Secondary batteries

Abstract

To provide a secondary battery that is stable in high potential and / or high temperature conditions. [Solution] A secondary battery having a positive electrode and a negative electrode, wherein either the positive electrode or the negative electrode, or both, have an active material and a composite compound having a crystalline structure. The composite compound functions as a binder. The composite compound can also be used as an electrolyte. The composite compound having a crystalline structure typically has molecular crystals. The composite compound having a crystalline structure can be obtained by mixing a mixture of a first compound and a second compound while heating it at a temperature above the melting point.

Description

[Technical Field]

[0001] This invention relates to a secondary battery having a positive electrode. Furthermore, this invention relates to an energy storage system and a vehicle, etc., having a secondary battery. Moreover, this invention relates to a method for manufacturing a secondary battery and a positive electrode.

[0002] The present invention also relates to processes, 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, electronic devices, or methods for manufacturing the same.

[0003] In this specification, the term "semiconductor device" refers to all devices that can function by utilizing semiconductor properties, and electro-optical devices, semiconductor circuits, and electronic devices are all included in the definition of a semiconductor device.

[0004] In this specification, "electronic equipment" refers to all devices having a positive electrode active material, a secondary battery, an energy storage device, or an energy storage system, and information terminal devices having a secondary battery are included in electronic equipment.

[0005] In this specification, the term "energy storage device" refers to all elements and devices that have an energy storage function. Energy storage devices include, for example, lithium-ion secondary batteries (also simply called secondary batteries), lithium-ion capacitors, and electric double-layer capacitors. [Background technology]

[0006] In recent years, there has been a surge in the development of various energy storage devices, including lithium-ion secondary batteries and lithium-ion capacitors. Lithium-ion secondary batteries, with their high output and high energy density, are rapidly gaining demand in conjunction with the development of the semiconductor industry. They are used in mobile information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical equipment, home energy storage systems, industrial energy storage systems, and clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), and plug-in hybrid vehicles (PHV). As a rechargeable energy source, they have become indispensable in today's information society.

[0007] Lithium-ion secondary batteries widely use lithium cobalt oxide or composite oxides such as lithium nickel-cobalt-manganate, which have a layered rock salt structure, as positive electrode active materials. Positive electrode active materials having these composite oxides can possess useful properties such as high capacity and high discharge voltage. Furthermore, in order to achieve high capacity, the positive electrode active material is exposed to a high potential during charging. In such a high potential state, a large amount of lithium is desorbed, which can reduce the stability of the crystal structure of the composite oxide and lead to greater degradation during charge-discharge cycles. Against this backdrop, there has been active research and development to improve positive electrode active materials for secondary batteries in order to create batteries with high capacity and high stability (for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2018-088400 [Patent Document 2] WO2018 / 203168 Brochure [Patent Document 3] Japanese Patent Publication No. 2020-140954 [Non-patent literature]

[0009] [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 Document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2(0.0≦x≦1.0)”, Physical Review B, 80(16) ,2009, 165114 [Non-Patent Document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-Patent Document 4] WE Counts et al, Journal of the American Ceramic Society, 1953, 36[1] 12-17. [Non-Patent Document 5] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., 2002, B58 364-369. [Overview of the project] [Problems that the invention aims to solve]

[0010] Although improvements to positive electrode active materials have been actively pursued as described in the above-mentioned Patent Documents 1 to 3, considering various aspects such as reliability and safety for secondary batteries, there is still room for improvement in positive electrode active materials.

[0011] Therefore, one aspect of the present invention aims to provide a secondary battery with high reliability or safety and a method for manufacturing the same. Alternatively, it aims to provide a secondary battery with excellent charge-discharge cycle characteristics and a method for manufacturing the same. Alternatively, it aims to provide a secondary battery with a large discharge capacity and a method for manufacturing the same.

[0012] In order to realize the secondary battery described above, one aspect of the present invention aims to provide a positive electrode or a negative electrode and a method for manufacturing the same that are stable in high potential and / or high temperature conditions.

[0013] To achieve the above-mentioned positive or negative electrodes, one of the objectives is to provide a positive or negative electrode active material or a method for producing the same, in which the crystal structure is less likely to collapse even after repeated charging and discharging. Alternatively, one of the objectives is to provide a positive or negative electrode active material or a method for producing the same, in which the charge-discharge cycle characteristics are excellent. Alternatively, one of the objectives is to provide a positive or negative electrode active material or a method for producing the same, in which the discharge capacity is large.

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

[0015] The inventors have found a configuration in which a positive or negative electrode in a secondary battery is stable in a high potential state and / or high temperature state, the positive or negative electrode having at least each active material and a composite compound. The composite compound preferably has crystalline properties, for example, it preferably has molecular crystals.

[0016] In secondary batteries, the composite compound preferably functions as a binder and preferably exhibits high ionic conductivity.

[0017] In a secondary battery, it is preferable that the composite compound functions as a solid electrolyte in addition to being a binder. If it functions as a solid electrolyte, the secondary battery does not need to have a separator. It is preferable that the composite compound is arranged so that each active material does not come into contact with the organic electrolyte (a liquid version is called an electrolyte solution). For example, it is preferable that the composite compound is arranged so as to cover a portion of each active material.

[0018] A specific aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, and the composite compound functions as a binder.

[0019] Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a binder function, and the composite compound having a region located between the active material and the electrolyte.

[0020] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, and the composite compound functions as a binder and an electrolyte.

[0021] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material, a composite compound having a crystalline structure, and a first binder, the composite compound having the functions of a second binder and an electrolyte.

[0022] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a binder function, and the composite compound has succinonitrile, lithium ions and bis(fluorosulfonyl)imide ions.

[0023] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a binder function, and the composite compound has glutaronitrile, lithium ions and bis(fluorosulfonyl)imide ions.

[0024] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a binder function, and the composite compound has adiponitrile, lithium ions and bis(fluorosulfonyl)imide ions.

[0025] Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a function as a binder, the composite compound having a region located between the active material and the electrolyte, and the composite compound having succinonitrile, lithium ions, and bis(fluorosulfonyl)imide.

[0026] Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a function as a binder, the composite compound having a region located between the active material and the electrolyte, and the composite compound having glutaronitrile, lithium ions, and bis(fluorosulfonyl)imide.

[0027] Another aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having a function as a binder, the composite compound having a region located between the active material and the electrolyte, and the composite compound having adiponitrile, lithium ions, and bis(fluorosulfonyl)imide ions.

[0028] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having functions as a binder and an electrolyte, and the composite compound has succinonitrile, lithium ions and bis(fluorosulfonyl)imide ions.

[0029] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having functions as a binder and an electrolyte, and the composite compound has glutaronitrile, lithium ions and bis(fluorosulfonyl)imide ions.

[0030] Another aspect of the present invention is a secondary battery having a positive electrode and a negative electrode, wherein either or both of the positive electrode and the negative electrode have an active material and a composite compound having a crystalline structure, the composite compound having functions as a binder and an electrolyte, and the composite compound has adiponitrile, lithium ions and bis(fluorosulfonyl)imide.

[0031] In one embodiment of the present invention, the active material of the positive electrode preferably has a composite oxide containing magnesium and cobalt, wherein the cobalt is present in the interior and surface of the active material, and the magnesium is present at least in the surface.

[0032] In one embodiment of the present invention, the active material of the positive electrode preferably has a surface roughness of at least 3 nm or less when the surface topography information is quantified in a cross-section observed by a scanning transmission electron microscope (STEM).

[0033] In one embodiment of the present invention, it is preferable to have a separator between the positive electrode and the negative electrode.

[0034] In one embodiment of the present invention, the active material of the positive electrode preferably has a layered rock salt type crystalline structure.

[0035] In one embodiment of the present invention, the active material of the negative electrode is preferably silicon or carbon.

[0036] In one embodiment of the present invention, it is preferable that either the positive electrode or the negative electrode, or both, have a conductive material.

[0037] In one embodiment of the present invention, the conductive material of the positive electrode preferably comprises carbon black, graphene, or carbon nanotubes.

[0038] In one embodiment of the present invention, the conductive material of the negative electrode preferably comprises carbon black, graphene, or carbon nanotubes.

[0039] Another aspect of the present invention is an energy storage system having the above-mentioned secondary battery and a protection circuit.

[0040] Another aspect of the present invention is a vehicle equipped with the above-mentioned secondary battery.

[0041] One aspect of the present invention is a method for producing a positive electrode, comprising a first step and a second step, wherein the first step is to produce a positive electrode slurry by heating a composite compound having a crystalline structure and a positive electrode active material while mixing them, and the second step is to apply the positive electrode slurry to a current collector, wherein the heating is performed at a temperature above the melting point of the composite compound having a crystalline structure.

[0042] Another aspect of the present invention is a method for producing a positive electrode, comprising a first step and a second step, wherein the first step is to produce a positive electrode slurry by heating a first compound, a second compound, and a positive electrode active material while mixing them, and the second step is to apply the positive electrode slurry to a current collector, and the heating in the first step is performed at a temperature above the melting points of the first compound and the second compound.

[0043] Another aspect of the present invention is a method for producing a positive electrode, comprising a first to third step, the first step of heating a first compound and a second compound while mixing them to produce a composite compound having a crystalline structure, the second step of heating a positive electrode active material and the composite compound while mixing them to produce a positive electrode slurry, and the third step of applying the positive electrode slurry to a current collector, wherein the heating in the first step is performed at a temperature above the melting point of the composite compound.

[0044] In one embodiment of the present invention, the first compound preferably has succinonitrile, glutaronitrile, or adiponitrile, and the second compound preferably has lithium bis(fluorosulfonyl)imide.

[0045] Another aspect of the present invention is a method for manufacturing a positive electrode, comprising the first to fifth steps, the first step of mixing a first binder mixture and a conductive material to produce a first mixture, the second step of mixing the first mixture and a positive electrode active material to produce a second mixture, the third step of mixing the second mixture, a second binder mixture and a dispersion medium to produce a third mixture, the fourth step of coating the third mixture onto a current collector and drying the dispersion medium to produce a coated electrode, and the fifth step of injecting a composite compound having a crystalline structure into the voids of the coated electrode while heating.

[0046] In one embodiment of the present invention, it is preferable that the crystalline complex compound is obtained by heating succinonitrile, glutaronitrile, or adiponitrile with lithium bis(fluorosulfonyl)imide while mixing them. [Effects of the Invention]

[0047] According to one aspect of the present invention, it is possible to provide a secondary battery with high reliability or safety and a method for manufacturing the same. Alternatively, it is possible to provide a secondary battery with excellent charge-discharge cycle characteristics and a method for manufacturing the same. Alternatively, it is possible to provide a secondary battery with a large discharge capacity and a method for manufacturing the same.

[0048] To realize the secondary battery described above, one aspect of the present invention can provide a positive electrode or a negative electrode and a method for manufacturing the same, which are stable in high potential and / or high temperature conditions.

[0049] To achieve the above-described positive or negative electrodes, we can provide a positive or negative electrode active material or a method for producing the same, in which the crystal structure is less likely to collapse even after repeated charging and discharging. Alternatively, we can provide a positive or negative electrode active material or a method for producing the same with excellent charge-discharge cycle characteristics. Alternatively, we can provide a positive or negative electrode active material or a method for producing the same with a large discharge capacity.

[0050] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0051] [Figure 1] Figures 1A to 1C4 illustrate a secondary battery according to one embodiment of the present invention. [Figure 2]Figures 2A and 2B illustrate a secondary battery according to one embodiment of the present invention. [Figure 3] Figures 3A and 3B illustrate an example of a method for manufacturing a positive electrode used in a lithium-ion secondary battery according to one embodiment of the present invention. [Figure 4] Figures 4A and 4B illustrate an example of a method for manufacturing a positive electrode used in a lithium-ion secondary battery according to one embodiment of the present invention. [Figure 5] Figures 5A and 5B illustrate an example of a method for manufacturing a lithium-ion secondary battery according to one embodiment of the present invention. [Figure 6] Figures 6A to 6C illustrate an example of a method for producing a positive electrode active material composite according to one aspect of the present invention. [Figure 7] Figures 7A and 7B show a model of a density functional theory calculation for a cathode active material composite according to one embodiment of the present invention. [Figure 8] Figures 8A to 8C are graphs of the calculation results using density functional theory for a cathode active material composite according to one embodiment of the present invention. [Figure 9] Figures 9A to 9C illustrate a method for producing a positive electrode active material according to one embodiment of the present invention. [Figure 10] Figure 10 illustrates a method for producing a positive electrode active material according to one embodiment of the present invention. [Figure 11] Figures 11A to 11C illustrate a method for producing a positive electrode active material according to one embodiment of the present invention. [Figure 12] Figure 12A is a front view of a positive electrode active material according to one embodiment of the present invention, and Figure 12B is a cross-sectional view of the positive electrode active material according to one embodiment of the present invention. [Figure 13] Figure 13 illustrates the crystal structure of a positive electrode active material according to one embodiment of the present invention. [Figure 14] Figure 14 shows the XRD pattern calculated from the crystal structure. [Figure 15] Figure 15 is a diagram illustrating the crystal structure of a conventional positive electrode active material. [Figure 16] Figure 16 shows the XRD pattern calculated from the crystal structure. [Figure 17]Figures 17A to 17C show the lattice constants calculated from the XRD pattern. [Figure 18] Figures 18A to 18C show the lattice constants calculated from the XRD pattern. [Figure 19] Figure 19 is a graph showing the charging curves of a secondary battery using a positive electrode active material according to one embodiment of the present invention and a positive electrode active material of a comparative example. [Figure 20] Figures 20A and 20B show the dQ / dV curve of a half-cell according to one embodiment of the present invention, and Figure 20C shows the dQ / dV curve of a half-cell in a comparative example. [Figure 21] Figure 21 is a schematic cross-sectional view of the positive electrode active material. [Figure 22] Figures 22A and 22B are SEM images of the positive electrode. [Figure 23] Figure 23A is a front view of the positive electrode active material based on FIB (Focused Ion Beam) processing and SEM observation, Figure 23B is a magnified view of a part thereof, Figure 23C is a cross-sectional view thereof, Figure 23D is a rotated side view of the positive electrode active material of Figure 23A, Figure 23E is a magnified view of a part thereof, and Figure 23F is a cross-sectional view thereof. [Figure 24] Figures 24A to 24C are SEM images of the positive electrode. [Figure 25] Figures 25A to 25C are SEM images of the positive electrode. [Figure 26] Figures 26A and 26B are STEM images of the positive electrode. [Figure 27] Figures 27A to 27C show the EDX analysis results of the positive electrode. [Figure 28] Figures 28A and 28B are cross-sectional TEM images of the positive electrode active material layer. [Figure 29] Figures 29A to 29C show the micro-electron diffraction patterns of the positive electrode active material layer. [Figure 30] Figures 30A to 30C show examples of crystal structures. [Figure 31] Figure 31A is a STEM image of the particles after pressing, and Figures 31B and 31C are schematic cross-sectional views. [Figure 32]Figure 32A is an exploded perspective view of a coin-type rechargeable battery, Figure 32B is a perspective view of a coin-type rechargeable battery, and Figure 32C is a cross-sectional perspective view thereof. [Figure 33] Figure 33A shows an example of a cylindrical secondary battery. Figure 33B shows an example of a cylindrical secondary battery. Figure 33C shows an example of multiple cylindrical secondary batteries. Figure 33D shows an example of an energy storage system with multiple cylindrical secondary batteries. [Figure 34] Figures 34A and 34B illustrate examples of secondary batteries, while Figure 34C shows the inside of a secondary battery. [Figure 35] Figures 35A to 35C illustrate examples of secondary batteries. [Figure 36] Figures 36A and 36B show the external appearance of a secondary battery. [Figure 37] Figures 37A to 37C illustrate the method for manufacturing a secondary battery. [Figure 38] Figures 38A to 38C show examples of battery pack configurations. [Figure 39] Figures 39A and 39B illustrate an example of a secondary battery. [Figure 40] Figures 40A to 40C illustrate examples of secondary batteries. [Figure 41] Figures 41A and 41B illustrate an example of a secondary battery. [Figure 42] Figure 42A is a perspective view of a battery pack showing one embodiment of the present invention, Figure 42B is a block diagram of the battery pack, and Figure 42C is a block diagram of a vehicle having a motor. [Figure 43] Figures 43A to 43D illustrate an example of a transport vehicle. [Figure 44] Figures 44A and 44B illustrate an energy storage device according to one aspect of the present invention. [Figure 45] Figure 45A shows an electric bicycle, Figure 45B shows the secondary battery of an electric bicycle, and Figure 45C is a diagram illustrating an electric motorcycle. [Figure 46] Figures 46A to 46D illustrate an example of an electronic device. [Figure 47] Figure 47A shows an example of a wearable device, Figure 47B shows a perspective view of a wristwatch-type device, and Figure 47C is a diagram illustrating the side view of a wristwatch-type device. Figure 47D is a diagram illustrating an example of wireless earphones. [Figure 48] Figures 48A to 48C show the structural formula of the compound and the magnitude of the charge of each nitrogen atom. [Figure 49] Figures 49A to 49C show examples of stable structures of complex compounds. [Figure 50] Figure 50A shows the method for preparing the composite compound, Figure 50B is a photograph of the prepared composite compound, and Figure 50C shows the analysis results. [Figure 51] Figure 51A shows the method for preparing the composite compound, Figure 51B is a photograph of the prepared composite compound, and Figure 51C shows the analysis results. [Modes for carrying out the invention]

[0052] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0053] In this specification, a secondary battery has, for example, a positive electrode and a negative electrode. The positive electrode has a positive electrode active material. The positive electrode active material is, for example, a substance that performs a reaction that contributes to the charge and discharge capacity. The positive electrode active material may also contain a portion of a substance that does not contribute to the charge and discharge capacity.

[0054] In this specification, the positive electrode active material may be expressed as a positive electrode material, a positive electrode material for secondary batteries, a composite oxide, etc. Furthermore, in this specification, it is preferable that the positive electrode active material has a compound corresponding to the composite oxide. Furthermore, in this specification, it is preferable that the positive electrode active material has a composition corresponding to the composite oxide. Furthermore, in this specification, it is preferable that the positive electrode active material has a composite corresponding to the composite oxide.

[0055] In this specification, the term "particle" is not limited to spherical (circular cross-section), but includes particles with elliptical, rectangular, trapezoidal, rounded-corner quadrilateral, asymmetrical shapes, and other cross-sectional shapes, and individual particles may also be irregular in shape.

[0056] In this specification, particle size can be measured, for example, by laser diffraction particle size distribution measurement and compared using the D50 value. Here, D50 is the particle size, i.e., the median, at which the cumulative amount accounts for 50% of the cumulative particle amount curve of the particle size distribution measurement results. The measurement of particle size is not limited to laser diffraction particle size distribution measurement; if it is below the lower limit of measurement for laser diffraction particle size distribution measurement, the major axis of the particle cross-section may be measured by analysis such as SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope).

[0057] In this specification, Miller indices are used to indicate crystal planes and directions. Individual crystal planes are indicated by parentheses ( ). In crystallography, crystal planes, directions, and space groups are indicated by superscripts above the numbers; however, due to limitations in patent application notation, in this specification, a minus sign (-) may be placed before the number instead of a superscript above it.

[0058] In this specification, the layered rock salt-type crystal structure of a composite oxide containing lithium and a transition metal refers to a rock salt-type ionic arrangement in which cations and anions are arranged alternately. In the layered rock salt-type crystal structure, the transition metal and lithium are regularly arranged to form a two-dimensional plane, thus enabling two-dimensional diffusion of lithium. The layered rock salt-type crystal structure may have defects such as vacancies in cations or anions. Furthermore, the layered rock salt-type crystal structure may have a distorted lattice structure of rock salt-type crystals.

[0059] In this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. The crystal structure may contain defects such as vacancies in cations or anions.

[0060] In this specification, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all of the insertable and detachable lithium present in the positive electrode active material has been detached. The theoretical capacity of LiFePO4 is 170 mAh / g, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0061] In this specification, the extent to which insertable and detachable lithium remains in the positive electrode active material is expressed by x in the composition formula, for example, Li x x in CoO2, or Li x Indicated by x in MO2. Li in this specification. x CoO2 contains Li as appropriate. x This can be interpreted as MO2. In the case of the positive electrode active material in a secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2 mAh / g, Li 0.2 It can be expressed as CoO2 or x=0.2. x A small x in CoO2 means, for example, 0.1 <x≦0.24をいう。

[0062] When properly synthesized lithium cobalt oxide, before being used as the positive electrode, approximately satisfies the stoichiometric ratio, it is LiCoO2, and the Li occupancy rate of the lithium sites is x=1. Similarly, a secondary battery that has finished discharging is also LiCoO2, and it can be said that x=1. Here, "finished discharging" refers to a state where, for example, with a current of 100mA / g, the voltage is 2.5V (counter electrode lithium) or less.

[0063] In this specification, when evaluating the positive electrode and positive electrode active material, cycle test examples using lithium metal as the counter electrode are sometimes shown, but the present invention is not limited to this. Instead of lithium metal, for example, graphite, lithium titanate, etc., may be used. In other words, properties such as the crystal structure of the positive electrode and positive electrode active material not collapsing even after repeated charging and discharging, and obtaining good cycle characteristics, are not affected by the negative electrode material.

[0064] In this specification, a cycle test is a test that involves repeatedly charging and discharging. A cycle test allows us to observe the degree of degradation of a secondary battery and evaluate the positive electrode and positive electrode active material.

[0065] In this specification, examples of charging and discharging secondary batteries with a lithium counter electrode at a relatively high voltage, such as 4.6V, are sometimes shown. However, charging and discharging may also be performed at a voltage lower than 4.6V. When charging and discharging at a lower voltage, it is expected that the cycle characteristics will be even better than those shown in this specification.

[0066] In this specification, a kiln refers to a device used to heat a material to be processed. For example, a furnace, kiln, heating device, etc., may be used instead of a kiln.

[0067] (Embodiment 1) This embodiment describes a secondary battery that is one aspect of the present invention. The secondary battery has a positive electrode and a negative electrode that are one aspect of the present invention. A secondary battery that uses lithium ions as carrier ions is called a lithium-ion secondary battery.

[0068] Figure 1A shows a cross-sectional view of a secondary battery 100. The secondary battery 100 has a positive electrode 101 and a negative electrode 102. A separator 110 is located between the positive electrode 101 and the negative electrode 102. In other words, the positive electrode 101 and the negative electrode 102 are separated by the separator 110. Note that the separator 110 is not necessary if the state in which the positive electrode 101 and the negative electrode 102 are separated can be maintained.

