Lithium ion secondary battery

Abstract

To provide a positive electrode whose deterioration due to charging and discharging is small, and a secondary battery, provide a positive electrode with high electrode density, and a secondary battery, or provide a positive electrode with the excellent rate characteristic, and a secondary battery.SOLUTION: A positive electrode has a positive electrode active material and a covering material. At least a part of a surface of the positive electrode active material is covered with the covering material. The positive electrode active material has lithium cobaltate having magnesium, fluorine, aluminum, and nickel. The lithium cobaltate has, in a surface layer part, a region in which the concentration of one or a plurality of concentrations selected from the magnesium, the fluorine, and the aluminum is the maximum. The covering material is preferably one or more selected from glass, carbon black, graphene, and a graphene compound.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[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, a 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. Another embodiment of the present invention particularly relates to a method for manufacturing a positive electrode or a positive electrode. Another 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. [Background technology]

[0006] In recent years, there has been active development of various types of energy storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, as they are used in a variety of applications, including mobile phones, smartphones, laptop computers, and other portable information terminals, as well as 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 high potential conditions, 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, highly stable secondary batteries (e.g., Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-088400 A [Patent Document 2] WO2018 / 203168 Brochure [Patent Document 3] Japanese Patent Publication No. 2020-140954 Summary of the Invention [Problem to be solved by the invention]

[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 the 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, a method for manufacturing a positive electrode that has excellent charge-discharge cycle characteristics, a method for manufacturing a positive electrode that can increase the charge-discharge rate, or 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 in the specification, drawings, and claims. [Means for solving the problem]

[0016] One embodiment of the present invention provides a positive electrode 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 glass, and at least a portion of the surface of the glass has a region covered with the second active material, the first active material comprising a first composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn), the second active material comprising a second composite oxide represented by LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn), and the glass has lithium ion conductivity.

[0017] Another embodiment of the present invention provides a positive electrode 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 the second active material, the first active material comprising a first composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn), the second active material comprising a second composite oxide represented by LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn), and the glass having lithium ion conductivity.

[0018] Another embodiment of the present invention is a positive electrode including a first active material, a second active material, glass, and a conductive material, 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 conductive material, the first active material includes a first composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn), the second active material includes a second composite oxide represented by LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn), the glass has lithium ion conductivity, and the conductive material includes a graphene compound or a carbon nanotube.

[0019] Another embodiment of the present invention is a positive electrode including a first active material, a second active material, glass, and a conductive material. At least a part of the surface of the first active material has a region covered with the glass, the second active material, and the conductive material. The first active material includes a first composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn). The second active material includes a second composite oxide represented by LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn). The glass has lithium ion conductivity. The conductive material includes 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, and the lithium nickel-manganese-cobalt oxide has 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. [Effects of the Invention]

[0031] Therefore, one embodiment of the present invention can provide a positive electrode active material that is stable at a high potential and / or at 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 with excellent charge and discharge cycle characteristics can be provided. Alternatively, a positive electrode active material with 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 at 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] Another embodiment of the present invention can provide a method for manufacturing a positive electrode that is stable at a high potential and / or at a high temperature. 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. [Brief explanation of the drawings]

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

[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, particles are not limited to those having a spherical shape (a circular cross-sectional shape), and the cross-sectional shape of each particle may be an ellipse, a rectangle, a trapezoid, a triangle, a square with rounded corners, an asymmetric shape, or the like, and further, each particle may have an irregular shape.

[0042] Particle diameters can be measured, for example, by laser diffraction particle size distribution measurement, and can be compared using the D50 value. Here, D50 is the particle diameter when the cumulative particle amount curve of the particle size distribution measurement results is 50%, i.e., the median. Particle size measurement 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 can also be measured by analysis using an SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope), etc.

[0043] Furthermore, in this specification and elsewhere, crystal planes and directions are indicated using Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar after the number; however, due to limitations in application notation, in this specification and elsewhere, 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 using [ ], collective orientations indicating all equivalent directions are expressed using < >, individual planes indicating crystal faces are expressed using ( ), and collective planes with equivalent symmetry are expressed using {}. 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, the theoretical capacity of LiFePO4 is 170 mAh / g, that of LiCoO2 is 274 mAh / g, that of LiNiO2 is 274 mAh / g, and that of LiMn2O4 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 the x in the composition formula, for example, Li x x in CoO2, or Li x In this specification, Li x CoO2 is appropriately Li x x can be considered as the occupancy rate, and in the case of the positive electrode active material in a secondary battery, x can be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2 mAh / g, Li 0.2 CoO2 or x=0.2. x A small value of x in CoO2 is, for example, 0.1 <x≦0.24をいう。

[0048] When lithium cobalt oxide approximately satisfies the stoichiometric ratio, it is LiCoO2, and the occupancy rate of Li on the lithium sites is x = 1. A secondary battery that has completed discharge is also LiCoO2, and x = 1. The completion of discharge here refers to a state where, for example, the voltage is 2.5 V (lithium counter electrode) or less at a current of 100 mA / g. In a lithium-ion secondary battery, when the occupancy rate of lithium on the lithium sites reaches x = 1 and no more lithium can enter, the voltage drops rapidly. At this point, discharge can be said to have completed. Generally, in lithium-ion secondary batteries that use LiCoO2, the discharge voltage drops rapidly before it reaches 2.5 V, so discharge is considered to have 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, the secondary battery of one embodiment of the present invention is not limited to this example. Other materials, such as graphite and lithium titanate, may also be used for the negative electrode. The properties of the positive electrode and the positive electrode active material of one embodiment of the present invention, such as their resistance to crystal structure collapse even after 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. Charging and discharging at a lower voltage is expected to result in even better cycle characteristics 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 positive electrode active material composite 100z including a first active material 100x that functions as a positive electrode active material and 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 having 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 have 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 described below.

[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). The composite process preferably includes 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, the composite process preferably includes one or more heat treatments. A specific method for producing the positive electrode active material composite 100z will be described later.

[0058] An example of a positive electrode 1101 of one embodiment of the present invention is shown in FIG. 1. 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 illustrates 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, the positive electrode active material layer 1105 may not include a conductive material. The type of conductive material is not limited to the example illustrated 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 illustrated in FIG. 1 , the positive electrode active material layer 1105 preferably includes a binder. Examples of binders that can be used include polymer materials such as polyvinylidene fluoride and molecular crystalline electrolytes such as Li(FSI)(SN)2.

[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] [Cathode active material composite] 2A1 to 2B2, 3A1 to 3B2, and 4A1 to 4B2 are cross-sectional schematic views illustrating the 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. A configuration in which multiple first active materials 100x are covered with the coating material 101 may also be used. For example, as shown in FIG. 2A2, a configuration in which at least a portion of the first active material 100xa and the first active material 100xb are covered with the coating material 101 may also be used. 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 particulate first active material 100x that functions as a positive electrode active material is covered with coating material 101, the area of ​​first active material 100x in direct contact with electrolyte 114 is reduced, and desorption of transition metal elements and / or oxygen from first active material 100x in a high-voltage charging state can be suppressed, thereby suppressing capacity reduction due to repeated charging and discharging. Furthermore, by being covered with coating material 101 that is electrochemically stable even at high temperatures and in a high-voltage charging state, a secondary battery using 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 is stable under high-voltage charging conditions, such as lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, or lithium nickel-cobalt-manganese oxide with 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 under high-voltage charging conditions can be further improved.Furthermore, 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 a high magnesium, fluorine, or aluminum content in the surface layer of the positive electrode active material, with nickel widely distributed throughout the particles. This makes it a particularly preferred material for the first active material 100x, as it exhibits significantly superior charge-discharge cycle characteristics at high voltages. 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 counts of characteristic X-rays derived from magnesium, fluorine, or aluminum reach their maximum values ​​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, which does not include conductive materials. Cracks in the positive electrode active material also have surface layers, and cracks that occurred before the addition of magnesium, fluorine, or aluminum during the preparation of the positive electrode active material have surface layers 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 a single 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 have to be in direct contact with each other.

