times or more and 1.0 times or less is more preferable. Also, the ratio of nickel atoms to the number of cobalt atoms is The number of offspring is preferably 0.15 times or less, and more preferably 0.03 times or more and 0.13 times or less. The number of aluminum atoms is preferably 0.12 times or less than the number of cobalt atoms, and 0.0 A ratio of 9 times or less is more preferable. Also, the number of fluorine atoms should be 0.3 times or less compared to the number of cobalt atoms. A ratio of 0.9 times or less is preferable, and a ratio of 0.1 times or more and 1.1 times or less is more preferable.

[0405] When performing XPS analysis, for example, monochromatic aluminum Kα rays are used as the X-ray source. This is possible. Furthermore, the extraction angle can be set to, for example, 45°. For example, the following apparatus and conditions It can be measured using [this method]. Measurement device: PHI QuanteraII X-ray source: Monochromatic Al Kα (1486.6eV) Detection area: 100 μmφ Detection depth: Approximately 4-5 nm (extraction angle 45°) Measurement spectrum: Wide scan, narrow scan of each detected element

[0406] Furthermore, when XPS analysis was performed on the positive electrode active material 100A according to one embodiment of the present invention, fluorine and other The peak indicating the elemental bond energy is preferably between 682 eV and 685 eV. Furthermore, it is even more preferable that the voltage be around 684.3 eV. This is because of the bonded lithium fluoride Energy is 685 eV, and the bond energy of magnesium fluoride is 686 eV. It is a value different from any of V. In other words, the positive electrode active material 100A in one embodiment of the present invention is fluorine If present, it is preferable that the bond is other than lithium fluoride and magnesium fluoride. stomach.

[0407] Furthermore, when XPS analysis was performed on the positive electrode active material 100A according to one embodiment of the present invention, the magnesium The peak indicating the bond energy between um and other elements is between 1302 eV and 1304 eV. It is preferable that it be present, and more preferably that it be about 1303 eV. This is because of the fluoride This value is different from the bond energy of magnesium, which is 1305 eV, and is different from that of magnesium oxide. This value is close to the binding energy. In other words, the positive electrode active material 100A of one aspect of the present invention is magnesium If sium is present, it is preferable that the bond is one other than magnesium fluoride.

[0408] ≪EDX≫ One or more elements selected from the additive elements A present in the positive electrode active material 100A have a concentration gradient. It is preferable that the positive electrode active material 100A has a concentration peak due to the addition of element A. It is more preferable that the depth from the surface is different. The concentration gradient of additive element A is, for example, F The cross-section of the positive electrode active material 100A is exposed by IB (Focused Ion Beam), etc. Then, the cross-section is analyzed using energy-dispersive X-ray spectroscopy (EDX). X-ray spectroscopy, EPMA (electron probe microanalysis), etc. It can be evaluated by analyzing it using [this method].

[0409] EDX measurement is a method of measuring while scanning within a region and evaluating that region in two dimensions. This is called DX surface analysis. Measurements are taken while scanning linearly, and the atomic concentration is determined within the positive electrode active material. Evaluating fabric is called line analysis. Furthermore, data from linear regions is extracted from EDX surface analysis. The results obtained are sometimes called line analysis. Also, measuring a certain area without scanning is sometimes called line analysis. This is called point analysis.

[0410] EDX surface analysis (e.g., elemental mapping) reveals the surface layer 100a of the positive electrode active material 100A. The concentration of additive element A in the interior 100b and near grain boundaries is analyzed semi-quantitatively. This can be done. Furthermore, EDX radiation analysis can be used to analyze the concentration distribution and maximum value of additive element A. It is possible to perform analyses that thin the sample, such as STEM-EDX, which can determine depth. Regardless of the distribution of direction, the depth from the surface to the center of the positive electrode active material in a specific region It is preferable because it allows for the analysis of the concentration distribution in one direction.

[0411] Therefore, EDX surface analysis or EDX point analysis of the positive electrode active material 100A according to one embodiment of the present invention When analyzed, the concentrations of each additive element A in the surface layer 100a, especially additive element X, are found in the interior 100b. A higher value is preferable.

[0412] For example, regarding the positive electrode active material 100A having magnesium as the additive element X, the EDX surface When analyzed or EDX point analysis was performed, the magnesium concentration in the surface layer 100a was compared to the internal layer 100b. It is preferable that the magnesium concentration is higher than that. Also, when EDX radiation analysis is performed, the surface layer 1 The magnesium concentration peak in 00a is a deep ray from the surface to the center of the positive electrode active material 100A. It is preferable that it is present up to 3 nm, and more preferably up to a depth of 1 nm. Furthermore, it is even more preferable that it be present up to a depth of 0.5 nm. Also, the magnesium concentration is P It is preferable that the peak attenuates to 60% or less at a point 1 nm deep from the position. It is preferable that the peak attenuation is less than 30% at a point 2 nm deep from the position.

[0413] Furthermore, in positive electrode active material 100A having magnesium and fluorine as additive elements X, The distribution of fluorine is preferably superimposed on the distribution of magnesium. For example, the fluorine concentration is Preferably, the difference in depth direction between the peak and the magnesium concentration peak is within 10 nm. It is more preferable if it is within nm, and even more preferable if it is within 1 nm.