[0069] The positive electrode 101 comprises a positive electrode current collector 104 and a positive electrode active material layer 105. The positive electrode active material layer 105 contains a positive electrode active material. The positive electrode active material is an active material capable of intercalating and releasing carrier ions. For example, a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, Mn, and Al) can be used as the active material. A composite oxide is, for example, made from a first oxide and a second oxide as starting materials, and the term "composite" may mean that two or more oxides are used as starting materials. Specific composite oxides will be described in subsequent embodiments.

[0070] Furthermore, the positive electrode active material is arranged in a manner that allows for the exchange of electrons with the positive electrode current collector 104. That is, the positive electrode active material has a configuration in which it is electrically in contact with the positive electrode current collector 104. The positive electrode current collector 104 may be provided with an undercoat layer. In this case, the positive electrode active material has a configuration in which it is electrically in contact with the positive electrode current collector 104 via the undercoat layer. Alternatively, the positive electrode active material may have a configuration in which it is electrically in contact with the positive electrode current collector 104 via a conductive material. The conductive material is also called a conductive additive, and a material with a lower resistivity than the positive electrode active material is used. The conductive material allows for the formation of an efficient current path between the positive electrode active material and the positive electrode current collector, or between the positive electrode active materials themselves. Therefore, it is preferable that the conductive material is appropriately dispersed in the positive electrode active material layer 105.

[0071] The negative electrode 102 comprises a negative electrode current collector 106 and a negative electrode active material layer 107. The negative electrode active material layer 107 contains a negative electrode active material. The negative electrode active material has an active material that can intercept and release carrier ions. Specific negative electrode active material materials will be described in subsequent embodiments.

[0072] Furthermore, the negative electrode active material is arranged in a manner that allows for the exchange of electrons with the negative electrode current collector 106. That is, the negative electrode active material has a configuration in which it is electrically in contact with the negative electrode current collector 106. The negative electrode current collector 106 may be provided with an undercoat layer. In this case, the negative electrode active material has a configuration in which it is electrically in contact with the negative electrode current collector 106 via the undercoat layer. Alternatively, the negative electrode active material may have a configuration in which it is electrically in contact with the negative electrode current collector 106 via a conductive material. The conductive material is also called a conductive additive, and a material with a lower resistivity than the negative electrode active material is used. The conductive material allows for the formation of an efficient current path between the negative electrode active material and the negative electrode current collector, or between the negative electrode active materials themselves. Therefore, it is preferable that the conductive material is appropriately dispersed in the negative electrode active material layer 107.

[0073] The configuration of the positive electrode active material and its vicinity will be described. Figure 1B1 corresponds to an enlarged view of region 112 in Figure 1A, and in Figure 1B1, at least the electrolyte (a liquid electrolyte is called an electrolyte solution) 114 and the positive electrode active material 115 are shown. It is preferable that the positive electrode active material 115 has a configuration covered with a composite compound 117.

[0074] The composite compound 117 is, for example, derived from a first compound and a second compound as starting materials, and the term "composite" may mean that two or more compounds were used as starting materials. It is preferable that the composite compound has a crystalline structure.

[0075] For complex compounds having a crystalline structure, molecular crystals are a good choice. Molecular crystals are a general term for crystals of molecular complex compounds formed by the bonding of compound A and compound B through physical intermolecular forces, such as coordination bonds. Molecular crystals are formed by mixing the first compound and the second compound, and it is preferable that they have a structure in which parts of the compounds are bonded together by coordination bonds.

[0076] The composite compound 117 can function as a binder for the positive electrode active material 115. In addition to the binder present in the positive electrode active material layer, the composite compound 117 may also function as a binder for the positive electrode active material 115.

[0077] The composite compound 117 preferably has high ionic conductivity. Through the composite compound 117, the positive electrode active material 115 can exchange carrier ions with the electrolyte 114. In other words, the composite compound 117 can function as an electrolyte.

[0078] Furthermore, the complex compound 117 can have both binder and electrolyte functions.

[0079] The composite compound 117 having a crystalline structure is in a solid state. Using the composite compound 117 having a crystalline structure as an electrolyte eliminates the need for a separator. In other words, a secondary battery using the composite compound 117 having a crystalline structure as an electrolyte can take the same form as an all-solid-state secondary battery.

[0080] Furthermore, the positive electrode active material 115 can have a region that does not come into contact with the electrolyte 114 by being covered with the composite compound 117. In this case, the composite compound 117 is arranged to have a region located between the positive electrode active material 115 and the electrolyte 114. It is believed that such a composite compound 117 suppresses the degradation of the positive electrode active material 115 caused by the electrolyte 114.

[0081] The degradation described above is explained below. Degradation is thought to be caused by defects in the positive electrode active material 115. These defects include what are called cracks or pits. During charging and discharging of a secondary battery, the positive electrode active material 115 repeatedly expands and contracts. It is thought that the volume changes associated with repeated expansion and contraction apply physical pressure to the positive electrode active material 115. It is thought that this pressure causes defects, such as cracks. A crack refers to a fissure that forms due to the application of physical pressure. A pit refers to a hole where several layers of the main component, such as cobalt or oxygen, have escaped, and includes holes caused by pitting corrosion. For example, cobalt is thought to sometimes dissolve into the electrolyte 114, and the dissolution of one layer of cobalt can result in a hole. This is called a pit. Pits can progress during charging and discharging of a secondary battery, and if they progress, they can become deep holes. In other words, pits can be considered progressive defects.

[0082] By providing a configuration in which the electrolyte 114 and the positive electrode active material 115 do not come into contact with each other through the composite compound 117, it is possible to suppress the occurrence and progression of defects that can cause degradation, such as pits. To obtain this degradation suppression effect, it is sufficient for the composite compound 117 to cover only a portion of the positive electrode active material 115. With such a configuration, degradation of the secondary battery can be suppressed.

[0083] Another positive electrode active material and its surrounding structure will be described. Figure 1B2 corresponds to an enlarged view of region 112 in Figure 1A, and in Figure 1B2, at least a positive electrode active material 115 covered with a conductive material 118 and a barrier layer 116 is shown. The positive electrode active material covered with a barrier layer is sometimes referred to as a positive electrode active material composite, and the positive electrode active material composite will be described in Embodiment 3, etc. The other structures of Figure 1B2 are the same as those of Figure 1B1. The barrier layer 116 exists as a region having a material different from the main active material material of the positive electrode active material 115. The barrier layer 116 also exists as a region having the additive elements that the positive electrode active material 115 has. The materials used for the specific additive elements will be described in subsequent embodiments.

[0084] The barrier layer 116 is preferably located on the surface of the positive electrode active material 115. The surface refers to, for example, the region within 50 nm from the surface of the positive electrode active material toward the interior, more preferably within 35 nm from the surface toward the interior, even more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm from the surface toward the interior. Surfaces formed by cracks and / or fissures may also be considered the surface.

[0085] The presence of the barrier layer 116 on the surface can suppress the degradation of the positive electrode active material 115 over time. To enable the suppression of degradation over time, it is preferable for the barrier layer 116 to cover the entire surface of the positive electrode active material 115, but it goes without saying that the degradation suppression effect can also be achieved if the barrier layer 116 covers only a part of the positive electrode active material 115.

[0086] It is preferable to form a positive electrode active material 115 having a barrier layer 116 on its surface, and then provide a composite compound 117 to the positive electrode active material 115. That is, the composite compound 117 should be located outside the barrier layer 116. This is to prevent the positive electrode active material 115 from coming into contact with the electrolyte 114. Furthermore, it is preferable that the composite compound 117 has a region that is thicker than the barrier layer 116.

[0087] The conductive material 118 is arranged to assist the conductivity of the positive electrode active material 115. Therefore, the conductive material 118 has a higher conductivity than the positive electrode active material 115. The specific materials used for the conductive material will be described in subsequent embodiments.

[0088] The conductive material 118 can carry out the current path between the positive electrode active material 115 and the positive electrode current collector 104. In some cases, the conductive material 118 is mixed with the composite compound 117. In the mixed region, the composite compound 117 may break, and the positive electrode active material 115 may be exposed from the composite compound 117. The conductive material 118 may also be applied to the configuration shown in Figure 1B1 above.

[0089] Another positive electrode active material and its surrounding configuration will be described. Figure 1B3 corresponds to an enlarged view of region 112 in Figure 1A, and shows a state in which at least the first positive electrode active material 115a and the second positive electrode active material 115b are bonded together. The other configurations of Figure 1B3 are the same as those of Figure 1B2. In addition, as an additional configuration of Figure 1B3, a barrier layer may be provided located on the surface of the first positive electrode active material 115a and the second positive electrode active material 115b, as shown in Figure 1B2.

[0090] Because the first positive electrode active material 115a and the second positive electrode active material 115b are bonded together, the composite compound 117 has a structure that covers both the first positive electrode active material 115a and the second positive electrode active material 115b. If a barrier layer is provided, the composite compound 117 is preferably located on the outside of the barrier layer. It can be considered that the first positive electrode active material 115a and the second positive electrode active material 115b do not come into contact with the electrolyte 114 due to the composite compound 117, and thus the degradation of the first positive electrode active material 115a and the second positive electrode active material 115b caused by the electrolyte 114 is suppressed.

[0091] Next, the composition of the negative electrode active material and its vicinity will be described. Figure 1C1 corresponds to an enlarged view of region 113 in Figure 1A, and in Figure 1C1, at least the electrolyte 114 and the first negative electrode active material 125 are shown. The electrolyte 114 is also included in the positive electrode 101. The first negative electrode active material 125 preferably has a structure covered with a composite compound 127. The composite compound 127 can function as a binder for the first negative electrode active material 125. The composite compound 127 preferably has a material with high ionic conductivity, and the first negative electrode active material 125 covered with the composite compound 127 can exchange carrier ions with the electrolyte 114 via the composite compound 127. That is, the composite compound 127 can function as an electrolyte.

[0092] The composite compound 127 may have the same material as the composite compound 117 in the positive electrode. Alternatively, the composite compound 127 may have a different material than the composite compound 117 in the positive electrode.

[0093] The composite compound 127 is a composite compound derived from the first compound and the second compound as starting materials, and the term "composite" may mean that two or more compounds were used as starting materials. It is preferable that the composite compound has a crystalline structure. A composite compound having a crystalline structure has a high ability to retain the first negative electrode active material 125 and is suitable for use as a binder. A composite compound having a crystalline structure is also suitable as an electrolyte, functioning as a so-called solid electrolyte and eliminating the need for a separator.

[0094] For complex compounds having a crystalline structure, molecular crystals, for example, may be used.

[0095] Furthermore, the first negative electrode active material 125, which is covered with the composite compound 127, can be positioned so as not to come into contact with the electrolyte 114. This suppresses the degradation of the first negative electrode active material 125 caused by the electrolyte.

[0096] To suppress this degradation, the composite compound 127 only needs to cover a portion of the first negative electrode active material 125. This configuration can suppress the degradation of the secondary battery.

[0097] The configuration of another negative electrode active material and its vicinity will now be described. Figure 1C2 corresponds to an enlarged view of region 113 in Figure 1A, and shows a state in which at least the first negative electrode active material 125a and the second negative electrode active material 125b are bonded together. The other configurations of Figure 1C2 are the same as those of Figure 1C1.

[0098] Because the first negative electrode active material 125a and the second negative electrode active material 125b are bonded together, the composite compound 127 has a structure that covers both the first negative electrode active material 125a and the second negative electrode active material 125b. It can be considered that the first negative electrode active material 125a and the second negative electrode active material 125b do not come into contact with the electrolyte 114 due to the composite compound 127, and thus the degradation of the first negative electrode active material 125a and the second negative electrode active material 125b caused by the electrolyte is suppressed.

[0099] The negative electrode active material and other configurations in its vicinity will be described. Figure 1C3 corresponds to an enlarged view of region 113 in Figure 1A, and in Figure 1C3, at least the first negative electrode active material 125a and the second negative electrode active material 125b are shown coupled together, and the conductive material 128 is also shown. The other configurations of Figure 1C3 are the same as those in Figure 1C2.

[0100] The conductive material 128 is arranged to assist the conductivity of the first negative electrode active material 125. Therefore, the conductive material 128 has a higher conductivity than the first negative electrode active material 125. The specific materials used for the conductive material will be described in subsequent embodiments.

[0101] The conductive material 128 can carry the current path between the first negative electrode active material 125 and the negative electrode current collector 106. In Figure 1C3, it is also considered to carry the current path between the first negative electrode active material 125a and the second negative electrode active material 125b. In some cases, the conductive material 128 is mixed with the composite compound 127. In the mixed region, the composite compound 127 may break, and parts of the first negative electrode active material 125a and the second negative electrode active material 125b may be exposed from the composite compound 127.

[0102] The negative electrode active material and other configurations in its vicinity will be described. Figure 1C4 corresponds to an enlarged view of region 113 in Figure 1A, and at least the first negative electrode active material 125 and the second negative electrode active material 129 are shown in Figure 1C4. Multiple instances of the first negative electrode active material 125 and the second negative electrode active material 129 are shown. It is preferable that the first negative electrode active material 125 differs from the second negative electrode active material 129 in terms of material or particle size. For example, the first negative electrode active material 125 may contain silicon and be small nanoparticles, while the second negative electrode active material 129 may contain graphite and have a particle size larger than that of the first negative electrode active material 125. The other configurations in Figure 1C4 are the same as in Figure 1C3.

[0103] Next, we will illustrate the configuration of a secondary battery by combining one of the positive electrode active materials described above with one of the negative electrode active materials described above. Figure 2A shows a cross-sectional view of the secondary battery 100. The secondary battery 100 is an example that uses the positive electrode active material etc. described in Figure 1B2 and the negative electrode active material etc. described in Figure 1C4. In this way, one of the positive electrode active materials etc. described above and one of the negative electrode active materials described above can be combined and used in a secondary battery.

[0104] The separator 110 is impregnated with electrolyte 114. This impregnation is sometimes referred to as "soaking."

[0105] Furthermore, since the positive electrode active material 115 covered with the composite compound 117, and the first negative electrode active material 125 and the second negative electrode active material 129 covered with the composite compound 127, have regions that do not come into contact with the electrolyte 114, degradation of the positive electrode active material 115, the first negative electrode active material 125, and the second negative electrode active material 129 due to the electrolyte is suppressed. This degradation is thought to be caused by defects that occur in the positive electrode active material 115, the first negative electrode active material 125, and the second negative electrode active material 129. These defects include cracks and pits. The configuration in which the electrolyte 114 does not come into contact with the positive electrode active material 115, the first negative electrode active material 125, and the second negative electrode active material 129 can suppress the occurrence and progression of the above defects, especially pits.

[0106] Furthermore, in order to suppress such degradation, it is sufficient for the positive electrode active material 115, the first negative electrode active material 125, and the second negative electrode active material 129 to have regions that do not come into contact with the electrolyte 114. Therefore, the composite compound 117 does not need to cover all of the positive electrode active material 115, the first negative electrode active material 125, and the second negative electrode active material 129, but only needs to cover a portion of them. With this configuration, the above-mentioned defects, particularly the occurrence and progression of pits, can be suppressed, and the degradation of the secondary battery can be suppressed.

[0107] The composite compound 117 has the function of binding multiple positive electrode active materials 115 together and functions as a binder. The composite compound 117 also has the function of binding the positive electrode current collector 104 and the positive electrode active materials 115 together and functions as a binder. The composite compound 117 may have regions in which conductive material 118 is mixed. If the conductivity of the composite compound 117 is low, the conductive material 118 can ensure a current path. On the surface of the positive electrode current collector 104, the positive electrode active materials 115 or the composite compound 117 may be compressed. That is, the surface of the positive electrode current collector 104 may have irregularities in the cross-sectional view of the secondary battery. Also, on the surface of the positive electrode current collector 104, the composite compound 117 may break, and the positive electrode active materials 115 may be exposed from the composite compound 117. Since the exposed region is in contact with the positive electrode current collector 104, it is considered that it will not be in contact with the electrolyte 114.

[0108] The composite compound 127 has the function of binding the first negative electrode active materials 125 together, the second negative electrode active materials 129 together, or the first negative electrode active material 125 and the second negative electrode active material 129 together, and thus functions as a binder. The composite compound 127 has the function of binding the negative electrode current collector 106 to the first negative electrode active material 125 or the second negative electrode active material 129, and thus functions as a binder. The composite compound 127 may have regions in which conductive material 128 is mixed. If the conductivity of the composite compound 127 is low, the conductive material 128 can ensure a current path. On the surface of the negative electrode current collector 106, the first negative electrode active material 125, the second negative electrode active material 129, or the composite compound 127 may be compressed. That is, the surface of the negative electrode current collector 106 may have irregularities in a cross-sectional view of the secondary battery. Furthermore, on the surface of the negative electrode current collector 106, the composite compound 127 may break, exposing the first negative electrode active material 125 or the second negative electrode active material 129 from the composite compound 127. Since the exposed area is in contact with the negative electrode current collector 106, it is considered that it will not come into contact with the electrolyte 114.

[0109] The composite compound 127 may have the same material as the composite compound 117, or it may have a different material. Both the composite compound 117 and the composite compound 127 only need to constitute a crystalline structure, and it is even more preferable that they have high ionic conductivity. When the ionic conductivity is high, the composite compound 117 and the composite compound 127 can function as an electrolyte.

[0110] The composite compound 117 or the composite compound 127 can be obtained using the first compound and the second compound as starting materials.

[0111] The first compound is the compound shown in the following general formula (G1). The following general formula (G1) is a compound having a cyano group.

[0112] [ka]

[0113] In the above general formula (G1), R represents a hydrocarbon having 1 to 5 carbon atoms. Preferably, in the above general formula (G1), R represents a hydrocarbon having 2 to 4 carbon atoms.

[0114] Examples of the above general formula (G1) include succinonitrile, glutalonitrile, and adiponitrile, and an example of a compound having a cyano group is acetonitrile. One or more of these can be used as the first compound.

[0115] As the second compound, one or more selected from lithium bis(fluorosulfonyl)imide (Li(FSO2)2N, abbreviation: LiFSI), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N, abbreviation: LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N, abbreviation: LiBETI) can be used.

[0116] Preferred combinations of the first compound and the second compound are shown below in (H1) to (H3).

[0117] [ka]

[0118] [ka]

[0119] [ka]

[0120] Whether the composite compounds obtained by combining the compounds shown in (H1) to (H3) above form molecular crystals can be confirmed by XRD measurement, etc. In the XRD measurement results, a deviation of ±0.50° in the peak position (2θ) value is permitted.

[0121] Furthermore, the composite compound obtained by combining the compounds shown in (H1) above is represented as Li(FSI)(SN)2 and may have a melting point of 63.4°C or nearby. Also, the composite compound obtained by combining the compounds shown in (H2) above is represented as Li(FSI)(GN)2 and may have a melting point of 89.3°C or nearby. Furthermore, the composite compound obtained by combining the compounds shown in (H3) above is represented as Li(FSI)(ADN)2 and may have a melting point of 90.9°C or nearby.

[0122] In other words, if you want to obtain a composite compound 117 with a high melting point, it is preferable to use a composite compound obtained by combining the compounds shown in (H2) and (H3) above, rather than a composite compound obtained by combining the compounds shown in (H1) above.

[0123] Next, the magnitude of the charge of the nitrogen atom in succinonitrile, glutaronitrile, and adiponitrile, which can be used in the first compound, was calculated. These nitrogen atoms can form coordinate bonds with lithium ions, and the strength of the coordinate bond between the lithium ion and the first compound can be determined and compared based on the magnitude of the nitrogen atom's charge. Gaussian09 was used as the quantum chemistry calculation software for the calculations. After optimizing the ground state molecular structures of succinonitrile, glutaronitrile, and adiponitrile, the intramolecular charge distribution was analyzed to determine the magnitude of the charge.

[0124] First, we performed structural optimization calculations for the ground state of succinonitrile, glutaronitrile, and adiponitrile, which can be used in the first compound. Density functional theory (DFT) was used for the structural optimization calculations. In DFT, the total energy is expressed as the sum of potential energy, interelectron electrostatic energy, and exchange-correlation energy, which includes the kinetic energy of electrons and complex interelectron interactions. DFT approximates the exchange-correlation interaction with a functional (a function of a function) of the one-electron potential expressed in terms of electron density, resulting in fast and highly accurate calculations. In this study, we used the mixed functional B3LYP to define the weights of each parameter related to exchange and correlation energy. Furthermore, we applied the 6-311G basis set (a triple-split valence basis set using three shortened functions for each valence orbital) to all atoms. With this basis set, for example, for a hydrogen atom, the 1s-3s orbitals are considered, and for a carbon atom, the 1s-4s and 2p-4p orbitals are considered. Furthermore, to improve calculation accuracy, a p-function was added to the polarization base system for hydrogen atoms, and a d-function was added for atoms other than hydrogen.

[0125] For the analysis of the charge distribution, points based on the Merz-Singh-Kollmans (MK) scheme were used to perform charge fitting of the electrostatic potential. The calculation conditions are summarized in Table 1 below.

[0126] [Table 1]

[0127] Figure 48A shows the structural formula of succinonitrile and the magnitude of the charge of the nitrogen atom in succinonitrile. The charge of the nitrogen atom in succinonitrile is -0.42. Figure 48B shows the structural formula of glutaronitrile and the magnitude of the charge of the nitrogen atom in glutaronitrile. The charge of the nitrogen atom in glutaronitrile is -0.44. Figure 48C shows the structural formula of adiponitrile and the magnitude of the charge of the nitrogen atom in adiponitrile. The charge of the nitrogen atom in adiponitrile is -0.46.

[0128] It is hypothesized that the longer the carbon chain of succinonitrile, glutaronitrile, and adiponitrile, the greater the charge of the nitrogen atom, and therefore the stronger the coordination bond with the lithium ion. For this reason, it is hypothesized that the coordination bond between adiponitrile and lithium ions is strong.

[0129] Next, Figure 49 shows an example of the calculation results regarding the stable structure of the composite compound. The calculation was performed using the calculation conditions shown in Table 2 below.

[0130] [Table 2]

[0131] Figure 49A shows an example of a stable structure of a composite compound having succinonitrile and lithium bis(fluorosulfonyl)imide. The composite compound shown in Figure 49A can be seen to have succinonitrile 182, lithium ion 180, and (fluorosulfonyl)imide ion 181.

[0132] Furthermore, in the case of a stable structure, the composite compound has a substructure in which a cyano group is coordinately bonded to a lithium ion, as shown in the general formula (G2) below.

[0133] [ka]

[0134] In the above general formula (G2), R represents a hydrocarbon having 1 to 5 carbon atoms. Preferably, in the above general formula (G2), R represents a hydrocarbon having 2 to 4 carbon atoms.