[0067] Note that Figures 2B1 and 2B2 show cases in which the second active material 100y forms a layer, where the second active material 100y is subjected to a composite treatment 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 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 in contact with the first active material 100x via the coating material 101, the area in which 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 under high temperature and high voltage conditions, covering with these 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 with 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-mentioned cathode active material composite 100z 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.

[0071] Lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel is characterized by a high content 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 high content of magnesium, fluorine, or aluminum, for example, in STEM-EDX line analysis, the counts of characteristic X-rays originating from magnesium, fluorine, or aluminum have 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 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.

[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 develop 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 with higher conductivity than the first active material 100x, charge / discharge characteristics, particularly 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 a 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 positive electrode active material composite 100z includes a second active material 100y that is in contact with the first active material 100x via the coating material 101, the positive electrode active material composite 100z can be said to have a dual structure in the surface layer portion. However, the positive electrode active material composite 100z of one embodiment of the present invention is not limited to a dual structure including the coating material 101 and the second active material 100y. As another example of the positive electrode 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] Also, as the positive electrode active material composite 100z of one aspect of the present invention, as shown in FIGS. 3B1, 3B2, 4B1, and 4B2, the graphene compound 102 may be provided in the surface layer portion of the positive electrode active material composite 100z or the mixed layer of the coating material 101 and the active material. Here, instead of the graphene compound 102, carbon fibers such as carbon black or carbon nanotubes may be used.

[0076] As the coating material 101, glass can be used. Glass is also referred to as a material having an amorphous part. As the material having an amorphous part, for example, a material having one or more selected from SiO2, SiO, Al2O3, TiO2, Li4SiO4, Li3PO4, Li2S, SiS2, B2S3, GeS4, AgI, Ag2O, Li2O, P2O5, B2O3, and V2O5, etc., Li7P3S 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. The material having an amorphous part can be used in an entirely amorphous state or in a state of crystallized glass (also referred to as glass ceramics) in which a part is crystallized. The coating material 101 desirably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusivity and lithium ion penetrability. Further, the coating material 101 preferably has a melting point of 800 °C or lower, more preferably 500 °C or lower. Further, it is preferable that the coating material 101 has electronic conductivity. Further, the coating material 101 preferably has a softening point of 800 °C or lower, and for example, Li2O - B2O3 - SiO2 - based glass can be used.

[0077] Also, as the coating material 101, a material containing carbon can be used. Examples of materials containing carbon include carbon blacks such as acetylene black and furnace black, graphites 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] Also, a material having an amorphous part and a material containing carbon may be mixed and used.

[0079] As the second active material 100y, one or more of oxides and LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn) can be used. Examples of oxides include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Also, examples of LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn) include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc.

[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] [Cathode active material] The first active material 100x may be a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) having a layered rock-salt crystal structure. Alternatively, the first active material 100x may be a composite oxide represented by LiM1O2 to which an additive element X has been added. 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 containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, 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-lithium aluminate, nickel-cobalt-lithium aluminate, nickel-cobalt-lithium aluminate containing magnesium and fluorine, and nickel-cobalt-lithium manganate containing magnesium and fluorine. The transition metal ratio of the nickel-cobalt-lithium manganate is preferably high, and for example, materials with a molar ratio of nickel:cobalt:manganese of 8:1:1 or nickel:cobalt:manganese of 9:0.5:0.5 are preferred. Furthermore, the lithium nickel-cobalt-lithium manganate preferably includes lithium nickel-cobalt-manganate containing calcium.

[0082] Alternatively, the first active material 100x may be formed by coating secondary particles of a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) 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, a metal oxide-coated composite oxide in which secondary particles of a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) are coated with aluminum oxide may be used as the first active material 100x. For example, a metal oxide-coated composite 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 may 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 contains 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 can be one or more of oxides and LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, and Mn) having an olivine-type crystal structure. Examples of oxides include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Examples of LiM2PO4 include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, and LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4(a+b is less than 1, 0 <a<1、0<b<1)、LiFec Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (where c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (where f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. Also, the particle surface of the second active material 100y may have a carbon coating layer.

[0085] [Conductive material] As the conductive material, for example, any one or two or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0086] In this specification, etc., the graphene compound includes multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. The graphene compound refers to a substance having carbon, having a flat plate shape, sheet shape, etc., and having a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may be referred to as a carbon sheet. The graphene compound may have a functional group. Also, the graphene compound preferably has a bent shape. Also, the graphene compound may be rounded like a carbon nanofiber.

[0087] In this specification, etc., graphene oxide refers to a substance having carbon and oxygen, having a sheet shape, and having a functional group, particularly an epoxy group, carboxy group or 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. Although a single sheet of reduced graphene oxide can function, multiple sheets may also be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is between 2 atomic % and 15 atomic %. 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 between the G band and 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 when thin, they may have very high conductivity, allowing a small amount of material 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. The graphene compound preferably 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] The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. The material used for the positive electrode current collector is preferably one that does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector can be in any suitable shape, such as a foil, plate, sheet, mesh, punched metal, or expanded metal. The current collector should preferably have 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] Method 1 for preparing a positive electrode active material composite shows a case in which a first active material 100x and a coating material 101 are combined together, method 2 for preparing a positive electrode active material composite shows a case in which the first active material 100x and the coating material 101 are combined together and then a second active material 100y is combined together, and method 3 for preparing a positive electrode active material composite shows a case in which 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 preparing a 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 can be a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) prepared by the method described in the embodiment below, to which an additive element X has been added. For example, lithium cobalt oxide containing magnesium and fluorine, or lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel can be used. In particular, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel is preferably subjected to the initial heating process described in the embodiment below. Another example of the first active material 100x is lithium nickel-cobalt-manganese oxide. Here, a high nickel ratio is preferred as the transition metal ratio of the nickel-cobalt-manganese lithium oxide. For example, a material with a molar ratio of nickel:cobalt:manganese = 8:1:1 or nickel:cobalt:manganese = 9:0.5:0.5 is preferred. Furthermore, a metal oxide-coated composite oxide can be used, in which secondary particles of nickel-cobalt-manganese lithium are coated with aluminum oxide. Here, the coating layer is preferably thin, for example, from 1 nm to 200 nm, more preferably from 1 nm to 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 a material having one or more selected from SiO2, SiO, Al2O3, TiO2, Li4SiO4, Li3PO4, Li2S, SiS2, B2S3, GeS4, AgI, Ag2O, Li2O, P2O5, B2O3, and V2O5, and Li7P3S 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 entirely amorphous state or in a state of crystallized glass (also referred to as glass-ceramics) in which a part is crystallized. The coating material 101 desirably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusivity and lithium ion penetrability. Further, the coating material 101 preferably has a melting point of 800°C or lower, more preferably 500°C or lower. Further, it is preferable that the coating material 101 has electronic conductivity. Further, the coating material 101 preferably has a softening point of 800°C or lower, and for example, a Li2O-B2O3-SiO2 based glass can be used.

[0098] Next, as step S103, the above-described first active material 100x and the coating material 101 are subjected to a compounding treatment. When performing the compounding treatment by mechanical energy, the compounding treatment can be performed by a mechanochemical method. Further, the treatment may be performed using a mechanofusion method.

