Positive electrode, secondary battery, electronic device, power storage system and vehicle

Abstract

Provided are a positive electrode having little deterioration caused by charging / recharging and a secondary battery. Provided are a positive electrode having high electrode density and a secondary battery. Also provided are a positive electrode having excellent rate characteristics and a secondary battery. The positive electrode has a positive electrode active substance and a coating material. At least part of the surface of the positive electrode active substance is covered by the coating material. The positive electrode active substance has a lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel. The lithium cobalt oxide has, on the surface thereof, a region having the greatest concentration of at least one selected from the magnesium, the fluorine, and the aluminum. The coating material is ideally at least one selected from glass, carbon black, graphene, and a graphene compound.

Description

Positive electrode, method for manufacturing positive electrode, secondary battery, electronic device, power storage system, and vehicle

[0001] TECHNICAL FIELD The present invention relates to a method for manufacturing a positive electrode active material, a method for manufacturing a positive electrode, a method for manufacturing a secondary battery, and a positive electrode active material, a positive electrode, a secondary battery, and a mobile information terminal, a power storage system, a vehicle, etc. that have the secondary battery.

[0002] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, manufacture, or a composition of matter. Another embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof. Note that one embodiment of the present invention particularly relates to a method for manufacturing a positive electrode active material or a positive electrode active material. Alternatively, one embodiment of the present invention particularly relates to a method for manufacturing a positive electrode or a positive electrode. Alternatively, one embodiment of the present invention particularly relates to a method for manufacturing a secondary battery or a secondary battery.

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

[0004] In this specification, an electronic device refers to a device in general that has a positive electrode active material, a secondary battery, or a power storage device, and electro-optical devices that have a positive electrode active material, a positive electrode, a secondary battery, or a power storage device, and information terminal devices that have a power storage device are all electronic devices.

[0005] In this specification, the term "power storage device" refers to all elements and devices having a power storage function, including, for example, power storage devices such as lithium ion secondary batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors.

[0006] In recent years, various types of power storage devices have been actively developed, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, demand for high-power, high-energy-density lithium-ion secondary batteries has rapidly expanded in conjunction with the development of the semiconductor industry, and they are now indispensable in the modern information society as a rechargeable energy source, and are used in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, home energy storage systems, industrial energy storage systems, and next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0007] Among these, composite oxides such as lithium cobalt oxide and lithium nickel-cobalt-manganese oxide, which have a layered rock salt structure, are widely used. These materials have useful properties as active materials for energy storage devices, such as high capacity and high discharge voltage. However, to achieve high capacity, the positive electrode must be exposed to a high potential relative to lithium during charging. Under such a high potential, large amounts of lithium are removed, which can reduce the stability of the crystal structure and lead to significant deterioration during charge-discharge cycles. Against this background, efforts have been made to improve the positive electrode active materials of secondary battery positive electrodes in order to develop high-capacity and highly stable secondary batteries (e.g., Patent Documents 1 to 3).

[0008] JP 2018-088400 A, WO 2018 / 203168 Pamphlet, JP 2020-140954 A

[0009] Although improvements to positive electrode active materials have been actively carried out in the above Patent Documents 1 to 3, there remains room for improvement in various aspects of lithium ion secondary batteries and positive electrode active materials used therein, such as charge / discharge capacity, cycle characteristics, reliability, safety, and cost.

[0010] In view of the above, an object of one embodiment of the present invention is to provide a positive electrode active material that is stable in a high potential state and / or a high temperature state. Another object is to provide a positive electrode active material whose crystal structure is not easily destroyed even after repeated charge and discharge. Another object is to provide a positive electrode active material with excellent charge and discharge cycle characteristics. Another object is to provide a positive electrode active material with large charge and discharge capacity. Another object is to provide a highly reliable or safe secondary battery.

[0011] Another object of one embodiment of the present invention is to provide a positive electrode that is stable in a high potential state and / or a high temperature state, to provide a positive electrode that has excellent charge-discharge cycle characteristics, to provide a positive electrode that can increase the charge-discharge rate, or to provide a highly reliable or safe secondary battery.

[0012] In view of the above, an object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material that is stable in a high potential state and / or a high temperature state. Another object is to provide a method for manufacturing a positive electrode active material whose crystal structure is not easily destroyed even after repeated charge and discharge. Another object is to provide a method for manufacturing a positive electrode active material that has excellent charge and discharge cycle characteristics. Another object is to provide a method for manufacturing a positive electrode active material that has large charge and discharge capacity. Another object is to provide a method for manufacturing a highly reliable or safe secondary battery.

[0013] Another object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode that is stable in a high potential state and / or a high temperature state.Another object is to provide a method for manufacturing a positive electrode that has excellent charge-discharge cycle characteristics.Another object is to provide a method for manufacturing a positive electrode that can increase the charge-discharge rate.Another object is to provide a method for manufacturing a highly reliable or safe secondary battery.

[0014] Another object of one embodiment of the present invention is to provide a novel substance, active material particles, an electrode, a secondary battery, a power storage device, or a manufacturing method thereof.Another object of one embodiment of the present invention is to provide a manufacturing method of a secondary battery or a secondary battery having one or more characteristics selected from high purity, high performance, and high reliability.

[0015] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, and claims.

[0016] One embodiment of the present invention provides a battery comprising a first active material, a second active material, and glass, wherein at least a portion of the surface of the first active material has a region covered with the glass, and at least a portion of the surface of the glass has a region covered with the second active material, and the first active material is LiMO ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), and the second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), and the glass serves as a positive electrode having lithium ion conductivity.

[0017] Another embodiment of the present invention is a cathode material including a first active material, a second active material, and glass, wherein at least a part of a surface of the first active material has a region covered with the glass and the second active material, and the first active material is LiMO ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), and the second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), and the glass serves as a positive electrode having lithium ion conductivity.

[0018] Another embodiment of the present invention is a battery comprising a first active material, a second active material, glass, and a conductive material, wherein at least a portion of a surface of the first active material has a region covered with the glass, and at least a portion of a surface of the glass has a region covered with the second active material and the conductive material, and the first active material is LiMO ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), and the second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), the glass has lithium ion conductivity, and the conductive material has a graphene compound or a carbon nanotube.

[0019] Another embodiment of the present invention is a lithium ion battery including a first active material, a second active material, glass, and a conductive material, wherein at least a part of a surface of the first active material has a region covered with the glass, the second active material, and the conductive material, and the first active material is LiMO ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), and the second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), the glass has lithium ion conductivity, and the conductive material has a graphene compound or a carbon nanotube.

[0020] In any one of the positive electrodes described above, it is preferable that the first active material includes lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, and that the lithium cobalt oxide has a region in a surface layer portion where the concentration of any one or more elements selected from magnesium, fluorine, and aluminum is maximum.

[0021] Another embodiment of the present invention is a positive electrode including a positive electrode active material and a conductive material, wherein at least a portion of a surface of the positive electrode active material is covered with the conductive material, the positive electrode active material includes lithium cobalt oxide including magnesium, fluorine, aluminum, and nickel, the lithium cobalt oxide having a region in a surface layer portion where the concentration of any one or more elements selected from magnesium, fluorine, and aluminum is maximized, and the conductive material includes carbon.

[0022] Another embodiment of the present invention is a positive electrode including a positive electrode active material and a conductive material, wherein at least a part of a surface of the positive electrode active material is covered with the conductive material, the positive electrode active material includes lithium nickel-manganese-cobalt oxide including one or more selected from calcium, fluorine, aluminum, and gallium, the lithium nickel-manganese-cobalt oxide having a region in a surface layer portion where the concentration of one or more selected from calcium, fluorine, aluminum, and gallium is maximum, and the conductive material includes carbon.

[0023] In any one of the above positive electrodes, the conductive material preferably includes one or more selected from carbon black, graphene, and a graphene compound.

[0024] Another embodiment of the present invention is a secondary battery including any one of the above positive electrodes.

[0025] Another embodiment of the present invention is a mobile object including the above-described secondary battery.

[0026] Another embodiment of the present invention is a power storage system including the above-described secondary battery.

[0027] Another embodiment of the present invention is an electronic device including any of the above secondary batteries.

[0028] Another embodiment of the present invention is a method for producing a positive electrode, including: forming a composite of lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel with acetylene black to produce a positive electrode active material composite; mixing the positive electrode active material composite with a binder and a solvent to produce a slurry; applying the slurry to a positive electrode current collector to produce an electrode layer; and pressurizing the electrode layer.

[0029] Another embodiment of the present invention is a method for manufacturing a positive electrode, including mixing lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, graphene oxide, a binder, and a solvent to prepare a slurry, applying the slurry to a positive electrode current collector to form an electrode layer, and performing chemical reduction and thermal reduction on the electrode layer.

[0030] In any one of the above methods for producing a positive electrode, the chemical reduction is preferably a step of immersing the electrode layer in an aqueous ascorbic acid solution, and the thermal reduction is preferably a step of heating the electrode layer at 125°C or higher and 200°C or lower.

[0031] Therefore, one embodiment of the present invention can provide a positive electrode active material that is stable at a high potential and / or a high temperature. Alternatively, a positive electrode active material whose crystal structure is not easily deformed even after repeated charge and discharge can be provided. Alternatively, a positive electrode active material having excellent charge and discharge cycle characteristics can be provided. Alternatively, a positive electrode active material having a large charge and discharge capacity can be provided. Alternatively, a highly reliable or safe secondary battery can be provided.

[0032] According to one embodiment of the present invention, a positive electrode that is stable at a high potential and / or a high temperature can be provided. Alternatively, a positive electrode that has excellent charge-discharge cycle characteristics can be provided. Alternatively, a positive electrode that can increase the charge-discharge rate can be provided. Alternatively, a highly reliable or safe secondary battery can be provided.

[0033] According to one embodiment of the present invention, a method for manufacturing a positive electrode active material that is stable at a high potential and / or a high temperature can be provided. Alternatively, a method for manufacturing a positive electrode active material whose crystal structure is not easily destroyed even after repeated charge and discharge can be provided. Alternatively, a method for manufacturing a positive electrode active material that has excellent charge and discharge cycle characteristics can be provided. Alternatively, a method for manufacturing a positive electrode active material that has a large charge and discharge capacity can be provided. Alternatively, a method for manufacturing a highly reliable or safe secondary battery can be provided.

[0034] According to one embodiment of the present invention, a method for manufacturing a positive electrode that is stable at a high potential and / or a high temperature can be provided. Alternatively, a method for manufacturing a positive electrode that has excellent charge-discharge cycle characteristics can be provided. Alternatively, a method for manufacturing a positive electrode that can increase the charge-discharge rate can be provided. Alternatively, a method for manufacturing a highly reliable or safe secondary battery can be provided.

[0035] According to one embodiment of the present invention, a novel substance, active material particles, a secondary battery, a power storage device, or a manufacturing method thereof can be provided. According to another embodiment of the present invention, a manufacturing method of a secondary battery or a secondary battery having one or more characteristics selected from high purity, high performance, and high reliability can be provided.

[0036] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0037] FIG. 1 is a diagram illustrating a cross-sectional structure of a positive electrode according to one embodiment of the present invention. FIGS. 2A1 to 2B2 are diagrams illustrating a cross-sectional structure of a positive electrode active material composite according to one embodiment of the present invention. FIGS. 3A1 to 3B2 are diagrams illustrating a cross-sectional structure of a positive electrode active material composite according to one embodiment of the present invention. FIGS. 4A1 to 4B2 are diagrams illustrating a cross-sectional structure of a positive electrode active material composite according to one embodiment of the present invention. FIGS. 5A and 5B are diagrams illustrating a method for manufacturing a positive electrode active material composite according to one embodiment of the present invention. FIGS. 6A and 6B are diagrams illustrating a method for manufacturing a positive electrode active material composite according to one embodiment of the present invention. FIGS. 7A and 7B are diagrams illustrating a method for manufacturing a positive electrode active material composite according to one embodiment of the present invention. FIG. 8A is a top view of a positive electrode active material according to one embodiment of the present invention, and FIGS. 8B and 8C are cross-sectional views of the positive electrode active material according to one embodiment of the present invention. FIG. 9 is a diagram illustrating a crystal structure of a positive electrode active material according to one embodiment of the present invention. FIG. 10 is an XRD pattern calculated from the crystal structure. FIG. 11 is a diagram illustrating a crystal structure of a positive electrode active material according to a comparative example. FIG. 12 shows an XRD pattern calculated from the crystal structure. FIG. 13 shows an example of a TEM image in which the crystal orientations are roughly consistent. FIG. 14A shows an example of an STEM image in which the crystal orientations are roughly consistent. FIG. 14B shows an FFT of the region of the rock salt crystal RS, and FIG. 14C shows an FFT of the region of the layered rock salt crystal LRS. FIGS. 15A to 15C are diagrams illustrating a method for producing a positive electrode active material. FIG. 16 is a diagram illustrating a method for producing a positive electrode active material. FIGS. 17A to 17C are diagrams illustrating a method for producing a positive electrode active material. FIG. 18A is an exploded perspective view of a coin-type secondary battery, FIG. 18B is a perspective view of the coin-type secondary battery, and FIG. 18C is a cross-sectional perspective view thereof. FIG. 19A shows an example of a cylindrical secondary battery. FIG. 19B shows an example of a cylindrical secondary battery. FIG. 19C shows an example of multiple cylindrical secondary batteries. FIG. 19D shows an example of an energy storage system having multiple cylindrical secondary batteries. Fig. 20A and Fig. 20B are diagrams for explaining an example of a secondary battery, and Fig. 20C is a diagram showing the internal state of the secondary battery. Figs. 21A to 21C are diagrams for explaining an example of a secondary battery. Figs. 22A and 22B are diagrams for showing the external appearance of a secondary battery. Figs. 23A to 23C are diagrams for explaining a method for manufacturing a secondary battery. Figs. 24A to 24C are diagrams for showing an example of the configuration of a battery pack. Figs. 25A and 25B are diagrams for explaining an example of a secondary battery.FIGS. 26A to 26C are diagrams illustrating an example of a secondary battery. FIGS. 27A and 27B are diagrams illustrating an example of a secondary battery. FIG. 28A is a perspective view of a battery pack illustrating one embodiment of the present invention, FIG. 28B is a block diagram of the battery pack, and FIG. 28C is a block diagram of a vehicle having a motor. FIGS. 29A to 29D are diagrams illustrating an example of a transportation vehicle. FIGS. 30A and 30B are diagrams illustrating an energy storage device according to one embodiment of the present invention. FIG. 31A is a diagram illustrating an electric bicycle, FIG. 31B is a diagram illustrating a secondary battery for the electric bicycle, and FIG. 31C is a diagram illustrating an electric motorcycle. FIGS. 32A to 32D are diagrams illustrating an example of an electronic device. FIG. 33A illustrates an example of a wearable device, FIG. 33B is a perspective view of a wristwatch-type device, and FIG. 33C is a diagram illustrating a side view of the wristwatch-type device. FIG. 33D is a diagram illustrating an example of a wireless earphone. FIG. 34A is a surface SEM image of the positive electrode active material composite of Example 1. FIG. 34B is a surface SEM image of the lithium cobalt oxide of Example 1. FIG. 35 is a graph of the electrode density of the positive electrode of Example 1. FIG. 36 is a surface SEM image of the positive electrode active material composite of Example 2. FIG. 37A is a graph showing the charge characteristics of the secondary battery of Example 2. FIG. 37B is a graph showing the discharge characteristics of the secondary battery of Example 2. FIG. 38 is a graph showing the cycle characteristics of the secondary battery of Example 2.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0039] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may contain a substance that does not contribute to the charge / discharge capacity.

[0040] In this specification and the like, the positive electrode active material of one embodiment of the present invention may be referred to as a positive electrode material, a positive electrode material for a secondary battery, a composite oxide, or the like. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a compound. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composition. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composite.

[0041] Furthermore, in this specification and the like, the term "particle" is not limited to referring only to spherical shapes (having a circular cross-sectional shape), and examples of the cross-sectional shape of individual particles include ellipsoids, rectangles, trapezoids, triangles, squares with rounded corners, and asymmetric shapes, and further, individual particles may have an irregular shape.

[0042] The particle size can be measured, for example, by laser diffraction particle size distribution measurement, and the D50 value can be used for comparison. Here, D50 refers to the particle size at which the cumulative amount in the cumulative particle amount curve of the particle size distribution measurement results accounts for 50%, i.e., the median. The measurement of particle size is not limited to laser diffraction particle size distribution measurement; when the particle size is below the lower measurement limit of laser diffraction particle size distribution measurement, the major axis of the particle cross section may be measured by analysis using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0043] In addition, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar. However, in this specification, due to limitations in application notation, instead of a bar above the number, a minus sign (-) may be placed before the number. Individual orientations indicating directions within a crystal are expressed with [ ], collective orientations indicating all equivalent directions with < >, individual planes indicating crystal faces with ( ), and collective planes with equivalent symmetry with {}. In addition, Miller indices for trigonal and hexagonal crystals, including R-3m, may use (hkil) instead of just (hkl). Here, i is -(h+k).

[0044] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice.

[0045] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately. Note that the crystal structure may have a deficiency of cations or anions in part.

[0046] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated. For example, LiFePO ４ The theoretical capacity of LiCoO is 170 mAh / g. ２ The theoretical capacity of LiNiO is 274 mAh / g. ２ The theoretical capacity of LiMn is 274mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0047] The amount of lithium remaining in the positive electrode active material that can be inserted or removed can be determined by x in the composition formula, for example, Li ｘ CoO ２ x in, or Li ｘ MO ２ In this specification, Li ｘ CoO ２ Li as appropriate ｘ MO ２ x can be considered as an occupancy rate, and in the case of a positive electrode active material in a secondary battery, x may be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, LiCoO ２ When a secondary battery using as a positive electrode active material is charged at 219.2 mAh / g, Li ０．２ CoO ２ Or we can say x = 0.2. ｘ CoO ２The small value of x in the formula means, for example, 0.1<x≦0.24.

[0048] When the lithium cobalt oxide satisfies the stoichiometric ratio, LiCoO ２ The occupancy rate of Li on the lithium site is x = 1. Also, the secondary battery after discharge is also LiCoO ２ In this case, x = 1. The end of discharge here refers to the state where the voltage is 2.5 V (lithium counter electrode) or less at a current of 100 mA / g, for example. In a lithium ion secondary battery, when the occupancy rate of lithium in the lithium site reaches x = 1 and no more lithium can enter, the voltage drops sharply. At this point, discharge can be said to be complete. Generally, LiCoO ２ In the case of a lithium ion secondary battery using the above method, the discharge voltage drops rapidly until it reaches 2.5 V, so it is assumed that the discharge is completed under the above conditions.

[0049] In addition, in this specification and the like, the depth of charge when all of the intercalable / deintercalable lithium in the positive electrode active material is intercalated may be referred to as 0, and the depth of charge when all of the intercalable / deintercalable lithium in the positive electrode active material is deintercalated may be referred to as 1.

[0050] Although the present specification and the like may show examples of secondary batteries using a positive electrode and a positive electrode active material of one embodiment of the present invention, in which lithium metal is used as the counter electrode, the secondary battery of one embodiment of the present invention is not limited thereto. Other materials, such as graphite or lithium titanate, may also be used for the negative electrode. The properties of the positive electrode and positive electrode active material of one embodiment of the present invention, such as their crystalline structure being resistant to repeated charge and discharge and their excellent cycle characteristics, are not affected by the material of the negative electrode. Although the present specification and the like may show examples of secondary batteries of one embodiment of the present invention, in which the secondary battery is charged and discharged at a relatively high voltage, such as a charge voltage of 4.6 V, using a lithium counter electrode, the secondary battery may also be charged and discharged at a lower voltage. When the secondary battery is charged and discharged at a lower voltage, the cycle characteristics are expected to be even better than those shown in the present specification and the like.