[0414] Furthermore, when EDX radiation analysis was performed, the peak in fluorine concentration in the surface layer 100a was found in the positive electrode active material 1. Preferably, it exists from the surface of 00A to a depth of 3 nm toward the center, and to a depth of 1 nm It is more preferable that it be present up to a certain depth, and even more preferable that it be present up to a depth of 0.5 nm. Furthermore, the peak of fluorine concentration is located slightly closer to the surface than the peak of magnesium concentration. This increases resistance to hydrofluoric acid, making it more desirable. For example, the peak of fluorine concentration is magnesium It is more preferable that the peak of the um concentration is 0.5 nm or more on the surface side, and more preferably 1.5 nm or more. It is even more preferable if it is on the surface side.

[0415] Furthermore, in the positive electrode active material 100A having nickel as the additive element X, the surface layer 100a is nickel The peak of the sacchar concentration is observed from the surface of the positive electrode active material 100A to a depth of 3 nm towards the center. It is preferable that it be present, more preferably that it be present up to a depth of 1 nm, and more preferably at a depth of 0.5 nm. It is even more preferable that they be present up to m. Also, a positive electrode having magnesium and nickel. In the active material 100A, it is preferable that the distribution of nickel overlaps with the distribution of magnesium. For example, the difference between the magnesium concentration peak and the depth of the magnesium concentration peak is 1. Preferably it is within 0 nm, more preferably within 3 nm, and preferably within 1 nm. It is preferable.

[0416] Furthermore, if the positive electrode active material 100A contains aluminum as the additive element Y, the EDX line segment When analyzed, the peak of magnesium and nickel was higher than the peak of aluminum concentration in the surface layer 100a. It is preferable that the peak of the concentration of Kel or fluorine is close to the surface. For example, aluminum concentration The peak is located at a depth of 0.5 nm to 50 nm from the surface to the center of the positive electrode active material 100A. It is preferable that it be located at the bottom, and more preferably at a depth of 5 nm to 50 nm. stomach.

[0417] Furthermore, when EDX radiation analysis, surface analysis, or point analysis was performed on the positive electrode active material 100A, the Magnesium The ratio of the number of magnesium atoms (Mg) to cobalt atoms (Co) at the peak of magnesium concentration (Mg / C) o) is preferably 0.05 to 0.6, and more preferably 0.1 to 0.4. The ratio of the number of aluminum atoms (Al) to cobalt atoms (Co) at the peak of the aluminum concentration (Al / C o) is preferably 0.05 or more and 0.6 or less, and more preferably 0.1 or more and 0.45 or less. The ratio of nickel (Ni) to cobalt (Co) atoms at the peak of the saturation concentration (Ni / Co) is A value of 0 or more and 0.2 or less is preferred, and a value of 0.01 or more and 0.1 or less is more preferred. In this mixture, the ratio of fluorine (F) to cobalt (Co) atoms (F / Co) should ideally be between 0 and 1.6. A value between 0.1 and 1.4 is preferable.

[0418] Furthermore, the surface of the positive electrode active material 100A in the EDX radiation analysis results can be analyzed as follows, for example: It can be determined that the elements uniformly present in the interior 100b of the positive electrode active material 100A are For example, for oxygen or cobalt, the point where the amount detected in internal 100b becomes half of that on the surface Let's assume that.

[0419] Since the positive electrode active material 100A is a composite oxide, the surface can be estimated using the amount of oxygen detected. This can be done. Specifically, first, from the region where the amount of oxygen detected in internal 100b is stable, oxygen Average concentration O ave We determine the area that is clearly outside the surface. Oxygen O, thought to be due to contact or background oxygen background Detected In that case, from the measurement value, background Subtracting this gives the average oxygen concentration O ave To do so This can be done. This average value is O ave Half of that value, that is, 1 / 2O ave Closest measurement The measurement point indicated can be presumed to be the surface of the positive electrode active material.

[0420] Furthermore, the surface can be estimated in the same way as above using the amount of cobalt detected. Similarly, estimation can be made using the sum of the detected amounts of several transition metals, including cobalt. The detection rate of transition metals is less affected by chemiadsorption, making it suitable for surface estimation.

[0421] Furthermore, when line analysis or surface analysis was performed on the positive electrode active material 100A, near the grain boundaries The ratio of additive element A to cobalt Co (A / Co) is preferably 0.020 to 0.50. Furthermore, a value of 0.025 or more and 0.30 or less is preferable. Furthermore, a value of 0.030 or more and 0.20 or less is preferable. The lower value is preferable. Or 0.020 or more and 0.30 or less is preferable. Or 0.020 or more and 0 A value of 0.20 or less is preferable. Or a value of 0.025 to 0.50 is preferable. Or 0.02 A value of 5 or more and 0.20 or less is preferable. Or a value of 0.030 or more and 0.50 or less is preferable. Or A value of 0.030 or higher and 0.30 or lower is preferable.

[0422] For example, when the additive element X is magnesium, line analysis or When surface analysis is performed, the ratio of magnesium to cobalt atoms near the grain boundary (Mg / Co) is preferably 0.020 to 0.50. More preferably 0.025 to 0.30. The lower value is preferable. Furthermore, a value between 0.030 and 0.20 is preferable. Or 0.020 or higher. A value of 0.30 or less is preferable. Or a value of 0.020 or more and 0.20 or less is preferable. Or 0.0 A value between 25 and 0.50 is preferable, or between 0.025 and 0.20 is preferable. It is preferable that it is between 0.030 and 0.50, or between 0.030 and 0.30. stomach.