[0099] Also, as step S103, when using a ball mill, for example, it is preferable to use zirconia balls as media. For the ball mill treatment, when the purpose is mixing, a dry treatment is desirable. When performing the ball mill treatment by a wet treatment, acetone can be used. When performing a wet ball mill treatment, dehydrated acetone having a water content of 100 ppm or less, preferably 10 ppm or less, may be used.

[0100] By the compounding treatment in step S103, a state can be produced in which at least a part, preferably substantially the whole, of the particle surface of the particulate first active material 100x 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, 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 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 preparing a 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. 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 zirconia balls as media, for example. If the ball mill process is intended for mixing, a dry process is preferable. When the ball mill process is performed as a wet process, acetone can be used. When performing a wet ball mill process, it is recommended to use dehydrated acetone with a water 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, and preferably almost the entirety, is covered with the coating material 101.

[0109] Next, a heat treatment is performed in step S104, and positive electrode active material composites 100z are 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 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. Step S104 may be followed by a step of crushing the fixed positive electrode active material composites 100z.

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

[0111] As the second active material 100y, LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, Mn) can be used. Alternatively, an oxide can be used as the second active material 100y. As examples of the oxide, aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, etc. can be used. As the LiM2PO4, the materials described above, such as LiFePO4, LiMnPO4, LiFe a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe<​​​​​​​​​​​​​​​​​​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, a positive electrode active material composite 100z′ according to 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 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 size of the second active material 100y to the particle size of the first active material 100x (particle size 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 size 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 preparing a 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 combined. When combining using mechanical energy, the combining can be performed by a mechanochemical method. Alternatively, the combining can be performed by a mechanofusion method.

[0123] Furthermore, when a ball mill is used in step S104, it is preferable to use zirconia balls as media, for example. If the ball mill process is intended for mixing, a dry process is preferable. When the ball mill process is performed as a wet process, acetone can be used. When performing a wet ball mill process, it is recommended to use dehydrated acetone with a water content of 100 ppm or less, preferably 10 ppm or less.

[0124] The composite 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, 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 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 carbon fiber conductive material such as a graphene compound, carbon black, or carbon nanotubes with the coating material 101 in step S104 of FIG. 7A.

[0129] [Method 4 for preparing a positive electrode active material composite] 5A to 7A, an example of the composite treatment using mechanical energy is described, but 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, so that 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] In FIG. 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 that can be used 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 shortens 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 using graphene oxide as the conductive material and PVDF as the binder, a temperature that sufficiently reduces the graphene oxide without adversely affecting the PVDF is preferable. Specifically, a temperature between 125°C and 200°C is preferable. Below 100°C, the reduction of graphene oxide may not proceed sufficiently. On the other hand, above 250°C, the PVDF may be adversely affected and the slurry may easily peel off from the current collector. A heating time between 1 hour and 20 hours is preferable. 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 reduction 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, positive electrode active material composite 100z of one embodiment of the present invention shown 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] [Positive electrode active material structure] 8A is a schematic top view of a positive electrode active material 100 according to one embodiment of the present invention. A schematic cross-sectional view taken along line AB in FIG. 8A is shown in FIG. 8B.

[0144] <Elements and distribution> The positive electrode active material 100 contains lithium, a transition metal, oxygen, and an additive element X. The positive electrode active material 100 may be said to be a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn) to which the additive element X has been added.

[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. The inclusion of nickel in addition to cobalt as a transition metal is preferable because it may result in a more stable crystal structure during high-voltage charging.

[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-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide containing magnesium and fluorine, and nickel-manganese-cobalt oxide containing magnesium and fluorine. Note that, in this specification and the like, the additive element X may be referred to interchangeably 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 to 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 portion 100a 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 upon charging.

[0149] Furthermore, it is preferable that the concentration gradient of the additive element X is uniformly distributed throughout the entire surface layer portion 100a of the positive electrode active material 100. Even if a portion of the surface layer portion 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 easily enters the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer portion 100a facilitates the maintenance of the layered rock-salt crystal structure. Furthermore, magnesium has a strong bond with oxygen, so it can suppress 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 decreases. 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 atoms occurs more smoothly. Therefore, when used in secondary batteries, charge / discharge characteristics, rate characteristics, etc. are improved, which is preferable.

[0153] Titanium oxide is known to have superhydrophilic properties. Therefore, by forming a cathode active material 100 having titanium oxide in the surface layer portion 100a, it is possible that the cathode active material 100 may have good wettability with highly polar solvents. When used in a secondary battery, this may improve the contact at the interface between the cathode active material 100 and a highly polar electrolyte, thereby suppressing an increase in resistance. In this specification and the like, the term "electrolyte" refers 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 the 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 the 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, using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, the measurement performed while scanning an area and evaluating the area two-dimensionally is sometimes called EDX area analysis. Furthermore, the extraction of data from a linear area from EDX area analysis and evaluation of the atomic concentration distribution 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 additional 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 line analysis can analyze the concentration distribution of the additional element X.

[0159] When EDX 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, and therefore, when EDX analysis is performed, the fluorine concentration peak (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 up to 1 nm, and even more preferably up to 0.5 nm.

[0161] It is not necessary for all of the additive elements X to 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 be slightly different from that of magnesium and fluorine. For example, when EDX 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 the number of 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 mentioned 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 result in the additive element not being distributed throughout the entire surface layer portion 100a, which may result in an insufficient effect of maintaining the crystalline structure. Thus, 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 the concentration of additive element X can be made appropriate in the interior and most of the surface layer portion of the positive electrode active material 100. By making the concentration of additive element X appropriate 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. Being able 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 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 as 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> Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock-salt crystal structure is a composite oxide represented by LiM1O2 (where 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 occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the influence of the Jahn-Teller effect is suggested to be small, and LiCoO2 may have better durability against charge and discharge at high voltages, which is preferable.

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

[0171] <Conventional positive electrode active materials> The positive electrode active material shown in Figure 11 is lithium cobalt oxide (LiCoO2, LCO) to which neither halogen nor magnesium is added. The crystal structure of the lithium cobalt oxide shown in Figure 11 changes depending on the depth of charge. In other words, when expressed as LixCoO2, the crystal structure changes depending on the occupancy rate x of lithium on the lithium site.

[0172] As shown in Figure 11, lithium cobalt oxide in the x=1 state (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and the layers are continuous in the planar direction with edge sharing.

[0173] When x = 0, the crystal structure has the space group P-3m1, and there is one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called the O1-type crystal structure.

[0174] Furthermore, when x is approximately 0.12, lithium cobalt oxide has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as the H1-3 crystal structure. Because actual lithium insertion and extraction can be uneven, the H1-3 crystal structure is experimentally observed from approximately x = 0.25. In practice, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in Figure 11 and other parts of this specification, the c-axis of the H1-3 crystal structure is shown as half the unit cell to facilitate comparison with other structures.

[0175] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 crystal structure can be expressed as Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 crystal structure is expressed 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 expressed 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 that the O3' crystal structure exhibits smaller changes 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 becomes 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 below 0.24, and then discharged, it undergoes repeated changes in its crystal structure (i.e., 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 have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 11, in the H1-3 crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. 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 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0179] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers such as P-3m1(O1), 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> <Internal> The positive electrode active material 100 of one embodiment of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charge and discharge. Furthermore, the change in volume 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 high-voltage charged state. 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 high-voltage charged state. In such cases, 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 additive element X contains magnesium. It is also preferable that the additive element X contains a halogen such as fluorine or chlorine.