[0051] In this specification, the term "kiln" refers to a device for heating an object to be treated. For example, the term "kiln" may be replaced with a furnace, a kiln, a heating device, or the like.

[0052] Embodiment 1 In this embodiment, a positive electrode, a positive electrode active material composite, and a manufacturing method of the positive electrode active material composite according to one embodiment of the present invention will be described with reference to FIGS.

[0053] The positive electrode 1101 includes a positive electrode active material layer 1105 and a positive electrode current collector 1104. The positive electrode active material layer 1105 includes a first active material 100x that functions as a positive electrode active material and a positive electrode active material composite 100z that includes a coating material 101 that covers at least a part of the first active material 100x, and may further include a conductive material and a binder.

[0054] Alternatively, the positive electrode active material layer 1105 may have a positive electrode active material composite 100z including a first active material 100x that functions as a positive electrode active material and a second active material 100y that is in contact with the first active material 100x via a coating material 101 that covers at least a portion of the first active material 100x, and may further include a conductive material and a binder.

[0055] The density of the positive electrode active material layer 1105 is preferably 3.0 g / cm ３ More preferably, 3.5 g / cm ３ More preferably, 3.8 g / cm ３ That is all. Therefore, a press treatment may be performed to increase the density of the positive electrode active material layer 1105. However, when the press treatment is performed, it is desirable to appropriately set the conditions for the press treatment so as not to damage the structures of the first active material 100x and the positive electrode active material composite 100z, which will be described later.

[0056] The positive electrode active material composite 100z is obtained by a composite process described below using at least the first active material 100x and the coating material 101. Examples of the composite process include one or more of the following: composite processes using mechanical energy, such as mechanochemical processes, mechanofusion processes, and ball milling processes; composite processes using liquid-phase reactions, such as wet mixing, spray drying, coprecipitation, hydrothermal processes, and sol-gel processes; and composite processes using gas-phase reactions, such as barrel sputtering, atomic layer deposition (ALD), vapor deposition, and chemical vapor deposition (CVD). In addition, the composite process preferably involves one or more heat treatments. In this specification, the composite process may also be referred to as a surface coating process or a coating process. A specific method for producing the positive electrode active material composite 100z will be described later.

[0057] Alternatively, the positive electrode active material composite 100z can be obtained by a composite process using the first active material 100x, the coating material 101, and the second active material 100y. Examples of the composite process include one or more of the following: a composite process using mechanical energy, such as a mechanochemical process, a mechanofusion process, or a ball mill process; a composite process using a liquid-phase reaction, such as a wet mixing process, a spray drying process, a coprecipitation process, a hydrothermal process, or a sol-gel process; and a composite process using a gas-phase reaction, such as a barrel sputtering process, an ALD process, a vapor deposition process, or a CVD process. Furthermore, it is preferable to perform a heat treatment one or more times during the composite process. A specific method for producing the positive electrode active material composite 100z will be described later.

[0058] 1 illustrates an example of a positive electrode 1101 of one embodiment of the present invention. The positive electrode 1101 includes a positive electrode current collector 1104 and a positive electrode active material layer 1105. The positive electrode active material layer 1105 includes a positive electrode active material composite 100z. The positive electrode active material composite 100z includes a first active material 100x capable of absorbing and releasing carrier ions and a coating material 101. Specific examples of the first active material 100x and the coating material 101 will be described later.

[0059] FIG. 1 shows an example in which a graphene compound 102 and carbon black 103 are used as conductive materials. However, if the positive electrode active material composite 100z has sufficient electronic conductivity, a conductive material need not be used in the positive electrode active material layer 1105. The type of conductive material is not limited to the example shown in FIG. 1 . Only a graphene compound, carbon black, or carbon fibers such as carbon nanotubes may be used. Alternatively, carbon fibers such as carbon nanotubes may be used in combination with carbon black. That is, a material containing carbon is preferably used as the conductive material. Although not shown in FIG. 1 , the positive electrode active material layer 1105 preferably contains a binder. Examples of binders include polymer materials such as polyvinylidene fluoride and Li(FSI)(SN). ２ A molecular crystal electrolyte such as the above can be used.

[0060] The positive electrode active material composite 100z is disposed in a state in which it can exchange electrons with the positive electrode current collector 1104. That is, the positive electrode active material composite 100z is in electrical contact with the positive electrode current collector 1104. An undercoat layer may be provided on the positive electrode current collector 1104. In this case, the positive electrode active material composite 100z is in electrical contact with the positive electrode current collector 1104 via the undercoat layer. The positive electrode active material composite 100z may also be in electrical contact with the positive electrode current collector 1104 via a conductive material.

[0061] [Positive Electrode Active Material Composite] FIGS. 2A1 to 2B2, 3A1 to 3B2, and 4A1 to 4B2 are schematic cross-sectional views illustrating a positive electrode active material composite 100z.

[0062] 2A1 and 2A2 are diagrams illustrating a cathode active material composite 100z having a first active material 100x functioning as a cathode active material and a coating material 101 covering at least a portion of the first active material 100x. While FIG. 2A1 illustrates a configuration in which one first active material 100x is covered with the coating material 101, the present invention is not limited thereto, and multiple first active materials 100x may be covered with the coating material 101. For example, as shown in FIG. 2A2, at least a portion of the first active material 100xa and the first active material 100xb may be covered with the coating material 101. While FIG. 2A2 illustrates a case in which the first active material 100xa and the first active material 100xb are at least partially in contact with each other, the first active material 100xa and the first active material 100xb do not necessarily have to be in direct contact with each other.

[0063] When at least a portion, preferably substantially the entire particle surface, of the particulate first active material 100x that functions as a positive electrode active material is covered with the coating material 101, the area in direct contact with the electrolyte 114 of the first active material 100x is reduced, and desorption of a transition metal element and / or oxygen from the first active material 100x in a high-voltage charging state can be suppressed, thereby suppressing a decrease in capacity due to repeated charging and discharging. Furthermore, by being covered with the coating material 101 that is electrochemically stable even at high temperatures and in a high-voltage charging state, a secondary battery using the positive electrode active material composite 100z of one embodiment of the present invention can achieve effects such as improved stability at high temperatures and improved fire resistance.

[0064] In particular, by using, as the first active material 100x, a material that has excellent stability in a high-voltage charged state, such as lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, or lithium nickel-cobalt-manganese oxide having a molar ratio of nickel:cobalt:manganese=8:1:1 or nickel:cobalt:manganese=9:0.5:0.5, the durability and stability of the above-mentioned cathode active material composite 100z in a high-voltage charged state can be further improved. Also, the heat resistance and / or fire resistance of a secondary battery using the above-mentioned cathode active material composite 100z can be further improved.

[0065] Lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel is characterized by having a high content of magnesium, fluorine, or aluminum in the surface layer of the positive electrode active material, with nickel widely distributed throughout the particles, and exhibiting significantly excellent charge-discharge cycle characteristics at high voltages, making it a particularly preferred material for the first active material 100x. When the surface layer of the positive electrode active material contains a high content of magnesium, fluorine, or aluminum, for example, in STEM-EDX line analysis, the count number of characteristic X-rays derived from magnesium, fluorine, or aluminum reaches a maximum value in the surface layer. Here, the surface layer refers to a region extending from the surface of the positive electrode active material to a depth of approximately 10 nm toward the interior, and does not include conductive materials. Note that cracks in the positive electrode active material also have surface layer portions, and cracks that occurred before the addition of magnesium, fluorine, or aluminum in the preparation of the positive electrode active material have surface layer portions rich in magnesium, fluorine, or aluminum.

[0066] 2B1, 2B2, and 3A1 to 3B2 are diagrams illustrating a cathode active material composite 100z having a first active material 100x functioning as a cathode active material and a second active material 100y in contact with the first active material 100x via a coating material 101 that covers at least a portion of the first active material 100x. While FIGS. 2B1, 3A1, and 3B1 illustrate a configuration in which one first active material 100x is covered by the coating material 101, the present invention is not limited thereto, and multiple first active materials 100x may be covered by the coating material 101. For example, as shown in FIGS. 2B2, 3A2, and 3B2, a configuration in which at least a portion of the first active material 100xa and the first active material 100xb is covered by the coating material 101 may be used. 2B2, 3A2, and 3B2 show the case where the first active material 100xa and the first active material 100xb are at least partially in contact with each other, but the first active material 100xa and the first active material 100xb do not necessarily have to be in direct contact with each other.

[0067] 2B1 and 2B2 show a case where the second active material 100y forms a layer by a composite treatment of the second active material 100y, for example, by a liquid phase reaction such as a coprecipitation method, a hydrothermal method, or a sol-gel method.

[0068] 3A1 to 3B2 show a case where a plurality of second active materials 100y are in contact with the first active material 100x via a coating material 101 that covers at least a portion of the first active material 100x, for example, a case where the second active material 100y is subjected to a composite treatment using mechanical energy such as a mechanochemical method, a mechanofusion method, or a ball mill method.

[0069] A cathode active material composite 100z will be described, in which at least a portion, preferably substantially the entire particle surface, of a particulate first active material 100x that functions as a cathode active material is covered with a coating material 101, and which has a second active material 100y that is in contact with the first active material 100x via the coating material 101. In the cathode active material composite 100z having the second active material 100y that is in contact with the first active material 100x via the coating material 101, the area where the first active material 100x is in direct contact with the electrolyte 114 is reduced, and desorption of transition metal elements and / or oxygen from the first active material 100x in a high-voltage charged state can be suppressed, thereby suppressing a decrease in capacity due to repeated charge and discharge. Furthermore, when the coating material 101 and the second active material 100y are materials that are electrochemically stable even at high temperatures and high voltages, covering them can provide effects such as improved stability at high temperatures and improved fire resistance of a secondary battery using the positive electrode active material composite 100z of one embodiment of the present invention.

[0070] In particular, by using, as the first active material 100x, a material that is stable under high-voltage charging, such as lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, or lithium nickel-cobalt-manganese oxide having a molar ratio of nickel:cobalt:manganese=8:1:1 or nickel:cobalt:manganese=9:0.5:0.5, the durability and stability under high-voltage charging of the above-described cathode active material composite 100z can be further improved. Also, the heat resistance and / or fire resistance of a secondary battery using the above-described cathode active material composite 100z can be further improved.

[0071] Lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel is characterized by having a large amount of magnesium, fluorine, or aluminum in the surface layer of the positive electrode active material, nickel being widely distributed throughout the particles, and exhibiting significantly excellent high-voltage charge / discharge cycle characteristics, making it a particularly preferred material for the first active material 100x. When the surface layer of the positive electrode active material contains a large amount of magnesium, fluorine, or aluminum, for example, in STEM-EDX line analysis, the count number of characteristic X-rays derived from magnesium, fluorine, or aluminum has a maximum value in the surface layer. Here, the surface layer refers to a region extending from the surface of the positive electrode active material to a depth of approximately 10 nm. Note that cracks in the positive electrode active material also have surface layer portions, and cracks that occurred before the magnesium, fluorine, or aluminum addition process in the preparation of the positive electrode active material have surface layer portions rich in magnesium, fluorine, or aluminum.

[0072] As described above, the cathode active material composite 100z of one embodiment of the present invention is not in contact with the electrolyte 114, thereby suppressing electrolyte-induced deterioration of the first active material 100x. Such deterioration may be due to defects in the first active material 100x, such as pits. Pits refer to regions where several layers of the main components of the first active material 100x, such as cobalt and oxygen, are missing during a charge-discharge cycle test. For example, cobalt is thought to dissolve into the electrolyte. Pits may progress during a charge-discharge cycle test, progressing toward the interior of the active material. The opening shape of the pits is not circular but has a deep, groove-like shape. The absence of contact between the electrolyte 114 and the first active material 100x can suppress the occurrence and progression of the defects, particularly pits.

[0073] Furthermore, if the coating material 101 is a material having a higher conductivity than the first active material 100x, the charge / discharge characteristics, particularly the charge capacity and discharge capacity at high rates, are improved, which is preferable. Furthermore, if the positive electrode active material and the conductive material are combined to form the positive electrode active material composite 100z having the coating material 101, a conductive path can be effectively formed with a small amount of conductive material, which is preferable because the electrode density of the positive electrode can be improved.

[0074] When the cathode active material composite 100z includes the second active material 100y in contact with the first active material 100x via the coating material 101, the cathode active material composite 100z can be said to have a dual structure in the surface layer portion. However, the cathode active material composite 100z of one embodiment of the present invention is not limited to the dual structure including the coating material 101 and the second active material 100y. As another example of the cathode active material composite 100z of one embodiment of the present invention, as shown in FIGS. 4A1 to 4B2 , a glass active material mixed layer including the coating material 101 and the second active material 100y may cover at least a portion of the surface of the first active material 100x.

[0075] 3B1 , 3B2 , 4B1 , and 4B2 , the positive electrode active material composite 100z of one embodiment of the present invention may include a graphene compound 102 in a surface layer portion of the positive electrode active material composite 100z or in a mixed layer of the coating material 101 and the active material. Here, instead of the graphene compound 102, carbon black or carbon fibers such as carbon nanotubes may be used.

[0076] Glass can be used as the coating material 101. Glass is also called a material having an amorphous portion. Examples of materials having an amorphous portion include SiO ２ , SiO, Al ２ O ３ , TiO ２ , Li ４ SiO ４ , Li ３ P.O. ４ , Li ２ S, SiS ２ , B ２ S ３ , GeS ４ , AgI, Ag ２ O, Li ２ O, P ２ O ５ , B ２ O ３ , and V ２ O ５ A material having one or more selected from the group consisting of Li, ７ P ３ S １１ , or Li １＋ｘ＋ｙ Al ｘ Ti ２−ｘ Si ｙ P ３−ｙ O １２(0<x<2, 0<y<3, etc.) can be used. A material having an amorphous portion can be used in an amorphous state as a whole, or in a partially crystallized state as crystallized glass (also called glass ceramics). The coating material 101 desirably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusibility and lithium ion penetration. The coating material 101 preferably has a melting point of 800°C or less, more preferably 500°C or less. The coating material 101 preferably has electronic conductivity. The coating material 101 preferably has a softening point of 800°C or less, for example, Li ２ O-B ２ O ３ -SiO ２ Glasses containing fluorine can be used.

[0077] Furthermore, a material containing carbon can be used as the coating material 101. Examples of the carbon-containing material include carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and materials that can be used as conductive materials, such as graphene compounds.

[0078] Furthermore, a material having an amorphous portion and a material having carbon may be mixed and used.

[0079] The second active material 100y includes oxides and LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn). Examples of oxides include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Also, LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn) ４ , LiNiPO ４ , LiCoPO ４ , LiMnPO ４ , LiFe ａ Ni ｂ P.O. ４ , LiFe ａ Co ｂP.O. ４ , LiFe ａ Mn ｂ P.O. ４ , LiNi ａ Co ｂ P.O. ４ , LiNi ａ Mn ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ｃ Ni ｄ Co ｅ P.O. ４ , LiFe ｃ Ni ｄ Mn ｅ P.O. ４ , LiNi ｃ Co ｄ Mn ｅ P.O. ４ (c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe ｆ Ni ｇ Co ｈ Mn ｉ P.O. ４ (f+g+h+i is 1 or less, 0<f<1, 0<g<1, 0<h<1, 0<i<1), etc.

[0080] Furthermore, the positive electrode active material composite 100z is preferably configured to be covered with a molecular crystalline electrolyte. The molecular crystalline electrolyte can function as a binder for the positive electrode active material layer 1105. The molecular crystalline electrolyte is preferably a material with high ionic conductivity, and the positive electrode active material composite 100z covered with the molecular crystalline electrolyte can exchange carrier ions with the electrolyte 114.

[0081] [Positive Electrode Active Material] The first active material 100x is LiMO having a layered rock salt crystal structure. ２ (M1 is one or more selected from Fe, Ni, Co, and Mn) can be used as the first active material 100x. ２A composite oxide represented by the formula (I) to which an additive element X has been added can be used. The additive element X contained in the first active material 100x is preferably one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, gallium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements may further stabilize the crystal structure of the first active material 100x. That is, the first active material 100x can include lithium cobalt oxide having magnesium and fluorine, lithium cobalt oxide having magnesium, fluorine, aluminum, and nickel, lithium cobalt oxide having magnesium, fluorine, and titanium, lithium nickel-cobalt oxide having magnesium and fluorine, lithium cobalt-aluminate having magnesium and fluorine, nickel-cobalt-aluminate, nickel-cobalt-aluminate, and nickel-cobalt-manganate having magnesium and fluorine. The transition metal ratio of the nickel-cobalt-manganese lithium oxide is preferably high, and for example, a material having a molar ratio of nickel:cobalt:manganese=8:1:1 or nickel:cobalt:manganese=9:0.5:0.5 is preferred. Furthermore, the nickel-cobalt-manganese lithium oxide preferably contains calcium.

[0082] The first active material 100x is LiMO ２ Secondary particles of a composite oxide represented by the formula (where M1 is one or more selected from Fe, Ni, Co, and Mn) may be coated with a metal oxide. The metal oxide may be an oxide of one or more metals selected from Al, Ti, Nb, Zr, La, and Li. For example, LiMO ２A metal oxide-coated complex oxide in which secondary particles of a complex oxide represented by the formula (M1) (where M1 is one or more selected from Fe, Ni, Co, and Mn) are coated with aluminum oxide can be used as the first active material 100x. For example, a metal oxide-coated complex oxide in which secondary particles of lithium nickel-cobalt-manganese oxide having a molar ratio of nickel:cobalt:manganese of 8:1:1 or nickel:cobalt:manganese of 9:0.5:0.5 are coated with aluminum oxide can be used. Here, the coating layer is preferably thin, for example, 1 nm to 200 nm, more preferably 1 nm to 100 nm. Furthermore, the lithium nickel-cobalt-manganese oxide preferably includes lithium nickel-cobalt-manganese oxide containing calcium.

[0083] As the first active material 100x, an active material described in an embodiment to be described later can be used.

[0084] The second active material 100y is an oxide and LiM2PO4 having an olivine-type crystal structure. ４ (M2 is one or more selected from Fe, Ni, Co, and Mn). Examples of oxides include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Also, LiM2PO ４ As an example, LiFePO ４ , LiNiPO ４ , LiCoPO ４ , LiMnPO ４ , LiFe ａ Ni ｂ P.O. ４ , LiFe ａ Co ｂ P.O. ４ , LiFe ａ Mn ｂ P.O. ４ , LiNi ａ Co ｂ P.O. ４ , LiNi ａ Mn ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ｃ Ni ｄ Co ｅ P.O.４ , LiFe ｃ Ni ｄ Mn ｅ P.O. ４ , LiNi ｃ Co ｄ Mn ｅ P.O. ４ (c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe ｆ Ni ｇ Co ｈ Mn ｉ P.O. ４ (f+g+h+i is 1 or less, 0<f<1, 0<g<1, 0<h<1, 0<i<1), etc. The second active material 100y may have a carbon coating layer on the particle surface.

[0085] [Conductive Material] As the conductive material, for example, one or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fiber such as carbon nanofiber and carbon nanotube, and graphene compound can be used.