[0423] ≪EPMA≫ EPMA (Electron Probe Microanalysis) can also quantify elements. With surface analysis, each element can be quantified. The distribution can be analyzed.

[0424] When EPMA surface analysis was performed on a cross-section of the positive electrode active material 100A according to one embodiment of the present invention, ED Similar to the analysis results for X, one or more elements selected from additive element A exhibit a concentration gradient. This is preferable. Also, the depth of the concentration peak from the surface differs depending on the added element A. This is more preferable. The preferred range of the concentration peaks for each additive element A is the same as in the case of EDX. That is the case.

[0425] However, EPMA analyzes the region from the surface down to a depth of about 1 μm. Therefore, each element The raw quantitative value may differ from the measurement result obtained using other analytical methods. For example, positive electrode active material 10 When surface analysis of 0A was performed by EPMA, the concentration of each additive element A present in the surface layer 100a was determined. However, the results may be lower than those obtained with XPS.

[0426] ≪Charging curve and dQ / dV vs sV curve≫ In one embodiment of the present invention, the positive electrode active material 100A exhibits a characteristic voltage change when charging. This can happen. The change in voltage can be obtained by differentiating the capacitance (Q) with respect to voltage (V) from the charging curve (dQ / dV). This can be read from the dQ / dVvsV curve obtained by ). For example, dQ / Around the peaks in the dVvsV curve, non-equilibrium phase transitions occur, and the crystal structure changes significantly. It is thought that this is the case. In this specification, a non-equilibrium phase change refers to a nonlinear physical change. This refers to the phenomenon of causing a change in shape.

[0427] According to one embodiment of the present invention, the positive electrode active material 100A exhibits a dQ / dVvsV curve of 4.55V There may be a broad peak nearby. The peak around 4.55V is from type O3 to O This reflects the voltage change during the phase transition to type 3'. Therefore, this peak is broad. One thing is that the energy required to extract lithium changes compared to when the peak is sharper. This means that there is little change in the crystal structure. However, this is preferable because it is less affected by the displacement and volume changes of the CoO2 layer.

[0428] More specifically, in the dQ / dV vs V curve of the charging curve, 4.5V to 4.6V When the maximum value appearing below is taken as the first peak, the full width at half maximum of the first peak is 0.10V or more. Having it present makes the flavor sufficiently broad, which is desirable.

[0429] When obtaining the dQ / dVvsV curve, charging is performed at a constant rate of 10mA / g up to, for example, 4.9V. Current charging is possible. Also, when obtaining the dQ / dV of the initial charge, 1 It is preferable to discharge the battery to 2.5V at 00mA / g before starting the above charging process.

[0430] The data acquisition interval during charging can be set to, for example, 1-second intervals or 1mV voltage fluctuations. The settings can be configured to capture the voltage and current at that time. The current value and time are integrated. The value is defined as the charging capacity.

[0431] The difference between the nth and (n+1)th data points of the above charging capacity data is the nth change in capacity dQ. This is the value of the nth element. Similarly, the difference between the nth and (n+1)th data points of the above voltage data is the voltage change. This is the nth value of the dV.

[0432] However, using the above data results in significant interference from minute noise, therefore, voltage and charging capacity The difference can also be calculated by taking a moving average of a certain number of intervals to find dQ / dV. It can be set to 500.

[0433] Specifically, calculate the average value of dQ from the nth to the n+500th element, and similarly calculate n of dV. Calculate the average value from the nth to the n+500th element. dQ(average of 500 elements) / dV(500) The average value (individual values) can be expressed as dQ / dV. In the dQ / dV vs V graph, the horizontal axis represents the voltage. Similarly, for pressure, the moving average values ​​from the nth to the n+500th interval are used as the number of intervals. This can be done. Note that when using a moving average as described above, the 501st data point from the end is used. The last data point will be heavily affected by noise, so it will not be used in the dQ / dV vs V graph. It is preferable.

[0434] Furthermore, when analyzing the dQ / dVvsV curve after multiple charge-discharge cycles, the multiple charge-discharge cycles are used. The conditions may differ from the above charging conditions. For example, charging may be at any voltage (e.g., 4.6 Constant current charging at 100mA / g (V, 4.65V, 4.7V, 4.75V or 4.8V) Then, it is charged at a constant voltage until the current value reaches 10mA / g, and discharged at 2.5V, 100mA. Constant current discharge can be achieved at / g.

[0435] Furthermore, the phase changes from O3 type to O3' type at around 4.55V, but at this time O3 The type is Li x The x value in CoO2 is approximately 0.3. This corresponds to the O3 type with x=1, as explained in Figure 31. It has the same symmetry, but the distance between the CoO2 layers is slightly different. In this specification, x When distinguishing between O3 types of different sizes, the O3 type with x=1 is designated as O3 (2θ=18.85°), Let's define O3 type with x = approximately 0.3 as O3 (2θ = 18.57°). This is XR In the D measurement, the position of the peak where 2θ appears around 19° corresponds to the interlayer distance of CoO2. That is the reason.