[0184] The crystal structure at x = 1 (discharged state) in Figure 9 is the same as that in Figure 11, i.e., R-3m(O3). On the other hand, a cathode active material 100 according to one embodiment of the present invention has a crystal structure different from the H1-3 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 sites. The symmetry of the CoO2 layers in this structure is the same as that of the O3 type. Therefore, this structure is referred to as the O3' type crystal structure in this specification. In the O3' type crystal structure shown in Figure 9, lithium is omitted to explain the symmetry of the cobalt atoms and the oxygen atoms. However, in reality, lithium is present between the CoO2 layers at, for example, 20 atomic % or less relative to cobalt. In both the O3 type and O3' type crystal structures, magnesium is preferably present in a dilute form between the CoO2 layers, i.e., at the lithium sites. Furthermore, halogens such as fluorine are preferably present randomly and dilutely at the oxygen sites.

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

[0186] It can also be said that the O3' type crystal structure is similar to the CdCl2 type crystal structure, although it has random lithium between the layers. This CdCl2 type-like crystal structure was observed when lithium nickel oxide was charged to a charge depth of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), 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 according to one embodiment of the present invention, when a large amount of lithium is released during 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, there is almost no displacement of the CoO layers in these crystal structures.

[0188] More specifically, the cathode active material 100 of one embodiment of the present invention exhibits high structural stability even at high charge voltages. For example, in conventional cathode active materials, even at charge voltages 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, there exists a region of charge voltages where the R-3m(O3) crystal structure can be maintained. Furthermore, even at higher charge voltages, for example, at voltages of about 4.65 V to 4.7 V relative to the potential of lithium metal, there exists a region where the O3' crystal structure can be maintained. Furthermore, when the charge voltage is further increased, for example, at voltages of 4.65 V to 4.7 V relative to the potential of lithium metal, the H1-3 crystal may finally be observed. Note that, in secondary batteries, when graphite is used as the anode active material, there exists a region of charge voltages where the R-3m(O3) crystal structure can be maintained even at secondary battery voltages of 4.3 V to 4.5 V, and even at higher charge voltages, for example, at voltages of 4.35 V to 4.55 V relative to the potential of lithium metal, there exists a region where the O3' crystal structure can be maintained.

[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 addition, the O3' type crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25.

[0192] An additive element X, such as magnesium, randomly and dilutely present between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the misalignment of the CoO2 layers. Therefore, the presence of magnesium between the CoO2 layers tends to form an O3'-type crystal structure. Therefore, magnesium is preferably distributed in at least a portion of the surface layer of the cathode active material 100 of one embodiment of the present invention, and more preferably distributed throughout the entire surface layer of the cathode active material 100. Furthermore, in order to distribute magnesium throughout the entire surface layer of the cathode active material 100, a heat treatment is preferably performed during the process of preparing the cathode 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 added element X, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site is ineffective in maintaining the R-3m structure under high-voltage charging conditions. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to a divalent state 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 throughout 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 throughout 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 against hydrofluoric acid produced by decomposition of the electrolyte.

[0195] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt 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 greater than 0.01 and less than 0.04, and even more preferably approximately 0.02. 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 during the production process of the positive electrode active material 100.

[0196] Lithium cobalt oxide may contain one or more metals other than cobalt (hereinafter, "additive element X") selected from nickel, aluminum, manganese, titanium, vanadium, and chromium, with the addition of at least one of nickel and aluminum being particularly preferred. Manganese, titanium, vanadium, and chromium may be stable due to their tetravalent nature, which 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 alter 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% to 4%, and particularly preferably 0.1% to 2%. 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 battery 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 leaching 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%, 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 the value of the composition of raw materials in the process of producing the positive electrode active material.

[0203] In addition, the positive electrode active material including an additional element X of one embodiment of the present invention 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, short circuits 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 the phosphorus, resulting in a decrease in the hydrogen fluoride concentration in the electrolyte solution.

[0206] When the electrolyte contains LiPF6 as the lithium salt, 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 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, a decrease in adhesion due to gelation and / or insolubilization of PVDF may be suppressed.

[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% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing elemental analysis of the entire cathode active material 100 using, for example, ICP-MS, 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 and O3' crystal structures. Specifically, in the O3 crystal structure, oxygen atoms are aligned along the dotted line, whereas in the O3' crystal structure, oxygen atoms are not strictly aligned. This is because, in the O3' crystal structure, as lithium decreases, tetravalent cobalt increases, increasing Jahn-Teller distortion and distorting the octahedral structure of CoO6. Another factor is that as lithium decreases, repulsion between oxygen atoms in the CoO2 layer becomes stronger.

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

[0211] In addition, when the positive electrode active material 100 of one embodiment of the present invention contains elements other than cobalt, such as 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 100a 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 essentially composed of crystal defects, and since lithium is released from the surface during charging, this portion is prone to have 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 100a of the positive electrode active material 100 according to one embodiment of the present invention is preferably higher than the overall average. The presence of halogen in the surface layer portion 100a, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0214] As described above, the surface 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 portion 100a may have a different crystal structure from the interior portion 100b. For example, at least a portion of the surface 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 portion 100a and the interior portion 100b have different crystal structures, it is preferable that the crystal orientations of the surface portion 100a and the interior portion 100b roughly match.

[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, the anions are referred to as having a cubic close-packed structure if they have a structure in which three layers of anions are stacked with a skewed relationship, such as ABCABC. Therefore, the anions do not necessarily have to be strictly cubic lattice structures. At the same time, because real crystals always have defects, analytical results do not necessarily align with theory. For example, in electron diffraction or FFT (fast Fourier transform) images of TEM images, spots may appear at positions slightly different from the theoretical positions. For example, a cubic close-packed structure can be said to exist if the orientation from the theoretical position is less than 5 degrees or less than 2.5 degrees.

[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. Layered rock-salt structures have space group R-3m and a rhombohedral structure, but to make the structure easier to understand, they are generally represented as a compound hexagonal lattice, and the (0001) plane of the layered rock-salt structure 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 structure. 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 groups 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 the rock salt type crystal with the simplest symmetry). 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 orientation of the two regions roughly coincides 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] Figure 13 shows an example of a TEM image in which the orientation of the layered rock salt-type crystals LRS and RS roughly coincides. Images that reflect the crystal structure can be obtained from TEM, STEM, HAADF-STEM, ABF-STEM, etc.

[0221] For example, in high-resolution TEM images, contrast originating from crystal planes can be observed. When an electron beam is incident perpendicular 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 is observed as a repetition of bright and dark lines. Therefore, a repetition of bright and dark lines is observed in the TEM image, and the bright lines (for example, the L shown in Figure 13) are not clearly distinguishable from each other. RS and L LRS If 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., that the crystal orientations are roughly aligned. Similarly, if 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, HAADF-STEM images exhibit contrast dependent on atomic number, with elements with higher atomic numbers appearing brighter. For example, in the case of layered rock-salt lithium cobaltate, which belongs to the space group R-3m, cobalt (atomic number 27) has the highest atomic number, so the electron beam is strongly scattered at the cobalt atoms, resulting in the arrangement of the cobalt atoms being observed as bright lines or an array of highly luminous dots. Therefore, when lithium cobaltate with 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 bright lines or an array of highly luminous dots, while the arrangements of lithium and oxygen atoms are observed as dark lines or low-luminance 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, if repeated 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 the same, i.e., that the crystal orientations are roughly the same. Similarly, if 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 the same.

[0224] Elements with smaller atomic numbers appear brighter in ABF-STEM, but like HAADF-STEM, contrast is obtained according to atomic number, making it possible to determine crystal orientation in the same way as with HAADF-STEM images.