[0086] In this specification and the like, graphene compounds include multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. Graphene compounds contain carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a curved shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0087] In this specification and the like, graphene oxide refers to a material that contains carbon and oxygen, has a sheet shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0088] In this specification, reduced graphene oxide refers to a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. It may also be called a carbon sheet. A single reduced graphene oxide can function, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is 2 atomic % or more and 15 atomic % or less. By achieving these carbon and oxygen concentrations, reduced graphene oxide can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D of the G band to the D band in a Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0089] Graphene compounds may have excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds may also have a sheet-like shape. Graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. Even thin graphene compounds may have very high conductivity, allowing a small amount of graphene to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive material can increase the contact area between the active material and the conductive material. It is preferable that the graphene compound covers 80% or more of the active material. It is preferable that the graphene compound clings to at least a portion of the active material particles. It is also preferable that the graphene compound overlaps at least a portion of the active material particles. It is also preferable that the shape of the graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a portion of the active material particles. The graphene compound may also have holes.

[0090] [Binder] Examples of binders that can be used include one or more of the following materials: polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose. Examples of dispersion media that can be used include one or more of the following: water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). A preferred combination of binder and dispersion medium is polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP).

[0091] [Current Collector] As the current collector, a highly conductive material such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy 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. Furthermore, an aluminum alloy containing an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can be used. The current collector can be appropriately shaped, such as a foil, plate, sheet, mesh, punched metal, or expanded metal. It is preferable to use a current collector with a thickness of 5 μm or more and 30 μm or less.

[0092] An example of a method for manufacturing a positive electrode active material composite according to one embodiment of the present invention will be described with reference to FIGS.

[0093] The method for producing the positive electrode active material composite is a method for producing the first active material 100x, the second active material 100y, and the coating material 101 using a composite treatment using mechanical energy. However, the present invention should not be construed as being limited to the contents of these descriptions.

[0094] In the positive electrode active material composite preparation method 1, a first active material 100x and a coating material 101 are combined together. In the positive electrode active material composite preparation method 2, the first active material 100x and the coating material 101 are combined together, and then a second active material 100y is combined with the combined material. In the positive electrode active material composite preparation method 3, the first active material 100x, the second active material 100y, and the coating material 101 are combined together at the same time.

[0095] [Method 1 for Producing Positive Electrode Active Material Composite] In step S101 of FIG. 5A, a first active material 100x is prepared, and in step S102, a coating material 101 is prepared.

[0096] The first active material 100x is LiMO produced by a production method shown in the embodiment described later. ２ (M1 is one or more selected from Fe, Ni, Co, and Mn) to which an additive element X has been added can be used, such as lithium cobalt oxide containing magnesium and fluorine, or lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel. In particular, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel is preferably subjected to the initial heating process described in the embodiment described below. Another example of the first active material 100x is lithium nickel-cobalt-manganese oxide. Here, the transition metal ratio of the lithium nickel-cobalt-manganese oxide is preferably a high nickel ratio, for example, a material with a molar ratio of nickel:cobalt:manganese = 8:1:1 or nickel:cobalt:manganese = 9:0.5:0.5. Furthermore, a metal oxide-coated complex oxide can be used, in which secondary particles of lithium nickel-cobalt-manganese oxide are coated with aluminum oxide. Here, the coating layer is preferably thin, for example, between 1 nm and 200 nm, more preferably between 1 nm and 100 nm.

[0097] A material having an amorphous portion can be used as the coating material 101. Examples of the material having an amorphous portion include SiO. ２ , SiO, Al ２ O ３ , TiO ２, Li ４ SiO ４ , Li ３ P.O. ４ , Li ２ S, SiS ２ , B ２ S ３ , GeS ４ , AgI, Ag ２ O, Li ２ O, P ２ O ５ , B ２ O ３ , and V ２ O ５ A material having one or more selected from the group consisting of Li, ７ P ３ S １１ , or Li １＋ｘ＋ｙ Al ｘ Ti ２−ｘ Si ｙ P ３−ｙ O １２ (0<x<2, 0<y<3, etc.) can be used. A material having an amorphous portion can be used in an amorphous state as a whole, or in a partially crystallized state as crystallized glass (also called glass ceramics). The coating material 101 desirably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusibility and lithium ion penetration. The coating material 101 preferably has a melting point of 800°C or less, more preferably 500°C or less. The coating material 101 preferably has electronic conductivity. The coating material 101 preferably has a softening point of 800°C or less, for example, Li ２ O-B ２ O ３ -SiO ２ Glasses containing fluorine can be used.

[0098] Next, in step S103, the first active material 100x and the coating material 101 are combined together. When the combining process is performed using mechanical energy, the combining process can be performed by a mechanochemical method. Alternatively, the process may be performed by a mechanofusion method.

[0099] Furthermore, when a ball mill is used in step S103, it is preferable to use, for example, zirconia balls as media. For the purpose of mixing, dry ball milling is preferable. When wet ball milling is used, acetone can be used. When wet ball milling is used, it is recommended to use dehydrated acetone with a moisture content of 100 ppm or less, preferably 10 ppm or less.

[0100] By the composite treatment in step S103, it is possible to create a state in which at least a part of the particle surface of the particulate first active material 100x, preferably substantially the entirety, is covered with the coating material 101.

[0101] Next, in step S104, a heat treatment is performed. The heat treatment in step S104 is desirably performed at a temperature equal to or higher than the melting point of the coating material 101. For example, the heat treatment may be performed 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. After step S104, a step of crushing the fixed positive electrode active material composites 100z may be included.

[0102] Through the above steps, the positive electrode active material composite 100z of one embodiment of the present invention shown in FIG. 5A can be manufactured (Step S105).

[0103] In order to obtain a good coating state in the composite treatment, the ratio of the particle diameter of the coating material 101 to the particle diameter of the first active material 100x (particle diameter of the coating material 101 / first active material 100x) is preferably 1 / 100 or more and 1 / 50 or less, and more preferably 1 / 200 or more and 1 / 100 or less. The particle diameter of the coating material 101 can be adjusted by performing an atomization treatment (step S102) using the method shown in FIG. 5B to obtain an atomized coating material 101′ (step S103).

[0104] It is desirable that the coating material 101 have electronic conductivity. However, if the coating material 101 has low electronic conductivity, in step S103 of FIG. 5A, a carbon fiber conductive material such as a graphene compound, carbon black, or carbon nanotubes can be mixed with the coating material 101 to impart electronic conductivity to the positive electrode active material composite 100z.

[0105] [Method 2 for Producing Positive Electrode Active Material Composite] In step S101 of FIG. 6A, a first active material 100x is prepared, and in step S102, a coating material 101 is prepared.

[0106] Next, in step S103, the first active material 100x and the coating material 101 are combined together. When the combining process is performed using mechanical energy, the combining process can be performed by a mechanochemical method. Alternatively, the process may be performed by a mechanofusion method.

[0107] Furthermore, when a ball mill is used in step S103, it is preferable to use, for example, zirconia balls as media. For the purpose of mixing, dry ball milling is preferable. When wet ball milling is used, acetone can be used. When wet ball milling is used, it is recommended to use dehydrated acetone with a moisture content of 100 ppm or less, preferably 10 ppm or less.

[0108] By the composite treatment in step S103, it is possible to create a state in which at least a part of the particle surface of the particulate first active material 100x, preferably substantially the entirety, is covered with the coating material 101.

[0109] Next, a heat treatment is performed in step S104, and a cathode active material composite 100z is obtained in step S105. The heat treatment in step S104 is desirably performed at a temperature equal to or higher than the melting point of the coating material 101. For example, the heat treatment may be performed 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. After step S104, a step of crushing the fixed cathode active material composite 100z may be included.

[0110] Next, in step S106, a second active material 100y is prepared.

[0111] As the second active material 100y, LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn). Alternatively, an oxide can be used as the second active material 100y. Examples of oxides that can be used include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. LiM2PO ４ Materials such as those mentioned above as LiFePO ４ , LiMnPO ４ , LiFe ａ Mn ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ａ Ni ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1) can be used. The particle surfaces of the second active material 100y may have a carbon coating layer.

[0112] When a material that functions as a positive electrode active material is used as the second active material 100y, it is possible to select a combination of the first active material 100x and the second active material 100y that is unlikely to cause a step in the charge / discharge curve, depending on the characteristics required of the secondary battery, or a combination that causes a step in the charge / discharge curve at a desired charging rate.

[0113] 6A, the cathode active material composite 100z of step S105 and the second active material 100y are combined together. When combining the cathode active material composite 100z and the second active material 100y using mechanical energy, the combining process can be performed by a mechanochemical method. Alternatively, the combining process can be performed by a mechanofusion method.

[0114] Furthermore, when a ball mill is used in step S107, it is preferable to use, for example, zirconia balls as media. For the purpose of mixing, dry ball milling is preferable. When wet ball milling is used, acetone can be used. When wet ball milling is used, it is recommended to use dehydrated acetone with a moisture content of 100 ppm or less, preferably 10 ppm or less.

[0115] The composite treatment in step S107 makes it possible to produce a state in which at least a portion, and preferably substantially the entire surface of positive electrode active material composite 100z is covered with second active material 100y.

[0116] Next, heat treatment is performed in step S108. The heat treatment in step S108 may be performed, for example, in an atmosphere containing oxygen or nitrogen, 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. Step S108 may be followed by a step of crushing the fixed positive electrode active material composites 100z′.

[0117] Through the above steps, the cathode active material composite 100z′ of one embodiment of the present invention shown in FIG. 6A can be produced (Step S109).

[0118] In order to obtain a good coating state in the composite treatment, the ratio of the particle diameter of the coating material 101 to the particle diameter of the first active material 100x (particle diameter of the coating material 101 / first active material 100x) is preferably 1 / 100 or more and 1 / 50 or less, and more preferably 1 / 200 or more and 1 / 100 or less. To adjust the particle diameter of the coating material 101, an atomization treatment may be performed by the method shown in FIG. 5B .

[0119] It is desirable that the coating material 101 have electronic conductivity. However, if the coating material 101 has low electronic conductivity, electronic conductivity can be imparted by mixing a carbon fiber conductive material such as a graphene compound, carbon black, or carbon nanotubes with the coating material 101 in step S103 of FIG. 6A.

[0120] In order to obtain a good coating state in the composite treatment, the ratio of the particle diameter of the second active material 100y to the particle diameter of the first active material 100x (particle diameter of the second active material 100y / first active material 100x) is preferably 1 / 100 or more and 1 / 50 or less, and more preferably 1 / 200 or more and 1 / 100 or less. In order to adjust the particle diameter of the second active material 100y, an atomization treatment (step S102) can be performed by the method shown in FIG. 6B to obtain an atomized second active material 100y′ (step S103).

[0121] [Method 3 for Producing Positive Electrode Active Material Composite] In step S101 of FIG. 7A, a first active material 100x is prepared, in step S102 a second active material 100y is prepared, and in step S103 a coating material 101 is prepared.

[0122] Next, in step S104, the first active material 100x, the second active material 100y, and the coating material 101 are subjected to a composite treatment. When the composite treatment is performed using mechanical energy, the composite treatment can be performed by a mechanochemical method. Alternatively, the treatment may be performed by a mechanofusion method.

[0123] Furthermore, when a ball mill is used in step S104, it is preferable to use, for example, zirconia balls as media. For the purpose of mixing, dry ball milling is preferable. When wet ball milling is used, acetone can be used. When wet ball milling is used, it is preferable to use dehydrated acetone with a moisture content of 100 ppm or less, preferably 10 ppm or less.

[0124] The compounding treatment in step S104 makes it possible to create a state in which at least a portion, and preferably almost the entire particle surface of the particulate first active material 100x is covered with a mixture of the second active material and the coating material 101.

[0125] Next, in step S105, a heat treatment is performed. The heat treatment in step S105 is desirably performed at a temperature equal to or higher than the melting point of the coating material 101. For example, the heat treatment may be performed in an atmosphere containing oxygen or nitrogen, 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. After step S104, a step of crushing the fixed positive electrode active material composites 100z may be included.

[0126] Through the above steps, the positive electrode active material composite 100z of one embodiment of the present invention shown in FIG. 7A can be manufactured (Step S106).

[0127] In order to obtain a good coating state in the composite treatment, the ratio of the particle diameter of the coating material 101 to the particle diameter of the first active material 100x (particle diameter of the coating material 101 / first active material 100x) is preferably 1 / 100 or more and 1 / 50 or less, and more preferably 1 / 200 or more and 1 / 100 or less. To adjust the particle diameter of the coating material 101, an atomization treatment may be performed by the method shown in FIG. 5B .

[0128] It is desirable that the coating material 101 have electronic conductivity. However, if the coating material 101 has low electronic conductivity, electronic conductivity can be imparted by mixing a graphene compound, carbon black, or a carbon fiber conductive material such as carbon nanotubes with the coating material 101 in step S104 of FIG. 7A.

[0129] 5A to 7A , an example of the composite treatment using mechanical energy is described. However, one embodiment of the present invention is not limited thereto. A method of wet-mixing the first active material 100x and the coating material 101 will be described with reference to FIG. 7B .

[0130] In step S101 of FIG. 7B, a first active material 100x is prepared, and in step S102, a coating material 101 is prepared.

[0131] An example of the coating material 101 suitable for wet mixing is graphene oxide. Graphene oxide is easily dispersed in polar solvents such as water and NMP, and therefore, a small amount of the coating material 101 can be easily attached to the surface of the first active material 100x.

[0132] The wet mixing composite process can be performed, for example, as follows: First, the coating material 101 and a solvent are mixed. Then, the first active material 100x is added and mixed. A binder is then added and mixed to prepare a slurry. For example, a planetary / revolving mixer can be used for mixing. It is preferable to add a solvent as needed to adjust the viscosity. The slurry is applied to a current collector and dried to prepare an electrode layer. For example, the current collector can be coated with the slurry by a doctor blade method. In this specification, coating refers to the process of forming a slurry to a specified thickness, and may also be referred to as forming, spreading, etc. Through these processes, the coating material 101 can be attached to the surface of the first active material 100x (step S104).

[0133] When graphene oxide is used as the coating material 101, the electrode layer fabricated as described above is subjected to a reduction treatment. The reduction treatment can be chemical reduction and / or thermal reduction. In particular, performing thermal reduction after chemical reduction is preferable because graphene oxide can be sufficiently reduced even if the temperature of the thermal reduction is lowered, and deterioration of the binder can be avoided.

[0134] 7B, chemical reduction is first performed in step S110. For example, chemical reduction is performed by immersing the electrode layer fabricated above in an aqueous solution of a reducing agent. Examples of the reducing agent include organic acids such as ascorbic acid, hydrogen, sulfur dioxide, sulfurous acid, sodium sulfite, sodium bisulfite, ammonium sulfite, and phosphorous acid.

[0135] When ascorbic acid is used as the reducing agent, ascorbic acid is first dissolved in a solvent to prepare a reducing agent solution (ascorbic acid solution). Examples of solvents that can be used include water, a mixture of water and NMP, ethanol, and a mixture of water and ethanol. The electrode layer prepared above is then immersed in the solution. This treatment can be carried out for, for example, 30 minutes to 10 hours, with approximately one hour being preferred. Heating is also preferred, as it can shorten the chemical reduction time. For example, the solution can be heated to a temperature between room temperature and 100°C, with approximately 60°C being preferred.

[0136] Next, in step S111, thermal reduction is performed. Thermal reduction refers to a process of heating the electrode layer fabricated above. Heating is preferably performed under reduced pressure. For example, a glass tube oven can be used for heating. The glass tube oven can be used for heating under reduced pressure of about 1 kPa.

[0137] The optimal heating temperature and heating time vary depending on the conductive material and binder materials. For example, when graphene oxide is used as the conductive material and PVDF is used as the binder, the temperature is preferably at a level that sufficiently reduces graphene oxide without adversely affecting the PVDF. Specifically, 125°C or higher and 200°C or lower are preferred. At 100°C or lower, the reduction of graphene oxide may not proceed sufficiently. On the other hand, at 250°C or higher, the PVDF may be adversely affected and the slurry may easily peel off from the current collector. The heating time is preferably 1 hour or higher and 20 hours or lower. If the heating time is less than 1 hour, the graphene oxide may not be sufficiently reduced. On the other hand, if the heating time exceeds 20 hours, productivity decreases.

[0138] Chemical reduction and thermal reduction differ in the functional groups that are easily reduced. Chemical reduction is effective in reducing the carbonyl groups (C=O) and carboxyl groups (-COOH) in graphene oxide through proton addition. On the other hand, thermal reduction is effective in reducing the hydroxyl groups (-OH) in graphene oxide through dehydration. Therefore, performing both chemical and thermal reductions can achieve more efficient reduction and increase the conductivity of the reduced graphene oxide.

[0139] During the wet mixing and chemical reduction described above, the crystalline structure of the positive electrode active material is easily disrupted by contact with water, etc. Therefore, when employing this manufacturing method, it is preferable to use a positive electrode active material with a highly stable crystalline structure. For example, lithium cobalt oxide containing magnesium, fluorine, nickel, and aluminum, which will be described in the following embodiment, has a highly stable crystalline structure and is therefore preferred. Furthermore, positive electrode active materials with an olivine-type crystalline structure, such as lithium phosphate, are also highly stable and preferred.

[0140] Through the above steps, the positive electrode active material composite 100z of one embodiment of the present invention illustrated in FIG. 7B can be manufactured (Step S106).

[0141] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0142] Embodiment 2 In this embodiment, a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0143] [Structure of Positive Electrode Active Material] Fig. 8A is a schematic top view of a positive electrode active material 100 according to one embodiment of the present invention. Fig. 8B is a schematic cross-sectional view taken along line A-B in Fig. 8A.

[0144] <Contained Elements and Distribution> The positive electrode active material 100 contains lithium, a transition metal, oxygen, and an additional element X. The positive electrode active material 100 is LiMO ２ It can be said that the additive element X is added to a composite oxide represented by the formula (M1 is one or more selected from Fe, Ni, Co, and Mn).

[0145] The transition metal contained in the positive electrode active material 100 is preferably a metal capable of forming a layered rock-salt composite oxide belonging to the space group R-3m with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, the transition metal contained in the positive electrode active material 100 may be cobalt alone, nickel alone, a combination of cobalt and manganese, or a combination of cobalt and nickel, or three of cobalt, manganese, and nickel. That is, the positive electrode active material 100 may contain a composite oxide containing lithium and a transition metal, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is replaced with manganese, lithium cobalt oxide in which some of the cobalt is replaced with nickel, or nickel-manganese-lithium cobalt oxide. Including nickel in addition to cobalt as a transition metal may result in a more stable crystal structure in a charged state at a high voltage, which is preferable.

[0146] The additive element X contained in the positive electrode active material 100 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 elements may further stabilize the crystalline structure of the positive electrode active material 100. That is, the positive electrode active material 100 may contain lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, and titanium, lithium nickel-cobalt oxide containing magnesium and fluorine, lithium cobalt-aluminate containing magnesium and fluorine, nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate containing magnesium and fluorine, or lithium nickel-manganese-cobalt oxide containing magnesium and fluorine. In this specification and the like, the additive element X may be referred to as a mixture, a part of a raw material, or the like.

[0147] As shown in FIG. 8B , the positive electrode active material 100 has a surface layer 100a and an interior 100b. The surface layer 100a preferably has a higher concentration of the additive element X than the interior 100b. Furthermore, as shown by the gradation in FIG. 8B , the additive element X preferably has a concentration gradient that increases from the interior toward the surface. In this specification, the surface layer 100a refers to the region extending from the surface of the positive electrode active material 100 to a depth of approximately 10 nm. Surfaces formed by cracks and / or fissures may also be referred to as the surface, and as shown in FIG. 8C , the region extending from the surface to a depth of approximately 10 nm is referred to as the surface layer 100c. Furthermore, the region of the positive electrode active material 100 deeper than the surface layer 100a and the surface layer 100c is referred to as the interior 100b. When the positive electrode active material 100 forms a positive electrode active material composite 100z, it is desirable that the surface formed by the cracks is also covered with the coating material 101.