[0436] ≪Discharge curves and dQ / dV vs. sV curves≫ Furthermore, the positive electrode active material 100A according to one aspect of the present invention, after being charged with a high voltage, for example, 40m When discharging with a low current of less than A / g, a characteristic voltage change appears near the end of the discharge. Yes, this change appears around 3.9V in the dQ / dVvsV ratio calculated from the discharge curve. At a voltage lower than the peak, there is at least one peak in the range up to 3.5V. This can be clearly confirmed.

[0437] ≪ESR≫ In one aspect of the present invention, the positive electrode active material 100A contains cobalt, and nickel is used as the additive element A. It is preferable to have magnesium as a result. 3+ Ni 3+ Replaced with And also some Li + is Mg 2+ It is preferable that it be replaced with Li. + is Mg 2+ Replace with As a result of this, the Ni 3+ It is reduced to Ni 2+ This can sometimes happen. Also, some Li + is Mg 2+ It is replaced by Mg 2+ Nearby Co 3+ It is reduced to Co 2 + This can happen. Also, some Co 3+ is Mg 2+ It is replaced by Mg 2+ Nearby Co3+ is oxidized to form Co 4+ in some cases.

[0438] Therefore, the positive electrode active material 100A preferably contains one or more selected from Ni 2+ , Ni 3+ , Co 2+ and Co 4+ of any one or more of the above. Further, the spin density attributed to one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ per weight of the positive electrode active material 100A is preferably 2.0× 10 17 spins / g or more and 1.0×10 21 spins / g or less . By using the positive electrode active material 100A having the above spin density, the crystal structure especially in a charged state is stabilized, which is preferable. Note that if the magnesium concentration is too high, the spin density attributed to one or more of Ni 2+ , Ni 3+ , Co 2+ and Co 4+ may be lowered in some cases.

[0439] The spin density in the positive electrode active material can be analyzed using, for example, electron spin resonance (ESR: Electron Spin Resonance).

[0440] <<Surface Roughness and Specific Surface Area>> The positive electrode active material 100A according to one embodiment of the present invention preferably has a smooth surface with few irregularities . A smooth surface with few irregularities indicates that the effect of the flux described later is sufficiently exerted, and the surface of the additive element A source and the composite oxide has been melted. Therefore, this is one factor indicating that the distribution of the additive element A in the surface layer portion 100a is favorable. Good distribution means that it is one indicator that the distribution of additive element A in the surface layer portion 100a is favorable. Good distribution means that In other words, it means that the concentration distribution of added element A in the surface layer 100a is uniform.

[0441] A smooth surface with few irregularities is important, for example, in the cross-sectional SEM image of the positive electrode active material 100A. Alternatively, this can be determined from cross-sectional TEM images, the specific surface area of ​​the positive electrode active material 100A, etc.

[0442] For example, the surface smoothness can be measured from a cross-sectional SEM image of the positive electrode active material 100A, as shown below. It can be converted into a value.

[0443] First, the positive electrode active material 100A is processed using FIB or the like to expose its cross-section. At this time, a protective film is applied. It is preferable to cover the positive electrode active material 100A with a protective agent or the like. Next, the protective film and the positive electrode active material 10 An SEM image of the interface with 0A is taken. Noise reduction is applied to the SEM image using image processing software. For example, after applying Gaussian blur (σ=2), binarization is performed. Furthermore, the image is processed using image processing software. Surface extraction is performed. Furthermore, the interface line between the protective film and the positive electrode active material 100A is identified using an automatic selection tool, etc. Select and extract the data into a spreadsheet program or similar software. Use the functions of the spreadsheet program or similar software to calculate the regression curve. After correcting the line (quadratic regression), parameters for calculating roughness are determined from the slope-corrected data. Next, calculate the root mean square (RMS) surface roughness by determining the standard deviation. The positive electrode active material has a surface roughness of at least 400 nm around its outer edge.

[0444] On the surface of the positive electrode active material 100A in this embodiment, the mean square of roughness is an indicator of roughness. The square root (RMS) surface roughness is less than 3 nm, preferably less than 1 nm, and more preferably 0 nm. It is preferable that the wavelength is less than 5 nm.

[0445] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited, however For example, "ImageJ" described in Non-Patent Documents 6 to 8 can be used.

[0446] For example, the actual specific surface area S measured by the gas adsorption method using the constant-volume method. R And, ideally Specific surface area S i From this ratio, it is possible to quantify the surface smoothness of the positive electrode active material 100A. can.

[0447] Ideal specific surface area S i In this case, the diameter of all positive electrode active materials is the same as that of D50, and the weight is the same. The calculation is performed assuming the shape is an ideal sphere.

[0448] The median diameter D50 is measured using a particle size analyzer that employs laser diffraction and scattering methods. This can be done. Specific surface area can be measured using, for example, a specific surface area measuring device using the gas adsorption method by constant volume. It can be measured by [method].

[0449] In one embodiment of the present invention, the positive electrode active material 100A is an ideal specific table obtained from the median diameter D50. Area A i And the actual specific surface area S R Ratio S R / S i It is preferable that the value is between 1.0 and 2.1. It seems so.

[0450] Alternatively, the surface of the positive electrode active material 100A can be obtained from a cross-sectional SEM image using the following method. Smoothness can be quantified.