[0135] In the case of the stable structure shown in Figure 49A, the composite compound has a substructure in which succinonitrile is coordinately bonded to the lithium ion, as shown in (H4) below.

[0136] [ka]

[0137] Figure 49B shows an example of a stable structure of a composite compound of glutaronitrile and lithium bis(fluorosulfonyl)imide. The composite compound shown in Figure 49B contains glutaronitrile 187, lithium ion 185, and bis(fluorosulfonyl)imide ion 186. In other words, in the stable structure of Figure 49B, the composite compound has a substructure in which glutaronitrile is coordinately bonded to the lithium ion.

[0138] Figure 49C shows an example of a stable structure of a complex compound of adiponitrile and lithium bis(fluorosulfonyl)imide. The complex compound shown in Figure 49C contains adiponitrile 192, lithium ion 190, and bis(fluorosulfonyl)imide ion 191. In other words, in the stable structure of Figure 49C, the complex compound has a substructure in which adiponitrile is coordinately bonded to the lithium ion.

[0139] Next, an example of the configuration of an all-solid-state secondary battery using composite compound 117 as the electrolyte will be given. Figure 2B shows a cross-sectional view of a secondary battery 150 that is an all-solid-state secondary battery. The secondary battery 150 does not contain a separator, uses composite compound 117 as the electrolyte, uses a positive electrode active material 115, at least a portion of which is covered with a barrier layer 116, etc., as the positive electrode active material, and uses a first negative electrode active material 125 and a second negative electrode active material 129, etc., as the negative electrode active material.

[0140] The structure of the positive electrode side of the secondary battery 150 is obtained by mixing the composite compound 117 with the positive electrode active material 115, etc. The composite compound 117 is arranged to fill the spaces between the positive electrode active material particles. The structure of the negative electrode side of the secondary battery 150 is obtained by mixing the composite compound 117 with the first negative electrode active material 125 and the second negative electrode active material 129, etc.

[0141] Although Figure 2B shows an all-solid-state secondary battery without a separator, a configuration including a separator is also possible.

[0142] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0143] (Embodiment 2) This embodiment describes a secondary battery according to one aspect of the present invention. The secondary battery comprises at least a positive electrode, a negative electrode, an electrolyte, and an outer casing. A separator may be provided between the positive electrode and the negative electrode. In the positive electrode, the positive electrode active material layer preferably comprises a positive electrode active material and a composite compound, and it is more preferable that the composite compound is positioned to cover the surface of the positive electrode active material. The composite compound preferably has crystalline properties, for example, a molecular crystal. The molecular crystal preferably has high ionic conductivity and can be used as an electrolyte. In this case, the composite compound can be called a molecular crystalline electrolyte.

[0144] An example of a method for manufacturing a secondary battery according to one aspect of the present invention will be explained with reference to Figures 3 to 5.

[0145] [Method for fabricating the positive electrode 1] A method for manufacturing a positive electrode according to one embodiment of the present invention will be explained using Figures 3 and 4. The positive electrode active material layer preferably has a positive electrode active material composite as shown in Embodiment 3, or a positive electrode active material as shown in Embodiment 4, and may further have a composite compound and a conductive material. It is desirable that the composite compound functions as a binder that binds multiple positive electrode active material composites together, or multiple positive electrode active materials together. Furthermore, it is desirable that the composite compound allows lithium ions to pass through.

[0146] In step S91 of Figure 3A, the first compound 15 is prepared, and in step S92, the second compound 16 is prepared. Next, in step S93, the first compound 15 and the second compound 16 are mixed while heating. Mixing may be done after heating if the temperature of the heated state can be maintained. The heating temperature in step S93 is preferably above the temperature at which the mixture of the first compound 15 and the second compound 16 completely melts (for example, above the melting point). The heating in step S93 may be multi-stage heating. After heating and mixing in step S93, the mixture is cooled to room temperature, and in step S94, the composite compound 117 is obtained. The composite compound 117 has molecular crystals and can cover the positive electrode active material, etc., as a composite compound 117 with a crystalline structure.

[0147] As the first compound 15, a nitrile solvent can be used, for example, one or more of acetonitrile, succinonitrile, glutalonitrile, and adiponitrile can be used.

[0148] As the second compound 16, one or more selected from lithium bis(fluorosulfonyl)imide (Li(FSO2)2N, abbreviation: LiFSI), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N, abbreviation: LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N, abbreviation: LiBETI) can be used.

[0149] It is desirable that the composite compound 117 functions as a binder that fixes multiple positive electrode active material composites together, or multiple positive electrode active materials together. Furthermore, it is desirable that the composite compound 117 is permeable to lithium ions. In addition, it is preferable that the composite compound 117 is crystalline, and more preferably that it is a molecular crystal having the first compound 15 and the second compound 16.

[0150] In step S95 of Figure 3B, the positive electrode active material 115 is prepared. The positive electrode active material 115 may be the positive electrode active material composite shown in Embodiment 3, or the positive electrode active material shown in Embodiment 4.

[0151] As step S96 in Figure 3B, prepare the composite compound 117. For example, the composite compound 117 prepared in Figure 3A can be used. Alternatively, instead of preparing the composite compound 117 as step S96, the first compound 15 in step S91 and the second compound 16 in step S92 of Figure 3A may be prepared as is.

[0152] Next, in step S97, the positive electrode active material 115 and the composite compound 117 are mixed while heating to obtain the mixture 140 in step S98. The mixture 140 is sometimes referred to as the positive electrode slurry. Alternatively, in step S97, the positive electrode active material 115, the first compound 15, and the second compound 16 from step S92 can be mixed while heating to obtain the mixture 140 in step S98.

[0153] Mixing may be performed after heating if the temperature achieved in step S97 can be maintained. In step S99, heating and coating onto the current collector are performed. After cooling in step S100, the positive electrode 101 of step S101 is obtained. It is preferable that the composite compound 117 is solid in the positive electrode 101.

[0154] Step S97 may also be a step of heating while mixing the positive electrode active material 115, the first compound 15, and the second compound 16.

[0155] Furthermore, in step S97, a conductive material may be added in addition to the positive electrode active material 115 and the composite compound 117. As the conductive material, one or more selected from carbon black such as acetylene black or furnace black, graphite such as artificial graphite or natural graphite, carbon fibers such as carbon nanofibers or carbon nanotubes, graphene, and graphene compounds can be used.

[0156] In this specification, graphene includes single-layer graphene or multilayer graphene (also called multigraphene). In this specification, graphene compounds include graphene oxide, multilayer graphene oxide, reduced graphene oxide, or reduced multilayer graphene oxide. Graphene is a material that has carbon atoms, has a plate-like or sheet-like shape, and has a two-dimensional structure formed by six-membered carbon rings. Graphene may also be called a carbon sheet. It is preferable that graphene or graphene compounds have a bent shape. It is preferable that graphene compounds have functional groups. Graphene or graphene compounds may also be rolled up into a tube shape.

[0157] The heating in steps S97 and S99 should preferably be carried out at a temperature above the temperature at which the composite compound 117 completely melts. For example, when Li(FSI)(SN)2 is used as the composite compound 117, it is preferable to heat at a temperature of 60°C to 100°C, preferably 65°C to 80°C. However, the heating temperature in step S97 does not need to be the same as the heating temperature in step S99, and it is preferable that the heating temperature in step S97 is higher than the heating temperature in step S99. It is preferable that the composite compound 117 is in a liquid state in steps S97 and S99.

[0158] As the positive electrode current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the positive electrode potential. Additionally, aluminum alloys to which elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, are added can be used for the positive electrode current collector. The positive electrode current collector can be in various shapes, such as foil, plate, sheet, mesh, perforated metal, or expanded metal. The positive electrode current collector should preferably have a thickness of 5 μm to 30 μm.

[0159] [Method for fabricating the positive electrode 2] Next, we will describe one embodiment of the present invention that differs from the positive electrode manufacturing method 1.

[0160] In step S102 of Figure 4A, the binder 111 is prepared, and in step S103, the dispersion medium 120 is prepared.

[0161] As the binder 111, one or more materials selected from, for example, polystyrene, methyl polyacrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose can be used. Preferably, the lithium ion conductivity of the materials used in the binder described above is lower than that of the composite compound 117.

[0162] As the dispersion medium 120, one or more selected from water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO) can be used, and if two or more are used, it may be referred to as a mixture. A suitable combination of binder 111 and dispersion medium 120 is a combination of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP).

[0163] Next, in step S104, the binder 111 and the dispersion medium 120 are mixed to obtain the mixture of step S105. This mixture is referred to as binder mixture 1001 to distinguish it from other mixtures. For example, a propeller-type mixer, a planetary-type mixer, or a thin-film swirling mixer can be used as a mixing method. It is desirable that the binder mixture 1001 is in a state where the binder 111 is well dispersed in the dispersion medium 120.

[0164] In step S111 of Figure 4B, the binder mixture 1001 is prepared, and in step S112, the conductive material 1002 is prepared. In order to perform solid kneading in a later step, the amount of binder mixture 1001 prepared in step S111 is less than the total amount required to form the positive electrode active material layer, so that the mixture is suitable for solid kneading. In this case, any shortage of binder mixture 1001 can be added in a step after solid kneading. Solid kneading refers to the kneading of a high-viscosity mixture.

[0165] As the conductive material 1002, one or more selected from carbon black such as acetylene black or furnace black, graphite such as artificial graphite or natural graphite, carbon fibers such as carbon nanofibers or carbon nanotubes, graphene, and graphene compounds can be used.

[0166] Next, in step S113, the binder mixture 1001 and the conductive material 1002 are mixed to obtain the mixture 1010 in step S121. For example, a propeller-type mixing device, a planetary-type mixing device, or a thin-film swirling-type mixing device can be used as a mixing method.

[0167] Next, in step S122 of Figure 4B, the positive electrode active material 115 is prepared.

[0168] Next, in step S123, the mixture 1010 and the positive electrode active material 115 are mixed to obtain the mixture 1020 from step S131. For mixing, for example, a propeller-type mixer, a planetary-type mixer, or a thin-film swirling mixer can be used. In step S123, if the viscosity is appropriately adjusted, solid kneading is possible, and solid kneading can loosen the agglomeration of powders such as the positive electrode active material.

[0169] Next, the binder mixture 1001 is prepared in step S132, and the dispersion medium 1003 is prepared in step S133. If, in step S111, less than the total amount of binder mixture 1001 required to form the positive electrode active material layer was prepared, the deficit in binder mixture 1001 can be added in step S132. When adjusting the dispersion medium for the binder mixture 1001, the same dispersion medium as in step S102 in Figure 4A can be prepared as the dispersion medium 1003. It is desirable to adjust the amount of dispersion medium 1003 to achieve a viscosity suitable for coating in later steps. Note that if the total amount of binder mixture 1001 required to form the positive electrode active material layer was prepared in step S111, it is not necessary to prepare the binder mixture 1001 in step S132. In other words, if the total amount of binder mixture 1001 required to form the positive electrode active material layer was prepared in step S111, steps S132, S133, and S134 can be omitted.

[0170] Next, in step S134, the mixture 1020 from step S131, the binder mixture 1001 prepared in step S132, and the dispersion medium 1003 prepared in step S133 are mixed to obtain mixture 1030 in step S135. Mixture 1030 is sometimes called positive electrode slurry.

[0171] Next, in step S136, the mixture 1030 is applied to the positive electrode current collector. As the positive electrode current collector, a highly conductive material such as stainless steel, gold, platinum, aluminum, titanium, or alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. As the application method in step S136, a slot die method, gravure, blade method, or a combination thereof can be used. A continuous coating machine may also be used for application. Following step S136, in step S137, the mixture 1030 applied to the positive electrode current collector is dried. As a drying method, one or more selected from batch methods such as hot plates, drying ovens, ventilated drying ovens, and vacuum drying ovens, as well as continuous methods combining hot air drying and infrared drying with a continuous coating machine, can be used. After drying, the coated electrode 1040 of step S140 is obtained.

[0172] Next, as step S141 in Figure 4B, the complex compound 117 from step S112 in Figure 3A is prepared.

[0173] Next, in step S142 of Figure 4B, the coated electrode 1040 and the composite compound 117 from step S140 are heated, and the composite compound 117 is injected into the voids in the coated electrode 1040. The heating temperature is preferably above the temperature at which the composite compound 117 completely melts. As for the injection method, one or more methods selected from the slot die method, gravure, blade method, and drop methods such as ODF (One Drop Filling), as well as the plate press method, roll press, and combinations thereof, can be used. When the injection is performed in a reduced pressure environment, it is desirable because the composite compound 117 can be effectively permeated into the voids in the coated electrode 1040. For example, when Li(FSI)(SN)2 is used as the composite compound 117, the heating temperature is 60°C to 100°C, preferably 65°C to 80°C.

[0174] The positive electrode active material is fixed to the positive electrode current collector or other positive electrode active material by the binder that has been mixed in advance. By injecting the liquid composite compound 117 in this state, the composite compound 117 can efficiently permeate into the voids. Since the composite compound 117 becomes solid at room temperature, it can also function as a binder. It is preferable that the composite compound 117 has high ionic conductivity. With this configuration, the proportion of binder in conventional positive electrodes can be reduced and the proportion of positive electrode active material can be increased. Furthermore, although a pressing process is sometimes performed on the coated electrode when forming the positive electrode, the pressing pressure can be reduced by performing the injection in a reduced pressure environment. Moreover, by performing the injection in a reduced pressure environment, the pressing process can be made unnecessary.

[0175] By following the above steps, a positive electrode 101 according to one embodiment of the present invention, as shown in Figure 4B, can be manufactured (step S143).

[0176] [Method for fabricating the negative electrode] The negative electrode can be manufactured in the same manner as the positive electrode 101 shown in Figures 3 and 4. When manufacturing the negative electrode 102 using the manufacturing method shown in Figures 3 and 4, the negative electrode active material is prepared in place of the positive electrode active material 115 prepared in step S121 of Figure 3B. Also, the negative electrode active material is prepared in place of the positive electrode active material 115 prepared in step S122 of Figure 4B.

[0177] As the negative electrode active material, for example, alloy-based materials, carbon-based materials, and mixtures thereof can be used.

[0178] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, composite compounds containing these elements may be used as the negative electrode active material. For example, composite compounds include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. In this context, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and composite compounds containing such elements, are sometimes referred to as alloying materials.

[0179] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO refers to SiO x It can also be expressed as follows. Here, x is preferably 1 or a value in its immediate vicinity. For example, x is preferably between 0.2 and 1.5, and preferably between 0.3 and 1.2.

[0180] Carbon-based materials may be used as the negative electrode active material. Suitable carbon-based materials include graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, or carbon black.

[0181] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. As artificial graphite, spherical graphite having a spherical shape can be used. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which is preferable. Examples of natural graphite include flake graphite or spheroidized natural graphite, etc.

[0182] Graphite exhibits a potential as low as that of metallic lithium when lithium ions are inserted into it. Thus, a lithium-ion secondary battery using graphite can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to metallic lithium, so it is preferable.

[0183] Also, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 )、niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0184] Also, as the negative electrode active material, lithium-graphite intercalation compounds (Li x C6), SiC, etc. can be used.

[0185] Also, as the negative electrode active material, Li 3-x M x N (M = Co, Ni, Cu), which is a nitride of lithium and a transition metal having a Li3N-type structure, can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large discharge capacity (900 mAh / g, 1890 mAh / cm 3 , which is preferable. )

[0186] Using lithium and transition metal nitrides is preferable because the negative electrode active material contains lithium ions, allowing it to be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode active material. Even when using a material containing lithium ions as the positive electrode active material, lithium and transition metal nitrides can be used as the negative electrode active material by removing the lithium ions contained in the positive electrode active material beforehand.

[0187] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 This can also occur with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, or Ge3N4, phosphides such as NiP2, FeP2, or CoP3, and fluorides such as FeF3 or BiF3.

[0188] The conductive material and binder that the negative electrode active material layer can have can be the same materials as the conductive material and binder that the positive electrode active material layer can have.

[0189] Furthermore, in addition to the same materials as the positive electrode current collector, copper and other materials can also be used as the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0190] The negative electrode can be fabricated using the negative electrode active material shown above, according to Figures 3A and 3B. In this case, the negative electrode 102 can be obtained in step S130 of Figure 3B. Alternatively, the negative electrode can be fabricated using the negative electrode active material shown above, according to Figures 4A and 4B. In this case, the negative electrode 102 can be obtained in step S143 of Figure 4B.

[0191] [Method for manufacturing a secondary battery 1] The manufacturing method of a secondary battery according to an aspect of the present invention will be described with reference to FIGS. 5A and 5B.

[0192] In step S141 of FIG. 5A, the positive electrode 101 is prepared; in step S142, the negative electrode 102 is prepared; in step S143, the separator 110 is prepared; and in step S144, the exterior body 230 is prepared.

[0193] As the separator, for example, a fiber having cellulose such as paper, a non-woven fabric, a glass fiber, a ceramic, or a synthetic fiber made of nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, polyimide, acrylic, polyolefin, polyurethane, etc. can be used.

[0194] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0195] Coating the above-described materials with a ceramic-based material improves the oxidation resistance, so that deterioration of the separator during high-voltage charging can be suppressed, and the reliability of the secondary battery can be improved. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere to each other, and the output characteristics can be improved. Coating with a polyamide-based material, particularly aramid, improves the heat resistance, so that the safety of the secondary battery can be improved.

[0196] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0197] For the outer casing, metal materials such as aluminum or resin materials can be used. Alternatively, a film-like outer casing can be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing.

[0198] Next, in step S145, assembly is performed using the positive electrode 101, negative electrode 102, separator 110, and outer casing 230. The separator 110 is placed between the positive electrode 101 and the negative electrode 102. The separator may be processed into a bag shape and placed to enclose either the positive electrode 101 or the negative electrode 102. Next, the positive electrode 101, negative electrode 102, and separator 110 are placed inside the outer casing 230. At this time, it is desirable that the outer casing 230 has an opening for injecting the electrolyte. Depending on the shape of the battery to be manufactured, electrode terminals such as leads may be provided as appropriate.

[0199] Next, in step S146, prepare the electrolyte 240.

[0200] As one form of electrolyte 240, an electrolyte solution comprising a solvent and an electrolyte dissolved in the solvent can be used. As the solvent for the electrolyte solution, an aprotic organic solvent is preferred, and one or more selected from, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone can be used.

[0201] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from rupturing or igniting even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0202] Furthermore, examples of electrolytes to be dissolved in the above solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10 Cl10 Li2B 12 Cl 12 One or more lithium salts selected from LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxalate) borate (Li(C2O4)2, LiBOB) can be used.

[0203] It is preferable to use a highly purified electrolyte with a low content of particulate matter or elements other than the constituent elements of the electrolyte (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0204] Furthermore, one or more additives selected from vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile complex compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the solvent in which the electrolyte is dissolved.

[0205] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0206] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0207] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, or fluorine-based polymer gels can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, as well as copolymers containing these, can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the formed polymer may have a porous structure.

[0208] Next, in step S147, the electrolyte 240 is injected through the opening of the outer casing 230. Then, in step S148, the opening of the outer casing 230 is sealed. Note that the injection in step S147 and the sealing in step S148 may be carried out under a reduced pressure atmosphere.

[0209] Through the above process, the secondary battery 250 can be manufactured in step S149.

[0210] [Method for manufacturing secondary batteries 2] Next, we will describe one embodiment of the present invention that differs from the secondary battery manufacturing method 1.

[0211] In step S141 of Figure 5B, the positive electrode 101 is prepared, and in step S142, the composite compound 117 is prepared. It is preferable to use the positive electrode 101 prepared using the method shown in Figure 4B.

[0212] Next, in step S143, the composite compound 117 is heated to a molten state and applied onto the active material layer of the positive electrode 101. As the application method, one or more selected from a slot die method, gravure, blade method, and a combination thereof can be used. Also, a continuous coater or the like may be used for the application. By step S143, a layer having the composite compound 117 can be formed on the positive electrode 101. The layer having the composite compound 117 functions as a separator that prevents direct contact between the positive electrode 101 and the negative electrode 102, and also functions as a solid electrolyte that enables lithium ion conduction between the positive electrode 101 and the negative electrode 102.

[0213] Next, in step S144, the negative electrode 102 is prepared. As the negative electrode 102, it is preferable to use the negative electrode 102 fabricated according to FIG. 4B shown in the above method for fabricating the negative electrode.

[0214] Next, as step S145, heating and lamination are performed. The negative electrode 102 is overlaid on the structure having the layer of the composite compound 117 on the positive electrode 101 fabricated in step S143, and they are laminated by heating. The heating in step S145 is preferably at a temperature below the temperature at which the composite compound 117 completely melts. That is, the heating in step S145 is preferably at a lower temperature than the heating in step S143. For example, when Li(FSI)(SN)2 is used as the composite compound 117, the heating temperature can be 55°C or higher and 65°C or lower.

[0215] Next, as step S146, the exterior body 230 is prepared.

[0216] Next, as step S147, the assembly of the positive electrode 101, the negative electrode 102, and the laminated body of the composite compound 117 and the exterior body 230 is carried out. Depending on the shape of the battery to be fabricated, electrode terminals such as leads may be provided as appropriate.

[0217] Next, in step S148, the outer casing 230 is sealed. It is preferable to perform the sealing under a reduced pressure atmosphere. Furthermore, it is preferable to heat and press the outer casing 230, which contains the positive electrode 101, the negative electrode 102, and the composite compound 117, from the outside during sealing, as this can reduce the voids inside the positive electrode, the negative electrode, or the outer casing.

[0218] In addition, instead of the composite compound 117 prepared in step S142, a solid electrolyte having an inorganic material such as a sulfide or oxide, or a solid electrolyte having a polymer material such as PEO (polyethylene oxide), can be used as the electrolyte.

[0219] Through the above process, the secondary battery 250 can be manufactured in step S149.

[0220] As described above, the secondary battery produced by secondary battery production method 2 can be called an all-solid-state secondary battery. All-solid-state secondary batteries are lithium-ion secondary batteries that are highly safe and have good characteristics.

[0221] The contents described in this embodiment can be combined with the contents described in other embodiments.

[0222] (Embodiment 3) In this embodiment, a positive electrode active material composite that can be used in a positive electrode active material 115 according to one aspect of the present invention, a method for producing the same, and a positive electrode and a method for producing the same will be described.

[0223] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material composite 100z having a first material 100x that functions as a positive electrode active material and a second material 100y that covers at least a portion of the first material 100x. The second material 100y can function as a barrier layer 116 as described in Embodiment 1 above. The barrier layer may also be referred to as a coating layer. The positive electrode active material layer may further have a conductive material and a binder. The binder may be a composite compound. If the binder is a composite compound, the composite compound 117 can be placed outside the second material 100y.