[0148] In the positive electrode active material 100 according to one embodiment of the present invention, the surface layer 100 a having a high concentration of the additive element X, i.e., the outer periphery of the particle, is reinforced so that the layered structure consisting of octahedra of cobalt and oxygen is not destroyed even when lithium is released from the positive electrode active material 100 due to charging.

[0149] Furthermore, it is preferable that the concentration gradient of the additive element X is uniformly distributed throughout the entire surface layer 100a of the positive electrode active material 100. Even if a portion of the surface layer 100a is reinforced, if there is a portion without reinforcement, stress may be concentrated in the unreinforced portion, which is undesirable. If stress is concentrated in a portion of the particle, defects such as cracks may occur there, which may lead to breakage of the positive electrode active material and a decrease in charge / discharge capacity.

[0150] Magnesium is divalent and is more stable at the lithium site than at the transition metal site in the layered rock-salt crystal structure, and therefore more likely to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer 100a facilitates the maintenance of the layered rock-salt crystal structure. Furthermore, magnesium has a strong bond with oxygen, which can inhibit the desorption of oxygen around magnesium. At an appropriate concentration, magnesium is preferable because it does not adversely affect the intercalation and deintercalation of lithium during charge and discharge. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium.

[0151] Aluminum is trivalent and can exist at the transition metal site in the layered rock salt crystal structure. Aluminum can suppress the elution of surrounding cobalt. Furthermore, because aluminum has a strong bond with oxygen, it can suppress the release of oxygen from the surrounding aluminum. Therefore, if aluminum is included as the additive element X, the positive electrode active material 100 can be made to have a crystal structure that is resistant to collapse even with repeated charge and discharge.

[0152] Fluorine is a monovalent anion, and when part of the oxygen in the surface layer portion 100a is substituted with fluorine, the lithium desorption energy is reduced. This is because the valence of cobalt ions changes with lithium desorption, from trivalent to tetravalent in the absence of fluorine, and from divalent to trivalent in the presence of fluorine, resulting in different oxidation-reduction potentials. Therefore, when part of the oxygen in the surface layer portion 100a of the positive electrode active material 100 is substituted with fluorine, it can be said that desorption and insertion of lithium ions near the fluorine is more likely to occur smoothly. Therefore, when used in a secondary battery, charge / discharge characteristics, rate characteristics, etc. are improved, which is preferable.

[0153] Titanium oxide is known to have superhydrophilic properties. Therefore, by forming the cathode active material 100 with titanium oxide in the surface layer portion 100a, it is possible that the cathode active material 100 has good wettability with highly polar solvents. When formed into a secondary battery, it is possible that the interface between the cathode active material 100 and a highly polar electrolyte solution will have good contact, thereby suppressing an increase in resistance. In this specification and the like, the electrolyte solution corresponds to a liquid electrolyte.

[0154] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can suppress a decrease in capacity due to repeated charge and discharge.

[0155] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and / or discharging operations of the secondary battery, but may also lead to heat generation and fire. To achieve a safe secondary battery, it is preferable that a short circuit current be suppressed even at a high charging voltage. The positive electrode active material 100 of one embodiment of the present invention suppresses a short circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high capacity and safety can be obtained.

[0156] A secondary battery using the positive electrode active material 100 of one embodiment of the present invention preferably simultaneously satisfies high capacity, excellent charge / discharge cycle characteristics, and safety.

[0157] The concentration gradient of the added element X can be evaluated, for example, by using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, measuring while scanning an area and evaluating the area two-dimensionally is sometimes called EDX area analysis. Extracting data of a linear area from EDX area analysis and evaluating the distribution of atomic concentration within the positive electrode active material particles is sometimes called line analysis.

[0158] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration of the additive element X in the surface layer portion 100a, the interior 100b, and the vicinity of the grain boundaries of the positive electrode active material 100. Furthermore, EDX ray analysis can analyze the distribution of the concentration of the additive element X.

[0159] When EDX-ray analysis is performed on the positive electrode active material 100, the peak of the magnesium concentration (the position where the concentration is maximum) in the surface layer portion 100a is preferably present at a depth of up to 3 nm from the surface toward the center of the positive electrode active material 100, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.

[0160] Furthermore, the fluorine distribution in the positive electrode active material 100 preferably overlaps with the magnesium distribution. Therefore, when EDX-ray analysis is performed, the peak of the fluorine concentration (the position where the concentration is maximum) in the surface layer portion 100 a is preferably present at a depth of up to 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.

[0161] It should be noted that not all of the additive elements X need have the same concentration distribution. For example, when the positive electrode active material 100 contains aluminum as the additive element X, it is preferable that the distribution is slightly different from that of magnesium and fluorine. For example, when EDX-ray analysis is performed, it is preferable that the magnesium concentration peak (the position where the concentration is maximum) is closer to the surface than the aluminum concentration peak (the position where the concentration is maximum) in the surface layer portion 100a. For example, the aluminum concentration peak is preferably present at a depth of 0.5 nm to 20 nm from the surface toward the center of the positive electrode active material 100, and more preferably at a depth of 1 nm to 5 nm.

[0162] Furthermore, when the positive electrode active material 100 is subjected to linear or area analysis, the ratio (X / M1) of the additive element X to the transition metal M1 near the grain boundary is preferably 0.020 or more and 0.50 or less. It is even more preferably 0.025 or more and 0.30 or less. It is even more preferably 0.030 or more and 0.20 or less. For example, when the additive element X is magnesium and the transition metal M1 is cobalt, the ratio of the number of magnesium atoms to cobalt atoms (Mg / Co) is preferably 0.020 or more and 0.50 or less. It is even more preferably 0.025 or more and 0.30 or less. It is even more preferably 0.030 or more and 0.20 or less.

[0163] As described above, an excess of the additive element contained in the positive electrode active material 100 may adversely affect the insertion and extraction of lithium. Furthermore, when used in a secondary battery, this may result in an increase in resistance and a decrease in capacity. On the other hand, an insufficient amount of the additive element may not be distributed throughout the entire surface layer portion 100a, resulting in an insufficient effect of maintaining the crystalline structure. In this way, the additive element X is adjusted to an appropriate concentration in the positive electrode active material 100.

[0164] Therefore, for example, the positive electrode active material 100 may have a region where excess additive element X is unevenly distributed. The presence of such a region allows excess additive element X to be removed from other regions, and an appropriate concentration of additive element X can be achieved in the interior and most of the surface layer portion of the positive electrode active material 100. By achieving an appropriate concentration of additive element X in the interior and most of the surface layer portion of the positive electrode active material 100, an increase in resistance and a decrease in capacity when the positive electrode active material 100 is used as a secondary battery can be suppressed. The ability to suppress an increase in resistance of a secondary battery is an extremely desirable characteristic, particularly in high-rate charge / discharge.

[0165] Furthermore, in the positive electrode active material 100 having a region where the excess additive element X is unevenly distributed, it is permissible to mix a certain amount of excess additive element X in the manufacturing process, which is preferable because it widens the margin in production.

[0166] In this specification and the like, uneven distribution refers to the difference in concentration of a certain element between a certain region A and a certain region B. It may also be referred to as segregation, precipitation, non-uniformity, deviation, high concentration or low concentration, etc.

[0167] <Crystal structure> Lithium cobalt oxide (LiCoO ２ Materials having a layered rock salt type crystal structure, such as LiM1O2, have a high discharge capacity and are known to be excellent as positive electrode active materials for secondary batteries. ２ (M1 is one or more selected from Fe, Ni, Co, and Mn).

[0168] It is known that the strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal.

[0169] In compounds containing nickel, distortion may easily occur due to the Jahn-Teller effect. ２ When LiCoO is charged and discharged at a high voltage, there is a concern that the crystal structure may be destroyed due to distortion. ２ It is suggested that the influence of the Jahn-Teller effect is small in this case, and the durability of charge and discharge at high voltages may be superior, which is preferable.

[0170] The structure of the positive electrode active material will be described with reference to Fig. 9 to Fig. 14. Fig. 9 to Fig. 14 describe the case where cobalt is used as the transition metal contained in the positive electrode active material.

[0171] <Conventional Positive Electrode Active Material> The positive electrode active material shown in FIG. 11 is lithium cobalt oxide (LiCoO ２ , LCO). The crystal structure of the lithium cobalt oxide shown in FIG. 11 changes depending on the charge depth. In other words, LixCoO ２ In this case, the crystal structure changes depending on the occupancy rate x of lithium at the lithium site.

[0172] As shown in FIG. 11, lithium cobalt oxide in the state of x=1 (discharged state) has a region having a crystal structure of the space group R-3m, and CoO ２ There are three layers. Therefore, this crystal structure is sometimes called an O3 type crystal structure. ２ The layer refers to a structure in which octahedral structures in which cobalt is six-coordinated with oxygen atoms are continuous in the plane direction with edge sharing.

[0173] When x = 0, the crystal structure has a space group P-3m1, and CoO ２ There is one layer, and therefore this crystal structure is sometimes called an O1-type crystal structure.

[0174] When x is about 0.12, lithium cobalt oxide has a crystal structure of the space group R-3m. This structure is similar to CoO such as P-3m1(O1). ２ and LiCoO such as R-3m(O3). ２ It can also be said that the structure of and are stacked alternately. Therefore, this crystal structure is sometimes called an H1-3 crystal structure. Note that, since actual lithium insertion and extraction can be uneven, the H1-3 crystal structure is experimentally observed from about x = 0.25. Note that, in reality, the number of cobalt atoms per unit cell in the H1-3 crystal structure is twice that of other structures. However, in Figure 11 and other parts of this specification, to make it easier to compare with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0175] As an example of the H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell are Co(0, 0, 0.42150±0.00016), O １ (0, 0, 0.27671±0.00045), O ２ It can be expressed as (0, 0, 0.11535±0.00045). １ and O ２ are oxygen atoms. In this way, the H1-3 crystal structure is represented by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the O3' crystal structure of one embodiment of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' crystal structure and the H1-3 structure, and the O3' crystal structure exhibits a smaller change from the O3 structure than the H1-3 structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (good of fitness) value is smaller in Rietveld analysis of the XRD pattern.

[0176] When lithium cobalt oxide is repeatedly charged at a high voltage of 4.6 V or higher based on the redox potential of lithium metal, or when it is deeply charged to a depth of x of 0.24 or lower, and then discharged, the crystal structure of the lithium cobalt oxide repeatedly changes (i.e., undergoes a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0177] However, these two crystal structures are different from CoO ２ As shown by the dotted lines and arrows in FIG. 11, in the H1-3 type crystal structure, CoO ２ The layers deviate significantly from R-3m(O3). Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0178] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 type crystal structure and the O3 type crystal structure in a discharged state is 3.0% or more.

[0179] In addition, the H1-3 type crystal structure has CoO such as P-3m1(O1). ２ A structure with continuous layers is likely to be unstable.

[0180] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is thought to be because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0181] <Positive Electrode Active Material of One Embodiment of the Present Invention> <Interior> The positive electrode active material 100 of one embodiment of the present invention is a material that, when repeatedly charged and discharged at a high voltage, ２ The layer misalignment can be reduced. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material of one embodiment of the present invention can have a stable crystal structure in a charged state at a high voltage. Therefore, the positive electrode active material of one embodiment of the present invention may be less likely to cause a short circuit when maintained in a charged state at a high voltage. In such a case, safety is further improved, which is preferable.

[0182] In the positive electrode active material of one embodiment of the present invention, the change in crystal structure and the difference in volume per the same number of transition metal atoms between a fully discharged state and a high-voltage charged state are small.

[0183] The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown in Figure 9. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal, and oxygen. In addition to the above, it is preferable that the positive electrode active material 100 contains magnesium as the additive element X. It is also preferable that the additive element X contains a halogen such as fluorine or chlorine.

[0184] The crystal structure of x=1 (discharged state) in Fig. 9 is the same as that of Fig. 11, R-3m(O3). On the other hand, the positive electrode active material 100 according to one embodiment of the present invention has a crystal structure different from the H1-3 type crystal structure when fully charged. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium ions occupy the oxygen hexacoordination positions. In addition, CoO in this structure２ The symmetry of the layers is the same as that of the O3 type. Therefore, this structure is referred to as an O3' type crystal structure in this specification. In the diagram of the O3' type crystal structure shown in FIG. 9, lithium is omitted in order to explain the symmetry of the cobalt atom and the symmetry of the oxygen atom. However, in reality, CoO ２ Between the layers, for example, 20 atomic % or less of lithium is present relative to cobalt. In both the O3 type crystal structure and the O3' type crystal structure, CoO ２ It is preferable that magnesium is present in a dilute form between the layers, i.e., at the lithium sites, and it is also preferable that halogen such as fluorine is present randomly and dilutely at the oxygen sites.

[0185] In the O3' type crystal structure, a light element such as lithium may occupy the oxygen tetracoordination position.

[0186] The O3' type crystal structure has random lithium between layers, but CdCl ２ It can be said that this crystal structure is similar to that of the CdCl type. ２ A crystal structure similar to the type was observed when lithium nickel oxide was charged to a charge depth of 0.94 (Li ０．０６ NiO ２ ), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0187] In the positive electrode active material 100 of one embodiment of the present invention, when a large amount of lithium is released by charging at a high voltage, the change in the crystal structure is suppressed more than in conventional positive electrode active materials. For example, as shown by the dotted line in FIG. 9 , in these crystal structures, CoO ２ There is almost no layer misalignment.

[0188] More specifically, the cathode active material 100 of one embodiment of the present invention has high structural stability even at high charge voltages. For example, in conventional cathode active materials, there exists a charge voltage region where the R-3m(O3) crystal structure can be maintained even at a charge voltage where the H1-3 crystal structure is formed, for example, at a voltage of about 4.6 V relative to the potential of lithium metal. Furthermore, there exists a region where the O3' crystal structure can be formed even at a higher charge voltage, for example, at a voltage of about 4.65 V to 4.7 V relative to the potential of lithium metal. Furthermore, there exists a region where the H1-3 crystal structure can be formed even at a higher charge voltage, for example, at a voltage of about 4.65 V to 4.7 V relative to the potential of lithium metal. Furthermore, there exists a region where the H1-3 crystal can be formed even at a higher charge voltage, for example, at a voltage of 4.3 V or higher and 4.5 V or lower relative to the potential of lithium metal.

[0189] Therefore, in the positive electrode active material 100 of one embodiment of the present invention, the crystal structure is not easily broken even when charge and discharge are repeated at a high voltage.

[0190] In the positive electrode active material 100, the difference in volume per unit cell between the O3 type crystal structure where x=1 and the O3' type crystal structure where x=0.2 is 2.5% or less, more specifically 2.2% or less.

[0191] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed within the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25.

[0192] CoO ２ The additive element X, for example, magnesium, which is present randomly and dilutely between the layers, i.e., at the lithium site, is ２ This has the effect of suppressing layer misalignment. ２When magnesium is present between layers, the O3'-type crystal structure is likely to be formed. Therefore, magnesium is preferably distributed in at least a part of the surface layer portion of the positive electrode active material 100 of one embodiment of the present invention, and more preferably distributed throughout the entire surface layer portion of the positive electrode active material 100. In order to distribute magnesium throughout the entire surface layer portion of the positive electrode active material 100, heat treatment is preferably performed in the process of manufacturing the positive electrode active material 100 of one embodiment of the present invention.

[0193] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that the additive element X, such as magnesium, will enter the cobalt site. Magnesium present at the cobalt site is ineffective in maintaining the R-3m structure under high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0194] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment for distributing magnesium over the entire surface layer of the positive electrode active material 100. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium over the entire surface layer of the positive electrode active material 100 at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0195] Note that if the magnesium concentration is increased above a desired value, the effect on stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters the cobalt site in addition to the lithium site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the transition metal, such as cobalt, more preferably more than 0.01 to less than 0.04 times, and even more preferably about 0.02 times. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition in the process of producing the positive electrode active material 100.

[0196] Lithium cobalt oxide may contain one or more metals selected from nickel, aluminum, manganese, titanium, vanadium, and chromium as a metal other than cobalt (hereinafter, "additive element X"). Addition of one or more of nickel and aluminum is particularly preferred. Manganese, titanium, vanadium, and chromium may be stable due to their tetravalent nature, and may contribute significantly to structural stability. Addition of the additive element X may further stabilize the crystal structure in a charged state at a high voltage. In the positive electrode active material of one embodiment of the present invention, the additive element X is preferably added at a concentration that does not significantly change the crystallinity of the lithium cobalt oxide. For example, the amount is preferably such that the aforementioned Jahn-Teller effect or the like is not exhibited.

[0197] The transition metals, such as nickel and manganese, and aluminum are preferably present at the cobalt site, but may be partially present at the lithium site. Magnesium is preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0198] As the magnesium concentration in the positive electrode active material of one embodiment of the present invention increases, the capacity of the positive electrode active material may decrease. One possible cause of this is the incorporation of magnesium into the lithium site, which may reduce the amount of lithium contributing to charge and discharge. When the positive electrode active material of one embodiment of the present invention contains nickel in addition to magnesium as the additive element X, the charge and discharge cycle characteristics may be improved. Furthermore, when the positive electrode active material of one embodiment of the present invention contains aluminum in addition to magnesium as the additive element X, the charge and discharge cycle characteristics may be improved. Furthermore, when the positive electrode active material of one embodiment of the present invention contains magnesium, nickel, and aluminum as the additive element X, the charge and discharge cycle characteristics may be improved.

[0199] The element concentrations of a positive electrode active material according to one embodiment of the present invention, which contains magnesium, nickel, and aluminum as the additional element X, will be discussed below.

[0200] The number of nickel atoms in the positive electrode active material of 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% or more and 4% or less, and particularly preferably 0.1% or more and 2% or less. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire positive electrode active material using, for example, ICP-MS or the like, or may be based on a value obtained by mixing raw materials in the process of producing the positive electrode active material.

[0201] If the positive electrode active material is charged at a high voltage for a long period of time, the constituent elements of the positive electrode active material may leach into the electrolyte, causing the crystal structure to collapse. However, by containing nickel in the above proportions, it may be possible to suppress the leach-out of the constituent elements from the positive electrode active material 100.

[0202] The number of aluminum atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.05% to 4%, and more preferably 0.1% to 2%, of the number of cobalt atoms. The aluminum concentration shown here may be a value obtained by performing elemental analysis of the entire positive electrode active material using, for example, ICP-MS or the like, or may be based on a value obtained by mixing raw materials in the process of producing the positive electrode active material.

[0203] In addition, the positive electrode active material of one embodiment of the present invention including an additional element X preferably uses phosphorus as the additional element X. In addition, the positive electrode active material of one embodiment of the present invention more preferably includes a compound containing phosphorus and oxygen.

[0204] When the positive electrode active material of one embodiment of the present invention includes a compound containing phosphorus as the additional element X, a short circuit may be less likely to occur when a charged state at high temperature and high voltage is maintained for a long period of time.

[0205] When the positive electrode active material of one embodiment of the present invention contains phosphorus as the additional element X, hydrogen fluoride generated by decomposition of the electrolyte solution may react with phosphorus, resulting in a decrease in the hydrogen fluoride concentration in the electrolyte solution.

[0206] The electrolyte is LiPF as a lithium salt. ６In the case where the electrolyte contains PVDF, hydrogen fluoride may be generated by hydrolysis. Hydrogen fluoride may also be generated by the reaction of PVDF, which is used as a component of the positive electrode, with an alkali. By reducing the hydrogen fluoride concentration in the electrolyte, corrosion of the current collector and / or peeling of the coating may be suppressed. Furthermore, gelation and / or insolubilization of PVDF may be suppressed, which may result in a decrease in adhesion.