[0451] First, a surface SEM image of the positive electrode active material 100A is obtained. At this time, a conductive pretreatment is performed. A coating may be applied. The observation surface is preferably perpendicular to the electron beam. Multiple sun When comparing pulls, the measurement conditions and observation area should be the same.

[0452] Next, using image processing software (e.g., "ImageJ"), the above SEM image is for example converted into an 8-bit image (this is referred to as a grayscale image). Graysca le images contain luminance (brightness information). For example, in an 8-bit grayscale image , luminance can be represented by 2 to the power of 8 = 256 gradations. Dark regions have lower gradation values, while bright re gions have higher gradation values. Luminance changes can be quantified in association with the gradation values. This quantified value is referred to as a grayscale value. By obtaining the grayscale values, the unevenness of the positive electrode active material can be evaluated as a numerical value.

[0453] Furthermore, it is also possible to represent luminance changes in a target region with a histogram. A histogram refers to a three-dimensional representation of the gradation distribution in the target region, and is also called a luminance histogram. By obtaining a luminance hi stogram, the unevenness of the positive electrode active material can be evaluated in a visually easy-to-understand manner .

[0454] The positive electrode active material 100A according to one embodiment of the present invention is characterized in that the difference between the maximum value and the minimum value of the above grayscale values is preferably 120 or less, more preferably 115 or less, and 70 or more and 115 or less is even more preferable. Further, the standard deviation of the grayscale values is preferably 11 or less , more preferably 8 or less, and even more preferably 4 or more and 8 or less .

[0455] <<Current Rest Method>> In the positive electrode active material 100A according to one embodiment of the present invention, additive elements A including magnesium contained in the surface layer portion may slightly change in distribution during repeated charge and discharge cycles. For example, the additive ele The distribution of A becomes better, and the electron conduction resistance may decrease. Therefore, the charge-discharge cycle In the initial stages of the process, electrical resistance, i.e., the fast-responding resistance measured by the current rest method, is the most effective resistance. The time interval R (0.1s) may decrease.

[0456] For example, if we compare the nth charge (where n is a natural number greater than 1) with the n+1th charge, Furthermore, the fast-responding resistance component R(0.1s) measured by the current pause method is n+ The discharge capacity may be lower on the first discharge. Consequently, the discharge capacity of the (n+1)th discharge may be lower than the discharge capacity of the nth discharge. The capacity may be high. When n is 1, that is, when comparing the first charge and the second charge, The increased charging capacity during the second charge cycle can occur even with cathode active materials that do not contain any additive elements. Therefore, n is preferably, for example, 2 or more and 10 or less. However, in the initial charge-discharge cycle... If so, this is not the only option. A charge / discharge capacity of approximately the same as the rated capacity, for example, 97% or more of the rated capacity. If there is a significant amount of charge present, it can be considered the initial stage of a charge-discharge cycle.

[0457] <Pit> The positive electrode active material is susceptible to conditions such as charging at 4.5V or higher, or high temperatures, for example, above 45°C. Charging and discharging in this environment can cause progressive defects that move deep from the surface into the interior. This can sometimes occur. In positive electrode active material, the phenomenon of defects progressing and forming holes is called pitting corrosion. This can also be called ing corrosion, and the holes caused by this phenomenon are referred to in this specification. It is also called a pit. Furthermore, the opening shape of the hole can be circular, elliptical, rectangular, or have a depth of... It may have a groove-like shape.

[0458] Figure 35 shows a schematic cross-sectional view of the positive electrode active material 51 having pits. Parallel to the arrangement of cations Crystal plane 55 is also shown. Since Figure 35 is a cross-sectional view, pits 54 and 58 are not shown as holes. Although shown as such, these openings are not circular but have depth and a groove-like shape. Also, as shown in pits 54 and 58, unlike recess 52, lithium ions It tends to occur parallel to the arrangement.

[0459] Furthermore, the surface layers of the positive electrode active material 51 where the added element A is present are indicated by 53 and 56. In the surface layer where the tide occurred, the amount of added element A was less than 53 and 56 or below the detection limit. It is suspected that the function of the rear film is diminishing. Also, complex oxide crystals are forming near where the pits are located. It is thought that the structure collapses, resulting in a crystal structure different from that of layered rock salt. The pit inhibits the diffusion and release of lithium ions, which are carrier ions, thus cycling. This is considered a factor in the degradation of performance.

[0460] The source of the pits may be point defects. Point defects in the positive electrode active material can cause repeated charging and discharging. It changes as a result, and is chemically or electrochemically eroded by surrounding electrolytes, etc. It is thought to be caused by material degradation. This degradation occurs uniformly on the surface of the positive electrode active material. It doesn't spread, but rather occurs locally and in concentrated areas.

[0461] Furthermore, as shown in crack 57 in Figure 35, the positive electrode active material expands and contracts due to charging and discharging. This may result in defects such as cracks (also called fissures). Cracks and pits are different. Cracks may exist immediately after the production of the positive electrode active material, but pits do not. No. The pit does not exist. For example, under high voltage conditions of 4.5V or higher or high temperature (45°C or higher) It can be said that the charging and discharging process creates holes where several layers of transition metal M and oxygen have been removed, and the transition metal M These are areas where the substance has leached out. Cracks can occur, for example, when physical pressure is applied. This refers to cracks that arise from new surfaces or grain boundaries. Cracks may also occur due to expansion and contraction. Also, cracks and / or Pits can also form from cavities within the positive electrode active material.