[0224] The positive electrode active material composite 100z is obtained by a composite treatment using at least a first material 100x and a second material 100y. The second material 100y may be an active material capable of intercalating and releasing lithium. As the composite treatment, one or more composite treatments selected from mechanical energy composite treatments such as mechanochemical methods, mechanofusion methods, and ball milling methods; liquid phase reaction composite treatments such as coprecipitation methods, hydrothermal methods, and sol-gel methods; and gas phase reaction composite treatments such as barrel sputtering, ALD (Atomic Layer Deposition), vapor deposition, and CVD (Chemical Vapor Deposition) methods can be used. In this specification, the composite treatment is also referred to as a surface coating treatment or coating treatment.

[0225] Furthermore, it is preferable to perform a heat treatment after the composite treatment. When a heat treatment is performed after the composite treatment, the second material 100y, which covers at least a portion of the first material 100x that functions as the positive electrode active material, sintersects or melts and spreads. Therefore, it is expected that the area in direct contact between the first material 100x and the electrolyte will be reduced. However, if the temperature of the heat treatment after the composite treatment is too high, the elements of the second material 100y may diffuse into the interior of the first material 100x more than necessary, which may reduce the chargeable and dischargeable capacity of the first material 100x as an active material, and may also reduce the effectiveness of the second material 100y as a barrier layer. Therefore, when performing a heat treatment after the composite treatment, it is advisable to appropriately set the heating temperature, heating time, and heating atmosphere.

[0226] [Cathode active material] As the first material 100x, a composite oxide represented by LiM1O2 (where M1 is one or more elements selected from Fe, Ni, Co, Mn, and Al) having a layered rock salt-type crystalline structure can be used. Alternatively, as the first material 100x, a composite oxide represented by LiM1O2 with added element X can be used. It is preferable that the added element X in the first material 100x be one or more elements selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements may further stabilize the crystalline structure of the first material 100x. To further stabilize the crystalline structure, the added element X is preferably located in the surface layer of the positive electrode active material. That is, the region containing the added element X is located in the surface layer. It is also possible to make the region containing the additive element X located in the surface layer function as a barrier layer 116. Furthermore, the barrier layer 116 may have a region containing the additive element X and a second material 100y located outside that region.

[0227] The first material 100x to which the additive element X is added in this manner can include lithium cobalt oxide with magnesium and fluorine, lithium cobalt oxide with magnesium, fluorine, aluminum, and nickel, lithium cobalt oxide with magnesium, fluorine, and titanium, lithium nickel-cobalt oxide with magnesium and fluorine, lithium cobalt-aluminate with magnesium and fluorine, lithium nickel-cobalt-aluminate with nickel and fluorine, lithium nickel-cobalt-aluminate with magnesium and fluorine, lithium nickel-cobalt-manganate with magnesium and fluorine, and the like. The region containing the additive element can be used as a barrier layer 116. Furthermore, a high nickel ratio is preferred as the transition metal ratio of nickel-cobalt-manganate lithium. For example, materials with ratios of nickel:cobalt:manganese = 8:1:1 and nearby, and nickel:cobalt:manganese = 9:0.5:0.5 and nearby are preferred. Furthermore, it is preferable that the above-mentioned lithium nickel-cobalt-manganate has calcium added to it.

[0228] Furthermore, as the first material 100x, secondary particles of a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, Mn, and Al) coated with a metal oxide may be used. As the metal oxide, oxides of one or more metals selected from Al, Ti, Nb, Zr, La, and Li can be used. For example, a composite oxide (sometimes referred to as a metal oxide coated composite oxide) in which secondary particles of a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, Mn, and Al) are coated with aluminum oxide can be used as the first material 100x. For example, a metal oxide coated composite oxide can be used in which secondary particles of lithium nickel-cobalt-manganate in ratios of nickel:cobalt:manganese = 8:1:1 and nickel:cobalt:manganese = 9:0.5:0.5 are coated with aluminum oxide. A region having a metal oxide such as aluminum oxide can be used as the barrier layer 116.

[0229] Here, the thickness of the region where the second material 100y that functions as the barrier layer is located is preferably thin, for example, 1 nm or more and 200 nm or less, more preferably 1 nm or more and 100 nm or less.

[0230] As a method for producing the first material 100x, the production method described in Embodiment 4 below can be used.

[0231] As the second material 100y, one or more selected from oxides and LiM2PO4 having an olivine-type crystal structure (M2 is one or more selected from Fe, Ni, Co, Mn) can be used. Many oxides have a stable crystal structure. Examples of oxides include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Also, many LiM2PO4 have a stable crystal structure. Examples of LiMPO4 include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), or LiFe f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc.

[0232] Furthermore, if the second material 100y is in particulate form, the surface of the particles may have a carbon coating layer.

[0233] [Cathode active material composite] In this embodiment, Method 1 for Fabricating a Positive Electrode Active Material Composite is shown as an example of a method for fabricating a positive electrode active material composite, in which at least a portion of the particle surface of a particulate first material 100x, which functions as a positive electrode active material, is covered with a second material 100y. A desirable form of the positive electrode active material composite is a structure in which at least a portion of the particle surface of the particulate first material 100x is covered with the second material 100y, and more preferably, a structure in which substantially the entire particle surface of the particulate first material 100x is covered with the second material 100y. Here, substantially covering the entire surface means that the second material 100y is positioned such that the first material 100x and the electrolyte do not come into direct contact.

[0234] Furthermore, a configuration in which the substantially entire surface of the particles of the first material 100x is covered with the second material 100y after composite processing may yield different charge and discharge characteristics compared to a configuration in which the second material 100y and the first material 100x are simply mixed.

[0235] By covering at least a portion, preferably substantially the entire, of the particle surface of the first material 100x, which functions as a positive electrode active material, with the second material 100y, the area in direct contact between the first material 100x and the electrolyte is reduced. This suppresses the detachment of transition metal elements and / or oxygen from the first material 100x, even in a high-voltage charging state, thereby suppressing capacity degradation due to repeated charging and discharging.

[0236] Furthermore, if a material with a stable crystal structure is used for the second material 100y, the secondary battery according to one embodiment of the present invention can suppress the detachment of transition metal elements and / or oxygen from the first material 100x even in a high-voltage charging state, improve stability at high temperatures, and improve fire resistance.

[0237] As the first material 100x, it is preferable to use lithium cobalt oxide with magnesium and / or fluorine added, and lithium cobalt oxide with magnesium, fluorine, aluminum, and / or nickel added. Magnesium, fluorine, and aluminum are characterized by being abundant in the surface layer of the positive electrode active material, while nickel is characterized by being widely distributed throughout the positive electrode active material. Furthermore, as the first material 100x, it is preferable to use secondary particles such as lithium nickel-cobalt-manganate with a ratio of nickel:cobalt:manganese = 8:1:1 and close to it, and nickel:cobalt:manganese = 9:0.5:0.5 and close to it. As the positive electrode active material composite, if a metal oxide coated composite oxide is used in which the above first material 100x is coated with aluminum oxide, it will have excellent stability in the high-voltage charging state. Therefore, the durability and stability of the positive electrode active material under high-voltage charging can be further improved. In addition, if the above positive electrode active material composite is used, the heat resistance and / or fire resistance of the secondary battery can be further improved.

[0238] The positive electrode active material that has undergone initial heating, as described later, exhibits remarkably superior repeated charge-discharge characteristics at high voltages, and is therefore particularly preferred as the first material 100x.

[0239] In the embodiments, the positive electrode of the present invention may have a structure in which at least a portion of the surface of the positive electrode active material composite is covered with graphene or a graphene compound. Preferably, a structure is preferred in which 80% or more of the surface of the positive electrode active material composite and / or the aggregate having the positive electrode active material composite is covered with graphene or a graphene compound.

[0240] [Method for fabricating positive electrode active material composites] An example of a method for producing a positive electrode active material composite, which is one aspect of the present invention, will be explained with reference to Figure 6. The method for producing the positive electrode active material composite describes a method in which a second material 100y and a first material 100x are combined using mechanical energy. However, the present invention is not limited to these descriptions.

[0241] In step S101 of FIG. 6A, the first material 100x is prepared, and in step S102, the second material 100y is prepared.

[0242] As the first material 100x, an additive element X is added to a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, Mn, and Al) prepared by the manufacturing method shown in Embodiment 4 described later. For example, lithium cobaltate to which magnesium and fluorine are added, and lithium cobaltate to which magnesium, fluorine, aluminum, and nickel are added can be used. In particular, as the lithium cobaltate to which magnesium, fluorine, aluminum, and nickel are added, those subjected to the initial heating shown in Embodiment 4 are preferable. As another example of the first material 100x, lithium nickel-cobalt-manganese oxide can be used. Here, as the transition metal ratio of lithium nickel-cobalt-manganese oxide, a high nickel ratio is preferable. For example, materials such as nickel:cobalt:manganese = 8:1:1 and its vicinity, and nickel:cobalt:manganese = 9:0.5:0.5 and its vicinity are preferable. Further, as another example of the first material 100x, a metal oxide-coated composite oxide in which secondary particles of lithium nickel-cobalt-manganese oxide are coated with aluminum oxide can be used. Here, the aluminum oxide is preferably thin, and the film thickness of the aluminum oxide is, for example, 1 nm or more and 200 nm or less, more preferably 1 nm or more and 100 nm or less.

[0243] Repeatedly stated, as the second material 100y, LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn) can be used. Alternatively, an oxide can be used as the second material 100y. As an example of the oxide, one or more selected from aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, etc. can be used. As the material described above for LiM2PO4, for example, LiFePO4, LiMnPO4, LiFe a Mn b PO4 (a + b is less than or equal to 1, 0 < a < 1, 0 < b < 1), or LiFe a Ni bPO4 (where a + b ≤ 1, 0 < a < 1, 0 < b < 1) can be used. Also, when the second material 100y is in particulate form, it may have a carbon coating layer on the surface of the particles.

[0244] In addition, it is also possible to use a material that functions as a positive electrode active material as the second material 100y. In this case, as a combination of the first material 100x and the second material 100y, according to the characteristics required for the secondary battery, it is possible to select a combination that is unlikely to cause a step in the charge-discharge curve, or to select a combination that causes a step in the charge-discharge curve at a desired charging rate. The step in the charge-discharge curve may be referred to as a plateau and includes a region where output can be stably extracted.

[0245] Next, as step S103, the above-mentioned first material 100x and the second material 100y are subjected to a composite treatment. When performing the composite treatment by mechanical energy, it can be performed by a mechanochemical method. Also, the composite treatment may be performed using a mechanofusion method.

[0246] Also, as step S103, when performing the composite treatment using a ball mill, it is preferable to use zirconia balls as media, for example. As the ball mill treatment, a dry treatment is desirable. When performing a wet treatment as the ball mill treatment, acetone can be used. When performing a wet ball mill treatment, dehydrated acetone with a water content of 100 ppm or less, preferably 10 ppm or less, may be used.

[0247] By the composite treatment in step S103, at least a part of the particle surface of the particulate first material 100x, preferably substantially the whole, can be covered with the second material 100y.

[0248] Through the above steps, the positive electrode active material composite 100z of one aspect of the present invention shown in Fig. 6A can be produced (step S104).

[0249] Next, a different manufacturing method for Figure 6B will be described. In Figure 6B, the manufacturing method is the same as shown in Figure 6A up to step S103, and after step S103, a heat treatment is performed as step S104. The heating in step S104 should be carried out in an oxygen-containing atmosphere at a temperature of 400°C to 950°C, preferably 450°C to 800°C, for 1 hour to 60 hours, preferably 2 hours to 20 hours.

[0250] By following the above steps, a positive electrode active material composite 100z according to one embodiment of the present invention, as shown in Figure 6B, can be produced (step S105).

[0251] In the compounding process, to obtain a good coating state, the ratio of the particle size of the second material 100y to the particle size of the first material 100x (particle size of the second material 100y / particle size of the first material 100x) is preferably 1 / 200 or more and 1 / 50 or less, and more preferably 1 / 200 or more and 1 / 100 or less. As adjustment of the particle size of the second material 100y, a micronization process as shown in Figure 6C may be performed. The micronization process involves preparing the second material 100y in step S102 in Figures 6A and 6B, and then performing crushing and classification via step S102a in Figure 6C. Through this micronization process, a second material 100y' with an adjusted particle size can be obtained in step S102b.

[0252] [Calculations related to positive electrode active material composites] As an example of a cathode active material composite, the first material uses LiCoO2 with a layered rock salt structure, and the second material uses LiFePO4, LiCoO2, and LiFe with an olivine structure. 0.5 Mn 0.5 PO4, or LiFe 0.5 Ni 0.5 Structures containing PO4 were evaluated using density functional theory (DFT). Specifically, structures in which LiCoO2 and LiFePO4 are bonded, and structures in which LiCoO2 and LiFe 0.5 Mn 0.5 PO4 or LiFe 0.5 Ni 0.5The structure formed by the combination of PO4 and was optimized and evaluated using DFT. The main calculation conditions are shown in Table 3.

[0253] [Table 3]

[0254] Figure 7A shows the initial state of the model used to calculate the structure in which LiCoO2 and LiFePO4 are bonded. 0.5 Mn 0.5 PO4 or LiFe 0.5 Ni 0.5 Figure 7B shows the initial state of the model used to calculate the structure in which PO4 and are bonded. In Figure 7B, LiFe 0.5 Mn 0.5 PO4 or LiFe 0.5 Ni 0.5 PO4 to LiFe 0.5 M 0.5 It is written as PO4. Note that LiFePO4 and LiFe 0.5 Mn 0.5 PO4 or LiFe 0.5 Ni 0.5 PO4 can be used as the barrier layer 116.

[0255] As the initial state of the model used in the calculation, Figure 7A shows a structure in which LiCoO2 and LiFePO4 are bonded. Also, Figure 7B shows LiCoO2 and LiFe 0.5 MPO4 (M=Mn or Ni, specifically LiFe) 0.5 Mn 0.5 PO4 or LiFe 0.5 Ni 0.5 This shows the structure in which PO4) is bonded.

[0256] In these structural models, the potential difference before and after Li extraction (corresponding to the potential difference during charging) was calculated. Figure 8A shows the theoretical capacity-charging voltage graph for LiCoO2, LiFePO4 (sometimes written as LFP), a structure in which LiCoO2 and LiFePO4 are stacked, and a structure in which LiCoO2 and LiFePO4 are mixed. The structure in which LiCoO2 and LiFePO4 are stacked, and the structure in which LiCoO2 and LiFePO4 are mixed are included in the structure in which LiCoO2 and LiFePO4 are bonded. Figure 8B shows LiCoO2, LiFe 0.5 Mn 0.5 Figure 8C shows a graph of theoretical capacity-charging voltage for a structure in which PO4 (sometimes written as LFMP) and LiCoO2 are stacked. The structure in which LiCoO2 and LFMP are stacked is included in the structure in which LiCoO2 and LFMP are bonded together. 0.5 Ni 0.5 The graph shows the theoretical capacitance-charging voltage for a structure in which PO4 (sometimes written as LFNP) and LiCoO2 are stacked. The structure in which LiCoO2 and LFNP are stacked is included in the structure in which LiCoO2 and LFNP are bonded together.

[0257] As shown in Figures 8(A), (B), and (C), the results confirm that the charging voltage is higher when some of the Fe in LiFePO4 is replaced with Mn compared to LiFePO4, and the charging voltage is even higher when some of the Fe in LiFePO4 is replaced with Ni.

[0258] This embodiment can be implemented in appropriate combination with other embodiments.

[0259] (Embodiment 4) In this embodiment, an example of a method for producing a first material that functions as a positive electrode active material according to one aspect of the present invention will be described with reference to Figures 9 to 11. Furthermore, a positive electrode active material according to one aspect of the present invention will be described with reference to Figures 12 to 20.

[0260] [Method for preparing positive electrode active material 1] <Step S11> In step S11 shown in Figure 9A, lithium sources (Li sources) and transition metal sources (M sources) are prepared as the starting materials, lithium and transition metals, respectively.

[0261] As a lithium source, it is preferable to use a lithium-containing compound, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. The lithium source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0262] The transition metal can be selected from elements listed in groups 4 through 13 of the periodic table, for example, at least one of manganese, cobalt, and nickel. The transition metal can be cobalt only, nickel only, cobalt and manganese, cobalt and nickel, or cobalt, manganese, and nickel. When cobalt only is used, the resulting positive electrode active material contains lithium cobalt oxide (LCO), and when cobalt, manganese, and nickel are used, the resulting positive electrode active material contains nickel-cobalt-lithium manganese oxide (NCM).

[0263] As a transition metal source, it is preferable to use a compound having the above-mentioned transition metal. For example, oxides of the metals exemplified as transition metals, or hydroxides of the exemplified metals, etc., can be used. As a cobalt source, cobalt oxide, cobalt hydroxide, etc., can be used. As a manganese source, manganese oxide, manganese hydroxide, etc., can be used. As a nickel source, nickel oxide, nickel hydroxide, etc., can be used. As an aluminum source, aluminum oxide, aluminum hydroxide, etc., can be used.

[0264] The transition metal source should preferably have high purity; for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher should be used. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and / or the reliability of the secondary battery is improved.

[0265] In addition, it is preferable that the transition metal source has high crystallinity, for example, that it has single crystal grains. The crystallinity of the transition metal source can be evaluated by TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. The above methods for evaluating crystallinity can be applied not only to transition metal sources but also to the evaluation of other materials.

[0266] Furthermore, when using two or more transition metal sources, it is preferable to prepare them in a mixing ratio such that the two or more transition metal sources can adopt a layered rock salt-type crystalline structure.

[0267] <Step S12> Next, as shown in step S12 in Figure 9A, the lithium source and the transition metal source are crushed and mixed to prepare a mixed material. Crushing and mixing can be done dry or wet. Wet crushing is preferred because it allows for finer crushing. If wet crushing is used, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal source with dehydrated acetone with a purity of 99.5% or higher, with a water content of 10 ppm or less, and then crush and mix them. By using dehydrated acetone of such purity as described above, the amount of impurities that may be introduced can be reduced.

[0268] A ball mill or bead mill can be used for mixing and other processes. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they produce less impurity. When using a ball mill or bead mill, the peripheral speed should be set to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0269] <Step S13> Next, in step S13 shown in Figure 9A, the mixed material is heated. The heating temperature is preferably between 800°C and 1100°C, more preferably between 900°C and 1000°C, and even more preferably around 950°C. If the temperature is too low, the decomposition and melting of the lithium source and transition metal source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to the evaporation of lithium from the lithium source and / or the excessive reduction of the metal used as the transition metal source. Such defects include, for example, when cobalt is used as a transition metal, excessive reduction which can change the cobalt from trivalent to divalent, inducing oxygen defects.

[0270] The heating time should ideally be between 1 hour and 100 hours, and preferably between 2 hours and 20 hours.

[0271] The heating rate depends on the target temperature, but a rate between 80°C / h and 250°C / h is generally recommended. For example, when heating to 1000°C for 10 hours, a heating rate of 200°C / h is appropriate.

[0272] The heating atmosphere should preferably be a dry air atmosphere with low moisture content, for example, an atmosphere with a dew point of -50°C or lower, more preferably -80°C or lower. In this embodiment, heating will be carried out in an atmosphere with a dew point of -93°C. Furthermore, in order to suppress impurities that may be mixed into the material, the concentrations of impurities such as CH4, CO, CO2, and H2 in the heating atmosphere should be kept below 5 ppb (parts per billion) each.

[0273] An atmosphere containing oxygen is preferred as the heating atmosphere. For example, one method is to continuously introduce dry air into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and having oxygen flow through the chamber is called flow.

[0274] When the heating atmosphere is an oxygen-containing atmosphere, a method that does not involve flowing oxygen is also acceptable. For example, the reaction chamber can be depressurized and then filled with oxygen, preventing the oxygen from entering or leaving the reaction chamber; this method is called purging. For example, the reaction chamber can be depressurized to -970 hPa and then filled with oxygen up to 50 hPa.

[0275] After heating, natural cooling is acceptable, but it is preferable that the cooling time from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary; it is sufficient if it cools to a temperature acceptable for the next step.

[0276] Heating in this process may be carried out using a rotary kiln or a roller hearth kiln. Heating using a rotary kiln can be performed while stirring, whether in a continuous or batch system.

[0277] The crucible or sheath used during heating is preferably made of a highly heat-resistant material such as alumina (aluminum oxide), mullite cordierite, magnesia, or zirconia. An alumina crucible is preferable because it is made of a material that does not easily release impurities. In this embodiment, it is preferable to use an alumina crucible with a purity of 99.9%. It is preferable to place a lid on the crucible or sheath before heating. Placing a lid during heating prevents the material from volatilizing.

[0278] After heating is complete, the material may be crushed and sieved as needed. When collecting the heated material, it may be transferred from the crucible to a mortar before collection. It is preferable to use an alumina mortar. Alumina mortars are made of a material that does not easily release impurities. Specifically, an alumina mortar with a purity of 90% or higher, preferably 99% or higher, should be used. In addition, the same heating conditions as in step S13 can be applied to the heating processes described later, other than step S13.

[0279] <Step S14> Through the above process, a composite oxide containing a transition metal (LiMO2) can be obtained in step S14 shown in Figure 9A. The composite oxide only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. When cobalt is used as the transition metal, it is called a composite oxide containing cobalt and is represented as LiCoO2. However, the composition is not strictly limited to Li:Co:O=1:1:2.

[0280] Although examples of producing composite oxides by solid-phase methods have been shown as in steps S11 to S14, composite oxides may also be produced by coprecipitation or by hydrothermal methods.

[0281] <Step S15> Next, as step S15 shown in Figure 9A, the composite oxide is heated. Because this is the first heating of the composite oxide, the heating in step S15 is sometimes called initial heating. Alternatively, because it is heated before step S20 shown below, it may be called preheating or pretreatment.

[0282] Initial heating may cause some lithium to be desorbed from the lithium composite oxide in step 14. Furthermore, it is expected to improve the crystallinity of the lithium composite oxide. Additionally, since the lithium source and / or transition metal M prepared in step S11, etc., contain impurities, initial heating can reduce these impurities from the lithium composite oxide in step 14.

[0283] After initial heating, the surface of the composite oxide becomes smooth. A smooth surface means that there are few irregularities, the composite oxide is generally rounded, and the corners are also rounded. Furthermore, a smooth surface is defined as having few foreign substances adhering to it. Foreign substances are thought to be a cause of irregularities, so it is preferable that they do not adhere to the surface. A smooth active material can have a surface roughness of at least 10 nm or less, preferably less than 3 nm, when the surface irregularity information is quantified from the measurement data in a cross-section observed with a scanning transmission electron microscope (STEM).