[0225] Figure 14A shows an example of a STEM image in which the orientations of the layered rock-salt-type crystal LRS and the rock-salt-type crystal RS roughly coincide. Figure 14B shows an FFT of the region of the rock-salt-type crystal RS, and Figure 14C shows an FFT of the region of the layered rock-salt-type 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 due to the 11-1 reflection of the cubic crystal. The spot marked A in Figure 14C is due to 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] Thus, in FFT and electron diffraction, when the orientations of the layered rock-salt crystal and the rock-salt crystal roughly coincide, the <0003> orientation of the layered rock-salt crystal or an equivalent plane orientation may roughly coincide with the <11-1> orientation of the rock-salt crystal or an equivalent plane orientation. In this case, it is preferable that these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points. Spot-like reciprocal lattice points that are not continuous with other reciprocal lattice points indicate high crystallinity.

[0228] Furthermore, even if 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 roughly the same as described above, 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 Figure 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 Figure 14C) originating from the 0003 reflection of the layered rock salt crystal, and at a location 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, a reciprocal lattice point equivalent to 0003 and 1014 may also be used.

[0229] Similarly, spots not originating from the cubic 11-1 may be observed in a reciprocal lattice space other than the orientation where the cubic 11-1 is observed. For example, the spot marked B in Figure 14B is originating from the cubic 200 reflection. This is because a diffraction spot may be observed at an angle of 54° to 56° (i.e., ∠AOB is 54° to 56°) from the orientation of the reflection (A in Figure 14B) originating from the cubic 11-1. Note that this index is just 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 cathode active materials, such as lithium cobalt oxide, tend to exhibit 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 cathode active material using an SEM or similar, it is possible to thin-section the observation sample using an FIB or similar technique so that the electron beam is [12-10] incident in a TEM or similar technique, making it easier to observe the (0003) plane. When determining whether the crystal orientation is consistent, it is preferable to thin-section the layered rock-salt cathode active material 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 be 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 material, but more preferably, a portion of the additional element X is segregated at the grain boundaries.

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

[0235] Grain boundaries can be considered as planar defects. Therefore, like particle surfaces, they are prone to instability and are prone to initiating changes in the crystal structure. Therefore, if the concentration of the added element X at and near the grain boundaries is high, changes 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 where the cracks occur. Therefore, the corrosion resistance to hydrofluoric acid of the positive electrode active material even after the cracks occur can be improved.

[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 may 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 the electrolyte may 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 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 because 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.

[0240] As described above, the cathode 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 50 wt% or more of a crystal structure exhibiting a significant change from a high-voltage charged state to a discharged state is present in a high-voltage charged state 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 of the O3'-type crystal structure and cases in which the H1-3-type crystal structure accounts for 50 wt% or more of the H1-3-type crystal structure when charged at a high voltage. Furthermore, at a certain voltage, the O3'-type crystal structure may be nearly 100 wt%, and further increasing the voltage may result in the H1-3-type crystal structure. Therefore, crystal structure analysis, such as XRD, is required to determine whether a material is the cathode active material 100 of one embodiment of the present invention.

[0241] However, when positive electrode active materials are charged or discharged at high voltage, their crystal structure may change when exposed to air. For example, they may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, it is recommended that all samples be handled 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, for example, by preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and charging it.

[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 used in the electrolytic solution is 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution can be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC).

[0246] The separator can be made of polypropylene with 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 fabricated under the above conditions was charged at a constant current of 4.6 V and 0.5 C, followed by constant voltage charging until the current reached 0.01 C. Here, 1 C corresponds to 137 mA / g. The temperature was 25°C. After charging in this manner, the coin cell was disassembled in an argon-filled glove box and the positive electrode was removed to obtain a positive electrode active material charged at high voltage. When various analyses were performed, it was preferable to seal the cell in an argon-filled container to prevent reactions with external components. For example, XRD could be performed by sealing the cell in an argon-filled container.

[0249] <xrd> Figures 10 and 12 show ideal powder XRD patterns calculated from the O3'-type crystal structure and H1-3-type crystal structure models using CuKα1 radiation. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) with x = 1 and CoO2(O1) with x = 0 are also shown. The LiCoO2(O3) and CoO2(O1) patterns were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, with a step size of 0.01 and a wavelength of λ1 = 1.540562 × 10 -10 m and λ2 were not set, and the monochromator was set to single. The 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), and an XRD pattern was created in the same manner as for the others.

[0250] As shown in Figure 10, the O3'-type crystal structure exhibits diffraction peaks 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, the H1-3-type crystal structure and CoO2(P-3m1, O1) do not exhibit peaks 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 the XRD diffraction peaks appear are close between the crystal structure with x = 1 and the crystal structure in the high-voltage charged 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] Although 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, the entire positive electrode active material 100 does not necessarily have to have an O3'-type crystal structure. The positive electrode active material 100 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] Furthermore, the crystallite size of the O3'-type crystal structure possessed by the particles of the positive electrode active material only decreases to about one-tenth of that of LiCoO2(O3) in the discharged state. Therefore, even under the same XRD measurement conditions as for the positive electrode before charging and discharging, a clear peak of the O3'-type crystal structure can be confirmed in the high-voltage charged state. On the other hand, with simple LiCoO2, even if some of the material adopts a structure similar to the O3'-type crystal structure, the crystallite size becomes smaller and the peak becomes broad and small. The crystallite size can be determined from the 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 additive 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, 2.817×10 -10 m and the c-axis lattice constant is 14.05×10 -10 m, 14.07 × 10 -10 It has been found that it is preferable that the value be smaller than m. The state in which no charge or discharge is performed may be, for example, the state of powder before the positive electrode of a 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 the layered rock salt crystal structure of particles of a positive electrode active material in a state where no charge or discharge is performed or in a discharged state, a first peak may be observed at 2θ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2θ of 38.00° or more and 38.80° or less.

[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 most of the volume of the positive electrode active material 100. The crystalline structure of the surface layer 100a, etc., 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), allowing quantitative analysis of the concentration of each element in 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 performing XPS analysis, 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 analyzed by XPS, 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 showing the bond energy between magnesium and other elements 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 or aluminum is exposed by processing and analyzed using TEM-EDX, the concentration of the surface layer 100a is preferably higher than the concentration of the inner portion 100b. The processing can be performed using, for example, FIB.

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

[0269] <Surface roughness and specific surface area> The cathode active material 100 according to one embodiment of the present invention preferably has a smooth surface with minimal irregularities. A smooth surface with minimal irregularities is one factor indicating that the distribution of the additive element X in the surface layer portion 100a is favorable. 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 additive element X is initially heated, the cathode active material 100 is particularly preferred because it exhibits significantly excellent high-voltage charge / discharge cycle characteristics.

[0270] Furthermore, if 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 may be 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 FIB or the like to expose its 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. The interface is then extracted 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 to a spreadsheet or the like. Using the functions of the spreadsheet or the like, correction is performed using a regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after slope correction. The root mean square (RMS) surface roughness is calculated by calculating the standard deviation. This surface roughness is the surface roughness within at least 400 nm of the outer periphery of the cathode active material particles.

[0274] On the particle surfaces of the positive electrode active material 100 of this 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. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

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

[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 producing a positive electrode active material 100, which is one embodiment of the present invention, will be described.

[0282] <<Method 1 for preparing 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 for example, it is recommended to use a material with a purity of 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). When 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. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity and / or reliability of the secondary battery can be increased.

[0287] In addition, it is preferable that the transition metal M1 source 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 fragments. 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 them. 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 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 to 1100°C, more preferably 900°C to 1000°C, and even more preferably around 950°C. If the temperature is too low, the decomposition and melting of the lithium source and transition metal source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to 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 should be between 80°C / h and 250°C / h. For example, if heating at 1000°C for 10 hours, the temperature should be raised at 200°C / h.