[0462] [Method for preparing positive electrode active material] The distribution, composition, and / or crystal structure of the additive element A as described in the previous embodiment The method of adding element A is crucial for producing the positive electrode active material 100A. It is also important that the internal 100b has good crystallinity.

[0463] Therefore, in the process of manufacturing the positive electrode active material 100A, first a compound having lithium and a transition metal is produced. It is preferable to synthesize a composite oxide, then mix it with the additive element A source and perform a heat treatment.

[0464] A transition metal M source and a lithium source are mixed together with an additive element A source, and the additive element A and lithium In a method for synthesizing a composite oxide having M and a transition metal M, the concentration of the added element A in the surface layer 100a is It is difficult to increase the degree. Also, after synthesizing a composite oxide containing lithium and a transition metal M, If only the additive element A source is mixed and no heating is performed, the additive element will not dissolve in the complex oxide. It only adheres without proper heating. Without sufficient heating, the added element A will not be properly distributed. It is difficult to do so. Therefore, a composite oxide is synthesized, then the additive element A source is mixed in, and then heat treatment is performed. It is preferable to perform this. When the heat treatment after mixing this additive element A source is called annealing, There is.

[0465] However, if the annealing temperature is too high, cation mixing occurs and the added element A, For example, magnesium is more likely to enter the transition metal M site. The magnesium present is Li x When x in CoO2 is small, layered rock salt crystals of R-3m form. It has no effect on maintaining the structure. Furthermore, if the heat treatment temperature is too high, the cobalt is reduced to 2 There are concerns about adverse effects such as lithium becoming valence and evaporating.

[0466] Therefore, it is preferable to mix a material that functions as a flux together with the additive element A source. If a composite oxide containing um and a transition metal M has a lower melting point, it can function as a flux. For example, fluorine compounds such as lithium fluoride are preferred. Add a flux. As a result, a melting point depression occurs in the composite oxide containing lithium and transition metal M, with the addition of element A as the source. By lowering the melting point, cation mixing is less likely to occur, and the added element A is properly separated. This makes it easier to cover the fabric.

[0467] Furthermore, after synthesizing a composite oxide containing lithium and a transition metal M, the additive element A is mixed in. Pre-heating is preferable. This pre-heating is sometimes called initial heating.

[0468] Initial heating causes a portion of the surface layer 100a of the composite oxide having lithium and transition metal M to... The desorption of lithium further improves the distribution of additive element A.

[0469] More specifically, the following mechanism causes the distribution to differ due to the addition of element A during initial heating. It is thought that the price will decrease. First, lithium will be detached from a portion of the surface layer 100a by initial heating. Next, a lithium and transition metal M are present in the lithium-deficient surface layer 100a. The complex oxides and additive elements including nickel sources, aluminum sources, and magnesium sources. Mix and heat source A. Of the added element A, magnesium is a divalent typical element, and nickel Although it is a transition metal, it readily forms a divalent ion. Therefore, in a part of the surface layer 100a, M g 2+ and Ni 2+ And, due to lithium deficiency, Co 2+ rock salt type having The following phase is formed.

[0470] Among the added element A, nickel is found in the surface layer 100a, which contains layered rock salt-type lithium and transition metal M. In the case of composite oxides, solid solution readily occurs and diffusion occurs to the interior 100b, but the surface layer 100a If part of it is rock salt, it tends to remain in the surface layer 100a.

[0471] Furthermore, in these rock salt types, the bond distance between metallic Me and oxygen (Me-O distance) is greater than in layered rock salt types. The length also tends to increase.

[0472] For example, rock salt mold 0.5 Mg 0.5 The Me-O distance in O is 2.09 × 10⁻⁶. -1 n The Me-O distance in rock salt-type MgO is 2.11 × 10⁻⁶. -1 It is nm. Also, assuming the surface Even if a spinel-type phase is formed in part of section 100a, the spinel-type NiAl2O4 The Me-O distance is 2.0125 × 10 -1 nm, Me-O distance of spinel-type MgAl2O4 is 2.02 × 10 -1 The distance is nm. In all cases, the Me-O distance is 2 × 10⁻⁶. -1 It exceeds nm.

[0473] On the other hand, in layered rock salt deposits, the bond distance between metals other than lithium and oxygen is shorter than described above. The Al-O distance in layered rock salt-type LiAlO2 is 1.905 × 10⁻⁶. -1 nm(Li-O The distance is 2.11 × 10 -1 It is (nm). Also, Co-O in layered rock salt type LiCoO2 The distance is 1.9224 × 10 -1 nm (Li-O distance is 2.0916 × 10⁻¹⁶) -1 nm) ru.

[0474] Note that Shannon's ionic radius (Shannon et al., Acta A 32( According to 1976) 751.), the ionic radius of 6-coordinate aluminum is 0.535 × 1 0 -1 The ionic radius of oxygen in nm and 6-coordinate state is 1.4 × 10⁻⁶. -1 The units are nm, and their sum is 1 0.935×10 -1 It is nm.