[0284] Initial heating involves heating the composite oxide after it has been completed. This initial heating is performed to smooth the surface, thereby reducing degradation after charging and discharging. A lithium source is not required for this initial heating process.

[0285] Alternatively, in the initial heating process to smooth the surface, it is not necessary to prepare an additive element source.

[0286] Alternatively, a flux agent does not need to be prepared during the initial heating to smooth the surface.

[0287] The lithium source or transition metal source prepared in step S11, etc., may contain impurities. Initial heating can reduce the impurities from the composite oxide completed in step S14.

[0288] The heating conditions for this step should be such that the surface of the composite oxide becomes smooth. For example, the heating conditions can be selected from those described in step S13. To add to the heating conditions, the heating temperature in this step should be lower than the temperature in step S13 in order to maintain the crystal structure of the composite oxide. Also, the heating time in this step should be shorter than the time in step S13 in order to maintain the crystal structure of the composite oxide. For example, heating at a temperature of 700°C to 1000°C for 2 to 20 hours is recommended.

[0289] The above-mentioned composite oxide may develop a temperature difference between its surface and interior due to heating in step S13. This temperature difference can induce a difference in shrinkage. It is thought that the difference in shrinkage occurs because the temperature difference causes a difference in fluidity between the surface and the interior. The energy associated with the shrinkage difference gives the composite oxide a difference in internal stress. This difference in internal stress is also called strain, and the energy associated with it is sometimes called strain energy. The internal stress is removed by the initial heating in step S15, or in other words, the strain energy is considered to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain of the composite oxide is relieved. Therefore, the surface of the composite oxide may become smoother after going through step S15. This is also called surface improvement. In other words, it is thought that the shrinkage difference that occurred in the composite oxide is relieved after going through step S15, and the surface of the composite oxide becomes smoother.

[0290] Furthermore, differences in shrinkage can cause microscopic displacements in the composite oxide, such as crystal displacements. This process is also recommended to reduce such displacements. This process makes it possible to homogenize the displacements in the composite oxide. When the displacements are homogenized, the surface of the composite oxide may become smoother. This is also referred to as crystal grain alignment. In other words, it is believed that step S15 alleviates crystal displacements and other issues in the composite oxide, resulting in a smoother surface.

[0291] Using a composite oxide with a smooth surface as the positive electrode active material reduces degradation during charging and discharging in a secondary battery and prevents cracking of the positive electrode active material.

[0292] A smooth surface of a composite oxide can be described as having a surface roughness of at least 10 nm, preferably less than 3 nm, when the surface irregularities information is quantified from measurement data in a cross-section of the composite oxide. A cross-section is, for example, a cross-section obtained when observing with a scanning transmission electron microscope (STEM).

[0293] In addition, a pre-synthesized composite oxide containing lithium, a transition metal, and oxygen may be used as step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on the pre-synthesized composite oxide, a composite oxide with a smooth surface can be obtained.

[0294] It is possible that the lithium content of the composite oxide decreases during the initial heating process. This decrease in lithium may make it easier for the additive elements, as explained in the next step S20, to penetrate the composite oxide.

[0295] <Step S20> Additive element X may be added to a composite oxide with a smooth surface, as long as it can adopt a layered rock salt-type crystalline structure. Adding additive element X to a composite oxide with a smooth surface allows for uniform addition of the additive element. Therefore, it is preferable to add the additive element after initial heating. The step of adding the additive element will be explained using Figures 9B and 9C.

[0296] <Step S21> In step S21 shown in Figure 9B, a source of additive elements (source X) to be added to the composite oxide is prepared. A lithium source may also be prepared along with the additive element source.

[0297] As additive elements, one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic can be used. Alternatively, one or more selected from bromine and beryllium can be used as additive elements. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive elements mentioned above.

[0298] When magnesium is selected as the additive element, the additive element source can be called a magnesium source. Suitable magnesium sources include magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate. Multiple magnesium sources may also be used.

[0299] When fluorine is selected as the additive element, the additive element source can be called a fluorine source. Examples of such fluorine sources include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3AlF6). Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later.

[0300] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Another lithium source used in step S21 is lithium carbonate.

[0301] The fluorine source may also be a gas, such as fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), which may be mixed into the atmosphere during the heating process described later. Multiple fluorine sources may also be used.

[0302] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. Mixing lithium fluoride and magnesium fluoride in a molar ratio of approximately LiF:MgF2 = 65:35 maximizes the effect of lowering the melting point (see Non-Patent Literature 4). On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (around x = 0.33). Note that "around" means a value greater than 0.9 times and less than 1.1 times that value.

[0303] <Step S22> Next, in step S22 shown in Figure 9B, the magnesium source and fluorine source are crushed and mixed. This step can be performed by selecting from the crushing and mixing conditions described in step S12.

[0304] A heating step may be performed after step S22 if necessary. The heating step can be performed by selecting from the heating conditions described in step S13. The heating time is preferably 2 hours or more, and the heating temperature is preferably 800°C to 1100°C.

[0305] <Step S23> Next, in step S23 shown in Figure 9B, the material that has been crushed and mixed above is recovered to obtain an additive element source (X source). The additive element source shown in step S23 has multiple starting materials and can be called a mixture.

[0306] The particle size of the above mixture is preferably such that the D50 (median diameter) is 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. Even when one material is used as the source of added elements, the D50 (median diameter) is preferably such that it is 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less.

[0307] When such a finely powdered mixture (including cases with only one additive element) is used, it is easier to uniformly adhere the mixture to the surface of the composite oxide particles when mixed with the composite oxide in a later process. Uniform adhesion of the mixture to the surface of the composite oxide is preferable because it facilitates the uniform distribution or diffusion of the additive element to the surface layer of the composite oxide after heating. The region where the additive element is distributed can also be called the surface layer. If there are regions in the surface layer that do not contain the additive element, it may be difficult to form the O3' type crystal structure described later in the charged state. Although fluorine was used in this explanation, fluorine can also be chlorine, and these can be considered as halogens.

[0308] <Step S21> A process different from that shown in Figure 9B will be explained using Figure 9C. In step S21 shown in Figure 9C, four types of additive element sources are prepared to be added to the composite oxide. In other words, the types of additive element sources in Figure 9C are different from those in Figure 9B. A lithium source may also be prepared along with the additive element sources.

[0309] Four types of additive element sources are prepared: a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source). The magnesium and fluorine sources can be selected from the compounds described in Figure 9B. Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0310] <Step S22> and <Step S23> Next, steps S22 and S23 shown in Figure 9C are the same as the steps described in Figure 9B.

[0311] <Step S31> Next, in step S31 shown in Figure 9A, the composite oxide and the additive element source (X source) are mixed. The ratio of the number of transition metal atoms M in the composite oxide having lithium, a transition metal, and oxygen to the number of magnesium atoms Mg in the additive element X is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0312] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the complex oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter time than the mixing in step S12. Also, dry mixing is generally milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the media.

[0313] In this embodiment, the mixing is performed dry using a ball mill with zirconia balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0314] <Step S32> Next, in step S32 of Figure 9A, the mixed materials are recovered to obtain mixture 903. During recovery, if necessary, the materials may be crushed and then sieved.

[0315] In this embodiment, a method is described in which lithium fluoride is added as a fluorine source and magnesium fluoride as a magnesium source to a composite oxide that has undergone initial heating. However, the present invention is not limited to the above method. At step S11, that is, at the stage of the starting material of the composite oxide, the magnesium source and fluorine source can be added to the lithium source and transition metal source. Then, in step S13, heating is performed to obtain LiMO2 with added magnesium and fluorine. In this case, it is not necessary to separate the processes of steps S11 to S14 from the processes of steps S21 to S23. This can be said to be a simple and highly productive method.

[0316] Alternatively, lithium cobalt oxide with magnesium and fluorine added beforehand may be used. Using lithium cobalt oxide with magnesium and fluorine added allows for the omission of steps S11 to S32 and step S20. This method is simple and highly productive.

[0317] Alternatively, magnesium and fluorine sources may be added to lithium cobalt oxide that has already been treated with magnesium and fluorine, according to step S20 in Figure 9B, or magnesium, fluorine, nickel, and aluminum sources may be added according to step S20 in Figure 9C.

[0318] <Step S33> Next, in step S33 shown in Figure 9A, the mixture 903 is heated. This can be performed by selecting from the heating conditions described in step S13. A heating time of 2 hours or more is preferable.

[0319] Let me add some information about the heating temperature. The lower limit of the heating temperature in step S33 must be above the temperature at which the reaction between the composite oxide (LiMO2) and the additive element source proceeds. The temperature at which the reaction proceeds is the temperature at which mutual diffusion occurs between the elements in LiMO2 and the elements in the additive element source, and it may be lower than the melting temperature of these materials. Let me explain using an oxide as an example, but the melting temperature Tm 0.757 times (Tammann temperature T) d It is known that solid-phase diffusion occurs from ). Therefore, the heating temperature in step S33 should be 500°C or higher.

[0320] Of course, the reaction proceeds more easily if the temperature is above the melting point of at least a portion of the mixture 903. For example, when LiF and MgF2 are used as the additive element sources, the eutectic point of LiF and MgF2 is around 742°C. Therefore, it is preferable to set the lower limit of the heating temperature in step S33 to 742°C or higher.

[0321] Furthermore, when mixture 903 is obtained by mixing LiCoO2:LiF:MgF2 in a molar ratio of 100:0.33:1, an endothermic peak is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, a lower limit of the heating temperature of 830°C or higher is more preferable.

[0322] A higher heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0323] The upper limit of the heating temperature should be below the decomposition temperature of LiMO2 (the decomposition temperature of LiCoO2 is 1130°C). At temperatures near the decomposition temperature, there is a concern that LiMO2 may decompose, albeit in small amounts. Therefore, it is more preferable to be 1000°C or lower, even more preferable to be 950°C or lower, and even more preferable to be 900°C or lower.

[0324] Based on these considerations, the heating temperature in step S33 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Furthermore, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 800°C to 1100°C, 830°C to 1130°C are preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C. The heating temperature in step S33 should be higher than that in step S13.

[0325] Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride, which may be caused by the fluorine source, to an appropriate range.

[0326] In the manufacturing method described in this embodiment, some materials, such as LiF, a fluorine source, may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of the composite oxide (LiMO2), for example, between 742°C and 950°C, enabling the distribution of additive elements, including magnesium, to the surface layer and producing a positive electrode active material with good properties.

[0327] However, since LiF is less dense than oxygen in its gaseous state, it may volatilize when heated, and if it volatilizes, the amount of LiF in mixture 903 will decrease. This weakens its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li on the surface of LiMO2 may react with F from the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is required.

[0328] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the volatilization of LiF in the mixture 903.

[0329] It is preferable to perform the heating in this process in a way that prevents the mixture 903 from sticking together. If the mixture 903 sticks together during heating, the contact area with oxygen in the atmosphere decreases, and the diffusion pathway of the added elements (e.g., fluorine) is obstructed, which may worsen the distribution of added elements (e.g., magnesium and fluorine) to the surface layer.

[0330] Furthermore, it is believed that if the additive elements (such as fluorine) are uniformly distributed on the surface, a smooth positive electrode active material with few irregularities can be obtained. Therefore, in order for the surface that has undergone heating in step S15 of this process to remain smooth, or to become even smoother, it is preferable that the particles do not stick together.

[0331] Furthermore, when heating with a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere inside the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to purge the atmosphere initially and then not allow the atmosphere to flow after introducing the oxygen atmosphere into the kiln. If oxygen flows, the fluorine source may evaporate, which is undesirable for maintaining surface smoothness.

[0332] When heating by roller hearth kiln, for example, the mixture 903 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 903.

[0333] A note regarding heating time: The heating time varies depending on conditions such as the heating temperature, the size of the LiMO2 in step S14, and its composition. When the size of the LiMO2 is small, a lower temperature or shorter time may be preferable than when the size of the LiMO2 is large.

[0334] When the median diameter (D50) of the composite oxide (LiMO2) in step S14 of Figure 9A is about 12 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0335] On the other hand, if the median diameter (D50) of the composite oxide (LiMO2) in step S14 is about 5 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0336] <Step S34> Next, in step S34 shown in Figure 9A, the heated material is recovered and crushed as necessary to obtain the positive electrode active material 115. At this time, it is preferable to further sift the recovered positive electrode active material 115.

[0337] By the above steps, a positive electrode active material 115 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

[0338] [Method for preparing positive electrode active material 2] Next, we will describe one embodiment of the present invention that differs from method 1 for producing the positive electrode active material.

[0339] In Figure 10, steps S11 to S15 are performed in the same manner as in Figure 9A to prepare a composite oxide (LiMO2) with a smooth surface.

[0340] <Step S20a> As mentioned above, it is possible to add element X to the composite oxide to the extent that it can take on a layered rock salt type crystal structure. In this manufacturing method 2, the step of adding the element in two or more separate steps will be explained with reference to Figure 11A.

[0341] <Step S21> Figure 11A shows the details of step S20a. In step S21, a first additive element source (X1 source) is prepared. The X1 source can be selected from the additive elements X described in step S21 shown in Figure 9B. For example, one or more additive elements selected from magnesium, fluorine, and calcium can be used as the additive element X1. Figure 11A illustrates the case where a magnesium source (Mg source) and a fluorine source (F source) are used as the additive element source (X1 source).

[0342] Steps S21 to S23 shown in Figure 11A can be prepared under the same conditions as steps S21 to S23 shown in Figure 9B. As a result, an additive element source (X1 source) can be obtained in step S23. This additive element source (X1 source) is the X1 source in step S20a shown in Figure 10.

[0343] Furthermore, steps S31 to S33 shown in Figure 10 can be manufactured using the same process as steps S31 to S33 shown in Figure 9A.

[0344] <Step S34a> Next, the material heated in step S33 shown in Figure 10 is recovered to produce a composite oxide containing the additive element X1. This is also called the second composite oxide to distinguish it from the composite oxide of step S14.

[0345] <Step S40> In step S40, shown in Figure 10, a second source of added elements (X2 source) is added. Step S40 will be explained in detail with reference to Figures 11B and 11C.

[0346] <Step S41> In step S41 shown in Figure 11B, a second additive element source (X2 source) is prepared. The X2 source can be selected from the additive elements X described in step S21 shown in Figure 9B. For example, one or more additive elements selected from nickel, titanium, boron, zirconium, and aluminum can be suitably used as the additive element X2. Figure 11B illustrates the case where a nickel source and an aluminum source are used as the additive element source (X2 source).

[0347] Steps S41 to S43 shown in Figure 11B can be prepared under the same conditions as steps S21 to S23 shown in Figure 9B. As a result, an additive element source (X2 source) can be obtained in step S43.

[0348] Furthermore, Figure 11C shows a modified version of the steps described using Figure 11B. In step S41 shown in Figure 11C, a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are each pulverized independently. As a result, in step S43, multiple second additive element sources (X2 sources) are prepared. The steps in Figure 11C differ from those in Figure 11B in that the additive elements are pulverized independently in step S42a.

[0349] <Steps S51 to S53> Next, steps S51 to S53 shown in Figure 10 can be carried out under the same conditions as steps S31 to S34 shown in Figure 9A. The conditions for the heating process in step S53 may be at a lower temperature and for a shorter time than in step S33. Through these steps, a positive electrode active material 115 of one embodiment of the present invention can be produced in step S53. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0350] As shown in Figures 10 and 11, in fabrication method 2, the additive elements to the composite oxide are introduced separately as a first additive element X1 and a second additive element X2. By introducing them separately, the depth profile of each additive element can be changed. For example, it is possible to profile the first additive element so that its concentration is higher in the surface layer than in the interior, and the second additive element so that its concentration is higher in the interior than in the surface layer.

[0351] As demonstrated in this embodiment, a positive electrode active material with a smooth surface can be obtained through the initial heating process.

[0352] The initial heating described in this embodiment is performed on the composite oxide. Therefore, it is preferable to perform the initial heating at a temperature lower than the heating temperature required to obtain the composite oxide, and for a shorter time than the heating time required to obtain the composite oxide. When adding additive elements to the composite oxide, it is preferable to perform the addition step after the initial heating. This addition step can be divided into two or more steps. Following this order of steps is preferable because it maintains the surface smoothness obtained by the initial heating. When the composite oxide contains cobalt as a transition metal, it can be interpreted as a composite oxide containing cobalt.

[0353] [Structure of the positive electrode active material] A positive electrode active material according to one embodiment of the present invention will be described with reference to Figures 12 to 20.

[0354] Figure 12A is a schematic top view of a positive electrode active material 115 according to one embodiment of the present invention. A schematic cross-sectional view of AB in Figure 12A is shown in Figure 12B.

[0355] <Elemental composition and distribution> The positive electrode active material 115 comprises lithium, a transition metal, oxygen, and an additive element. The additive element should preferably be different from the transition metal present in the positive electrode active material 115. In other words, the positive electrode active material 115 can be described as a composite oxide represented by LiMO2 to which elements other than M are added.

[0356] The transition metal in the positive electrode active material 115 is preferably a metal that can form a layered rock salt type composite oxide belonging to space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, the transition metal in the positive electrode active material 115 may be cobalt only, nickel only, two types of cobalt and manganese, two types of cobalt and nickel, or three types of cobalt, manganese, and nickel. In other words, the positive electrode active material 115 can have composite oxides containing lithium and a transition metal, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is substituted with manganese, lithium cobalt oxide in which part of the cobalt is substituted with nickel, and nickel-manganese-lithium cobalt oxide. It is preferable to have nickel in addition to cobalt as a transition metal because the crystal structure becomes more stable in the charged state at high voltage.

[0357] The additive element X in the positive electrode active material 115 is preferably one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These additive elements may further stabilize the crystal structure of the positive electrode active material 115. In other words, the positive electrode active material 115 can include lithium cobalt oxide having magnesium and fluorine, lithium cobalt oxide having magnesium, fluorine and titanium, lithium nickel-cobalt oxide having magnesium and fluorine, lithium cobalt-aluminate having magnesium and fluorine, lithium nickel-cobalt-aluminate having magnesium and fluorine, lithium nickel-manganese-cobalt oxide having magnesium and fluorine, etc. In this specification, the additive element X may be referred to as a mixture, part of a raw material, etc.

[0358] As shown in Figure 12B, the positive electrode active material 115 has a surface layer 115s and an interior 115c. The main component of the positive electrode active material 115, a transition metal (e.g., cobalt), is present in the surface layer 115s and the interior 115c. Additive elements (e.g., magnesium) only need to be present in the surface layer 115s, but may also be present in the interior 115c. It is preferable that the concentration of the additive elements is higher in the surface layer 115s than in the interior 115c. It is also preferable that the concentration of the additive elements has a gradient that increases from the interior to the surface, as shown by the gradient in Figure 12B. In this specification, the surface layer 115s refers to the region from the surface of the positive electrode active material 115 up to 50 nm, preferably up to 30 nm, and more preferably up to 10 nm. A surface created by cracks and / or fissures may also be called a surface, and the region from that surface up to 50 nm, preferably up to 30 nm, and more preferably up to 10 nm is called the surface layer 115s. Furthermore, the region deeper than the surface layer 115s of the positive electrode active material 115 is defined as the interior 115c.

[0359] In one embodiment of the present invention, the positive electrode active material 115 is reinforced in a surface layer 115s, i.e., the outer periphery of the positive electrode active material 115, where the concentration of added elements is high, so that even if lithium is removed from the positive electrode active material 115 due to charging, the layered structure consisting of octahedra of cobalt and oxygen does not break down.

[0360] Furthermore, it is preferable that the additive elements are present throughout the entire surface layer 115s of the positive electrode active material 115, and moreover, that they be present homogeneously. This is because even if there is reinforcement in a part of the surface layer 115s, if there are parts without reinforcement, stress may concentrate in those parts. If stress concentrates in a part of the positive electrode active material 115, defects such as cracks may occur from that point, which may lead to cracking of the positive electrode active material 115 and a decrease in discharge capacity.

[0361] Magnesium is divalent and is more stable in lithium sites than transition metal sites in layered rock salt crystal structures, thus readily occupying lithium sites. The presence of magnesium at an appropriate concentration in the surface lithium sites (115s) facilitates the maintenance of the layered rock salt crystal structure. Furthermore, magnesium has a strong affinity for oxygen, which can suppress the desorption of oxygen from its surroundings. Magnesium is preferable because, at appropriate concentrations, it does not adversely affect lithium insertion and desorption during charging and discharging.

[0362] However, an excess of magnesium may adversely affect the insertion and removal of lithium. Therefore, the ratio of the number of atoms of magnesium to the transition metal cobalt (Mg / Co) is preferably between 0.020 and 0.50. Furthermore, the number of atoms is preferably between 0.025 and 0.30. Even more preferably, the number of atoms is preferably between 0.030 and 0.20.

[0363] Aluminum is trivalent and can exist at transition metal sites in layered rock salt crystal structures. Aluminum can suppress the leaching of surrounding cobalt. Furthermore, because aluminum has a strong bonding force with oxygen, it can suppress the desorption of oxygen from around the aluminum. Therefore, by using aluminum as an additive element, a positive electrode active material 115 can be made that is resistant to crystal structure collapse even after repeated charging and discharging.

[0364] Fluorine is a monovalent anion, and if some of the oxygen in the surface layer 115s is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of cobalt ions associated with lithium desorption differs: from trivalent to tetravalent when fluorine is absent, and from divalent to trivalent when fluorine is present, resulting in different oxidation-reduction potentials. Therefore, if some of the oxygen in the surface layer 115s of the positive electrode active material 115 is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. This is preferable because it improves charge-discharge characteristics, rate characteristics, etc., when used in secondary batteries.

[0365] Titanium oxide is known to be superhydrophilic. Therefore, by using a positive electrode active material 115 having titanium oxide in its surface layer 115s, it is possible to improve wettability with highly polar solvents. When used in a secondary battery, good contact at the interface between the positive electrode active material 115 and the highly polar electrolyte may be achieved, potentially suppressing an increase in resistance. In this specification, the term "electrolyte" refers to a liquid electrolyte.

[0366] Generally, as the charging voltage of a secondary battery increases, the voltage at the positive electrode also increases. The positive electrode active material according to one embodiment of the present invention has a stable crystal structure even at high voltages. Because the crystal structure of the positive electrode active material is stable in the charged state, the decrease in capacity due to repeated charging and discharging can be suppressed.