[0207] When the cathode active material 100 of one embodiment of the present invention contains phosphorus and magnesium as the additive element X, the stability in a high-voltage charged state is extremely high. When the additive element X contains phosphorus and magnesium, 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%, more preferably 0.5% to 5%, and even more preferably 0.7% to 4% of the number of cobalt atoms. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing elemental analysis of the entire cathode active material 100 using, for example, ICP-MS or the like, or may be based on values ​​of the composition of raw materials in the process of producing the cathode active material 100.

[0208] When the positive electrode active material 100 has cracks, the presence of phosphorus, more specifically, a compound containing phosphorus and oxygen, inside the cracks may inhibit the progression of the cracks.

[0209] As shown in Figure 9, the symmetry of oxygen atoms is slightly different between the O3 type crystal structure and the O3' type crystal structure. 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 aligned strictly. This is because in the O3' type crystal structure, as lithium decreases, tetravalent cobalt increases, causing Jahn-Teller distortion to increase, resulting in CoO ６ This is because the octahedral structure of CoO is distorted. ２ Another factor is the increased repulsion between oxygen atoms in the layers.

[0210] <Surface Layer 100a> Magnesium is preferably distributed throughout the entire surface layer of the positive electrode active material 100 of one embodiment of the present invention, and in addition, the magnesium concentration in the surface layer 100a is preferably higher than the overall average. For example, the magnesium concentration in the surface layer 100a measured by XPS or the like is preferably higher than the overall average magnesium concentration measured by ICP-MS or the like.

[0211] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention contains an element other than cobalt, for example, one or more metals selected from nickel, aluminum, manganese, iron, and chromium, the concentration of the metal near the particle surface is preferably higher than the overall average. For example, the concentration of the element other than cobalt in the surface layer 100 a measured by XPS or the like is preferably higher than the overall average concentration of the element measured by ICP-MS or the like.

[0212] The surface layer of the positive electrode active material 100 is, so to speak, entirely composed of crystal defects. Furthermore, lithium is released from the surface during charging, making this portion prone to a lower lithium concentration than the interior. This makes the surface unstable and prone to collapse of the crystal structure. A high magnesium concentration in the surface layer 100a can more effectively suppress changes in the crystal structure. Furthermore, a high magnesium concentration in the surface layer 100a can be expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0213] Furthermore, the concentration of halogen such as fluorine in the surface layer portion 100 a of the positive electrode active material 100 of one embodiment of the present invention is preferably higher than the overall average. The presence of halogen in the surface layer portion 100 a, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0214] As described above, the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention preferably has a different composition from the interior portion 100b, i.e., a higher concentration of additive elements, such as magnesium and fluorine, than the interior portion 100b. Furthermore, the composition preferably has a stable crystal structure at room temperature. Therefore, the surface layer portion 100a may have a different crystal structure from the interior portion 100b. For example, at least a portion of the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention may have a rock salt crystal structure. Furthermore, when the surface layer portion 100a and the interior portion 100b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 100a and the interior portion 100b are approximately the same.

[0215] Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in O3'-type crystals also have a cubic close-packed structure. In this specification, if the anions have a structure in which three layers are stacked with a skewed relationship, such as ABCABC, it is referred to as a cubic close-packed structure. Therefore, the anions do not necessarily have to be strictly cubic lattices. At the same time, because real crystals always have defects, the analysis results do not necessarily conform to theory. For example, in electron diffraction or FFT (fast Fourier transform) of TEM images, etc., spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical positions is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close-packed structure.

[0216] When layered rock salt crystals come into contact with each other, there are crystal faces where the cubic close-packed structures formed by anions are oriented in the same direction.

[0217] Alternatively, it can be explained as follows: Anions on the (111) plane of the cubic crystal structure have a triangular arrangement. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic (111) has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt type. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0218] However, the space group of the layered rock salt type crystal and the O3' type crystal is R-3m, which is different from the space group of the rock salt type crystal, Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of a rock salt type crystal having the simplest symmetry), and therefore the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt type crystal and the O3' type crystal and the rock salt type crystal. In this specification, when the orientations of the cubic close-packed structures formed by anions are aligned in the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal, it may be said that the crystal orientations are approximately the same.

[0219] The fact that the crystal orientations of the two regions roughly coincide can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, electron diffraction, FFT of TEM images, etc. X-ray diffraction (XRD), neutron diffraction, etc. can also be used as materials for determination.

[0220] 13 shows an example of a TEM image in which the orientations of the layered rock salt crystals LRS and the rock salt crystals RS are roughly the same. Images reflecting the crystal structure can be obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.

[0221] For example, in a high-resolution TEM image, contrast originating from a crystal plane can be observed. When an electron beam is incident perpendicularly to the c-axis of a layered rock-salt type composite hexagonal lattice, for example, due to the diffraction and interference of the electron beam, contrast originating from the (0003) plane can be observed as a repetition of bright and dark lines. Therefore, a repetition of bright and dark lines can be observed in the TEM image, and the bright lines (for example, the L shown in FIG. 13) can be observed. ＲＳ and L ＬＲＳ When the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are roughly aligned, i.e., the crystal orientations are roughly aligned. Similarly, when the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are roughly aligned.

[0222] Furthermore, in HAADF-STEM images, contrast corresponding to the atomic number is obtained, with elements with higher atomic numbers being observed brighter. For example, in the case of layered rock-salt lithium cobaltate belonging to the space group R-3m, cobalt (atomic number 27) has the highest atomic number, so the electron beam is strongly scattered at the position of the cobalt atoms, and the arrangement of the cobalt atoms is observed as a bright line or an arrangement of highly bright dots. Therefore, when lithium cobaltate having a layered rock-salt crystal structure is observed perpendicular to the c-axis, the arrangement of the cobalt atoms perpendicular to the c-axis is observed as a bright line or an arrangement of highly bright dots, while the arrangements of lithium atoms and oxygen atoms are observed as dark lines or low-brightness regions. The same is true when lithium cobaltate contains fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.

[0223] Therefore, in an HAADF-STEM image, when repetitions of bright and dark lines are observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less or 2.5 degrees or less, it can be determined that the atomic arrangements are roughly consistent, i.e., the crystal orientations are roughly consistent. Similarly, when the angle between the dark lines is 5 degrees or less or 2.5 degrees or less, it can also be determined that the crystal orientations are roughly consistent.

[0224] In ABF-STEM, elements with smaller atomic numbers are observed brighter, but like HAADF-STEM, contrast according to the atomic number is obtained, so the crystal orientation can be determined in the same way as with HAADF-STEM images.

[0225] Figure 14A shows an example of an STEM image in which the orientations of the layered rock salt crystal LRS and the rock salt crystal RS are roughly the same. Figure 14B shows the FFT of the region of the rock salt crystal RS, and Figure 14C shows the FFT of the region of the layered rock salt crystal LRS. Literature values ​​are shown on the left of Figures 14B and 14C, and measured values ​​are shown on the right. The spot marked with O is the zeroth-order diffraction.

[0226] The spot marked A in Figure 14B is derived from the 11-1 reflection of the cubic crystal. The spot marked A in Figure 14C is derived from the 0003 reflection of the layered rock salt type. From Figures 14B and 14C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 14B is roughly parallel to the line passing through AO in Figure 14C. Here, "roughly coincident" and "roughly parallel" mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0227] In this way, in FFT and electron diffraction, when the orientations of the layered rock salt type crystal and the rock salt type crystal are roughly the same, the <0003> orientation of the layered rock salt type or a plane orientation equivalent thereto may roughly coincide with the <11-1> orientation of the rock salt type or a plane orientation equivalent thereto. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. A reciprocal lattice point being spot-like and not continuous with other reciprocal lattice points means high crystallinity.

[0228] Furthermore, as described above, when the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt crystal are approximately the same, depending on the incident orientation of the electron beam, spots not originating from the 0003 reflection of the layered rock salt crystal may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt crystal. For example, the spot marked B in FIG. 14C originates from the 1014 reflection of the layered rock salt crystal. This spot may be observed at an angle of 52° to 56° (i.e., ∠AOB is 52° to 56°) from the orientation of the reciprocal lattice point (A in FIG. 14C) originating from the 0003 reflection of the layered rock salt crystal, and at a position where d is 0.19 nm to 0.21 nm. Note that this index is merely an example and does not necessarily have to be identical. For example, reciprocal lattice points equivalent to 0003 and 1014 may also be used.

[0229] Similarly, spots not originating from cubic 11-1 may be observed in a reciprocal lattice space other than the orientation where cubic 11-1 is observed. For example, the spot marked B in FIG. 14B is originating from cubic 200 reflection. This is because a diffraction spot may be observed at an angle of 54° or more and 56° or less (i.e., ∠AOB is 54° or more and 56° or less) from the orientation of the reflection (A in FIG. 14B) originating from cubic 11-1. Note that this index is merely an example and does not necessarily have to match. For example, a reciprocal lattice point equivalent to 11-1 and 200 may also be used.

[0230] It is known that layered rock-salt type positive electrode active materials, including lithium cobalt oxide, tend to have the (0003) plane and its equivalents, as well as the (10-14) plane and its equivalents, as crystal planes. Therefore, by carefully observing the shape of the positive electrode active material using an SEM or the like, it is possible to thin-section the observation sample using an FIB or the like so that the electron beam is [12-10] incident in a TEM or the like, making the (0003) plane easier to observe. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock-salt type so that the (0003) plane can be easily observed.

[0231] However, if the surface layer 100a is composed of only MgO or only a solid solution of MgO and CoO(II), it becomes difficult to insert and extract lithium. Therefore, the surface layer 100a must contain at least cobalt, and in a discharged state, it must also contain lithium, providing a path for lithium insertion and extraction. It is also preferable that the concentration of cobalt is higher than that of magnesium.

[0232] The additional element X is preferably located in the surface layer portion 100a of the particle of the positive electrode active material 100 of one embodiment of the present invention. For example, the positive electrode active material 100 of one embodiment of the present invention may be covered with a coating containing the additional element X.

[0233] <Grain Boundary> The additional element X contained in the positive electrode active material 100 of one embodiment of the present invention may be present randomly and dilutely inside the positive electrode active material 100, but it is more preferable that a part of the additional element X segregates at the grain boundary.

[0234] In other words, the concentration of the additional element X in and near the grain boundaries of the positive electrode active material 100 of one embodiment of the present invention is preferably higher than that in other regions inside the grain boundaries.

[0235] The grain boundaries can be considered as planar defects. Therefore, like the particle surfaces, they are easily unstable and tend to initiate changes in the crystal structure. Therefore, if the concentration of the added element X at and near the grain boundaries is high, the change in the crystal structure can be more effectively suppressed.

[0236] Furthermore, when the concentration of the additive element X is high at and near the grain boundaries, even if cracks occur along the grain boundaries of particles of the positive electrode active material 100 of one embodiment of the present invention, the concentration of the additive element X becomes high near the surface formed by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after the cracks occur.

[0237] In this specification and the like, the vicinity of the grain boundary refers to the region up to about 10 nm from the grain boundary.

[0238] <Particle size> If the particle size of the positive electrode active material 100 of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium or excessive roughness of the surface of the active material layer when applied to a current collector occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector or excessive reaction with an electrolyte solution occur. Therefore, the average particle size (D50: also referred to as 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.

[0239] <Analysis Method> Whether or not a certain positive electrode active material is the positive electrode active material 100 of one embodiment of the present invention that exhibits an O3′-type crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred in that it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery as is.

[0240] As described above, the positive electrode active material 100 of one embodiment of the present invention is characterized by minimal change in crystal structure between a high-voltage charged state and a discharged state. Materials in which a crystal structure that exhibits a significant change between a high-voltage charged state and a discharged state accounts for 50 wt % or more are undesirable because they cannot withstand high-voltage charging and discharging. It should be noted that the desired crystal structure may not be achieved simply by adding an additive element. For example, even if both materials share the common feature of being lithium cobalt oxide containing magnesium and fluorine, there are cases in which the O3′-type crystal structure accounts for 60 wt % or more and cases in which the H1-3-type crystal structure accounts for 50 wt % or more when charged at a high voltage. Furthermore, at a predetermined voltage, the O3′-type crystal structure may be nearly 100 wt %, and further increasing the predetermined voltage may result in the H1-3-type crystal structure. Therefore, to determine whether a material is the positive electrode active material 100 of one embodiment of the present invention, analysis of the crystal structure, such as XRD, is required.

[0241] However, when a positive electrode active material is charged or discharged at a high voltage, its crystal structure may change when exposed to air. For example, it 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.

[0242] <Charging Method> High-voltage charging for determining whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention can be performed by preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using a lithium counter electrode, for example, and charging the coin cell.

[0243] More specifically, the positive electrode may be prepared by coating a positive electrode current collector made of aluminum foil with a slurry containing a positive electrode active material, a conductive agent, and a binder.

[0244] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery differs from the potential of the positive electrode. Unless otherwise specified, voltages and potentials in this specification refer to the potential of the positive electrode.

[0245] The electrolyte contained in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF ６ ) is used, and the electrolyte may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7 with 2 wt % vinylene carbonate (VC).

[0246] The separator can be made of polypropylene having a thickness of 25 μm.

[0247] The positive electrode can and the negative electrode can may be made of stainless steel (SUS).

[0248] The coin cell prepared under the above conditions is charged at a constant current of 4.6 V and 0.5 C, and then charged at a constant voltage until the current reaches 0.01 C. Here, 1 C is 137 mA / g. The temperature is 25°C. After charging in this manner, the coin cell is disassembled in an argon-atmosphere glove box and the positive electrode is removed to obtain a positive electrode active material charged at a high voltage. When various analyses are performed after this, it is preferable to seal the cell in an argon atmosphere to prevent reactions with external components. For example, XRD can be performed by sealing the cell in an airtight container in an argon atmosphere.

[0249] <XRD> Ideal powder XRD patterns calculated from the O3'-type crystal structure and H1-3-type crystal structure models using CuKα1 radiation are shown in Figures 10 and 12. For comparison, LiCoO ２ (O3) and CoO with x = 0 ２ The ideal XRD pattern calculated from the crystal structure of LiCoO (O1) is also shown. ２ (O3) and CoO ２ The pattern of (O1) was created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, step size = 0.01, and wavelength λ = 1.540562 × 10 −１０The crystal structure pattern of the O3'-type crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker Corporation), and an XRD pattern was created in the same manner as for the others.

[0250] As shown in Figure 10, 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 12, in the H1-3 type crystal structure and CoO ２ In the case of (P-3m1, O1), no peaks appear at these positions. Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0251] This can be said to mean that the positions at which XRD diffraction peaks appear are close between the crystal structure with x = 1 and the crystal structure in the high-voltage charging state. More specifically, the difference in the positions at which two or more, preferably three or more, of the main diffraction peaks of both structures appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less.

[0252] Note that the positive electrode active material 100 of one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage. However, the entire positive electrode active material 100 does not necessarily have an O3'-type crystal structure. It may contain other crystal structures, or may be partially amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50 wt % or more, more preferably 60 wt % or more, and even more preferably 66 wt % or more. When the O3'-type crystal structure is 50 wt % or more, more preferably 60 wt % or more, and even more preferably 66 wt % or more, the positive electrode active material can have sufficiently excellent cycle characteristics.

[0253] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0254] The crystallite size of the O3'-type crystal structure of the positive electrode active material particles is ２ Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3' type crystal structure can be confirmed in the high voltage charging state. ２ In this case, even if a part of the crystal structure resembles the O3'-type crystal structure, the crystallite size will be small and the peak will be broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0255] As described above, the positive electrode active material of one embodiment of the present invention preferably has a small influence of the Jahn-Teller effect. The positive electrode active material of one embodiment of the present invention preferably has a layered rock salt crystal structure and contains cobalt as a transition metal. Furthermore, the positive electrode active material of one embodiment of the present invention may contain the aforementioned additional element X in addition to cobalt, as long as the influence of the Jahn-Teller effect is small.

[0256] A preferable range of the lattice constant was considered, and it was found that in the positive electrode active material of one embodiment of the present invention, the layered rock-salt crystal structure of the particles of the positive electrode active material in a state where no charge / discharge is performed or in a discharged state, which can be estimated from the XRD pattern, has an a-axis lattice constant of 2.814 × 10 −１０ m is greater than 2.817 x 10 −１０ m and the lattice constant of the c-axis is 14.05 × 10 −１０ m or larger, 14.07 x 10 −１０ It has been found that the value is preferably smaller than m. The state in which no charge and discharge are performed may be, for example, the state of powder before the positive electrode of the secondary battery is produced.

[0257] Alternatively, in the layered rock-salt crystal structure of the particles of the positive electrode active material in a state where no charge or discharge is performed or in a 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 smaller than 0.20049.

[0258] Alternatively, when XRD analysis is performed on a layered rock salt type crystal structure possessed by particles of a positive electrode active material in a state where no charge / discharge is performed or in a discharged state, a first peak may be observed at 2θ of not less than 18.50° and not more than 19.30°, and a second peak may be observed at 2θ of not less than 38.00° and not more than 38.80°.

[0259] The peaks appearing in the powder XRD pattern reflect the crystalline structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100. The crystalline structure of the surface layer 100a and the like can be analyzed by electron diffraction or the like of a cross section of the positive electrode active material 100.

[0260] <XPS> X-ray photoelectron spectroscopy (XPS) can analyze a region from the surface to a depth of about 2 to 8 nm (usually about 5 nm), so the concentration of each element can be quantitatively analyzed for about half of the surface layer 100a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is often about ±1 atomic %, and the lower detection limit is about 1 atomic %, depending on the element.

[0261] When XPS analysis is performed on the positive electrode active material 100 of one embodiment of the present invention, the number of atoms of the additive element X is preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of atoms of the transition metal. When the additive element X is magnesium and the transition metal M1 is cobalt, the number of atoms of magnesium is preferably 1.6 to 6.0 times, and more preferably 1.8 to less than 4.0 times, the number of atoms of cobalt. Furthermore, the number of atoms of halogen such as fluorine is preferably 0.2 to 6.0 times, and more preferably 1.2 to 4.0 times, the number of atoms of the transition metal.

[0262] When XPS analysis is performed, for example, monochromated aluminum can be used as the X-ray source, and the take-off angle can be set to, for example, 45°.

[0263] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between fluorine and another element is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably about 684.3 eV. This value is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV). In other words, when the positive electrode active material 100 of one embodiment of the present invention contains fluorine, the bond is preferably other than that of lithium fluoride or magnesium fluoride.

[0264] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between magnesium and another element is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 of one embodiment of the present invention contains magnesium, the bond is preferably other than that of magnesium fluoride.

[0265] The concentration of the additive element X, such as magnesium and aluminum, which is preferably present in large amounts in the surface layer portion 100a, measured by XPS or the like is preferably higher than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0266] When a cross section of magnesium and aluminum is exposed by processing and analyzed using TEM-EDX, the concentration of the surface layer 100 a is preferably higher than the concentration of the inner portion 100 b. The processing can be performed using, for example, FIB.

[0267] In an XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms, while in an ICP-MS analysis, the ratio of the number of magnesium atoms, Mg / Co, is preferably 0.001 to 0.06.

[0268] On the other hand, it is preferable that nickel contained in the transition metal is not unevenly distributed in the surface layer portion 100a but is distributed throughout the positive electrode active material 100. However, this does not apply when there is a region where the excess additional element X described above is unevenly distributed.

[0269] <Surface Roughness and Specific Surface Area> The cathode active material 100 of one embodiment of the present invention preferably has a smooth surface with little unevenness. A smooth surface with little unevenness is one factor indicating that the distribution of the additive element X in the surface layer portion 100a is good. Note that, in the process of producing the cathode active material 100, if the lithium cobalt oxide or the lithium nickel-cobalt-manganese oxide before the addition of the additive element X is initially heated, the cathode active material 100 is particularly preferred because it has significantly excellent high-voltage charge / discharge cycle characteristics.