[0475] From the above, aluminum is cheaper than lithium from layered rock salt sites than from rock salt sites. It is thought to be present in a constant state. Therefore, aluminum is rock salt type even in the surface layer 100a. Deeper regions with layered salt formations and / or interiors have a more pronounced layered salt formation than the surface-level regions with a specific phase. It is more likely to be distributed in section 100b.

[0476] Furthermore, the initial heating is expected to enhance the crystallinity of the layered rock salt-type crystalline structure within the interior 100b. It's possible to wait.

[0477] However, initial heating is not always necessary. Other heating processes, such as annealing, are also required. By controlling the atmosphere, temperature, time, etc., Li x When x in CoO2 is small, O In some cases, it is possible to produce a positive electrode active material 100A having a 3' type.

[0478] Figure 3 shows an example of the fabrication flow of the positive electrode active material 100A, which undergoes annealing and initial heating. This will be explained using Figures 6A through 36C.

[0479] <Step S11> In step S11 shown in Figure 36A, the starting materials are lithium and transition metal M. Then, prepare a lithium source (Li source) and a transition metal M source (M source).

[0480] As a lithium source, it is preferable to use a compound containing lithium, for example, lithium carbonate Lithium hydroxide, lithium nitrate, or lithium fluoride can be used. The um source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0481] The transition metal M can be selected from the elements listed in groups 3 through 11 of the periodic table, for example. For example, at least one of manganese, cobalt, and nickel is used. In other words, transition metals. For M, the cases where only cobalt is used, where only nickel is used, and where cobalt and manganese are used. When using two types, when using two types, cobalt and nickel, or cobalt, man In some cases, three types of materials are used: gun, nickel, and cobalt. When only cobalt is used, the resulting positive electrode activity The substance contains lithium cobalt oxide (LCO) and is composed of three types of minerals: cobalt, manganese, and nickel. When using this method, the resulting positive electrode active material is lithium nickel-cobalt-manganate (NCM ) has.

[0482] As the transition metal M source, it is preferable to use a compound having the above transition metal M, for example, The transition metal M is an oxide of one of the exemplified metals, or a hydroxide of one of the exemplified metals. This can be done. For cobalt sources, cobalt oxide, cobalt hydroxide, etc., can be used. For manganese sources, manganese oxide, manganese hydroxide, etc., can be used. For aluminum sources, nickel oxide, nickel hydroxide, etc. can be used. In that case, aluminum oxide, aluminum hydroxide, etc., can be used.

[0483] The transition metal M source is preferably of high purity, for example, a purity of 3N (99.9%) or higher is preferable. More preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and furthermore Preferably, a material with a purity of 5N (99.999%) or higher should be used. This allows for control of impurities in the positive electrode active material. As a result, the capacity of the secondary battery increases. , and / or the reliability of secondary batteries is improved.

[0484] In addition, it is preferable that the transition metal M source has high crystallinity, for example, having single crystal grains. For evaluating the crystallinity of the metal transfer source M, TEM (transmission electron microscope) images and STEM (scanning transmission electron microscope) images are used. Electron microscope image, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) image, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) image, enhanced Holo w-Cone Illumination-TEM (Improved Hollow Cone Illumination Transmitted Electron Microscope) Judgment based on mirror images, etc., or judgment based on X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. Yes. Furthermore, the above methods for evaluating crystallinity apply not only to transition metal M sources, but also to other sources. It can also be applied to the evaluation of crystallinity.

[0485] Furthermore, when using two or more transition metal M sources, if the two or more transition metal M sources are of the layered rock salt type It is preferable to prepare the materials in proportions (mixing ratios) that allow them to form a crystalline structure.

[0486] <Step S12> Next, as step S12 shown in Figure 36A, the lithium source and the transition metal M source are crushed and The materials are mixed to produce a mixed material. Grinding and mixing can be done dry or wet. The wet method is preferable because it allows for finer pulverization. When using the wet method, prepare a solvent. The solvents include ketones such as acetone, and alcohols such as ethanol and isopropanol. , ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It can be used. An aprotic solvent that does not react easily with lithium can be used. More preferable. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. To do this, use dehydrated acetone with a water content of 10 ppm or less and a purity of 99.5% or higher. It is preferable to mix the lithium source and the transition metal M source, and then perform crushing and mixing. By using highly purified dehydrated acetone, the amount of impurities that may be present can be reduced.

[0487] A ball mill or bead mill can be used for mixing and other processes. When using aluminum oxide balls or zirconium oxide balls as the grinding media, It is preferable to use a ball. Zirconium oxide balls are preferable because they release fewer impurities. When using a bead mill or similar device, suppress contamination from the media. To achieve this, the peripheral speed should be set to between 100 mm / s and 2000 mm / s. In terms of configuration, the peripheral speed is 838 mm / s (rotational speed 400 rpm, ball mill diameter 40 mm). We will implement it.

[0488] <Step S13> Next, as step S13 shown in Figure 36A, the mixed material is heated. The heating temperature is: It is preferable to carry out the process at a temperature between 800°C and 1100°C, and preferably between 900°C and 1000°C. It is more preferable that the temperature is around 950°C, and even more preferable that the temperature is too low, the lithium source and Furthermore, the decomposition and melting of the transition metal M source may be insufficient. On the other hand, if the temperature is too high, Lithium evaporates from the lithium source, and / or there is an excess of the metal used as the transition metal M source. Defects may occur due to reduction, etc. Such defects include, for example, transition metals. When cobalt is used as the group M, if it is reduced in excess, the cobalt changes from trivalent to divalent. This can induce oxygen deficiency and other problems.