[0294] Heating is preferably carried out in an atmosphere with little moisture, 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, to suppress impurities that may be mixed into the material, it is preferable that the impurity concentrations of CH4, CO, CO2, and H2 in the heating atmosphere be each 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 having oxygen flow through the reaction chamber is called flow.

[0296] When the heating atmosphere is an oxygen-containing atmosphere, a non-flow method is also possible. For example, the reaction chamber can be depressurized and then filled with oxygen to prevent the oxygen from entering or leaving the reaction chamber. This method is called purging. For example, the reaction chamber can be depressurized to -970 hPa and then filled with oxygen to 50 hPa.

[0297] After heating, the material can be cooled naturally, but it is preferable that the time required to cool the material from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary, 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. An alumina mortar is preferably used as the mortar. An alumina mortar is 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. Note that heating conditions equivalent to those of step S13 can be applied to heating steps other than step S13, which will be described later.

[0301] <Step S14> Through the above steps, a composite oxide (LiM1O2) containing a transition metal can be obtained in step S14 shown in FIG. 15A. The composite oxide only needs to have the crystal structure of a lithium composite oxide expressed as LiM1O2, and its composition is not strictly limited to Li:M1:O = 1:1:2. When cobalt is used as the transition metal, it is called a composite oxide containing cobalt and is expressed as LiCoO2. The composition is not strictly limited to Li:Co:O = 1:1:2.

[0302] Although the composite oxide is produced by the solid phase method in steps S11 to S14, 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 for 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 interior of the composite oxide. This temperature difference may induce a contraction difference. It is thought that the temperature difference causes a difference in fluidity between the surface and interior, resulting in a contraction difference. The energy associated with the contraction difference causes an internal stress difference 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 misalignment in the composite oxide, such as misalignment of crystals. This step is preferably carried out in order to reduce such misalignment. This step makes it possible to equalize the misalignment of the composite oxide. When the misalignment is 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 the misalignment of crystals and the like that has occurred in the composite oxide is alleviated after step S15, and the surface of the composite oxide becomes smooth.

[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] A smooth surface of a complex oxide can be said to have a surface roughness of 10 nm or less when the surface irregularity information of a cross section of the complex oxide is quantified from measurement data. The cross section is, for example, a cross section obtained when observing 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 lithium in the composite oxide is reduced by the initial heating. The lithium in the composite oxide may be more easily incorporated into the additive element, which will be explained in the next step S20.

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

[0317] <Step S21> 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 source of the additive element.

[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 that can be used include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). 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 be a gas, such as fluorine (F), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF, OF, OF, OF, OF), which may be mixed into the atmosphere during the heating step described below. A plurality of the above-mentioned fluorine sources may also be used.

[0323] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The melting point is most effectively lowered when lithium fluoride and magnesium fluoride are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium content will be excessive, resulting in poor cycle performance. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is preferably LiF:MgF2 = x:1 (0 ≦ x ≦ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≦ x ≦ 0.5), and even more preferably LiF:MgF2 = x:1 (near x = 0.33). In this specification, "near" refers to a value greater than 0.9 times but less than 1.1 times the value.

[0324] <Step S22> 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] <Step S23> 15B, the pulverized and mixed materials are collected to obtain an additive element source (X source). The additive element source shown in step S23 contains 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 pulverized mixture (including cases where only one 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 subsequent process. Having the mixture uniformly adhered 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 of the composite oxide after heating. The region where fluorine and magnesium are distributed can also be referred to as the surface layer. If there is a region in the surface layer that does not contain fluorine or 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 so be interpreted as 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, steps S22 and S23 shown in FIG. 15C are similar to the steps described in FIG. 15B.

[0332] <Step S31> 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, 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, the mixing conditions are preferably lower in rotation speed or shorter in time than those in step S12. It can also be said that dry mixing conditions are milder than wet mixing. For example, a ball mill, bead mill, etc. 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 initial heating. However, the present invention is not limited to the above method. In step S11, that is, at 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, heating is performed in step S13 to obtain LiM1O2 doped with magnesium and fluorine. In this case, there is no need to separate the processes from steps S11 to S14 from the processes from steps S21 to S23. This method can be said to be simple and highly productive.

[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] <Step S33> 15A, the mixture 903 is heated under heating conditions 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 provided. The lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the composite oxide (LiM1O2) and the additive element source proceeds. The temperature at which the reaction proceeds may be any temperature at which mutual diffusion of elements contained in LiM1O2 and the additive element source occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, and the melting temperature T m 0.757 times (Tanman 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 at a temperature equal to or higher than the temperature at which at least a portion of mixture 903 melts. For example, when LiF and MgF2 are used as the additive element source, the eutectic point of LiF and MgF2 is around 742°C, so the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0342] Furthermore, a mixture 903 obtained by mixing so as to achieve a molar ratio of LiCoO2:LiF:MgF2=100:0.33:1 exhibits an endothermic peak at around 830°C in differential scanning calorimetry (DSC measurement). 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 set to be below the decomposition temperature of LiM1O2 (the decomposition temperature of LiCoO2 is 1130°C). At temperatures close to the decomposition temperature, there is a concern that LiM1O2 may decompose, albeit in a small amount. 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] Considering these, 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 fabrication method described in this embodiment, some materials, such as LiF, a fluorine source, may function as a flux. This function allows the heating temperature to be lowered below the decomposition temperature of the composite oxide (LiM1O2), for example, to 742°C or higher and 950°C or lower, and allows magnesium and other additive elements to be distributed in the surface layer, resulting in the fabrication of a positive electrode active material with excellent characteristics.

[0348] However, because LiF has a lighter specific gravity in its gaseous state than oxygen, it may volatilize when heated. 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 the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, the Li on the LiM1O2 surface may react with the F fluorine source, producing 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, the volatilization of LiF in the mixture 903 can be suppressed.

[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.

[0351] It is also believed that uniform distribution of an additive element (e.g., fluorine) in the surface layer results in a smooth, less uneven cathode active material. Therefore, in order to maintain or further smooth the surface after heating in step S15 in this process, it is better for the particles not to stick together.

[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 placing a lid on a container containing the mixture 903, for example.

[0354] Regarding the heating time, the heating time varies depending on conditions such as the heating temperature, the size and composition of the LiM1O2 particles in step S14, etc. When the particles are small, a lower temperature or shorter heating time may be preferable than when the particles are large.

[0355] When the median diameter (D50) of the composite oxide (LiM1O2) in step S14 of Figure 15A is about 12 μm, the heating temperature is preferably, for example, 600°C or higher and 950°C or lower. The heating time is preferably, for example, 3 hours or higher, more preferably 10 hours or higher, and even more preferably 60 hours or higher. The temperature reduction time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0356] On the other hand, when the median diameter (D50) of the composite oxide (LiM1O2) in step S14 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 temperature reduction 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 preparing positive electrode active material>> Next, a method for carrying out the present invention, which is different from the positive electrode active material preparation method 1, will be described.

[0359] In FIG. 16, steps S11 to S15 are carried out in the same manner as in FIG. 15A to prepare a composite oxide (LiM1O2) with a smooth surface.

[0360] <Step S20a> As described above, the additive element X may be added to the composite oxide within a range that allows the composite oxide to have a layered rock-salt type crystal structure. In this production method 2, however, the 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. 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, in step S33, the heated material is recovered to produce a composite oxide containing the additive element X1, which is also called a second composite oxide to distinguish it from the composite oxide in 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. 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 each 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, a cathode active material 100 according to one embodiment of the present invention can be produced. The cathode active material according to one embodiment of the present invention has a smooth surface.