[0270] Furthermore, since the surface of the positive electrode active material 100 is smooth and has few irregularities, the stability of the surface of the positive electrode active material 100 is improved, and it is possible to suppress the occurrence of pits.

[0271] Whether the surface is smooth and has few irregularities can be determined from, for example, a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of ​​the positive electrode active material 100, or the like.

[0272] For example, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows.

[0273] First, the cathode active material 100 is processed using an FIB or the like to expose a cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, Gaussian blurring (σ = 2) is performed, followed by binarization. Interface extraction is then performed using image processing software. The interface line between the protective film or the like and the cathode active material 100 is selected using a magic hand tool or the like, and the data is extracted into a spreadsheet or the like. Using the functions of the spreadsheet or the like, correction is performed from the regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after slope correction, and the root mean square (RMS) surface roughness is calculated from the standard deviation. This surface roughness is the surface roughness at least within 400 nm of the outer periphery of the particle of the cathode active material.

[0274] On the particle surfaces of the positive electrode active material 100 of the present embodiment, the root mean square (RMS) surface roughness, which is an index of roughness, is preferably 10 nm or less, less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0275] The image processing software used for noise processing, boundary extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. The spreadsheet software is also not particularly limited, but for example, Microsoft Office Excel can be used.

[0276] For example, the actual specific surface area A measured by a gas adsorption method using a constant volume method Ｒ and the ideal specific surface area A ｉ The smoothness of the surface of the positive electrode active material 100 can also be quantified from the ratio of

[0277] Ideal specific surface area A ｉ is calculated assuming that all particles have the same diameter as D50, the same weight, and an ideal spherical shape.

[0278] The median diameter D50 can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. The specific surface area can be measured by a specific surface area measuring device using a gas adsorption method based on a constant volume method, for example.

[0279] The positive electrode active material 100 according to one embodiment of the present invention has an ideal specific surface area A calculated from the median diameter D50. ｉ and the actual specific surface area A Ｒ Ratio A Ｒ / A ｉ is preferably 2 or less.

[0280] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0281] Embodiment 3 In this embodiment, a method for manufacturing a positive electrode active material 100, which is one embodiment of the present invention, will be described.

[0282] <<Method 1 for Producing Positive Electrode Active Material>> <Step S11> In step S11 shown in FIG. 15A, a lithium source (Li source) and a transition metal source (M1 source) are prepared as starting materials for lithium and transition metal, respectively.

[0283] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and it is preferable to use a material with a purity of, for example, 99.99% or higher.

[0284] The transition metal M1 can be selected from elements in Groups 4 to 13 of the periodic table, and for example, at least one of manganese, cobalt, and nickel is used. The transition metal may be only cobalt, only nickel, two elements (cobalt and manganese), two elements (cobalt and nickel), or three elements (cobalt, manganese, and nickel). When only cobalt is used, the resulting positive electrode active material has lithium cobalt oxide (LCO), and when three elements (cobalt, manganese, and nickel) are used, the resulting positive electrode active material has lithium nickel-cobalt-manganese oxide (NCM).

[0285] As the transition metal M1 source, it is preferable to use a compound containing the above transition metal, and for example, an oxide or hydroxide of the metal exemplified above as the transition metal 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.

[0286] The transition metal M1 source preferably has a high purity. For example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher may 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.

[0287] In addition, the transition metal M1 source preferably has high crystallinity, for example, single crystal grains. The crystallinity of the transition metal source can be evaluated using TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. Note that the above-mentioned methods for evaluating crystallinity can be applied not only to transition metal sources but also to evaluating the crystallinity of other sources.

[0288] When two or more transition metal sources are used, the two or more transition metal M1 sources are preferably prepared in a ratio (mixing ratio) that allows the two or more transition metal M1 sources to form a layered rock salt type crystal structure.

[0289] <Step S12> Next, in step S12 shown in FIG. 15A, the lithium source and the transition metal M1 source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed by either a dry or wet method. The wet method is preferred because it allows for smaller particles to be crushed. When using the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal source in dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then pulverize and mix the mixture. Using dehydrated acetone with the above purity can reduce potential impurities.

[0290] A ball mill, a bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, it is preferable to use alumina balls or zirconia balls as grinding media. Zirconia balls are preferable because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0291] <Step S13> Next, in step S13 shown in FIG. 15A , the mixed material is heated. Heating is preferably performed at a temperature of 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably at approximately 950°C. If the temperature is too low, the decomposition and melting of the lithium source and transition metal source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium evaporation from the lithium source and / or excessive reduction of the metal used as the transition metal source. For example, when cobalt is used as the transition metal, excessive reduction can cause cobalt to change from trivalent to divalent, which can induce oxygen defects.

[0292] The heating time is preferably from 1 hour to 100 hours, more preferably from 2 hours to 20 hours.

[0293] The temperature rise rate depends on the heating temperature reached, but is preferably 80° C. / h to 250° C. / h. For example, when heating at 1000° C. for 10 hours, the temperature rise rate should be 200° C. / h.

[0294] Heating is preferably carried out in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of -50°C or less, more preferably an atmosphere with a dew point of -80°C or less. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In addition, in order to suppress impurities that may be mixed into the material, the CH ４ , CO, CO ２ , and H ２ The impurity concentrations of the above should be 5 ppb (parts per billion) or less.

[0295] An oxygen-containing atmosphere is preferred as the heating atmosphere. For example, dry air can be continuously introduced into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and allowing oxygen to flow through the reaction chamber is called flow.

[0296] When the heating atmosphere is an atmosphere containing oxygen, a method of not allowing oxygen to flow may be used. For example, a method of reducing the pressure of the reaction chamber and then filling it with oxygen to prevent the oxygen from entering or leaving the reaction chamber may be used, which is called purging. For example, the reaction chamber may be reduced in pressure to -970 hPa and then filled with oxygen to 50 hPa.

[0297] After heating, the material may be cooled naturally, but it is preferable that the time required for the temperature to drop from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not necessarily required, as long as the material is cooled to a temperature acceptable for the next step.

[0298] The heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be carried out while stirring, whether in a continuous or batch system.

[0299] The crucible used for heating is preferably an alumina crucible. Alumina crucibles are made of a material that does not easily release impurities. In this embodiment, an alumina crucible with a purity of 99.9% is used. It is preferable to heat the crucible with a lid on, as this can prevent the material from volatilizing.

[0300] After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. 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 more, preferably 99% or more, is used. Heating conditions equivalent to those of step S13 can also be applied to heating steps other than step S13, which will be described later.

[0301] <Step S14> By the above steps, a composite oxide containing a transition metal (LiMO) is obtained in step S14 shown in FIG. 15A. ２ The composite oxide can be obtained as follows: ２The composition is not strictly limited to Li:M1:O=1:1:2, as long as it has a crystalline structure of a lithium composite oxide represented by the formula: ２ The composition is not strictly limited to Li:Co:O=1:1:2.

[0302] Although the example of producing the composite oxide by the solid phase method in steps S11 to S14 has been shown, the composite oxide may also be produced by a coprecipitation method or a hydrothermal method.

[0303] <Step S15> Next, in step S15 shown in FIG. 15A, 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. After initial heating, the surface of the composite oxide becomes smooth. A smooth surface refers to a state in which there are few irregularities, the composite oxide is rounded overall, and the corners are also rounded. Furthermore, a state in which there is little foreign matter adhering to the surface is called smooth. Foreign matter is thought to be a cause of irregularities, so it is preferable that it does not adhere to the surface.

[0304] The initial heating is performed after the composite oxide is completed, and the inventors have found that initial heating for the purpose of smoothing the surface can reduce deterioration after charge and discharge. The initial heating for smoothing the surface does not require the preparation of a lithium compound source.

[0305] Alternatively, the initial heating to smooth the surface does not require the provision of a source of the additive element.

[0306] Alternatively, initial heating to smooth the surface does not require the use of a fluxing agent.

[0307] The initial heating is performed before step S20 described below, and may be called preheating or pretreatment.

[0308] The lithium source and the transition metal source prepared in step S11 etc. may contain impurities. The initial heating can reduce the amount of impurities in the composite oxide completed in step S14.

[0309] The heating conditions for this step may be any conditions that result in a smooth surface of the composite oxide. For example, the heating conditions may be selected from those described in step S13. Regarding the heating conditions, the heating temperature for this step should be lower than the temperature for step S13 in order to maintain the crystalline structure of the composite oxide. Furthermore, the heating time for this step should be shorter than the time for step S13 in order to maintain the crystalline structure of the composite oxide. For example, heating at a temperature of 700°C or higher and 1000°C or lower for 2 hours or longer is recommended.

[0310] The heating in step S13 may cause a temperature difference between the surface and the interior of the composite oxide. The temperature difference may induce a contraction difference. It is also thought that the temperature difference causes a difference in fluidity between the surface and the interior, resulting in a contraction difference. The energy associated with the contraction difference causes a difference in internal stress in the composite oxide. The internal stress difference is also called strain, and this energy is sometimes called strain energy. The internal stress is removed by the initial heating in step S15; in other words, the strain energy is thought to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in the composite oxide is alleviated. Therefore, the surface of the composite oxide may become smoother after step S15. This is also called an improved surface. In other words, it is thought that the contraction difference that occurred in the composite oxide is alleviated after step S15, resulting in a smoother surface of the composite oxide.

[0311] Furthermore, the difference in shrinkage may cause microscopic deviations in the composite oxide, such as deviations in crystals. This step is preferably carried out in order to reduce such deviations. This step makes it possible to equalize the deviations in the composite oxide. When the deviations are equalized, the surface of the composite oxide may become smooth. This is also referred to as the alignment of crystal grains. In other words, it is believed that step S15 reduces the deviations of crystals and the like that have occurred in the composite oxide, resulting in a smooth surface of the composite oxide.

[0312] When a composite oxide with a smooth surface is used as a positive electrode active material, deterioration during charge and discharge in a secondary battery is reduced, and cracking of the positive electrode active material can be prevented.

[0313] The smooth surface of a composite oxide can be said to have a surface roughness of 10 nm or less when surface irregularity information is quantified from measurement data at a cross section of the composite oxide. The cross section is obtained, for example, when observed with a scanning transmission electron microscope (STEM).

[0314] Alternatively, a composite oxide containing lithium, a transition metal, and oxygen that has been synthesized in advance may be used in step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on a composite oxide that has been synthesized in advance, a composite oxide with a smooth surface can be obtained.

[0315] It is possible that the amount of lithium in the composite oxide is reduced by the initial heating, and the added element, which will be explained in the next step S20, etc., may be more likely to be incorporated into the composite oxide due to the reduced amount of lithium.

[0316] <Step S20> An additional element X may be added to a composite oxide having a smooth surface, as long as it can form a layered rock salt crystal structure. Adding the additional element X to a composite oxide having a smooth surface allows the additional element to be added evenly. Therefore, it is preferable to add the additional element after initial heating. The step of adding the additional element will be described with reference to FIGS. 15B and 15C.

[0317] 15B, a source of an additive element to be added to the composite oxide is prepared. A lithium source may be prepared together with the additive element source.

[0318] The additive element may be 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. The additive element may be one or more selected from bromine and beryllium. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive elements described above.

[0319] When magnesium is selected as the additive element, the source of the additive element can be called a magnesium source. As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used. Furthermore, a plurality of the above-mentioned magnesium sources may be used.

[0320] When fluorine is selected as the additive element, the source of the additive element can be called a fluorine source. Examples of the fluorine source include lithium fluoride (LiF) and magnesium fluoride (MgF ２ ), aluminum fluoride (AlF ３ ), titanium fluoride (TiF ４ ), cobalt fluoride (CoF ２ , CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF ２ ), cerium fluoride (CeF ２ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６ Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0321] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as a lithium source. Another lithium source that can be used in step S21 is lithium carbonate.

[0322] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O３ F ２ , O ４ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0323] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF) is prepared as the fluorine source and magnesium source. ２ Lithium fluoride and magnesium fluoride are prepared as LiF:MgF ２ The effect of lowering the melting point is greatest when the molar ratio is about 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is set to LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x: 1 (x = near 0.33) is more preferable. In this specification, "near" refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.

[0324] 15B, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0325] If necessary, a heating step may be performed after step S22. The heating step can be performed under heating conditions selected from those described in step S13. The heating time is preferably 2 hours or more, and the heating temperature is preferably 800°C or higher and 1100°C or lower.

[0326] 15B, the pulverized and mixed materials are collected to obtain an additive element source (X source). The additive element source shown in step S23 includes a plurality of starting materials and can be called a mixture.

[0327] The particle size of the mixture is preferably D50 (median diameter) of 10 nm to 20 μm, more preferably 100 nm to 5 μm. Even when a single material is used as the additive element source, the D50 (median diameter) is preferably 10 nm to 20 μm, more preferably 100 nm to 5 μm.

[0328] Such a finely powdered mixture (including the case where only one type of additive element is added) makes it easier to uniformly adhere the mixture to the surface of the composite oxide particles when mixed with the composite oxide in a later step. Uniform adhesion of the mixture to the surface of the composite oxide is preferable because it makes it easier to uniformly distribute or diffuse fluorine and magnesium in the surface layer portion of the composite oxide after heating. The region where fluorine and magnesium are distributed can also be referred to as the surface layer portion. If there is a region in the surface layer that does not contain fluorine and magnesium, it may be difficult to obtain the O3'-type crystal structure described below in the charged state. Although fluorine has been used in the explanation, fluorine may also be chlorine, and chlorine can be read as including these and therefore halogen.

[0329] <Step S21> A step different from that shown in Fig. 15B will be described with reference to Fig. 15C. In step S21 shown in Fig. 15C, four types of additive element sources to be added to the composite oxide are prepared. That is, the types of additive element sources in Fig. 15C are different from those in Fig. 15B. A lithium source may be prepared together with the additive element sources.

[0330] As sources of four additive elements, a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared. The magnesium source and the fluorine source can be selected from the compounds described in FIG. 15B . Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0331] <Step S22> and <Step S23> Next, step S22 and step S23 shown in FIG. 15C are the same as the steps described in FIG. 15B.

[0332] 15A , the composite oxide and an additive element source (X source) are mixed. The ratio of the number of atoms of the transition metal M1 (M1) in the composite oxide containing lithium, a transition metal, and oxygen to the number of atoms of magnesium (Mg) in the additive element X source is preferably M1:Mg=100:y (0.1≦y≦6), and more preferably M1:Mg=100:y (0.3≦y≦3).

[0333] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the composite oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than those in step S12. It can also be said that dry mixing provides milder conditions than wet mixing. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media.

[0334] In this embodiment, dry mixing is performed in a ball mill using zirconia balls with a diameter of 1 mm at 150 rpm for 1 hour in a dry room with a dew point of −100° C. or higher and −10° C. or lower.

[0335] <Step S32> Next, in step S32 of Fig. 15A, the mixed materials are collected to obtain a mixture 903. When collecting the materials, they may be crushed and then sieved, if necessary.

[0336] In this embodiment, a method is described in which lithium fluoride as a fluorine source and magnesium fluoride as a magnesium source are added to the composite oxide after the initial heating. However, the present invention is not limited to the above method. In step S11, that is, in the stage of the starting materials for the composite oxide, a magnesium source, a fluorine source, etc. can be added to the lithium source and the transition metal source. Then, in step S13, heating is performed to obtain LiMO to which magnesium and fluorine have been added. ２ In this case, it is not necessary to separate the steps S11 to S14 from the steps S21 to S23. This method is simple and has high productivity.

[0337] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used. If lithium cobalt oxide to which magnesium and fluorine have been added is used, steps S11 to S32 and step S20 can be omitted. This method can be said to be simple and highly productive.

[0338] Alternatively, a magnesium source and a fluorine source, or a magnesium source, a fluorine source, a nickel source and an aluminum source may be further added to lithium cobalt oxide to which magnesium and fluorine have been added in advance in step S20.

[0339] 15A, the mixture 903 is heated. The heating conditions can be selected from those described in step S13. The heating time is preferably 2 hours or more.

[0340] Here, a supplementary note about the heating temperature will be given. The lower limit of the heating temperature in step S33 is ２ The temperature at which the reaction between LiMO and the additive element source proceeds must be equal to or higher than the temperature at which the reaction between LiMO and the additive element source proceeds. ２ The temperature may be lower than the melting point of these materials as long as it is a temperature at which mutual diffusion of elements contained in the oxide and the additive element source occurs. ｍ 0.757 times (Tammann temperature T ｄ ) solid-phase diffusion occurs. Therefore, the heating temperature in step S33 should be 500° C. or higher.

[0341] Of course, the reaction proceeds more easily when the temperature is equal to or higher than the temperature at which at least a part of the mixture 903 melts. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0342] Also, LiCoO ２ :LiF:MgF ２A mixture 903 obtained by mixing the components so that the molar ratio was 100:0.33:1 exhibits an endothermic peak at around 830° C. in differential scanning calorimetry (DSC). Therefore, the lower limit of the heating temperature is more preferably 830° C. or higher.

[0343] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0344] The upper limit of the heating temperature is LiMO ２ Decomposition temperature of LiCoO ２ The decomposition temperature of LiM1O is less than 1130°C. At temperatures close to the decomposition temperature, a small amount of LiM1O ２ Therefore, the temperature is more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0345] Taking these factors into consideration, 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. Also, it is preferably 742°C to 1130°C, 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, it is preferably 800°C to 1100°C, or 830°C to 1130°C, 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 is preferably higher than that in step S13.

[0346] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0347] In the manufacturing method described in this embodiment, some materials, for example, LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature to be controlled by the composite oxide (LiMO). ２) can be heated to a temperature lower than the decomposition temperature, for example, 742°C to 950°C, and additive elements such as magnesium can be distributed in the surface layer, thereby producing a positive electrode active material with good characteristics.

[0348] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF will volatilize when heated, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, etc., LiM1O ２ There is a possibility that Li on the surface reacts with F in the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0349] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization of LiF in the mixture 903.

[0350] The heating in this step is preferably performed so as not to cause adhesion of particles of the mixture 903. If the particles of the mixture 903 adhere to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the additive elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the additive elements (e.g., magnesium and fluorine) in the surface layer portion.

[0351] Furthermore, it is believed that uniform distribution of the additive element (e.g., fluorine) in the surface layer portion results in a smooth cathode active material with minimal irregularities. Therefore, in order to maintain or further smooth the surface after the heating in step S15 in this process, it is preferable that the particles do not adhere to each other.

[0352] Furthermore, when heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and then not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen may cause the fluorine source to evaporate, which is undesirable in terms of maintaining surface smoothness.

[0353] When heating is performed using a roller hearth kiln, the mixture 903 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 903 .

[0354] The heating time is determined by the heating temperature, the amount of LiM1O in step S14, ２ The temperature and time required for the reaction may vary depending on the particle size, composition, etc. Small particles may be more suitable at lower temperatures or for shorter times than large particles.

[0355] The composite oxide (LiMO) in step S14 of FIG. ２ When the median diameter (D50) of the powder is about 12 μm, the heating temperature is preferably, for example, 600° C. or higher and 950° C. or lower. The heating time is, for example, preferably 3 hours or higher, more preferably 10 hours or higher, and even more preferably 60 hours or higher. The cooling time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0356] On the other hand, the composite oxide (LiMO) of step S14 ２ When the median diameter (D50) of the powder is about 5 μm, the heating temperature is preferably, for example, 600° C. or higher and 950° C. or lower. The heating time is preferably, for example, 1 hour or higher and 10 hours or lower, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0357] <Step S34> Next, in step S34 shown in Fig. 15A, the heated material is recovered and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. Through the above steps, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

[0358] <<Method 2 for Producing Positive Electrode Active Material>> Next, a method for carrying out the present invention, which is different from Method 1 for Producing Positive Electrode Active Material, will be described.