[0367] Furthermore, a short circuit in a secondary battery can not only cause malfunctions in the charging and / or discharging operations of the secondary battery, but can also lead to overheating and ignition. To realize a safe secondary battery, it is preferable that the short-circuit current is suppressed even at high charging voltages. The positive electrode active material 115 in one aspect of the present invention suppresses the short-circuit current even at high charging voltages. Therefore, it is possible to create a secondary battery that achieves both high capacity and safety.

[0368] A secondary battery using the positive electrode active material 115 according to one aspect of the present invention preferably satisfies high capacity, excellent charge-discharge cycle characteristics, and safety simultaneously.

[0369] The concentration gradient of additive elements can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, the method of scanning within a region to evaluate it in two dimensions is sometimes called EDX surface analysis. Furthermore, the method of extracting linear region data from EDX surface analysis and evaluating the distribution of each atomic concentration within the positive electrode active material is sometimes called line analysis.

[0370] EDX surface analysis (e.g., elemental mapping) allows for the quantitative analysis of the concentrations of added elements in the surface layer 115s, interior 115c, and near grain boundaries of the positive electrode active material 115. The area near grain boundaries includes the position corresponding to the surface layer at the grain boundary. Furthermore, EDX radiation analysis allows for the analysis of the concentration distribution of added elements.

[0371] When EDX radiation analysis is performed on the positive electrode active material 115, the magnesium concentration peak in the surface layer 115s is preferably located within a depth of 3 nm from the surface toward the center of the positive electrode active material 115, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm.

[0372] Furthermore, it is preferable that the distribution of fluorine in the positive electrode active material 115 overlaps with the distribution of magnesium. Therefore, when EDX radiation analysis is performed, the peak of fluorine concentration in the surface layer 115s is preferably located within a depth of 3 nm from the surface toward the center of the positive electrode active material 115, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm.

[0373] It should be noted that not all additive elements have the same concentration distribution. For example, if the positive electrode active material 115 further contains aluminum as an additive element, it is preferable that the aluminum has a slightly different distribution from magnesium and fluorine. For example, when EDX radiation analysis is performed, it is preferable that the peak of magnesium concentration is closer to the surface than the peak of aluminum concentration in the surface layer 115s. For example, it is preferable that the peak of aluminum concentration is located at a depth of 0.5 nm to 20 nm from the surface toward the center of the positive electrode active material 115, and more preferably at a depth of 1 nm to 5 nm.

[0374] Furthermore, when line analysis or surface analysis is performed on the positive electrode active material 115, the ratio of the added element X to the transition metal (X / M) near the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably 0.025 or more and 0.30 or less. Even more preferably 0.030 or more and 0.20 or less. For example, when the added element is magnesium and the transition metal is cobalt, the ratio of the number of atoms of magnesium to cobalt (Mg / Co) is preferably 0.020 or more and 0.50 or less. Even more preferably 0.025 or more and 0.30 or less. Even more preferably 0.030 or more and 0.20 or less.

[0375] As mentioned above, if the additive elements in the positive electrode active material 115 are in excess, they may adversely affect the insertion and removal of lithium. Furthermore, when used in a secondary battery, this may lead to increased resistance and decreased capacity. On the other hand, if the additive elements are insufficient, they may not be distributed throughout the entire surface layer 115s, resulting in insufficient maintenance of the crystal structure. Therefore, the concentration of the additive elements in the positive electrode active material 115 should be adjusted to an appropriate level.

[0376] For example, the positive electrode active material 115 may have regions where excess additive elements are unevenly distributed. These unevenly distributed regions may be located internally or on the surface. The presence of such regions allows for the location of the unevenly distributed excess additive elements, enabling an appropriate additive element concentration to be maintained in most of the internal and surface parts of the positive electrode active material 115. Maintaining an appropriate additive element concentration in most of the internal and surface parts of the positive electrode active material 115 can suppress increases in resistance and decreases in capacity when used as a secondary battery. Suppressing increases in the resistance of a secondary battery is an extremely desirable characteristic, especially during high-rate charging and discharging.

[0377] Furthermore, in the positive electrode active material 115 having regions where excess additive elements are unevenly distributed, it is permissible to mix the additive elements in a certain degree of excess during the manufacturing process. This is preferable as it widens the margin in production.

[0378] In this specification, "non-uniformity" refers to a difference in the concentration of an element between a region A and a region B. Other terms that may be used include segregation, precipitation, heterogeneity, bias, high concentration, or low concentration.

[0379] <Crystal structure> Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiMO2.

[0380] It is known that the strength of the Jahn-Teller effect in complex oxides varies depending on the number of electrons in the d orbitals of the transition metal.

[0381] In nickel-containing composite oxides, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the effect of the Jahn-Teller effect is suggested to be smaller, and it may have better resistance to high-voltage charging and discharging, making it preferable.

[0382] The positive electrode active material will be explained using Figures 13 to 16. Figures 13 to 16 describe the case where cobalt is used as the transition metal in the positive electrode active material.

[0383] ≪Li x When x in CoO2 is 1 >> In one aspect of the present invention, the positive electrode active material 115 is in a discharge state, i.e., Li x In the case of x=1 in CoO2, it is preferable to have a layered rock salt type crystal structure belonging to space group R-3m. Layered rock salt type composite oxides have high discharge capacity, possess a two-dimensional lithium ion diffusion pathway, are suitable for lithium ion insertion / desorption reactions, and are excellent as positive electrode active materials for secondary batteries. For this reason, it is particularly preferable that the interior 115c, which accounts for most of the volume of the positive electrode active material 115, has a layered rock salt type crystal structure.

[0384] In FIG. 13, in the layered rock salt-type crystal structure, in addition to the space group R-3m, O3 is added. O3 may be named based on the fact that in this crystal structure, lithium occupies an octahedral site and there are three CoO2 layers in the unit cell. In some cases, this crystal structure is also referred to as the O3-type crystal structure. Note that the CoO2 layer refers to a structure in which an octahedral structure with cobalt coordinated by six oxygen atoms is continuous in a plane in a state of sharing edges. In some cases, the CoO2 layer may be referred to as a layer composed of octahedrons of cobalt and oxygen.

[0385] ≪Li x ≫ State where x in CoO2 is small The positive electrode active material 115 of one embodiment of the present invention has a crystal structure in a state where x in Li x CoO2 is small, which is different from that of the conventional positive electrode active material. Here, when x is small, it means 0.1 < x ≤ 0.24. FIG. 13 shows the crystal structure at x = 0.2.

[0386] Li x Regarding the change in the crystal structure accompanying the change in x in CoO2, the conventional positive electrode active material and the positive electrode active material 115 of one embodiment of the present invention are compared.

[0387] <Conventional positive electrode active material> The change in the crystal structure of the conventional positive electrode active material is shown in FIG. 15. The conventional positive electrode active material shown in FIG. 15 is lithium cobalt oxide (LiCoO2, LCO) to which no additive elements such as halogen and magnesium are added. As described in Non-Patent Documents 1 to Non-Patent Documents 3 and the like, the crystal structure of the lithium cobalt oxide shown in FIG. 15 changes.

[0388] Li is shown in FIG. 15 xThe crystal structure of lithium cobalt oxide at x=1 in CoO2 is shown with R-3m O3. x=1 corresponds to the discharge state of a secondary battery. Next, the crystal structure of lithium cobalt oxide at x=0.5 is shown with P2 / m monoclinic O1. Conventional lithium cobalt oxide has a crystal structure that belongs to the monoclinic space group P2 / m when x=0.5, as the symmetry of lithium increases. In this structure, one CoO2 layer exists in the unit cell. For this reason, this crystal structure is sometimes referred to as O1 type or monoclinic O1 type.

[0389] Also Li x The crystal structure of lithium cobalt oxide in CoO2 at x=0 is shown, with the P-3m1 trigonal O1 structure added. Conventional lithium cobalt oxide has a crystal structure that belongs to the P-3m1 space group of the trigonal system at x=0. In this structure, there is one CoO2 layer in the unit cell. For this reason, this crystal structure is sometimes called the O1 type or trigonal O1 type. In addition, the trigonal structure is sometimes converted to a composite hexagonal lattice, and this crystal structure is sometimes called the hexagonal O1 type.

[0390] Also Li x The crystal structure of lithium cobalt oxide in CoO2 at x=0.12 is shown with R-3m H1-3. Conventional lithium cobalt oxide has a crystal structure belonging to the space group R-3m at x=0.12. This structure can be described as a structure in which the structure of CoO2, such as the trigonal O1 type, and the structure of LiCoO2, such as the R-3m O3, are alternately stacked. For this reason, this crystal structure is sometimes referred to as the H1-3 type crystal structure. In reality, irregularities can occur in the insertion and deinsertion of lithium, so the H1-3 type crystal structure is observed from x=0.25. In addition, the H1-3 type crystal structure actually has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 15, the c-axis of the H1-3 type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0391] As an example, in the H1-3 type crystal structure, as described in Non-Patent Literature 2, the coordinates of cobalt and oxygen in the unit cell can be represented as Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are oxygen atoms, respectively. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, the unit cell that yields the smallest GOF (goodness of fit) value should be adopted.

[0392] Li x When charging and discharging are repeated such that x in CoO2 becomes 0.24 or less, conventional lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0393] However, these two crystal structures exhibit a significant displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 15, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m O3. Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0394] Furthermore, these two crystal structures also have a large volume difference. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the discharged R-3m O3 type crystal structure exceeds 3.5%, and is typically 3.9% or more.

[0395] In addition, the H1-3 crystal structure, unlike the trigonal O1 type, lacks lithium between the CoO2 layers, and the continuous CoO2 layers are likely to be unstable.

[0396] Therefore, when charging and discharging is repeated such that x becomes 0.24 or less, the crystal structure of conventional lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of cycle characteristics. This is because when the crystal structure collapses, the sites where lithium can exist stably decrease, and the insertion and extraction of lithium become difficult.

[0397] <The positive electrode active material of one embodiment of the present invention> In the positive electrode active material 115 of one embodiment of the present invention shown in FIG. 13, Li x The change in the crystal structure in the discharged state where x is 1 in LiCoO2 and the state where x is 0.24 or less, for example X = 0.2, is less than that of the conventional positive electrode active material. More specifically, the shift of the CoO2 layer in the state where x is 1 and the state where x is 0.2 which is 0.24 or less can be reduced. Furthermore, the change in volume when compared per cobalt atom can be reduced. Therefore, the positive electrode active material 115 of one embodiment of the present invention is less likely to have its crystal structure collapse even when charging and discharging is repeated such that x becomes 0.24 or less, and excellent cycle characteristics can be realized.

[0398] Also, the positive electrode active material 115 of one embodiment of the present invention is Li x In the state where x is 0.24 or less in CoO2, it can have a more stable crystal structure than the conventional positive electrode active material. Therefore, the positive electrode active material 115 of one embodiment of the present invention is Li x When the state where x is 0.24 or less in CoO2 is maintained, it is less likely to cause a short circuit, and the safety of the secondary battery is further improved, which is preferable.

[0399] Li x The crystal structures of lithium cobaltate when x is about 1 and 0.2 in LiCoO2 are shown in FIG. 13. It is a composite oxide having lithium cobaltate, cobalt as a transition metal, and oxygen. In addition to the above, it is preferable to have magnesium as an additive element. Furthermore, it is preferable to have a halogen such as fluorine or chlorine as an additive element.

[0400] Lithium cobalt oxide according to one aspect of the present invention has the same R-3m O3 crystal structure as conventional lithium cobalt oxide when x=1. However, when x is 0.24 or less, for example around 0.2, the lithium cobalt oxide according to one aspect of the present invention has a crystal structure different from that of conventional lithium cobalt oxide, such that conventional lithium cobalt oxide has an H1-3 type crystal structure.

[0401] When x = approximately 0.2, lithium cobalt oxide according to one embodiment of the present invention has a crystal structure that belongs to the trigonal space group R-3m. This is because the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure will be called the O3' type crystal structure. In Figure 13, the R-3m O3' is shown alongside the crystal structure when x = approximately 0.2.

[0402] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co(0,0,0.5), O(0,0,x), and 0.20≦x≦0.25. The lattice constant of the unit cell is preferably 2.797≦a≦2.837(Å) for the a-axis, more preferably 2.807≦a≦2.827(Å), and typically a=2.817(Å). For the c-axis, it is preferably 13.681≦c≦13.881(Å), more preferably 13.751≦c≦13.811, and typically c=13.781(Å).

[0403] As shown by the dotted line in Figure 13, there is almost no displacement of the CoO2 layer between the R-3m O3 in the discharged state and the O3' type crystal structure.

[0404] Furthermore, the volume difference per unit number of cobalt atoms between R-3m O3 in the discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%, indicating a small volume difference.

[0405] Thus, in the positive electrode active material 115, Li xWhen x in CoO₂ is small, that is, when a large amount of lithium has desorbed, the change in the crystal structure is suppressed more than that of conventional cathode active materials. Also, the volume change when compared per the same number of cobalt atoms is suppressed. Therefore, even when the charge and discharge are repeated such that x becomes 0.24 or less, the crystal structure of the cathode active material 115 is difficult to collapse. Therefore, the decrease in the charge-discharge capacity in the charge-discharge cycle of the cathode active material 115 is suppressed. Also, since more lithium can be stably utilized than conventional cathode active materials, the cathode active material 115 has a large discharge capacity per unit weight and per unit volume. Therefore, by using the cathode active material 115, a secondary battery with a high discharge capacity per unit weight and per unit volume can be manufactured.

[0406] Note that the cathode active material 115 is Li x It has been confirmed that CoO₂ may have an O3'-type crystal structure when x is 0.15 or more and 0.24 or less, and it is estimated that it has an O3'-type crystal structure even when x exceeds 0.24 and is 0.27 or less. However, since the crystal structure is affected not only by x in LiCoO₂ but also by factors such as the number of charge-discharge cycles, charge-discharge current, temperature, electrolyte, etc., it may sometimes have an O3'-type crystal structure regardless of the above range of x. x

[0407] Also, the cathode active material 115 is Li x When x in CoO₂ exceeds 0.1 and is 0.24 or less, not all of the inside of the cathode active material 115 needs to have an O3'-type crystal structure. It may contain other crystal structures or a part may be amorphous.

[0408] Also, Li x To make x in CoO₂ small, generally, it is necessary to charge at a high charging voltage. Therefore, Li xA state where x in CoO2 is small can be rephrased as a state where it has been charged at a high charging voltage. For example, when charging at a voltage of 4.6V or higher relative to the potential of lithium metal in an environment of 25°C, the H1-3 type crystal structure appears in conventional positive electrode active materials. Therefore, a high charging voltage relative to the potential of lithium metal can be said to be a charging voltage of 4.6V or higher. Furthermore, unless otherwise specified in this specification, the charging voltage is expressed relative to the potential of lithium metal.

[0409] When the positive electrode active material 115 is charged at a high voltage, it can be said that this is preferable because it can maintain a crystal structure with the symmetry of R-3m O3. Examples of high charging voltages include a voltage of 4.6V or higher at 25°C. Examples of even higher charging voltages include a voltage of 4.65V to 4.7V at 25°C.

[0410] Even with the positive electrode active material 115, if the charging voltage is further increased, H1-3 type crystals may gradually be observed. Furthermore, as mentioned above, the crystal structure is affected by the number of charge / discharge cycles, charge / discharge current, electrolyte, etc., so even at lower charging voltages, for example, when the charging voltage is 4.5V or higher but less than 4.6V at 25°C, the positive electrode active material 115 of one embodiment of the present invention may take on an O3' type crystal structure.

[0411] Furthermore, in the case of a secondary battery, if graphite is used as the negative electrode active material, for example, the voltage of the secondary battery will decrease by the amount of the graphite's potential compared to the above. The potential of graphite is approximately 0.05V to 0.2V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystal structure is observed when the voltage obtained by subtracting the graphite's potential from the above voltage is obtained.

[0412] Furthermore, while Figure 13 shows O3' with lithium present at all lithium sites with equal probability, this is not the only way. It may be concentrated at some lithium sites, or, for example, as shown in Figure 15, monoclinic O1(Li 0.5 It may have symmetry similar to that of CoO2. The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0413] Furthermore, the O3' type crystal structure, although it has lithium randomly between the CoO2 layers, can be said to be a crystal structure similar to the CdCl2 type crystal structure. This crystal structure similar to the CdCl2 type is formed by lithium nickelate being Li 0.06 Although the crystal structure is similar to that of NiO2 when charged to this level, it is known that pure lithium cobalt oxide, or layered rock salt-type cathode active materials containing a large amount of cobalt, do not usually adopt a CdCl2-type crystal structure.

[0414] Additive elements, such as magnesium, that are randomly and dilutely present between the CoO2 layers, i.e., at the lithium sites, have the effect of suppressing the displacement of the CoO2 layers when charged at high voltage. Therefore, when magnesium is present between the CoO2 layers, an O3' type crystal structure is more likely to be formed. For this reason, it is preferable that magnesium is distributed in at least the surface layer of the positive electrode active material 115 in one embodiment of the present invention, and moreover, distributed throughout the positive electrode active material 115. Furthermore, in order to distribute magnesium throughout the positive electrode active material 115, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 115 in one embodiment of the present invention.

[0415] However, if the heat treatment temperature is too high, cation mixing will occur, increasing the likelihood that additive elements, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site does not help maintain the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation of lithium.

[0416] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute magnesium to the positive electrode active material 115. Adding a halogen compound causes a decrease in the melting point of lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute magnesium to the positive electrode active material 115 at a temperature at which cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte will be improved.

[0417] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of transition metal atoms such as cobalt, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. The magnesium concentration shown here may be a value obtained, for example, from elemental analysis of the entire particle of the positive electrode active material 115 using ICP-MS, or it may be based on the value of the raw material blend during the process of manufacturing the positive electrode active material.

[0418] Lithium cobalt oxide may be mixed with one or more metals other than cobalt (hereinafter referred to as metal Z), such as nickel, aluminum, manganese, titanium, vanadium, and chromium, and it is particularly preferable to add nickel and one or more aluminum. Manganese, titanium, vanadium, and chromium may be more likely to stably form the tetravalent state and may contribute significantly to structural stability. Adding metal Z may make the crystal structure more stable in a high-voltage charged state. Here, in one embodiment of the present invention, it is preferable that metal Z is added at a concentration that does not significantly change the crystallinity of lithium cobalt oxide. For example, it is preferable that the amount is such that the aforementioned Jahn-Teller effect does not occur.

[0419] Nickel, manganese, and other transition metals, as well as aluminum, are preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0420] In one embodiment of the present invention, the capacity of the positive electrode active material may decrease as the magnesium concentration increases. One possible reason for this is that the amount of lithium contributing to charging and discharging decreases due to the presence of magnesium at the lithium sites. In addition, excess magnesium may generate magnesium compounds that do not contribute to charging and discharging. In one embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including nickel as metal Z in addition to magnesium. In another embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including aluminum as metal Z in addition to magnesium. In yet another embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including nickel and aluminum in addition to magnesium.

[0421] The concentrations of elements such as magnesium and metal Z in the positive electrode active material according to one embodiment of the present invention are examined below.

[0422] In one embodiment of the present invention, when the positive electrode active material contains magnesium in addition to element X, it exhibits extremely high stability in a high-voltage charged state. When element X is phosphorus, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. The concentrations of phosphorus and magnesium shown herein may be values ​​obtained, for example, from elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or they may be based on the values ​​of the raw material composition during the manufacturing process of the positive electrode active material.

[0423] The number of nickel atoms in the positive electrode active material according to one embodiment of the present invention is preferably 10% or less of the number of cobalt atoms, more preferably 7.5% or less, even more preferably 0.05% to 4%, and particularly preferably 0.1% to 2%. The nickel concentration shown herein may be, for example, a value obtained from elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0424] If the positive electrode active material is charged at a high voltage for an extended period, transition metals may dissolve into the electrolyte, potentially disrupting its crystal structure. However, by including nickel in the above proportion, it may be possible to suppress the dissolution of transition metals from the positive electrode active material 115.

[0425] The number of aluminum atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, and more preferably 0.1% to 2%. The aluminum concentration shown here may be, for example, a value obtained from elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0426] The positive electrode active material according to one aspect of the present invention preferably contains element X, and it is preferable that phosphorus is used as element X. Furthermore, the positive electrode active material according to one aspect of the present invention more preferably contains a composite oxide containing phosphorus and oxygen.

[0427] In one embodiment of the present invention, the positive electrode active material has a composite oxide containing element X, which may make it less likely for a short circuit to occur when a high-voltage charge state is maintained.

[0428] In one embodiment of the present invention, if the positive electrode active material contains phosphorus as element X, the hydrogen fluoride generated by the decomposition of the electrolyte may react with the phosphorus, potentially reducing the concentration of hydrogen fluoride in the electrolyte.

[0429] When the electrolyte contains LiPF6 as a lithium salt, hydrolysis may generate hydrogen fluoride. Hydrogen fluoride may also be generated by the reaction between PVDF, used as a component of the positive electrode, and alkali. Reducing the hydrogen fluoride concentration in the electrolyte may suppress corrosion of the current collector and / or peeling of the coating. Furthermore, it may suppress the decrease in adhesion due to gelation and / or insolubilization of the PVDF.

[0430] When the positive electrode active material has cracks, the presence of phosphorus, or more specifically, a complex oxide containing phosphorus and oxygen, within the cracks may suppress the progression of the cracks.

[0431] As is evident from the oxygen atoms indicated by arrows in Figure 13, the symmetry of oxygen atoms differs slightly between the O3-type and O3'-type crystal structures. Specifically, in the O3-type crystal structure, oxygen atoms are aligned along the dotted line, whereas in the O3'-type crystal structure, oxygen atoms are not strictly aligned. This is because, in the O3'-type crystal structure, the amount of tetravalent cobalt increases with decreasing lithium, leading to a larger Jahn-Teller strain and distortion of the octahedral structure of CoO6. The increased repulsion between oxygen atoms in the CoO2 layer with decreasing lithium also plays a role.

[0432] ≪Surface layer 115s≫ It is preferable that magnesium is distributed throughout the particles of the positive electrode active material 115 according to one embodiment of the present invention, but in addition, it is preferable that the magnesium concentration in the surface layer 115s is higher than the average concentration of the entire particle. For example, it is preferable that the magnesium concentration in the surface layer 115s measured by XPS or the like is higher than the average magnesium concentration of the entire particle measured by ICP-MS or the like.

[0433] Furthermore, in one embodiment of the present invention, when the positive electrode active material 115 contains one or more metals other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal near the particle surface is higher than the average concentration of the entire particle. For example, it is preferable that the concentration of elements other than cobalt in the surface layer 115s, as measured by XPS or the like, is higher than the average concentration of the elements in the entire particle, as measured by ICP-MS or the like.