[0489] If the heating time is too short, LiMO2 will not be synthesized, but if it is too long, productivity will decrease. For example, the heating time should be between 1 hour and 100 hours, or between 2 hours and 20 hours. It is preferable to do so.

[0490] The heating rate depends on the target temperature, but a rate between 80°C / h and 250°C / h is preferable. For example, when heating at 1000°C for 10 hours, the heating rate should be 200°C / h.

[0491] The heating atmosphere should preferably be one with low moisture content, such as dry air, for example, with a dew point of - An atmosphere with a temperature of 50°C or lower, and more preferably a dew point of -80°C or lower, is preferred. The heating will be carried out in an atmosphere with a dew point of -93°C. Furthermore, any impurities that may be present in the material will be considered. To suppress this, the concentration of impurities such as CH4, CO, CO2, and H2 in the heating atmosphere is reduced. The levels should be kept below 5 ppb (parts per billion) each.

[0492] An atmosphere containing oxygen is preferred as the heating atmosphere. For example, dry air is introduced into the reaction chamber and continuously There is a method to do this. In this case, it is preferable that the flow rate of dry air be 10 L / min. The method of continuously introducing elements into the reaction chamber, allowing oxygen to flow within the chamber, is called flow.

[0493] When the heating atmosphere is an oxygen-containing atmosphere, a method that does not involve flow is also acceptable. For example The reaction chamber is depressurized and then filled with oxygen, and the oxygen is prevented from entering or leaving the reaction chamber. This is also commonly referred to as purging. For example, in a reaction chamber, the differential pressure gauge reads -970 hPa. After reducing the pressure to the desired level, you can then fill it with oxygen up to 50 hPa.

[0494] After heating, natural cooling is acceptable, but the cooling time from the spe...

Claims

1. A lithium-ion secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer, The positive electrode active material layer comprises first positive electrode active material particles and second positive electrode active material particles having a larger particle size than the first positive electrode active material particles. The first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide. The aforementioned negative electrode active material layer has a negative electrode active material, The electrolyte layer comprises a gelled polymer material, and the lithium-ion secondary battery.

2. A lithium-ion secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer, The positive electrode active material layer comprises first positive electrode active material particles and second positive electrode active material particles having a larger particle size than the first positive electrode active material particles. The particle size of the first positive electrode active material particle is 500 nm or more and 5 μm or less. The particle size of the second positive electrode active material particle is 1 μm or more and 35 μm or less. The first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide. The aforementioned negative electrode active material layer has a negative electrode active material, The electrolyte layer comprises a gelled polymer material, and the lithium-ion secondary battery.

3. A lithium-ion secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer, The positive electrode active material layer comprises first positive electrode active material particles and second positive electrode active material particles having a larger particle size than the first positive electrode active material particles. The ratio Rb / Ra of the particle size Rb of the second positive electrode active material particles to the particle size Ra of the first positive electrode active material particles is 2 or more and 15 or less. The first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide. The aforementioned negative electrode active material layer has a negative electrode active material, The electrolyte layer comprises a gelled polymer material, and the lithium-ion secondary battery.

4. A lithium-ion secondary battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer, The positive electrode active material layer comprises first positive electrode active material particles and second positive electrode active material particles having a larger particle size than the first positive electrode active material particles. The first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide. The mass ratio of the first positive electrode active material particles to the second positive electrode active material particles is such that the mass of the second positive electrode active material particles : the mass of the first positive electrode active material particles = 1 : 0.05 or more and 0.5 or less. The aforementioned negative electrode active material layer has a negative electrode active material, The electrolyte layer comprises a gelled polymer material, and the lithium-ion secondary battery.

5. In any one of claims 1 to 4, The aforementioned particle size is the median diameter, in a lithium-ion secondary battery.

6. In any one of claims 1 to 4, A lithium-ion secondary battery in which the particle size of the first positive electrode active material particle is the cross-sectional diameter of the first positive electrode active material particle, and the particle size of the second positive electrode active material particle is the cross-sectional diameter of the second positive electrode active material particle.

7. In any one of claims 1 to 4, A lithium-ion secondary battery wherein the positive electrode active material layer has third positive electrode active material particles having a particle size between that of the first positive electrode active material particles and the second positive electrode active material particles.

8. In any one of claims 1 to 4, A lithium-ion secondary battery wherein the first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide having a different additive element.

9. In any one of claims 1 to 4, A lithium-ion secondary battery wherein the first positive electrode active material particles and the second positive electrode active material particles each contain lithium cobalt oxide having the same additive element at different concentrations.

10. In any one of claims 1 to 4, The electrolyte layer is capable of moving lithium ions from the positive electrode active material layer to the negative electrode active material layer during charging, in a lithium-ion secondary battery.

11. In any one of claims 1 to 4, A lithium-ion secondary battery comprising one or more gelled polymer materials selected from silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, and fluorine-based polymer gel.

12. In any one of claims 1 to 4, The gelled polymer material comprises a polymer having a polyalkylene oxide structure, PVDF, polyacrylonitrile, or a copolymer containing two or more of these, in a lithium-ion secondary battery.

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