[0359] In FIG. 16, steps S11 to S15 are performed in the same manner as in FIG. 15A to obtain a composite oxide (LiMO) with a smooth surface. ２ ) to prepare.

[0360] <Step S20a> As described above, the additive element X may be added to the composite oxide to the extent that a layered rock salt type crystal structure can be formed. In this production method 2, however, a step of adding the additive element in two or more batches will be described with reference to FIG. 17A as well.

[0361] <Step S21> In step S21 shown in Fig. 17A, a first additive element source is prepared. The first additive element source can be selected from the additive elements X described in step S21 shown in Fig. 15B and used. For example, one or more selected from magnesium, fluorine, and calcium can be suitably used as the additive element X1. Fig. 17A illustrates an example in which a magnesium source (Mg source) and a fluorine source (F source) are used as the additive element X1.

[0362] Steps S21 to S23 shown in Fig. 17A can be performed under the same conditions as steps S21 to S23 shown in Fig. 15B. As a result, an additional element source (X1 source) can be obtained in step S23.

[0363] Furthermore, steps S31 to S33 shown in FIG. 16 can be performed in the same manner as steps S31 to S33 shown in FIG. 15A.

[0364] <Step S34a> Next, the material heated in step S33 is recovered to produce a composite oxide containing the additional element X1. This is also called a second composite oxide to distinguish it from the composite oxide of step S14.

[0365] <Step S40> In step S40 shown in Fig. 16, a source of a second additive element is added. This will be described with reference to Figs. 17B and 17C.

[0366] <Step S41> In step S41 shown in Fig. 17B, a second additive element source is prepared. The second additive element source can be selected from the additive elements X described in step S21 shown in Fig. 15B and used. For example, the additive element X2 can be one or more selected from nickel, titanium, boron, zirconium, and aluminum. Fig. 17B illustrates an example in which nickel and aluminum are used as the additive element X2.

[0367] Steps S41 to S43 shown in Fig. 17B can be performed under the same conditions as steps S21 to S23 shown in Fig. 15B. As a result, an additional element source (X2 source) can be obtained in step S43.

[0368] 17C shows a modified example of the steps described with reference to FIG. 17B. In step S41 shown in FIG. 17C, a nickel source (Ni source) and an aluminum source (Al source) are prepared, and in step S42a, they are independently pulverized. As a result, in step S43, a plurality of second additive element sources (X2 sources) are prepared. The steps in FIG. 17C differ from those in FIG. 17B in that the additive elements are independently pulverized in step S42a.

[0369] <Steps S51 to S54> Next, steps S51 to S53 shown in Fig. 16 can be performed under the same conditions as steps S31 to S33 shown in Fig. 15A. The conditions for step S53, which is a heating step, may be a lower temperature and a shorter time than those for step S33. Through the above steps, in step S54, the positive electrode active material 100 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

[0370] 16 and 17 , in the preparation method 2, the additive element to the composite oxide is introduced separately as a first additive element X1 and a second additive element X2. By introducing the additive elements separately, the profile of each additive element in the depth direction can be changed. For example, it is possible to profile the first additive element so that its concentration is higher in the surface layer portion than in the interior, and profile the second additive element so that its concentration is higher in the interior than in the surface layer portion.

[0371] After the initial heating described in this embodiment, a positive electrode active material with a smooth surface can be obtained.

[0372] The initial heating shown in this embodiment is performed on the composite oxide. Therefore, the initial heating is preferably performed under conditions that are lower than the heating temperature for obtaining the composite oxide and shorter than the heating time for obtaining the composite oxide. When an additional element is added to the composite oxide, it is preferable to perform the addition step after the initial heating. The addition step can be divided into two or more steps. Following this step order is preferable because the surface smoothness obtained by the initial heating is maintained. When the composite oxide contains cobalt as a transition metal, it can be interpreted as a composite oxide containing cobalt.

[0373] This embodiment can be used in combination with other embodiments.

[0374] Embodiment Mode 4 In this embodiment mode, examples of various shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0375] [Coin-Type Secondary Battery] An example of a coin-type secondary battery will be described. Fig. 18A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 18B is an external view, and Fig. 18C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices. In this specification, coin-type batteries include button-type batteries.

[0376] 18A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 18A and 18B are not completely identical corresponding views.

[0377] In Fig. 18A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed by a negative electrode can 302 and a positive electrode can 301. Note that a gasket for sealing is not shown in Fig. 18A. The spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0378] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0379] To prevent short-circuiting between the positive electrode and the negative electrode, a separator 310 and a ring-shaped insulator 313 are arranged so as to cover the side and top surfaces of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0380] FIG. 18B is a perspective view of the completed coin-type secondary battery.

[0381] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. 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 the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be formed of lithium metal foil or a lithium-aluminum alloy foil.

[0382] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0383] The positive electrode can 301 and the negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals, or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, etc. 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.

[0384] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 18C , the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, thereby producing a coin-shaped secondary battery 300.

[0385] The above-described configuration allows the coin-type secondary battery 300 to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that, when a secondary battery having a solid electrolyte layer between the negative electrode 307 and the positive electrode 304 is used, the separator 310 may be unnecessary.

[0386] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be described with reference to Fig. 19A. As shown in Fig. 19A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0387] 19B is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 19B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0388] A battery element is provided inside a hollow cylindrical battery can 602, which includes a strip-shaped positive electrode 604 and a negative electrode 606 wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal, such as nickel, aluminum, or titanium, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel, aluminum, or the like to prevent corrosion by the electrolyte. Inside the battery can 602, the wound battery element, which includes the positive electrode, negative electrode, and separator, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, which contains the battery element. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0389] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector. While the secondary battery 616 shown in Figures 19A to 19D has a cylinder whose height is greater than its diameter, this is not limiting. A secondary battery whose diameter is greater than its height may also be used. This configuration, for example, can reduce the size of the secondary battery.

[0390] By using the positive electrode active material composite 100z obtained in the above embodiment for the positive electrode 604, a cylindrical secondary battery 616 can be obtained that has a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0391] 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 a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO ３ )-based semiconductor ceramics, etc. can be used.

[0392] 19C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via wiring 626. A protection circuit or the like that prevents overcharging or overdischarging can be used as the control circuit 620.

[0393] 19D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel or in series. By configuring the power storage system 615 to have a plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0394] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0395] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes it difficult for the performance of the power storage system 615 to be affected by the outside air temperature.

[0396] 19D , the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via a conductive plate 614.

[0397] [Another Structural Example of Secondary Battery] Structural examples of secondary batteries will be described with reference to FIGS. 20 and 21. FIG.

[0398] The secondary battery 913 shown in FIG. 20A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 20A , for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the 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.

[0399] 20B, the housing 930 shown in Fig. 20A may be formed of a plurality of materials. For example, the secondary battery 913 shown in Fig. 20B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0400] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0401] 20C shows the structure of the wound body 950. 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 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0402] 21A to 21C may be used as a secondary battery 913 having a wound body 950a. The wound body 950a shown in Fig. 21A includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

[0403] By using the positive electrode active material composite 100z obtained in the above embodiment for the positive electrode 932, a secondary battery 913 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0404] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0405] 21B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0406] 21C , wound body 950 a and the electrolyte are covered by casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of casing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0407] As shown in Fig. 21B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a allows the secondary battery 913 to have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 21A and 21B, the descriptions of the secondary battery 913 shown in Figs. 20A to 20C can be referred to.

[0408] 22A and 22B show examples of external views of a laminated secondary battery, which includes 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.

[0409] 23A shows an external view of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a 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 a tab region). The negative electrode 506 has a negative electrode current collector 504, and a 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., a tab region. The areas and shapes of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 23A .

[0410] <Method of Manufacturing Laminated Secondary Battery> Here, an example of a method of manufacturing the laminated secondary battery whose external view is shown in FIG. 22A will be described with reference to FIGS. 23B and 23C.

[0411] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 23B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0412] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0413] Next, as shown in Fig. 23C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0414] Next, the electrolyte solution is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0415] By using the cathode active material composite 100z obtained in the above-described embodiment for the cathode 503, the secondary battery 500 can be made to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0416] [Example of Battery Pack] An example of a secondary battery pack according to one embodiment of the present invention that can be wirelessly charged using an antenna will be described with reference to FIGS. 24A to 24C.

[0417] Fig. 24A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (also called a thick flat plate shape). Fig. 24B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is affixed to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0418] The interior of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0419] 24B , the secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to the terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one 551 of the positive electrode lead and the negative electrode lead of the secondary battery 513, and the other 552 of the positive electrode lead and the negative electrode lead of the secondary battery 513.

[0420] Alternatively, as shown in FIG. 24C, the device may have a circuit system 590 a provided on a circuit board 540 and a circuit system 590 b electrically connected to the circuit board 540 via a terminal 514 .

[0421] The antenna 517 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Furthermore, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may also 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 a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0422] The secondary battery pack 531 includes a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 513. The layer 519 can be formed using, for example, a magnetic material.

[0423] [Negative Electrode] As the negative electrode active material, for example, an alloy-based material, a carbon-based material, or a mixture thereof can be used.

[0424] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying / de-alloying with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. These 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, a compound containing these elements may be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0425] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0426] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0427] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is therefore preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0428] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋ This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety than metallic lithium.

[0429] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten oxide (WO ２ ), molybdenum oxide (MoO ２ ) and other oxides can be used.

[0430] In addition, as the negative electrode active material, a composite nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co０．４ N ３ has a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0431] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, can be used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the composite nitride of lithium and a transition metal can be used as the negative electrode active material, even when a material containing lithium ions is used as the positive electrode active material, by first removing the lithium ions contained in the positive electrode active material.

[0432] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ , CuO, Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0433] The conductive agent and binder that can be contained in the negative electrode active material layer can be the same materials as the conductive agent and binder that can be contained in the positive electrode active material layer.

[0434] In addition to the same materials as the positive electrode current collector, copper etc. can also be used as the current collector. It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0435] [Electrolyte Solution] An electrolyte solution having a solvent and an electrolyte dissolved in the solvent can be used as one form of the electrolyte 114. The solvent for the electrolyte solution is preferably an aprotic organic solvent, and for example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio.

[0436] 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 electricity storage device from exploding or catching fire even if the internal temperature of the electricity storage device rises due to an internal short circuit, overcharging, or the like. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0437] The electrolyte to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0438] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0439] The electrolyte solution may contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % relative to the solvent in which the electrolyte is dissolved.

[0440] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0441] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0442] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0443] [Separator] The separator may be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane.

[0444] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide-based material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Note that a glass-like material can also be used as the ceramic material, but unlike the coating material 101 used in the electrodes, it is preferable that the material has low electronic conductivity. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide-based materials include nylon and aramid (meta-aramid, para-aramid).

[0445] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0446] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0447] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0448] Fifth Embodiment In this embodiment, an example of fabricating an all-solid-state battery using the cathode active material composite 100z obtained in the above-described embodiment will be described.

[0449] As shown in FIG. 25A , a secondary battery 400 of one embodiment of the present invention includes a positive electrode 410 , a solid electrolyte layer 420 , and a negative electrode 430 .

[0450] Positive electrode 410 includes positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 includes positive electrode active material 411 and solid electrolyte 421. Positive electrode active material 411 is made of positive electrode active material composite 100z obtained in the above-described embodiment. Positive electrode active material layer 414 may also include a conductive agent and a binder.

[0451] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0452] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive agent and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form the material into particles, and therefore, as shown in FIG. 25B , the negative electrode 430 can be free of the solid electrolyte 421. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0453] The solid electrolyte 421 of the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0454] The sulfide-based solid electrolytes include thiolithium-based (Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ etc.), sulfide glass (70Li ２ S・30P ２ S ５ , 30Li ２ S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４SiO ４ , 50Li ２ S・50GeS ２ etc.), sulfide crystallized glass (Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0455] The oxide-based solid electrolyte includes a material having a perovskite crystal structure (La ２／３−ｘ Li ３ｘ TiO ３ etc.), materials having a NASICON type crystal structure (Li １−Ｙ Al Ｙ Ti ２−Ｙ (P.O. ４ ) ３ etc.), materials having a garnet-type crystal structure (Li ７ La ３ Zr ２ O １２ etc.), materials having a LISICON type crystal structure (Li １４ ZnGe ４ O １６ etc.), LLZO (Li ７ La ３ Zr ２ O １２ ), oxide glass (Li ３ P.O. ４ -Li ４ SiO ４ , 50Li ４ SiO ４ ・50Li ３ BO ３ etc.), oxide crystallized glass (Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0456] Halide-based solid electrolytes include LiAlCl ４ , Li ３ InBr ６ , LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as the solid electrolyte.

[0457] Also, different solid electrolytes may be mixed and used.

[0458] Among them, Li having a NASICON type crystal structure １＋ｘ Al ｘ Ti ２−ｘ (P.O. ４ ) ３ (0<x<1) (hereinafter, LATP) is preferable because it contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and therefore a synergistic effect can be expected in improving cycle characteristics. In addition, productivity can be expected to be improved by reducing the number of steps. Note that in this specification and the like, the NASICON-type crystal structure refers to a structure having a NASICON-type crystal structure, which is a structure having a NASICON-type crystal structure, and which is ... ２ (XO ４ ) ３ (M: transition metal, X: S, P, As, Mo, W, etc.), ６ Octahedron and XO ４ It refers to a structure in which tetrahedrons are arranged three-dimensionally with their vertices shared.

[0459] [Exterior Body and Shape of Secondary Battery] Various materials and shapes can be used for the exterior body of the secondary battery 400 of one embodiment of the present invention, but it is preferable that the exterior body has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0460] For example, FIG. 26 shows an example of a cell for evaluating materials for an all-solid-state battery.

[0461] 26A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw or wing nut 764 that fixes them together, and electrode plate 753 is pressed to fix the evaluation material by rotating a holding screw 763. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is also provided between upper member 762 and holding screw 763 to provide a tight seal.

[0462] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. Figure 26B is an enlarged perspective view of the evaluation material and its surroundings.

[0463] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 26C. Note that the same reference numerals are used for the same parts in Figs. 26A to 26C.

[0464] The electrode plate 751 and the lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and the upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0465] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0466] Fig. 27A is a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 26. The secondary battery in Fig. 27A has external electrodes 771 and 772 and is sealed in an exterior body having a plurality of package members.

[0467] 27B shows an example of a cross section taken along the dashed line in FIG. 27A. A stack including a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed within a package member 770a having a flat plate with an electrode layer 773a, a frame-shaped package member 770b, and a package member 770c having a flat plate with an electrode layer 773b. The package members 770a, 770b, and 770c can be made of insulating materials, such as resin materials and ceramics.

[0468] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0469] By using the positive electrode active material composite 100z obtained in the above-described embodiment, an all-solid-state secondary battery having high energy density and good output characteristics can be realized.

[0470] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0471] Embodiment 6 In this embodiment, an example in which a secondary battery different from the cylindrical secondary battery shown in FIG. 19D is applied to an electric vehicle (EV) will be described with reference to FIG. 28C.

[0472] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0473] The internal structure of the first battery 1301a may be a wound type shown in Fig. 20A or 21C or a stacked type shown in Fig. 22A or 22B. The first battery 1301a may use the all-solid-state battery of Embodiment 5. Use of the all-solid-state battery of Embodiment 5 for the first battery 1301a allows for a high capacity, improved safety, and reductions in size and weight.

[0474] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0475] In addition, in a secondary battery for vehicle use, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a in order to cut off power from multiple secondary batteries.

[0476] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering (power steering) 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0477] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0478] The first battery 1301a will be described with reference to FIG. 28A.

[0479] FIG. 28A shows an example in which nine prismatic secondary batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries using fixing portions 1413 and 1414 and a battery housing box. Furthermore, one electrode is electrically connected to a control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0480] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0481] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein 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, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In—Ga oxide or an In—Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface where the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region is also a region with a uniform lattice arrangement. Furthermore, a CAAC-OS has a region where multiple crystalline regions are connected in the a-b plane direction, and the region may have distortion. Note that distortion refers to a portion where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with another uniform lattice arrangement in a region where multiple crystalline regions are connected. In other words, a CAAC-OS is an oxide semiconductor with a c-axis aligned and no clear orientation in the a-b plane direction. CAC-OS is a material in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof. Note that hereinafter, a state in which one or more metal elements are unevenly distributed in a metal oxide and regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof, is also referred to as a mosaic or patch state.

[0482] Furthermore, the CAC-OS has a mosaic structure in which a material is separated into a first region and a second region, and the first region is distributed throughout the film (hereinafter also referred to as a cloud structure). That is, the CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0483] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In—Ga—Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In—Ga—Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0484] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be referred to as a region whose main component is In. The second region can be referred to as a region whose main component is Ga.

[0485] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0486] For example, in the case of CAC-OS in an In—Ga—Zn oxide, EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) can confirm that the CAC-OS has a structure in which a region containing In as a main component (first region) and a region containing Ga as a main component (second region) are unevenly distributed and mixed.

[0487] When a CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act complementarily, thereby providing the CAC-OS with a switching function (a function of turning on / off). That is, a CAC-OS has a conductive function in a part of the material and an insulating function in a part of the material, and functions as a semiconductor as a whole. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using a CAC-OS in a transistor, a high on-current (I ｏｎ ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0488] Oxide semiconductors have a variety of structures, each of which has different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0489] Furthermore, because the control circuit unit 1320 can be used in high-temperature environments, it is preferable to use transistors using oxide semiconductors. To simplify the process, the control circuit unit 1320 may be formed using unipolar transistors. Transistors using oxide semiconductors in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from −40° C. to 150° C., and their characteristics change less even when the secondary battery overheats than single-crystal Si transistors. The off-current of transistors using oxide semiconductors is below the lower limit of measurement even at 150° C., whereas the off-current characteristics of single-crystal Si transistors are highly temperature-dependent. For example, at 150° C., the off-current of single-crystal Si transistors increases, and the current on / off ratio is not sufficiently large. The control circuit unit 1320 can improve safety. Furthermore, combining the cathode active material composite 100z obtained in the above-described embodiment with a secondary battery using the cathode as the cathode can provide a synergistic effect in terms of safety.

[0490] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for the secondary battery to address causes of instability such as micro-short circuits. Functions for eliminating causes of secondary battery instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of deterioration, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits, and the control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for the secondary battery can be made ultra-miniaturized.

[0491] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0492] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0493] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0494] FIG. 28B shows an example of a block diagram of the battery pack 1415 shown in FIG. 28A.

[0495] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits of the secondary battery is within the recommended voltage range, and when the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0496] The switch unit 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon, and may be, 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 ｘThe switch portion 1324 may be formed using a power transistor having, for example, gallium oxide (x is a real number greater than 0). Furthermore, a memory element using an OS transistor can be freely arranged by stacking it on a circuit using a Si transistor, and therefore integration can be easily achieved. Furthermore, an OS transistor can be manufactured using the same manufacturing equipment as a Si transistor, and therefore can be manufactured at low cost. That is, a control circuit portion 1320 using an OS transistor can be stacked on the switch portion 1324 and integrated into a single chip. The volume occupied by the control circuit portion 1320 can be reduced, enabling miniaturization.

[0497] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of the 42V system (high voltage system), and the second battery 1311 supplies power to in-vehicle devices of the 14V system (low voltage system).

[0498] In this embodiment, an example in which lithium ion secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown. A lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, high capacity can be achieved, and miniaturization and weight reduction are possible.