[0434] The surface layer of the positive electrode active material is, in essence, entirely composed of crystal defects, and during charging, lithium escapes from the surface, making it a region where the lithium concentration tends to be lower than in the interior. Therefore, it is prone to instability and the crystal structure is easily disrupted. A higher magnesium concentration in the surface layer 115s can more effectively suppress changes in the crystal structure. Furthermore, a higher magnesium concentration in the surface layer 115s can also be expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0435] Furthermore, it is preferable that the concentration of halogens such as fluorine in the surface layer 115s of the positive electrode active material 115 in one embodiment of the present invention is higher than the average concentration of the entire positive electrode active material 115. The presence of halogens in the surface layer 115s, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0436] Thus, in one aspect of the present invention, the surface layer 115s of the positive electrode active material 115 preferably has a different composition from the interior 115c, with higher concentrations of additive elements, such as magnesium and fluorine. Furthermore, it is preferable that its composition adopts a crystalline structure that is stable at room temperature. For this reason, the surface layer 115s may have a different crystalline structure from the interior 115c. For example, at least a portion of the surface layer 115s of the positive electrode active material 115 in one aspect of the present invention may have a rock salt-type crystalline structure. Also, when the surface layer 115s and the interior 115c have different crystalline structures, it is preferable that the crystal orientations of the surface layer 115s and the interior 115c are roughly the same.

[0437] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0438] The general agreement of crystal orientation between two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc., can also be used as a basis for determination. When the crystal orientations are general agreement, it can be observed in TEM images, etc., that the difference in direction of the rows in which cations and anions are arranged alternately in a linear fashion is 5 degrees or less, more preferably 2.5 degrees or less. Note that light elements such as oxygen and fluorine may not be clearly visible in TEM images, etc., but in such cases, the agreement of orientation can be determined from the arrangement of metallic elements.

[0439] However, if the surface layer 115s consists only of MgO, or only of a solid solution of MgO and CoO(II), lithium insertion and removal becomes difficult. Therefore, the surface layer 115s must contain at least cobalt, and in the discharge state, it must also contain lithium and have pathways for lithium insertion and removal. Furthermore, it is preferable that the concentration of cobalt is higher than that of magnesium.

[0440] Furthermore, it is preferable that element X is located in the surface layer 115s of the positive electrode active material 115 according to one aspect of the present invention. For example, the positive electrode active material 115 according to one aspect of the present invention may be covered with a coating (barrier layer) having element X.

[0441] ≪Grain boundary≫ The additive element X in the positive electrode active material 115 of one aspect of the present invention may be present randomly and dilutely inside, but it is more preferable that a portion of it is segregated at the grain boundaries.

[0442] In other words, in one embodiment of the present invention, it is preferable that the concentration of the additive element X at the grain boundaries and in the vicinity of the positive electrode active material 115 is higher than that of other regions inside.

[0443] Similar to particle surfaces, grain boundaries are also surface defects. Therefore, they are prone to instability and easily initiate changes in crystal structure. For this reason, increasing the concentration of additive element X at and near the grain boundaries can more effectively suppress changes in crystal structure.

[0444] Furthermore, if the concentration of additive element X is high at and near the grain boundaries, even if cracks occur along the grain boundaries of the positive electrode active material 115 according to one embodiment of the present invention, the concentration of additive element X will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.

[0445] In this specification, the vicinity of a grain boundary refers to the region within 50 nm of the grain boundary, more preferably within 35 nm of the grain boundary, even more preferably within 20 nm of the grain boundary, and most preferably within 10 nm of the grain boundary.

[0446] ≪Particle size≫ If the particle size of the positive electrode active material 115 in one aspect of the present invention is too large, problems arise such as difficulty in lithium diffusion or the surface of the active material layer becoming too rough when coated onto the current collector. On the other hand, if the particle size is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector or excessive reaction with the electrolyte. For this reason, the average particle size (D50: also called the median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0447] <Analysis method> Whether a certain positive electrode active material is a positive electrode active material 115 according to one embodiment of the present invention that exhibits an O3' type crystal structure when charged with a high voltage can be determined by analyzing the positive electrode charged with a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, compare the crystallinity and crystal orientation, analyze the periodic distortion of the lattice and crystallite size, and obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0448] One aspect of the present invention, the positive electrode active material 115, is characterized by minimal change in its crystal structure between the high-voltage charged state and the discharged state, as described above. Materials in which the crystal structure that changes significantly from the discharged state accounts for 50 wt% or more when charged at high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that simply adding additive elements may not result in the desired crystal structure. For example, even if both materials are lithium cobalt oxide containing magnesium and fluorine, there are cases where the O3' type crystal structure accounts for 60 wt% or more when charged at high voltage, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a predetermined voltage, the O3' type crystal structure may account for almost 100 wt%, and if the predetermined voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, to determine whether or not a material is the positive electrode active material 115 of one aspect of the present invention, analysis of the crystal structure, including XRD, is necessary.

[0449] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they may change from an O3' type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0450] ≪Charging method≫ High-voltage charging to determine whether a certain composite oxide is the positive electrode active material 115 according to one aspect of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) with lithium as the counter electrode.

[0451] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry containing a mixture of positive electrode active material and conductive material.

[0452] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode will differ. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0453] The electrolyte in the electrolyte solution may be 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7, and vinylene carbonate (VC) at 2 wt%.

[0454] Polypropylene with a thickness of 25 μm can be used for the separator.

[0455] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0456] The coin cell prepared under the above conditions is charged with a constant current of 4.6V and 0.5C, and then charged with a constant voltage until the current value becomes 0.01C. Here, 1C is defined as 137mA / g. The temperature is set to 25℃. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere, and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When performing various analyses thereafter, it is preferable to seal it under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing it in a sealed container under an argon atmosphere.

[0457] ≪XRD≫ Figures 14 and 16 show the ideal powder XRD patterns calculated from the O3' type crystal structure and the H1-3 type crystal structure model using the CuKα1 line. For comparison, Li x The ideal XRD patterns calculated from the crystal structures of LiCoO2O3 at x=1 in CoO2, H1-3 type, and trigonal O1 at x=0 are also shown. The patterns for LiCoO2O3 and CoO2O1 were created using Reflex Powder Diffraction, a module in Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 5). The 2θ range was set to 15° to 75°, with a step size of 0.01 and a wavelength λ1 = 1.540562 × 10⁻¹⁰ -10 m and λ2 were not set, and the Monochromator was set to single. The H1-3 type crystal structure pattern was similarly created from the crystal structure information described in Non-Patent Literature 3. For the O3' type crystal structure pattern, the crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0458] As shown in Figure 14, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 16, these peaks do not appear in the H1-3 type crystal structure and CoO2O1. Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° when charged at high voltage is a characteristic feature of the positive electrode active material 115 in one embodiment of the present invention.

[0459] This also means that the positions where the XRD diffraction peaks appear are close at x=1 and x≦0.24. More specifically, for two or more, more preferably three or more, of the main diffraction peaks in both cases, the difference in the positions where the peaks appear is 2θ=0.7 or less, and more preferably 2θ=0.5 or less.

[0460] In one embodiment of the present invention, the positive electrode active material 115 has an O3' type crystal structure when x in LixCoO2 is small, but not all of the positive electrode active material 115 has to have an O3' type crystal structure. It may contain other crystal structures, or part of it may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that the O3' type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3' type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be obtained.

[0461] Furthermore, even after more than 100 charge-discharge cycles from the start of cycle measurement, it is preferable that the O3' type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more when Rietveld analysis is performed.

[0462] Furthermore, the crystallite size of the O3'-type crystal structure in the positive electrode active material decreases to only about 1 / 10th of that of LiCoO2O3 in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3'-type crystal structure can be observed when x in LixCoO2 is small. On the other hand, in simple LiCoO2, even if some parts can adopt a structure similar to the O3'-type crystal structure, the crystallite size becomes small, and the peak becomes broad and small. The crystallite size can be determined from the full width at half maximum of the XRD peak.

[0463] In one embodiment of the present invention, the positive electrode active material preferably has a small effect of the Jahn-Teller effect, as described above. The positive electrode active material in one embodiment of the present invention preferably has a layered rock salt type crystal structure and mainly contains cobalt as a transition metal. In addition, in one embodiment of the present invention, the positive electrode active material may contain metal Z as described above, in addition to cobalt, as long as the effect of the Jahn-Teller effect is small.

[0464] In the cathode active material, we will use XRD analysis to investigate the range of lattice constants in which the Jahn-Teller effect is presumed to be small.

[0465] Figure 17 shows the results of estimating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material according to one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and nickel. The positive electrode active material is prepared using steps S11 to S34 described later, and at least a nickel source is used in step S21. Figure 17A shows the results for the a-axis, and Figure 17B shows the results for the c-axis. Note that Figures 17A and 17B are the results for the powder of the positive electrode active material obtained according to steps S11 to S34. That is, the results are for the material before it is incorporated into the positive electrode. The nickel concentration (%) on the horizontal axis shows the concentration ratio (percentage) of nickel when the sum of the number of atoms of cobalt and nickel is taken as 100%. The concentration ratio (percentage) of nickel can be determined using a cobalt source and a nickel source.

[0466] Figure 18 shows the results of estimating the lattice constants of the a-axis and c-axis using an XRD pattern when the positive electrode active material according to one embodiment of the present invention has a layered rock salt type crystal structure and contains cobalt and manganese. The positive electrode active material is prepared using steps S11 to S34 described later, and at least a manganese source is used in step S21. Figure 18A shows the results for the a-axis, and Figure 18B shows the results for the c-axis. Note that Figures 18A and 18B are the results for the powder of the positive electrode active material obtained according to steps S11 to S34. That is, the results are for the material before it is incorporated into the positive electrode. The manganese concentration (%) on the horizontal axis represents the manganese concentration ratio (percentage) when the sum of the number of atoms of cobalt and manganese is taken as 100%. The manganese concentration ratio (percentage) can be determined using a cobalt source and a manganese source.

[0467] Figure 17C shows the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 17A and 17B. Figure 18C shows the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) for the positive electrode active material whose lattice constant results are shown in Figures 18A and 18B.

[0468] Figure 17C shows that the a / c axis tends to change significantly at nickel concentrations of 5% and 7.5%, suggesting that the a-axis distortion is increasing. This distortion may be Jahn-Teller distortion. This suggests that a superior cathode active material with low Jahn-Teller distortion can be obtained at nickel concentrations below 7.5%.

[0469] Next, Figure 18A suggests that when the manganese concentration is 5% or higher, the behavior of the lattice constant changes is different and does not follow Vegard's law. Therefore, it is suggested that the crystal structure is different when the manganese concentration is 5% or higher. For this reason, a manganese concentration of, for example, 4% or less is preferable.

[0470] Furthermore, the above-mentioned ranges for nickel and manganese concentrations do not necessarily apply to the surface layer 115s of the particles. In other words, the concentrations in the surface layer 115s of the particles may be higher than those mentioned above.

[0471] Based on the above considerations regarding the preferred range of lattice constants, in a positive electrode active material according to one embodiment of the present invention, the layered rock salt type crystal structure of the particles of the positive electrode active material in a non-charged or discharged state, as estimated from the XRD pattern, has a lattice constant of 2.814 × 10⁻¹⁴ in the a-axis. -10 Larger than m, 2.817 × 10 -10 It is smaller than m, and the lattice constant of the c axis is 14.05 × 10⁻¹⁰. -10 Larger than m, 14.07 × 10 -10 It was found that a value smaller than m is preferable. The state without charging and discharging may, for example, be the powder state before the positive electrode of the secondary battery is manufactured.

[0472] Alternatively, in the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, it is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is greater than 0.20000 and less than 0.20049.

[0473] Alternatively, when XRD analysis is performed on the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, a first peak may be observed when 2θ is between 18.50° and 19.30°, and a second peak may be observed when 2θ is between 38.00° and 38.80°.

[0474] The peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 115c of the positive electrode active material 115, which occupies the majority of the volume of the positive electrode active material 115. The crystal structure of the surface layer 115s and other parts can be analyzed by electron diffraction of the cross-section of the positive electrode active material 115.

[0475] ≪XPS≫ X-ray photoelectron spectroscopy (XPS) allows for analysis of regions from the surface to a depth of 2 nm to 8 nm (usually around 5 nm), enabling quantitative analysis of the concentration of each element in approximately half of the surface layer (115s). Furthermore, narrow-scan analysis allows for the analysis of elemental bonding states. The quantitative accuracy of XPS is generally around ±1 atomic percent, and the detection limit is approximately 1 atomic percent, although this varies depending on the element.

[0476] When XPS analysis is performed on the positive electrode active material 115 according to one embodiment of the present invention, the number of atoms of the additive element is preferably 1.6 to 6.0 times the number of atoms of the transition metal, and more preferably 1.8 to less than 4.0 times. When the additive element is magnesium and the transition metal is cobalt, the number of magnesium atoms is preferably 1.6 to 6.0 times the number of cobalt atoms, and more preferably 1.8 to less than 4.0 times. Furthermore, the number of halogen atoms such as fluorine is preferably 0.2 to 6.0 times the number of atoms of the transition metal, and more preferably 1.2 to 4.0 times.

[0477] When performing XPS analysis, for example, monochromatic aluminum can be used as the X-ray source. The extraction angle can also be set to, for example, 45°.

[0478] Furthermore, when the positive electrode active material 115 of one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably around 684.3 eV. This value is different from both the bond energy of lithium fluoride, which is 685 eV, and the bond energy of magnesium fluoride, which is 686 eV. In other words, when the positive electrode active material 115 of one embodiment of the present invention contains fluorine, it is preferable that the bond is with something other than lithium fluoride and magnesium fluoride.

[0479] Furthermore, when the positive electrode active material 115 of one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably around 1303 eV. This value is different from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 115 of one embodiment of the present invention contains magnesium, it is preferable that the bond is with an element other than magnesium fluoride.

[0480] For additive elements that are preferably abundant in the surface layer 115s, such as magnesium or aluminum, it is preferable that the concentration measured by XPS or the like is higher than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0481] When magnesium or aluminum is processed to expose its cross-section and analyzed using TEM-EDX, it is preferable that the concentration in the surface layer 115s is higher than the concentration in the interior 115c. Processing can be carried out, for example, by FIB.

[0482] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms. On the other hand, the ratio of magnesium atoms (Mg / Co) determined by ICP-MS analysis is preferably 0.001 to 0.06.

[0483] On the other hand, it is preferable that the nickel contained in the transition metal is not concentrated in the surface layer 115s but is distributed throughout the entire positive electrode active material 115. However, this does not apply if there are regions where the aforementioned excess additive elements are concentrated.

[0484] ≪Charging curve and dQ / dV curve≫ It is believed that a non-equilibrium phase change occurs around the peak in the dQ / dV curve, which is obtained by differentiating the capacitance (Q) with respect to voltage (V) from the charging curve (dQ / dV), and that the crystal structure changes significantly. In this specification, a non-equilibrium phase change refers to a phenomenon that causes a nonlinear change in a physical quantity.

[0485] Figure 19 shows the charging curves of a secondary battery using a positive electrode active material according to one embodiment of the present invention and a secondary battery using a comparative example positive electrode active material.

[0486] The positive electrode active material 1 of the present invention shown in Figure 19 was prepared by the method shown in Figures 9A and 9B of Embodiment 4. More specifically, lithium cobalt oxide (C-10N manufactured by Nippon Chemical Industrial Co., Ltd.) was used as LiMO2 in step S14, and LiF and MgF2 were mixed and heated. A half cell was prepared and charged using this positive electrode active material in the same manner as in the XRD measurement.

[0487] The positive electrode active material 2 of the present invention shown in Figure 19 was prepared by the method shown in Figures 9A and 9C of Embodiment 4. More specifically, lithium cobalt oxide (C-10N manufactured by Nippon Chemical Industrial Co., Ltd.) was used as LiMO2 in step S14, and LiF, MgF2, Ni(OH)2, and Al(OH)3 were mixed and heated. A half cell was prepared and charged using this positive electrode active material in the same manner as in the XRD measurement.

[0488] The positive electrode active material in the comparative example shown in Figure 19 was prepared by forming an aluminum-containing layer on the surface of lithium cobalt oxide (C-5H, manufactured by Nippon Chemical Industrial Co., Ltd.) using the sol-gel method, and then heating it at 500°C for 2 hours. Using this positive electrode active material, a half-cell was prepared and charged in the same manner as in the XRD measurement.

[0489] Figure 19 shows the charging curves when these half-cells were charged to 4.9V at 25°C with 10mA / g. For positive electrode active material 1, n=2 was used for the comparison example, while for positive electrode active material 2, n=1 was used.

[0490] Figures 20A to 20C show the dQ / dV curves representing the change in voltage with respect to charging capacity, obtained from the data in Figure 19. Figure 20A shows the dQ / dV curve for a half-cell using positive electrode active material 1 according to one embodiment of the present invention, Figure 20B shows the dQ / dV curve for a half-cell using positive electrode active material 2 according to one embodiment of the present invention, and Figure 20C shows the dQ / dV curve for a half-cell using a comparative positive electrode active material.

[0491] As is clear from Figures 20A to 20C, in both one embodiment of the present invention and the comparative example, peaks were observed at voltages of approximately 4.06V and 4.18V, and the change in capacitance with respect to voltage was nonlinear. Between these two peaks, Li x This is thought to be the crystal structure (space group P2 / m) in CoO2 when x is 0.5. x In CoO2, the space group P2 / m with x = 0.5 shows that lithium atoms are aligned, as shown in Figure 15. It is thought that energy is used for this lithium alignment, resulting in a nonlinear change in capacitance with respect to voltage.

[0492] Furthermore, in the comparative example shown in Figure 20C, large peaks were observed at approximately 4.54V and 4.61V. The area between these two peaks is thought to represent an H1-3 phase crystal structure.

[0493] On the other hand, in the secondary battery of one embodiment of the present invention shown in Figures 20A and 20B, which exhibits extremely good cycle characteristics, a small peak was observed at around 4.55V, but it was not clear. Furthermore, in positive electrode active material 2, no further peaks were observed even above 4.7V, indicating that the O3' structure was maintained. Thus, in the dQ / dV curve of a secondary battery using the positive electrode active material of one embodiment of the present invention, some peaks may be extremely broad or small at 25°C. In such cases, it is possible that two crystal structures are coexisting. For example, it is possible that two phases of O3 and O3' are coexisting, or two phases of O3' and H1-3 are coexisting.

[0494] ≪Discharge curve and dQ / dV curve≫ Furthermore, in one embodiment of the present invention, when the positive electrode active material is charged at a high voltage and then discharged at a low rate of, for example, 0.2C or less, a characteristic voltage change may appear near the end of discharge. This change can be clearly confirmed by the presence of at least one peak in the dQ / dV curve obtained from the discharge curve, at a voltage lower than the peak that appears around 3.9V and in the range up to 3.5V.

[0495] ≪Surface roughness and specific surface area≫ In one embodiment of the present invention, the positive electrode active material 115 preferably has a smooth surface with few irregularities. A smooth surface with few irregularities is one factor indicating that the distribution of additive elements in the surface layer 115s is good.

[0496] The smoothness and minimal irregularities of the surface can be determined, for example, from a cross-sectional SEM image or TEM image of the positive electrode active material 115, or from the specific surface area of ​​the positive electrode active material 115.

[0497] For example, the surface smoothness of the positive electrode active material 115 can be quantified from a cross-sectional SEM image as shown below.

[0498] First, the positive electrode active material 115 is processed using FIB or the like to expose its cross-section. At this time, it is preferable to cover the positive electrode active material 115 with a protective film, protective agent, etc. Next, an SEM image of the interface between the protective film, etc. and the positive electrode active material 115 is taken. Noise processing is performed on the SEM image using image processing software. For example, Gaussian blurring (σ=2) is performed, followed by binarization. Interface extraction is then performed using image processing software. Furthermore, the interface line between the protective film, etc. and the positive electrode active material 115 is selected using a tool such as Magic Hand, and the data is extracted into spreadsheet software, etc. Using the functions of the spreadsheet software, correction is performed from the regression curve (quadratic regression), parameters for roughness calculation are obtained from the slope-corrected data, and the root mean square (RMS) surface roughness is calculated by calculating the standard deviation.

[0499] In this embodiment, the particle surface of the positive electrode active material 115 preferably has a root mean square (RMS) surface roughness of 10 nm or less, less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0500] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited, but for example, "ImageJ" can be used. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

[0501] For example, the actual specific surface area A measured by the gas adsorption method using the constant-volume method. R And the ideal specific surface area A i The smoothness of the surface of the positive electrode active material 115 can also be quantified from this ratio.

[0502] Ideal specific surface area A i This is calculated by assuming that all particles have the same diameter as D50, the same weight, and are ideal spheres.

[0503] The median diameter D50 can be measured using a particle size analyzer that employs laser diffraction and scattering methods. The specific surface area can be measured using a specific surface area measuring device that employs a gas adsorption method based on constant volume, for example.

[0504] In one embodiment of the present invention, the positive electrode active material 115 has an ideal specific surface area A determined from the median diameter D50. i And the actual specific surface area A R Ratio A R / A i It is preferable that the value is 2 or less.

[0505] This embodiment can be used in combination with other embodiments.

[0506] [Defects in positive electrode active material] Examples of defects that may occur in the positive electrode active material are shown in Figures 21 to 31. According to one embodiment of the present invention, the positive electrode active material is expected to have the effect of suppressing the occurrence of such defects.

[0507] Charging and discharging under high voltage conditions of 4.5V or higher or at high temperatures (45°C or higher) may cause progressive defects such as pits in the positive electrode active material. Additionally, crack-like defects may occur due to the expansion and contraction of the positive electrode active material during charging and discharging. Figure 21 shows a schematic cross-sectional view of the positive electrode active material 51. In the positive electrode active material 51, pits 54 and 58 are shown as holes, but their opening shape is not circular and has depth. The positive electrode active material 51 may also have cracks 57. The positive electrode active material 51 has crystal planes 55 and may also have recesses 52. The barrier layers 53 and 56 may cover the positive electrode active material 51, but they may also be separated. The barrier layer 53 covers the recesses 52.

[0508] The positive electrode active material of lithium-ion secondary batteries is typically LCO or NCM, which can be described as an alloy containing multiple metallic elements (such as cobalt and nickel). At least one of the positive electrode active materials has a defect, and this defect may change before and after charging and discharging. When used in secondary batteries, the positive electrode active material may be chemically or electrochemically eroded by the surrounding environmental substances (such as the electrolyte), or the material may deteriorate. This deterioration does not occur uniformly on the surface of the positive electrode active material, but rather concentrates locally, and repeated charging and discharging of the secondary battery can cause defects to develop deeply from the surface into the interior.