[0370] 16 and 17, in production method 2, the additive element into the composite oxide is introduced separately as a first additive element X1 and a second additive element X2. By introducing them separately, the depth profile of each additive element can be changed. For example, it is possible to profile the first additive element so that its concentration is higher in the surface layer 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 required to obtain the composite oxide and shorter than the heating time required to obtain 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 order of steps is preferable because it maintains the surface smoothness obtained by the initial heating. When the composite oxide contains cobalt as a transition metal, it can be interpreted as a composite oxide containing cobalt.

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

[0374] (Fourth embodiment) In this embodiment mode, examples of a plurality of 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 together. These are sealed between 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 interior or to fix the position within 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 made 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] Positive electrode can 301 and negative electrode can 302 can be made of metals such as nickel, aluminum, titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, to prevent corrosion by the electrolyte, etc., they are preferably coated with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to 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 gasket 303 to produce a coin-type secondary battery 300.

[0385] The above-described configuration allows for a coin-type secondary battery 300 with a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that when a secondary battery has a solid electrolyte layer between the negative electrode 307 and the positive electrode 304, 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 the 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, in which a strip-shaped positive electrode 604 and a negative electrode 606 are 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. To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. 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 Figures 19A to 19D illustrate a secondary battery 616 in which the height of the cylinder is greater than the diameter, this is not limiting. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder may also be used. This configuration, for example, can contribute to miniaturization 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 with an increase in temperature. This increase in resistance limits the amount of current and prevents abnormal heat generation. The PTC element can be made of a barium titanate (BaTiO3)-based semiconductor ceramic or the like.

[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 the performance of the power storage system 615 less susceptible to the outside 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] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS. 20 and 21. FIG.

[0398] A 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 (such as aluminum) or a resin material.

[0399] 20B, the housing 930 shown in Fig. 20A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 20B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 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 prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking effect of 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 wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the stacked sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked.

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

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

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

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

[0406] 21C, wound body 950a 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] <Laminated secondary battery> 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] FIG. 23A shows the appearance 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 area and shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 23A.

[0410] <Method for manufacturing laminated secondary batteries> Here, an example of a method for 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 a 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 a 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 placed on the exterior body 509 .

[0413] Next, as shown in Fig. 23C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of 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 positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode 503, it is possible to obtain a secondary battery 500 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0416] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be 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 (which can also be 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 attached to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0418] The inside 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 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via the terminals 514.

[0421] The antenna 517 is not limited to a coil shape, and may be, for example, a wire or plate shape. Also, 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 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 has 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 caused by the secondary battery 513. The layer 519 can be made of, 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] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium 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, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called 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 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 lithium-graphite intercalation compounds are 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. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0429] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0430] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / 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, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0432] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[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] An electrolytic 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 electrolytic 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 or overcharging. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, 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] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalato)borate (Li(C2O4)2, LiBOB), etc. can be used alone or in any combination and ratio of two or more of these.

[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 may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)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 of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Note that glass-like materials can also be used as ceramic materials, but unlike the coating material 101 used in the electrodes, it is preferable that they have low electronic conductivity. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide-based materials that can be used 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] (Embodiment 5) In this embodiment, an example will be shown in which an all-solid-state battery is produced using the cathode active material composite 100z obtained in the above-described embodiment.

[0449] As shown in FIG. 25A, a secondary battery 400 according to 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 has positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 has 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 contain 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 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive 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 one that does not have a 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] As the solid electrolyte 421 of the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0454] Sulfide-based solid electrolytes include thiolithium-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 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] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON-type crystal structure (Li 1-Y Al Y Ti 2-Y (PO4)3, etc.), materials with garnet-type crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON-type crystal structure (Li 14 ZnGeO 16 etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystallized glasses (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) are included. Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0456] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can be used as solid electrolytes.

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

[0458] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 1) (hereinafter, LATP) contains aluminum and titanium, which are elements that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. Also, an improvement in productivity due to reduction of processes can be expected. In this specification, etc., the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra share vertices and are three-dimensionally arranged.

[0459] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it is preferable to have a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

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

[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 of which are 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. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 26B.

[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 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 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 shows 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 multiple package members.

[0467] An example of a cross section taken along the dashed line in Figure 27A is shown in Figure 27B. A laminate including positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is enclosed and sealed within package member 770a, which is a flat plate with electrode layer 773a provided thereon, frame-shaped package member 770b, and package member 770c, which is a flat plate with electrode layer 773b provided thereon. Package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[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) is shown 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 as shown in Fig. 20A or 21C, or may be a stacked type as shown in Fig. 22A or 22B. The first battery 1301a may use the all-solid-state battery of Embodiment 5. Using the all-solid-state battery of Embodiment 5 for the first battery 1301a allows for a high capacity, improved safety, and reduction 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 may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack 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 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 DC-DC 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] Furthermore, 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 used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by 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 control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to 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 unit 1320. A charge control circuit or a battery control system having 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.

[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 M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) can 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 of which has a c-axis aligned in a specific direction. The specific direction may be the thickness direction of the CAAC-OS film, a normal direction to the surface on which the CAAC-OS film is formed, or a normal direction to the surface of the CAAC-OS film. A crystalline region is a region in which the atomic arrangement is periodic. Considering the atomic arrangement as a lattice arrangement, a crystalline region is also a region in which the lattice arrangement is uniform. Furthermore, a CAAC-OS has a region in which multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a point in the region in which multiple crystalline regions are connected, where the lattice arrangement changes direction between a region with a uniform lattice arrangement and another region with a different uniform lattice arrangement. In other words, a CAAC-OS is an oxide semiconductor that is c-axis oriented but not clearly oriented in the ab-plane direction. A CAC-OS is, for example, 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 a similar size range. Hereinafter, a metal oxide in which one or more metal elements are unevenly distributed and the 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 a similar size range, is also referred to as a mosaic or patch structure.

[0482] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions 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 rephrased as a region whose main component is In. The second region can be rephrased 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 In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0487] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using 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 with 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 ambient operating 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 that eliminate 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. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for the secondary battery can be 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 unit 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 unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside and the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent 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. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise 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 configured using, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO x The switch unit 1324 may be formed using a power transistor having gallium oxide (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, which facilitates integration. Furthermore, OS transistors can be manufactured using the same manufacturing equipment as Si transistors, which allows for low-cost manufacturing. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The volume occupied by the control circuit unit 1320 can be reduced, enabling miniaturization.

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

[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. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor. 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, regenerated 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 regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[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 the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the charger's outlet or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also 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 is also possible by receiving power from external charging equipment using methods such as contactless power supply.

[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 range 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 in the positive electrode, 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, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, secondary batteries 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 that uses 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 includes a charge control device electrically connected to the secondary battery module.

[0509] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in method, a contactless power supply method, or the like. Charging can be performed using a predetermined method, such as CHAdeMO (registered trademark) or Combo, as appropriate, for the charging method and connector specifications. The secondary battery may be charged at a charging station provided in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electric storage device mounted on 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 power transmitting device for charging. In the case of this contactless power supply method, by incorporating a power transmitting device into the 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, and the secondary battery can be charged 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 cathode, 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] As an example, Fig. 29D shows 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 transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and includes the secondary battery module and a charge control device.

[0514] The secondary battery module of the aircraft 2004 has, for example, eight 4V secondary batteries connected in series to produce a maximum voltage of 32V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those 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 according to 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 which is one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 through a wiring 2611 or the like. The power storage device 2612 may 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 power storage device 791 may be provided with the control circuit described in Embodiment 6. 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 for its positive electrode.