[0499] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0500] 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 charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0501] Although not shown, when an external charger is connected, the charger's outlet or charger connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The charger's outlet or charger connection cable may also be provided with 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) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0502] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0503] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0504] The secondary battery of the present embodiment described above uses the positive electrode active material composite 100z obtained in the above-described embodiment. Furthermore, by using graphene as a conductive agent, a secondary battery with significantly improved electrical characteristics can be realized, as a synergistic effect of suppressing capacity reduction and maintaining high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and can provide a vehicle with a long driving range, specifically, a driving distance of 500 km or more per charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0505] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the cathode active material composite 100z described in the above embodiment, and can increase the usable capacity as the charging voltage increases. Furthermore, by using the cathode active material composite 100z described in the above embodiment for the cathode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0506] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0507] 19D , 21C , and 28A can be installed in a vehicle to realize next-generation clean energy automobiles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). Furthermore, the secondary battery can also be installed in transportation vehicles, such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0508] 29A to 29D illustrate a transportation vehicle as an example of a moving object using one embodiment of the present invention. The automobile 2001 illustrated in FIG. 29A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 4 is installed in one or more locations. The automobile 2001 illustrated in FIG. 29A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further include a charge control device electrically connected to the secondary battery module.

[0509] Furthermore, the automobile 2001 can charge its secondary battery by receiving power from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method and connector standards, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station installed in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electric storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device, such as an AC-DC converter.

[0510] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0511] 29B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series for a maximum voltage of 170 V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 29A, and therefore a description thereof will be omitted.

[0512] FIG. 29C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, in which one hundred or more secondary batteries with a nominal voltage of 3.0 V or more and 5.0 V or less are connected in series. By using a secondary battery in which the cathode active material composite 100z described in the above embodiment is used as the positive electrode, a secondary battery with excellent rate characteristics and charge / discharge cycle characteristics can be manufactured, contributing to improved performance and a longer life of the transport vehicle 2003. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those of FIG. 29A are provided, and therefore a description thereof will be omitted.

[0513] Fig. 29D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 29D has wheels for takeoff and landing, it can also be considered a type of transport vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and the secondary battery module and a charge control device.

[0514] The secondary battery module of the aircraft 2004 has, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, the secondary battery module has the same functions as those shown in Fig. 29A, and therefore a description thereof will be omitted.

[0515] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0516] Embodiment 7 In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 30A and 30B.

[0517] The house illustrated in FIG. 30A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611 or the like. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The power obtained by the solar panel 2610 can be charged to the power storage device 2612. The power stored in the power storage device 2612 can be charged to a secondary battery included in the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0518] The power stored in the power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0519] 30B illustrates an example of a power storage device according to one embodiment of the present invention. As illustrated in FIG. 30B , a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. The control circuit described in Embodiment 6 may be provided in the power storage device 791. The power storage device 791 can have a long lifetime by using a secondary battery in which the positive electrode active material composite 100z obtained in the above embodiment is used as a positive electrode for the power storage device 791.

[0520] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to the distribution board 703, the power storage controller 705 (also called the control device), the display 706, and the router 709 by wiring.

[0521] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment portion 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via outlets (not shown).

[0522] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0523] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during a day (e.g., from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791 based on the amount of power demand predicted by the prediction unit 712.

[0524] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on electrical appliances such as televisions and personal computers via the router 709. It can also be confirmed on portable electronic devices such as smartphones and tablets via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical appliances, and the portable electronic devices.

[0525] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0526] Embodiment 8 In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

[0527] 31A illustrates an example of an electric bicycle using the power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 31A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0528] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state detached from the bicycle in FIG. 31B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery, an example of which is shown in Embodiment 6. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. The control circuit 8704 may be provided with the small solid-state secondary battery shown in FIGS. 27A and 27B. By providing the small solid-state secondary battery shown in FIGS. 27A and 27B in the control circuit 8704, power can be supplied to retain data in a memory circuit included in the control circuit 8704 for a long period of time. Furthermore, by combining the cathode active material composite 100z obtained in the above-described embodiment with a secondary battery using the cathode active material composite 100z obtained in the above-described embodiment as a cathode, a synergistic effect in terms of safety can be obtained. The secondary battery using the cathode active material composite 100z obtained in the above-described embodiment as a cathode and the control circuit 8704 can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0529] 31C illustrates an example of a two-wheeled vehicle using the power storage device of one embodiment of the present invention. A scooter 8600 illustrated in FIG. 31C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602 includes a plurality of secondary batteries each using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode, and thus can have a high capacity, which can contribute to miniaturization.

[0530] 31C can store a power storage device 8602 in an under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0531] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0532] Embodiment 9 In this embodiment, an example of mounting a secondary battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a secondary battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0533] 32A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a secondary battery 2107. By including the secondary battery 2107 using the positive electrode active material composite 100z described in the above embodiment as a positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0534] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0535] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0536] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0537] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0538] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0539] FIG. 32B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes referred to as a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be mounted on the unmanned aerial vehicle 2300.

[0540] Fig. 32C shows an example of a robot. A robot 6400 shown in Fig. 32C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0541] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0542] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0543] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. Furthermore, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0544] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as the secondary battery 6409 to be mounted on the robot 6400.

[0545] 32D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0546] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine the presence or absence of an obstacle such as a wall, furniture, or a step. Furthermore, if an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0547] 33A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0548] For example, a secondary battery according to one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 33A . The eyeglasses-type device 4000 includes a frame 4000a and a display unit 4000b. Mounting a secondary battery on the temples of the curved frame 4000a makes it possible to provide an eyeglasses-type device 4000 that is lightweight, has a good weight balance, and has a long continuous use time. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as its positive electrode has a high energy density, and can realize a configuration that can accommodate space-saving associated with a smaller housing.

[0549] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A secondary battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has a high energy density and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[0550] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0551] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0552] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and a secondary battery can be mounted in an internal region of the belt portion 4006a. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has a high energy density and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[0553] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the wristwatch-type device 4005. The wristwatch-type device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided in the display portion 4005a or the belt portion 4005b. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as a positive electrode has high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0554] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0555] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0556] FIG. 33B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0557] 33C shows a side view of the display portion 4005a. The side view of the display portion 4005a also shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided in a position overlapping with the display portion 4005a, and can have high density and high capacity, and is small and lightweight.

[0558] Since the wristwatch-type device 4005 is required to be small and lightweight, by using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode of the secondary battery 913, it is possible to obtain a high-energy density and small-sized secondary battery 913.

[0559] 33D shows an example of a wireless earphone. Here, the wireless earphone is shown having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0560] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0561] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0562] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played back on the main units 4100a and 4100b. If the main units 4100a and 4100b have microphones, the sound picked up by the microphones can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the devices to be used as, for example, translation devices.

[0563] Furthermore, the secondary battery 4103 included in the main body 4100a can be charged from the secondary battery 4111 included in the case 4110. The coin-type secondary battery, the cylindrical secondary battery, or the like described in the above embodiment can be used as the secondary battery 4111 and the secondary battery 4103. A secondary battery using the positive electrode active material composite 100z obtained in the above embodiment as its positive electrode has a high energy density, and by using the secondary battery 4103 and the secondary battery 4111, a configuration that can accommodate space saving associated with miniaturization of wireless earphones can be realized.

[0564] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0565] In this example, a positive electrode active material composite 100z was produced by compounding a positive electrode active material with acetylene black, and the electrode density thereof was evaluated.

[0566] A commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M1 and no additional elements was prepared as the positive electrode active material. Acetylene black (AB) was prepared as the conductive material, polyvinylidene fluoride (PVDF) was prepared as the binder, and NMP was prepared as the solvent.

[0567] Next, lithium cobalt oxide and acetylene black were composited to prepare a cathode active material composite. The composite was performed using a Picobond (manufactured by Hosokawa Micron) at 3500 rpm for 10 minutes, with a processing volume of 50 g. The mixture ratio of lithium cobalt oxide to acetylene black was LCO:AB = 95:3 (weight ratio).

[0568] Figure 34A shows an SEM image of the positive electrode active material composite. It was observed that a portion of the lithium cobalt oxide surface was covered with acetylene black. For comparison, Figure 34B shows an SEM image of lithium cobalt oxide that had not been subjected to a composite treatment. The SEM observation in this example was performed using a scanning electron microscope SU8030 manufactured by Hitachi High-Tech Corporation, with measurement conditions of an acceleration voltage of 5 kV and a magnification of 5000x.

[0569] Next, the positive electrode active material composite and PVDF dissolved in NMP were mixed to prepare a slurry, which was then coated on a positive electrode current collector and dried to prepare an electrode layer measuring 12 cm in length and 4 cm in width. The positive electrode current collector was made of 20 μm thick aluminum foil.

[0570] Next, the electrode layer was pressed with a calender roll to prepare a positive electrode. A 4 cm wide electrode layer was pressed at 210 kN / m, 461 kN / m, 964 kN / m, and 1467 kN / m in this order. The thickness of the positive electrode was measured at nine points with a micrometer for each press, and the thickness of the current collector was subtracted to determine the thickness of the electrode layer. Finally, nine positive electrodes with a diameter of 12 mm were cut out, each including the nine measured points. Each was weighed, and the weight of the electrode layer was calculated by subtracting the weight of the current collector. The electrode density was determined from the thickness, area, and weight of the electrode layer for each press, and the average value was calculated.

[0571] As a comparative example, a slurry was prepared using uncomposite-treated lithium cobalt oxide, acetylene black, PVDF, and a solvent. The mixture ratio was lithium cobalt oxide:AB:PVDF = 95:3:2 (weight ratio). NMP was used as the solvent. The slurry was applied to a positive electrode current collector, dried, and pressed in the same manner as above, and the electrode density was calculated.

[0572] Table 1 shows the conditions for producing a positive electrode using the positive electrode active material composite and a positive electrode using lithium cobalt oxide that was not subjected to a composite treatment.

[0573]

[0574] The calculated average values ​​of electrode density are shown in a graph in Figure 35. The positive electrode using the positive electrode active material composite was able to increase the electrode density at a lower pressure than the comparative example. Specifically, the electrode density was able to reach 3.80 g / cc at a pressure of 210 kN / m. The maximum electrode density also showed a higher value than the comparative example, with a maximum value of 4.15 g / cc when pressures of 210 kN / m and 461 kN / m were applied.

[0575] In this example, a positive electrode active material composite 100z was produced by wet mixing a positive electrode active material and graphene oxide to form a composite, and its charge / discharge characteristics were evaluated.

[0576] <Preparation of Positive Electrode Active Material> First, a positive electrode active material containing cobalt as the transition metal M1, to which magnesium, fluorine, nickel, and aluminum were added, was heated, and prepared by the following steps.

[0577] A commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M1 and no particular additive element was prepared.

[0578] Next, a magnesium source, a fluorine source, a nickel source and an aluminum source were prepared as sources of additional elements.

[0579] Specifically, LiF was prepared as a fluorine source, and MgF was prepared as a fluorine source and a magnesium source. ２ LiF:MgF was prepared. ２ were weighed out so that the molar ratio was 1:3. Next, LiF and MgF were dissolved in dehydrated acetone.２ The mixture was mixed and stirred at a rotation speed of 400 rpm for 12 hours to obtain the additive element source X. Ａ Then, the powder was sieved through a sieve with 300 μm openings to obtain the additive element source X having a uniform particle size. Ａ obtained.

[0580] Also, Ni(OH) ２ Similarly, dehydrated acetone was used as a solvent and stirred at a rotation speed of 400 rpm for 12 hours, and sieved to obtain additive element source X having a uniform particle size. Ｎｉ obtained.

[0581] Also, Al(OH) ３ Similarly, dehydrated acetone was used as a solvent and stirred at a rotation speed of 400 rpm for 12 hours, and sieved to obtain additive element source X having a uniform particle size. Ａｌ obtained.

[0582] Next, the additive element source X Ａ is 1 at% of the transition metal M1, and the additive element source X Ｎｉ is 0.5 at% of the transition metal M1, and the additive element source X Ａｌ The added element source X was weighed out so that the amount of the added element X was 0.5 at % of the transition metal M1, and mixed with lithium cobalt oxide in a dry state. The mixture was stirred at a rotation speed of 1500 rpm for 1.5 minutes. Ａ Finally, the mixture was sieved through a sieve with 300 μm openings to obtain a mixture A having a uniform particle size.

[0583] Next, mixture A was heated. Heating was performed three times using a muffle furnace at 900°C for 10 hours. During heating, a lid was placed on the crucible containing mixture A. An oxygen atmosphere was created inside the muffle furnace, and the oxygen flow rate was 10 L / min. Between the three heating steps, mixture A was removed from the muffle furnace and crushed with a mortar and pestle. By these heating steps, a positive electrode active material containing magnesium, fluorine, nickel, and aluminum was obtained.

[0584] <Preparation of Positive Electrode> A positive electrode was prepared using the positive electrode active material prepared above. Graphene oxide (GO) or acetylene black (AB) was prepared as the conductive material. Polyvinylidene fluoride (PVDF) was used as the binder. NMP or a mixture of ethanol and water in a 7:3 (volume ratio) was prepared as the solvent. 20 μm aluminum foil was prepared as the current collector.

[0585] A positive electrode using graphene oxide as the conductive material was fabricated as follows. First, dried graphene oxide was weighed and mixed with a solvent. NMP was used as the solvent. A positive electrode active material and a binder were added to the mixture in this order and mixed to prepare a slurry. The slurry was applied to a current collector and dried to prepare an electrode layer. The compounding ratio of the electrode layer was positive electrode active material:GO:binder = 97:1:2.

[0586] The electrode layer was first subjected to chemical reduction. An aqueous solution containing 0.075 mol / L of ascorbic acid and 0.074 mol / L of lithium hydroxide was prepared. The aqueous solution and NMP were mixed at a volume ratio of aqueous solution:NMP = 1:9, and the mixed solution was kept at 60°C. The electrode layer was then immersed in the mixed solution for 1 hour. The electrode layer was then washed.

[0587] Next, the electrode layer was subjected to thermal reduction, specifically, by heating at 170° C. for 10 hours using a vacuum dryer.

[0588] By performing the reduction treatment, the graphene oxide (GO) in the electrode layer is converted to reduced graphene oxide (RGO), which gives it electrical conductivity. Furthermore, by performing chemical reduction before thermal reduction as described above, the graphene oxide can be sufficiently reduced even if the thermal reduction temperature is lowered, and deterioration of the PVDF binder can be avoided.

[0589] A positive electrode using acetylene black as a conductive material was fabricated as follows. A positive electrode active material, acetylene black (AB), PVDF, and NMP were mixed to prepare a slurry. The slurry was applied to a current collector and dried to prepare an electrode layer. The compounding ratio of the electrode layer was positive electrode active material:acetylene black:binder = 95:3:2.

[0590] Table 2 shows the conditions for preparing the two types of positive electrodes.

[0591]

[0592] A surface SEM image of an electrode having reduced graphene oxide (RGO) as a conductive material is shown in Figure 36. As indicated by the arrows in the figure, it was confirmed that the reduced graphene oxide widely covered the surface of the positive electrode active material.

[0593] <Charge / Discharge Characteristics> A coin cell was prepared using the above two types of positive electrodes.

[0594] The electrolyte solution used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, to which 2 wt% vinylene carbonate (VC) was added as an additive. The electrolyte contained 1 mol / L of lithium hexafluorophosphate (LiPF ６ ) was used. Polypropylene was used as the separator.

[0595] Metallic lithium was prepared as the counter electrode, and a coin-shaped half cell equipped with the above-mentioned positive electrode and other components was formed, and the rate characteristics and cycle characteristics were measured.

[0596] Here, the discharge rate and charge rate will be explained. The discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1 C is X (A). When a battery is discharged at a current of 2X (A), it is said to have been discharged at 2C, and when a battery is discharged at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same applies to the charge rate; when a battery is charged at a current of 2X (A), it is said to have been charged at 2C, and when a battery is charged at a current of X / 5 (A), it is said to have been charged at 0.2C. In this example, 1C = 200 mA / g.

[0597] The rate characteristics were measured as follows. For the evaluation of the charge rate, the charge method was CC (each rate, end voltage 4.6 V), and the discharge method was CC (0.2 C, end voltage 2.5 V). For the evaluation of the discharge rate, the charge method was CC / CV (0.2 C, 4.6 V, end current 0.02 C), and the discharge method was CC (each rate, end voltage 2.5 V). The measurement temperature was 25°C in both cases. Figure 37A shows the charge capacities at 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C. Figure 37B shows the discharge capacities at 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C. n = 2 for each case.

[0598] As shown in FIGS. 37A and 37B, in charge / discharge at a high rate of 10 C, the positive electrode having reduced graphene oxide (RGO) as the conductive material exhibited better rate characteristics.

[0599] In measuring the cycle characteristics, the charge method was (0.5 C, 4.6 V, final current 0.05 C), and the discharge method was CC (0.5 C, final voltage 2.5 V). The measurement temperature was 45°C. Figure 38 shows a graph of the cycle characteristics. n=2 for each case.

[0600] As shown in FIG. 38, the positive electrode using acetylene black as the conductive material exhibited slightly better cycle characteristics than the positive electrode having reduced graphene oxide (RGO) as the conductive material, but no significant difference was observed.

[0601] 100: positive electrode active material, 100x: first active material, 100xa: first active material, 100xb: first active material, 100y: second active material, 100z: positive electrode active material composite, 101: coating material, 102: graphene compound, 103: carbon black, 114: electrolyte, 1101: positive electrode, 1104: positive electrode current collector, 1105: positive electrode active material layer

Claims

1. A first active material, a second active material, and a glass, At least a portion of the surface of the first active material has an area covered with the glass, At least a portion of the surface of the glass has an area covered with the second active material, The first active material is LiM1O ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), The second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), The glass has lithium ion conductivity.

2. A first active material, a second active material, and a glass, At least a portion of a surface of the first active material has an area covered with the glass and the second active material, The first active material is LiM1O ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), The second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), The glass has lithium ion conductivity.

3. A first active material, a second active material, glass, and a conductive material, At least a portion of the surface of the first active material has an area covered with the glass, At least a portion of the surface of the glass has an area covered with the second active material and the conductive material, The first active material is LiM1O ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), The second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), The glass has lithium ion conductivity, The conductive material comprises a graphene compound or a carbon nanotube.

4. A first active material, a second active material, glass, and a conductive material, At least a portion of a surface of the first active material has an area covered with the glass, the second active material, and the conductive material; The first active material is LiM1O ２ (M1 is one or more selected from Fe, Ni, Co, and Mn), The second active material is LiM2PO ４ (M2 is one or more selected from Fe, Ni, Co, and Mn), The glass has lithium ion conductivity, The conductive material comprises a graphene compound or a carbon nanotube.

5. In any one of claims 1 to 4, the first active material comprises lithium cobalt oxide having magnesium, fluorine, aluminum, and nickel; the lithium cobalt oxide has a surface region in which the concentration of any one or more elements selected from the group consisting of magnesium, fluorine, and aluminum is at its maximum;

6. In any one of claims 1 to 4, the first active material comprises lithium nickel-manganese-cobalt oxide having one or more selected from calcium, fluorine, aluminum, and gallium; The nickel-manganese-cobalt lithium oxide has a surface region in which the concentration of any one or more elements selected from the group consisting of calcium, fluorine, aluminum and gallium is maximized.

7. A secondary battery comprising the positive electrode according to any one of claims 1 to 6.

8. A vehicle comprising the secondary battery according to claim 7.

9. An electricity storage system comprising the secondary battery according to claim 7.

10. An electronic device comprising the secondary battery according to claim 7.