[0509] The phenomenon in which defects in the positive electrode active material progress and form holes can also be called pitting corrosion.

[0510] In this specification, cracks and pits are different. Immediately after the production of the positive electrode active material, there are cracks but no pits. Pits are holes where several layers of cobalt or oxygen have escaped under high voltage conditions of 4.5 V or higher or at high temperature (45 °C or higher) during charge and discharge, and can also be said to be the locations where cobalt has eluted. Therefore, there are no pits immediately after the production of the positive electrode active material. Cracks refer to new surfaces caused by physical pressure being applied, or cracks resulting from grain boundaries. Cracks may also occur due to the expansion and contraction of particles during charge and discharge. Additionally, pits may occur from cracks or cavities within the particles.

[0511] <Disassembly of the secondary battery> The charge and discharge test was carried out up to 50 cycles. The discharge capacity at the 50th cycle had decreased to less than 40% of that at the 1st cycle. The secondary battery was disassembled and the positive electrode was taken out. The disassembly was carried out under an argon atmosphere. After disassembly, it was washed with DMC and then the solvent was volatilized. Observations were made on the positive electrode that had undergone the charge and discharge test up to 50 cycles, and the positive electrode before being incorporated into the secondary battery, that is, the positive electrode immediately after production.

[0512] <SEM observation> The positive electrode was observed by a scanning electron microscope (SEM). Fig. 22A shows the SEM image of the positive electrode of the secondary battery after 50 cycles. Fig. 22B shows the SEM image of the positive electrode before being incorporated into the secondary battery. For the SEM observation, a scanning electron microscope device SU8030 manufactured by Hitachi High-Tech Corporation was used.

[0513] Next, the cross-section of the positive electrode active material was processed by FIB, and the cross-section of the positive electrode active material was observed by SEM. By repeating the cross-section processing by FIB and SEM observation, three-dimensional information on the structure as shown in Fig. 23A or Fig. 23D can be obtained. For the FIB processing and SEM observation, XVision210B manufactured by Hitachi High-Tech was used.

[0514] Fig. 23B is an enlarged view of a part of the three-dimensional information in Fig. 23A from the front, and a cross-section taken in steps is shown in Fig. 23C. Also, the three-dimensional information of the side surface obtained by rotating the three-dimensional information in Fig. 23A corresponds to Fig. 23D. Fig. 23E is an enlarged view of a part of Fig. 23D, and a cross-section taken in steps is shown in Fig. 23F. As shown in Fig. 23F, the pit is not a hole but a groove or crack having a width.

[0515] Fig. 24A shows a SEM image of the upper surface of the positive electrode of the secondary battery after 50 cycles. Fig. 24B is a cross-sectional view of the broken line portion in Fig. 像24A. Also, Fig. 24C is an enlarged view of the portion surrounded by the square frame in Fig. 24B. Pits 90a, 90b, and 90c are shown in Fig. 24C.

[0516] Fig. 25A shows a SEM image of the upper surface of the positive electrode before being incorporated into the secondary battery. Fig. 25B is a cross-sectional view of the broken line portion in Fig. 25A. Also, Fig. 25C is an enlarged view of the portion surrounded by the square frame in Fig. 25B. A crack 91b is shown in Fig. 25C.

[0517] As described above, when the positive electrode after 50 cycles was observed, pits and cracks were observed.

[0518] <STEM Observation> Next, regarding the positive electrode of the secondary battery after 50 cycles, the cross-section was observed by a scanning transmission electron microscope (STEM). The sample for cross-section observation was processed using FIB.

[0519] <EDX Analysis> Regarding the positive electrode of the secondary battery after 50 cycles, it was evaluated using energy dispersive X-ray spectroscopy (EDX).

[0520] Fig. 26A shows the cross-sectional STEM image of the positive electrode. Fig. 26B is an enlarged view of the portion surrounded by the square frame in Fig. 26A.

[0521] Figures 27A to 27C show the EDX mapping in the region shown in Figure 26B. Figure 27A shows the EDX mapping for magnesium, Figure 27B shows the mapping for aluminum, and Figure 27C shows the mapping for cobalt. A Hitachi High-Tech HD-2700 was used for the EDX analysis. The acceleration voltage was set to 200kV. The EDX mapping suggested that magnesium and aluminum are present in at least a portion of the surface layer of the positive electrode active material particles.

[0522] <Microelectron diffraction> Next, the crystal structure of lithium cobalt oxide at and near the grain boundaries was analyzed using microelectron diffraction.

[0523] Figure 28A is a cross-sectional TEM image of degraded lithium cobalt oxide after 50 cycles. Figure 28B is a magnified view of the area enclosed by the black line in Figure 28A. The areas analyzed by micro-electron diffraction are indicated by the asterisks NBED1, NBED2, and NBED3 in Figure 28B.

[0524] Figure 29A shows the micro-electron diffraction pattern of the NBED1 region marked with a star. Transmitted light is denoted as O, and parts of the diffraction spots are denoted as DIFF1-1, DIFF1-2, and DIFF1-3, as shown in the figure. Analysis of the NBED1 region marked with a star revealed that the interplanar spacing of DIFF1-1 was 0.475 nm, DIFF1-2 was 0.199 nm, and DIFF1-3 was 0.238 nm. The interplanar angles were ∠1O2=55°, ∠1O3=80°, and ∠2O3=24°. The electron beam incidence direction was [0-10], and from the interplanar spacing and angles, 1 was considered to be 10-2 of a layered rock salt type crystal, 2 was similarly 10-5, and 3 was similarly 00-3, suggesting the presence of a LiCoO2 crystal structure.

[0525] Figure 29B shows the microelectron diffraction pattern of the NBED2 region marked with a star. Transmitted light is denoted as O, and parts of the diffraction spots are denoted as DIFF2-1, DIFF2-2, and DIFF2-3, as shown in the figure. Analysis of the NBED2 region marked with a star revealed that the interplanar spacing of 1 was 0.468 nm, 2 was 0.398 nm, and 3 was 0.472 nm. The interplanar angles were ∠1O2=54°, ∠1O3=110°, and ∠2O3=56°. Based on the interplanar spacing and angles, 1, 2, and 3 are spinel-type crystals and are considered to have either a Co3O4 crystal structure or a LiCo2O4 crystal structure.

[0526] Figure 29C shows the microelectron diffraction pattern of the NBED3 region marked with a star. Transmitted light is labeled O, and parts of the diffraction spots are labeled DIFF3-1, DIFF3-2, and DIFF3-3, as shown in the figure. Analysis of the NBED1 region marked with a star revealed that the interplanar spacing of 1 was 0.241 nm, 2 was 0.210 nm, and 3 was 0.246 nm. The interplanar angles were ∠1O2=55°, ∠1O3=110°, and ∠2O3=55°. Based on the interplanar spacing and angles, 1, 2, and 3 were considered to be rock salt type crystals with a CoO crystal structure.

[0527] Figure 30A shows the crystal structure of LiCoO2, which has a layered rock salt structure. Figure 30B shows the crystal structure of LiCo2O4, which has a spinel structure. Figure 30C shows the crystal structure of CoO, which has a rock salt structure.

[0528] <Slip> Figure 31A is a cross-sectional STEM image of a portion of the positive electrode active material layer after the slurry that forms the positive electrode active material layer has been applied to the current collector and pressed. Due to the pressing, a step is observed on the particle surface perpendicular to the grid pattern (c-axis direction), and evidence of deformation along the grid pattern direction (ab-plane direction) can be seen.

[0529] Figure 31B is a schematic cross-sectional view of the particles before pressing. In the particles before pressing, a relatively uniform barrier layer exists on the particle surface perpendicular to the grid pattern.

[0530] Figure 31C is a schematic cross-sectional view of the particles after pressing. The pressing process causes displacement in the grid pattern direction (ab-plane direction). The barrier layer also has multiple steps and becomes non-uniform. Regarding the displacement in the ab-plane direction, the particle surface on the opposite side of the surface where irregularities were observed also has irregularities with a similar shape, indicating that some particles are displaced in the ab-plane direction.

[0531] The multiple steps illustrated in Figure 31C are observed as striped patterns on the particle surface. These striped patterns on the particle surface, observed due to steps caused by displacement during pressing, are called slip (stack faults). Such particle slip can lead to unevenness in the barrier layer, potentially causing degradation. Therefore, it is desirable to minimize or eliminate slip in the positive electrode active material.

[0532] This embodiment can be implemented in appropriate combination with other embodiments.

[0533] (Embodiment 5) This embodiment describes examples of multiple shapes of secondary batteries having a positive or negative electrode, manufactured by the manufacturing method described in the previous embodiment.

[0534] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 32A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 32B is an external view, and Figure 32C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices. In this specification, the term "coin-type battery" includes button-type batteries.

[0535] Figure 32A is a schematic diagram to show the overlapping (upper and lower relationships and positional relationships) of the components for clarity. Therefore, Figures 32A and 32B are not perfectly identical corresponding diagrams.

[0536] In Figure 32A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 32A. The spacer 322 and washer 312 are used to protect the inside or to fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are pressed together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0537] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0538] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0539] Figure 32B is a perspective view of the completed coin-type rechargeable battery.

[0540] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0541] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side of the current collector.

[0542] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (for example, stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel and aluminum, etc., to prevent corrosion caused by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0543] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 32C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are crimped together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0544] The coin-type secondary battery 300 has high capacity, high discharge capacity, and excellent cycle characteristics. Furthermore, a separator 310 is not required between the negative electrode 307 and the positive electrode 304.

[0545] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 33A. As shown in Figure 33A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0546] Figure 33B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 33B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0547] Inside the hollow cylindrical battery casing 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of metals such as nickel, aluminum, and titanium, or alloys thereof, or alloys of these with other metals (for example, stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery casing 602 with nickel and aluminum, etc., to prevent corrosion by the electrolyte. Inside the battery casing 602, the battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0548] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector. Figures 33A to 33D illustrate a secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder, but the battery is not limited to this configuration. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder is also possible. Such a configuration allows for, for example, miniaturization of the secondary battery.

[0549] By using the positive electrode active material 115 obtained in Embodiment 1 as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0550] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0551] Figure 33C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a protective circuit to prevent overcharging or over-discharging, etc.

[0552] Figure 33D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0553] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0554] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0555] Furthermore, in Figure 33D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0556] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 34 and 35.

[0557] The secondary battery 913 shown in Figure 34A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 34A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0558] Furthermore, as shown in Figure 34B, the housing 930 shown in Figure 34A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 34B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0559] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0560] Furthermore, the structure of the wound body 950 is shown in Figure 34C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0561] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figures 35A to 35C. The wound body 950a shown in Figure 35A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0562] By using the positive electrode active material 115 obtained in Embodiment 1 as the positive electrode 932, a secondary battery 913 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0563] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0564] As shown in Figure 35B, the negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0565] As shown in Figure 35C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that releases gas when the inside of the housing 930 reaches a predetermined pressure in order to prevent the battery from rupturing.

[0566] As shown in Figure 35B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 35A and 35B can be referenced from the description of the secondary battery 913 shown in Figures 34A to 34C.

[0567] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 36A and 36B, which show an example of its external appearance. Figures 36A and 36B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0568] Figure 37A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 37A.

[0569] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 36A, will be explained using Figures 37B and 37C.

[0570] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 37B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0571] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0572] Next, as shown in Figure 37C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0573] Next, an electrolyte (not shown) is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0574] By using the positive electrode active material 115 obtained in Embodiment 1 as the positive electrode 503, a secondary battery 500 with high capacity, high discharge capacity, and excellent cycle characteristics can be obtained.

[0575] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which is capable of wireless charging using an antenna, will be explained with reference to Figures 38A to 38C.

[0576] Figure 38A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 38B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 has a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0577] The internal structure of the secondary battery 513 may have a wound structure or a laminated structure.

[0578] In the secondary battery pack 531, for example, as shown in Figure 38B, a control circuit 590 is located on the circuit board 540. The circuit board 540 is electrically connected to terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0579] Alternatively, as shown in Figure 38C, the system may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0580] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0581] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0582] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0583] (Embodiment 6) This embodiment shows an example of fabricating an all-solid-state secondary battery using the positive electrode active material 115 obtained in Embodiment 1.

[0584] As shown in Figure 39A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0585] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is the positive electrode active material 115 obtained in Embodiment 1. The positive electrode active material layer 414 may also have a conductive material and a binder.

[0586] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0587] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive material and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form it into particles, so the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 39B. Using metallic lithium in the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0588] For example, the solid electrolyte 421 in the solid electrolyte layer 420 can be a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halogen-based solid electrolyte, or the like.

[0589] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 Li 3.25 P 0.95 It contains S4, etc. Sulfide-based solid electrolytes have advantages such as the availability of materials with high conductivity, the ability to be synthesized at low temperatures, and their relatively soft nature which helps maintain conductive paths even after charging and discharging.

[0590] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x Materials having a NASICON-type crystal structure (Li 1-Y Al Y Ti 2-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.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glass (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc. are included. Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0591] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Further, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0592] Also, different solid electrolytes may be mixed and used.

[0593] Among them, Li 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 the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. Also, an improvement in productivity due to reduction of processes can be expected. In this specification and the like, the NASICON-type crystal structure refers to a composite oxide represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0594] 〔Shape of the exterior body and secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it preferably has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode. <00021​​​​​​Figure 40A is a schematic cross-sectional view of the evaluation cell, which has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 that secure them together. The evaluation material is fixed by pressing the electrode plate 753 by rotating the retaining screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762, which are made of stainless steel. An O-ring 765 for sealing is provided between the upper member 762 and the retaining screw 763.

[0597] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and pressed from above by an electrode plate 753. Figure 40B is a magnified perspective view of the area around this evaluation material.

[0598] As an example of the evaluation material, an example of a stacked structure consisting of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in Figure 40C. Note that the same parts are referred to in Figures 40A to 40C.

[0599] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be considered to correspond to the positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be considered to correspond to the negative electrode terminal. Electrical resistance and other parameters can be measured while applying pressure to the evaluation material via the electrode plates 751 and 753.

[0600] Furthermore, it is preferable to use a package with excellent airtightness for the outer casing of a secondary battery according to one embodiment of the present invention. For example, a ceramic package or a resin package can be used. Also, when sealing the outer casing, it is preferable to block out the outside air and perform the sealing in a sealed atmosphere, for example, inside a glove box.

[0601] Figure 41A shows a perspective view of a secondary battery according to one embodiment of the present invention, having a different exterior and shape from that shown in Figure 40. The secondary battery in Figure 41A has external electrodes 771 and 772 and is sealed with an exterior having a plurality of package members.

[0602] Figure 41B shows an example of a cross-section cut by the dashed line in Figure 41A. The laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a having an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c having an electrode layer 773b on a flat plate. Insulating materials, such as resin materials and ceramics, can be used for the package members 770a, 770b, and 770c.

[0603] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. The external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0604] By using the positive electrode active material 115 obtained in Embodiment 1, an all-solid-state secondary battery with high energy density and good output characteristics can be realized.

[0605] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0606] (Embodiment 7) This embodiment is a different example from Figure 33D, which shows a cylindrical secondary battery. Figure 42C shows an example of its application to an electric vehicle (EV).

[0607] Electric vehicles are equipped with a first battery 1301a and 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery or starter battery. The second battery 1311 only needs to be able to output power, and does not require a large capacity, so the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0608] The internal structure of the first battery 1301a may be a wound type as shown in Figure 34A or Figure 35C, or a stacked type as shown in Figure 36A or Figure 36B. Alternatively, the first battery 1301a may use the all-solid-state secondary battery of Embodiment 6. Using the all-solid-state secondary battery of Embodiment 6 for the first battery 1301a allows for higher capacity, improved safety, and miniaturization and weight reduction.

[0609] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0610] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and this is provided in the first battery 1301a.

[0611] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0612] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0613] Furthermore, the first battery 1301a will be explained using Figure 42A.

[0614] Figure 42A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0615] Furthermore, the control circuit section 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a BTOS (Battery operating system or Battery oxide semiconductor).

[0616] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium) is preferable. In particular, the In-M-Zn oxide that can be applied as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. Furthermore, a crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region in which the lattice arrangement is aligned. In addition, CAAC-OS has regions in which multiple crystalline regions are connected in the ab-plane direction, and these regions may have distortion. Distortion refers to a point in a region in which multiple crystalline regions are connected where the orientation of the lattice arrangement changes between a region in which the lattice arrangement is aligned and another region in which the lattice arrangement is aligned. In other words, CAAC-OS is an oxide semiconductor that is c-axis oriented and does not have a clear orientation in the ab-plane direction. Furthermore, CAC-OS is a material composition in which, for example, the elements constituting the metal oxide are unevenly distributed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size. In the following, in a metal oxide, a state in which one or more metal elements are unevenly distributed, and the regions containing these metal elements are mixed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size, is also referred to as a mosaic or patchy state.

[0617] Furthermore, CAC-OS is a composite metal oxide having a mosaic-like structure formed by the separation of the material into a first region and a second region, with the first region distributed within the film (hereinafter also referred to as a cloud-like structure). In other words, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0618] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS of In-Ga-Zn oxide, the first region is the region where [In] is greater than the [In] in the composition of the CAC-OS film. The second region is the region where [Ga] is greater than the [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is the region where [In] is greater than the [In] in the second region, and [Ga] is smaller than the [Ga] in the second region. The second region is the region where [Ga] is greater than the [Ga] in the first region, and [In] is smaller than the [In] in the first region.

[0619] Specifically, the first region described above is a region whose main components are indium oxide, indium zinc oxide, etc. The second region described above is a region whose main components are gallium oxide, gallium zinc oxide, etc. In other words, the first region can be rephrased as a region whose main component is In. Similarly, the second region can be rephrased as a region whose main component is Ga.

[0620] Furthermore, a clear boundary may not be observed between the first region and the second region described above.

[0621] For example, in CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using energy-dispersive X-ray spectroscopy (EDX) confirms that it has a structure in which regions mainly composed of In (first region) and regions mainly composed of Ga (second region) are unevenly distributed and mixed.

[0622] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulation due to the second region work complementaryly to give CAC-OS a switching function (on / off function). In other words, CAC-OS has conductive function in part of the material, insulating function in part of the material, and semiconductor function as a whole. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I) can be achieved. on This enables high field-effect mobility (μ) and good switching operation.

[0623] Oxide semiconductors can take on diverse structures, each possessing different properties. One embodiment of the present invention may include two or more of the following: amorphous oxide semiconductors, polycrystalline oxide semiconductors, a-like OS, CAC-OS, nc-OS, and CAAC-OS.

[0624] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have an operating ambient temperature range of -40°C to 150°C, which is wider than that of single-crystal Si, and the change in characteristics is smaller than that of single crystal even when the secondary battery is heated. The off-current of a transistor using an oxide semiconductor has low temperature dependence and is below the lower limit of measurement even at 150°C, whereas the off-current characteristics of a single-crystal Si transistor are highly temperature dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery that uses the positive electrode active material 115 obtained in Embodiment 1, etc., as the positive electrode.

[0625] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. Functions to eliminate the 10 causes of instability include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0626] Furthermore, a micro-short refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short-circuit in a small area can cause a large voltage change, the abnormal voltage value may affect subsequent estimations.

[0627] One of the causes of micro-short circuits is said to be that multiple charge-discharge cycles result in an uneven distribution of the positive electrode active material, causing localized current concentration in parts of the positive and negative electrodes, leading to areas where the separator malfunctions, or causing micro-short circuits due to the generation of by-reactants from side reactions.

[0628] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0629] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 42A is shown in Figure 42B.

[0630] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current and the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch in the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0631] The switch unit 1324 can be constructed by combining an n-channel transistor and a p-channel transistor. The switch unit 1324 is not limited to a switch having a Si transistor using single-crystal silicon, but can also be made of, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO x The switch section 1324 may be formed using a power transistor having a gallium oxide (where x is a real number greater than 0) or the like. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, by stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip. Since the volume occupied by the control circuit section 1320 can be reduced, miniaturization becomes possible.

[0632] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle equipment, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle equipment.

[0633] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state secondary battery, or an electric double-layer capacitor. For example, the all-solid-state secondary battery of Embodiment 6 may be used. By using the all-solid-state secondary battery of Embodiment 6 for the second battery 1311, high capacity can be achieved, and the device can be made smaller and lighter.

[0634] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0635] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0636] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some chargers, a control circuit is provided, and the functions of the battery controller 1302 may not be used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU or GPU.

[0637] External chargers installed at charging stations and other locations include 100V outlets, 200V outlets, and 3-phase 200V with 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0638] For rapid charging, a rechargeable battery capable of withstanding high-voltage charging is desired to achieve quick charging.

[0639] Furthermore, the secondary battery of this embodiment described above uses the positive electrode active material 115 obtained in Embodiment 1, etc. Moreover, by using graphene as a conductive material and increasing the electrode layer thickness to increase the load, capacity reduction is suppressed and high capacity is maintained, resulting in a secondary battery with significantly improved electrical characteristics as a synergistic effect. T...

Claims

1. A secondary battery having a positive electrode and a negative electrode, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The aforementioned composite compound comprises succinonitrile, lithium ions, and bis(fluorosulfonyl)imide ions, and is a secondary battery.

2. A secondary battery having a positive electrode and a negative electrode, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The aforementioned composite compound comprises glutalonitrile, lithium ions, and bis(fluorosulfonyl)imide ions, and is a secondary battery.

3. A secondary battery having a positive electrode and a negative electrode, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The aforementioned composite compound comprises adiponitrile, lithium ions, and bis(fluorosulfonyl)imide ions, and is a secondary battery.

4. A secondary battery having a positive electrode, a negative electrode, and an electrolyte, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The composite compound has a region located between the active material and the electrolyte, The aforementioned composite compound comprises succinonitrile, lithium ions, and bis(fluorosulfonyl)imide, and is a secondary battery.

5. A secondary battery having a positive electrode, a negative electrode, and an electrolyte, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The composite compound has a region located between the active material and the electrolyte, The aforementioned composite compound comprises glutaronitrile, lithium ions, and bis(fluorosulfonyl)imide, and is a secondary battery.

6. A secondary battery having a positive electrode, a negative electrode, and an electrolyte, Either the positive electrode or the negative electrode, or both, comprises an active material and a composite compound having a crystalline structure. The composite compound has a region located between the active material and the electrolyte, The aforementioned composite compound comprises adiponitrile, lithium ions, and bis(fluorosulfonyl)imide ions, and is a secondary battery.

7. In any one of claims 1 to 6, The active material of the positive electrode has a composite oxide containing magnesium and cobalt. The cobalt is present in the interior and surface of the active material. A secondary battery in which the magnesium is present at least in the surface layer.

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