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

[0521] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 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 an outlet (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 has 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 one day (for example, 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, 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, the power storage device 8602 can be stored in the under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 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 in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a secondary battery is mounted 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. Mobile phone 2100 includes a display unit 2102 built into a housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that mobile phone 2100 also includes secondary battery 2107. By including secondary battery 2107 using cathode active material composite 100z described in the above embodiment as a cathode, high capacity can be achieved, and a configuration that can accommodate space savings associated with a smaller 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 built into 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 has 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. Charging may also 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 shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 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-described embodiment as a positive electrode has a high energy density and is highly safe, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be installed in 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 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. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize 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 6409 is suitable for use in 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 surface, 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 whether or not there is 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] Figure 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 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, a 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 savings associated with a smaller housing.

[0550] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. 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 savings associated with a smaller housing can be realized.

[0551] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. 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 the 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 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 a wristwatch device 4005. The wristwatch 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 its positive electrode has high energy density, and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[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 wrist, 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. FIG. 33C 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 at 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, which is shown here as having a pair of 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 also preferably 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, etc.

[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, they can send sounds picked up by the microphones to the other electronic devices, and the sound data after processing by the electronic devices can be sent back to the main units 4100a and 4100b for playback. This allows them to be used as, for example, translation devices.

[0563] Furthermore, the secondary battery 4111 in the case 4110 can charge the secondary battery 4103 in the main body 4100a. The coin-type secondary battery, the cylindrical secondary battery, or the like described in the previous 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 previous embodiment as a 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. [Example]

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

[0566] The positive electrode active material was 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. Acetylene black (AB) was used as the conductive material, and polyvinylidene fluoride (PVDF) was used as the binder. NMP was used as the solvent.

[0567] Next, lithium cobalt oxide and acetylene black were composited to produce a cathode active material composite. A Hosokawa Micron Picobond was used for the composite process, operating at 3500 rpm for 10 minutes, with a processing volume of 50 g. The mixture ratio of lithium cobalt oxide and 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 part 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 accelerating 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 onto 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 calendar roll to create a positive electrode. A 4 cm wide electrode layer was pressed with pressures of 210 kN / m, 461 kN / m, 964 kN / m, and 1467 kN / m, in that order. After each press, the thickness of the positive electrode was measured at nine points with a micrometer, and the thickness of the current collector was subtracted to determine the thickness of the electrode layer. Finally, nine 12 mm diameter positive electrodes were cut out, each including one of the nine measured points. Each was weighed, and the weight of the current collector was subtracted to determine the weight of the electrode layer. The electrode density was calculated from the thickness, area, and weight of the electrode layer after each press, and the average value was calculated.

[0571] As a comparative example, a slurry was prepared using lithium cobalt oxide that had not been subjected to a composite treatment, 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 has not been subjected to a composite treatment.

[0573] [Table 1]

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

[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, magnesium, fluorine, nickel, and aluminum was added, and heated, according to the following process.

[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 MgF2 was prepared as a fluorine source and magnesium source. LiF:MgF2 was weighed out so that the molar ratio was 1:3. Next, LiF and MgF2 were mixed in dehydrated acetone 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 with a uniform particle size. A obtained.

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

[0581] Similarly, Al(OH)3 was prepared as an aluminum source. Similarly, dehydrated acetone was used as a solvent and stirred at a rotation speed of 400 rpm for 12 hours, and sieved to obtain an additive element source X with 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 so that the amount of 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 Mixture A with 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 set to 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 fabricated 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 this for 1 hour. The electrode layer was then washed.

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

[0588] By performing the reduction process, the graphene oxide (GO) in the electrode layer is transformed into reduced graphene oxide (RGO), which becomes conductive. 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 the 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] [Table 2]

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

[0593] <Charge / discharge characteristics> Coin cells were fabricated using the above two types of positive electrodes.

[0594] The electrolyte used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC) added as an additive. The electrolyte contained 1 mol / L lithium hexafluorophosphate (LiPF6). Polypropylene was used for 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, we will explain the discharge rate and charge rate. 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 charge rate evaluation, the charge method was CC (each rate, end voltage 4.6V) and the discharge method was CC (0.2C, end voltage 2.5V). For the discharge rate evaluation, the charge method was CC / CV (0.2C, 4.6V, end current 0.02C) and the discharge method was CC (each rate, end voltage 2.5V). The measurement temperature was 25°C in both cases. Figure 37A shows the charge capacities at 0.2C, 0.5C, 1C, 2C, 5C, and 10C. Figure 37B shows the discharge capacities at 0.2C, 0.5C, 1C, 2C, 5C, and 10C. n=2 for each.

[0598] As shown in Figures 37A and 37B, at a high charge / discharge 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 (0.5C, 4.6V, end current 0.05C) and the discharge method was CC (0.5C, end voltage 2.5V). The measurement temperature was 45°C. Figure 38 shows a graph of the cycle characteristics. n=2 for each case.

[0600] As shown in Figure 38, the positive electrode using acetylene black as the conductive material exhibited slightly better cycle performance than the positive electrode with reduced graphene oxide (RGO) as the conductive material, but no significant difference was observed. [Explanation of symbols]

[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< / xps> < / xrd>

Claims

1. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound covering at least a portion of the positive electrode active material particles, the positive electrode active material particles contain lithium cobalt oxide, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a surface layer region in which the concentration of one or more elements selected from magnesium, fluorine, and aluminum is at its maximum; Lithium-ion secondary battery.

2. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound clinging to at least a portion of the positive electrode active material particles, the positive electrode active material particles contain lithium cobalt oxide, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a region in a surface layer portion in which the count number of characteristic X-rays derived from magnesium, fluorine, or aluminum reaches a maximum value in a line analysis by STEM-EDX; Lithium-ion secondary battery.

3. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound covering at least a portion of the positive electrode active material particles, the positive electrode active material particles have a lithium cobalt oxide having a layered rock salt crystal structure and a rock salt crystal structure on a surface side of the layered rock salt crystal structure, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a surface layer region in which the concentration of one or more elements selected from magnesium, fluorine, and aluminum is at its maximum; Lithium-ion secondary battery.

4. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound overlapping at least a portion of the positive electrode active material particles, the positive electrode active material particles have a lithium cobalt oxide having a layered rock salt crystal structure and a rock salt crystal structure on a surface side of the layered rock salt crystal structure, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a surface layer region in which the concentration of one or more elements selected from magnesium, fluorine, and aluminum is at its maximum; Lithium-ion secondary battery.

5. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound having a shape that corresponds to at least a part of the shape of the positive electrode active material particles, the positive electrode active material particles have a lithium cobalt oxide having a layered rock salt crystal structure and a rock salt crystal structure on a surface side of the layered rock salt crystal structure, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a surface layer region in which the concentration of one or more elements selected from magnesium, fluorine, and aluminum is at its maximum; Lithium-ion secondary battery.

6. A lithium ion secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes positive electrode active material particles and a graphene compound surrounding at least a portion of the positive electrode active material particles, the positive electrode active material particles have a lithium cobalt oxide having a layered rock salt crystal structure and a rock salt crystal structure on a surface side of the layered rock salt crystal structure, the positive electrode active material particles contain magnesium, fluorine, aluminum, and nickel, the positive electrode active material particles have a surface layer region in which the concentration of one or more elements selected from magnesium, fluorine, and aluminum is at its maximum; Lithium-ion secondary battery.

7. In any one of claims 1 to 6, The graphene compound includes multilayer graphene, multilayer graphene oxide, reduced multilayer graphene oxide, or graphene quantum dots. Lithium-ion secondary battery.

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