Method for preparing positive electrode active material

Abstract

The present invention provides a method for producing a positive electrode active material which is stable in a high potential state and / or in a high temperature state. This method for producing a positive electrode active material comprises: a step in which a first mixture containing barium fluoride, magnesium fluoride and lithium fluoride is obtained by mixing a barium source, a magnesium source and a fluorine source into a composite oxide that comprises lithium and cobalt; a step in which the first mixture is heated at a temperature of 800°C to 1100°C for 2 hours or more; a step in which a second mixture is obtained by mixing a nickel source and an aluminum source into the first mixture; and a step in which the second mixture is heated at a temperature of 800°C to 1100°C for 2 hours or more. With respect to the molar ratio of magnesium fluoride to barium fluoride in the first mixture, y is from 0.5 to 10 if MgF2:BaF2 = y:1.

Description

Technical Field

[0001] One aspect 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. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof. Note that one aspect of the present invention particularly relates to a method for producing a positive electrode active material or a positive electrode active material. Alternatively, one aspect of the present invention relates to a positive electrode. Alternatively, one aspect of the present invention relates to a secondary battery. Alternatively, one aspect of the present invention relates to a portable information terminal having a secondary battery, a power storage system, a vehicle, or the like.

[0002] Note that in this specification, the semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all semiconductor devices.

[0003] Note that in this specification, the electronic device refers to all devices having a positive electrode active material, a secondary battery, or a power storage device, and electro-optical devices having a positive electrode active material, a positive electrode, a secondary battery, or a power storage device, information terminal devices having a power storage device, etc. are all electronic devices.

[0004] Note that in this specification, the power storage device refers to all elements and devices having a power storage function. For example, it includes power storage devices (also referred to as secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double layer capacitors.

Background Art

[0005] In recent years, various energy storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries have been actively developed. In particular, lithium-ion secondary batteries with high output and high energy density are applied to portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, household energy storage systems, industrial energy storage systems, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV). Along with the development of the semiconductor industry, the demand for them has rapidly expanded, and they have become indispensable in modern information society as a source of rechargeable energy supply.

[0006] Among them, composite oxides such as lithium cobaltate and lithium nickel-cobalt-manganese having a layered rock salt structure are widely used. These materials have useful characteristics as active material materials for energy storage devices, such as high capacity and high discharge voltage. However, in order to exhibit high capacity, during charging, the positive electrode is exposed to a high counter lithium potential. In such a high potential state, when a large amount of lithium desorbs, the stability of the crystal structure decreases, and the deterioration during charge-discharge cycles may increase. Under such a background, in order to develop high-capacity and highly stable secondary batteries, the improvement of the positive electrode active material of the secondary battery is actively carried out (for example, Patent Documents 1 to Patent Documents 3).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0008]

Non-Patent Document 1

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

[0010] Therefore, one aspect of the present invention aims to provide a method for producing a positive electrode active material that is stable in a high potential state (also called a high voltage charging state) and / or a high temperature state. Alternatively, it aims to provide a method for producing a positive electrode active material with excellent charge-discharge cycle characteristics. Alternatively, it aims to provide a method for producing a positive electrode active material with a large charge-discharge capacity. Alternatively, it aims to provide a method for producing a secondary battery with high reliability or safety.

[0011] Furthermore, one aspect of the present invention aims to provide a positive electrode active material that is stable in high potential and / or high temperature states. Alternatively, it aims to provide a positive electrode active material with excellent charge-discharge cycle characteristics. Alternatively, it aims to provide a positive electrode active material with a large charge-discharge capacity. Alternatively, it aims to provide a secondary battery with high reliability or safety.

[0012] Furthermore, one aspect of the present invention aims to provide a novel substance, active material particles, electrode, secondary battery, energy storage device, or method for producing the same. Another aspect of the present invention aims to provide a method for producing a secondary battery having one or more characteristics selected from high purity, high performance, and high reliability, or to provide a secondary battery.

[0013] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description in the specification, drawings, and claims. [Means for solving the problem]

[0014] One aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, and a fluorine source with a composite oxide having lithium and cobalt to produce a first mixture having barium fluoride, magnesium fluoride, and lithium fluoride; heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more; mixing a nickel source and an aluminum source with the first mixture to produce a second mixture; and heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of magnesium fluoride to barium fluoride in the first mixture satisfies 0.5 ≤ y ≤ 10 when MgF2:BaF2 = y:1.

[0015] Another aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, and a fluorine source with a composite oxide having lithium and cobalt to produce a first mixture having barium fluoride, magnesium fluoride, and lithium fluoride; heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more; mixing a nickel source and an aluminum source with the first mixture to produce a second mixture; and heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of lithium fluoride to barium fluoride in the first mixture satisfies 3≦z≦7 when LiF:BaF2=z:1.

[0016] Another aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, and a fluorine source with a composite oxide having lithium and cobalt to produce a first mixture having barium fluoride, magnesium fluoride, and lithium fluoride; heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more; mixing a nickel source and an aluminum source with the first mixture to produce a second mixture; and heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of magnesium fluoride to barium fluoride in the first mixture satisfies 0.5 ≤ y ≤ 10 when MgF2:BaF2 = y:1, and the molar ratio of lithium fluoride to barium fluoride in the first mixture satisfies 3 ≤ z ≤ 7 when LiF:BaF2 = z:1.

[0017] Another aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide having lithium and cobalt to produce a mixture having barium fluoride, magnesium fluoride, and lithium fluoride; and heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of magnesium fluoride to barium fluoride in the mixture satisfies 0.5 ≤ y ≤ 10 when MgF2:BaF2 = y:1.

[0018] Another aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide having lithium and cobalt to produce a mixture having barium fluoride, magnesium fluoride, and lithium fluoride; and heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of lithium fluoride to barium fluoride in the mixture satisfies 3≦z≦7 when LiF:BaF2=z:1.

[0019] Another aspect of the present invention is a method for producing a positive electrode active material, comprising the steps of: mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide having lithium and cobalt to produce a mixture having barium fluoride, magnesium fluoride, and lithium fluoride; and heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more, wherein the molar ratio of magnesium fluoride to barium fluoride in the mixture satisfies 0.5 ≤ y ≤ 10 when MgF2:BaF2 = y:1, and the molar ratio of lithium fluoride to barium fluoride in the mixture satisfies 3 ≤ z ≤ 7 when LiF:BaF2 = z:1.

[0020] Another aspect of the present invention is a positive electrode having a positive electrode active material prepared using the method for preparing a positive electrode active material described in any one of the above.

[0021] Another aspect of the present invention is a lithium-ion secondary battery having a negative electrode, an electrolyte, and the positive electrode described above.

[0022] In the lithium-ion secondary battery described above, the negative electrode preferably has a carbon-based material.

[0023] In the lithium-ion secondary battery described above, it is preferable that the electrolyte has a solid electrolyte.

[0024] Another aspect of the present invention is a mobile device having a lithium-ion secondary battery as described in any one of the above.

[0025] Another aspect of the present invention is an energy storage system having a lithium-ion secondary battery as described in any one of the above.

[0026] Another aspect of the present invention is an electronic device having a lithium-ion secondary battery as described in any one of the above. [Effects of the Invention]

[0027] According to one aspect of the present invention, a method for producing a positive electrode active material that is stable in a high potential state (also called a high voltage charging state) and / or a high temperature state can be provided. Alternatively, according to one aspect of the present invention, a method for producing a positive electrode active material with excellent charge-discharge cycle characteristics can be provided. Alternatively, according to one aspect of the present invention, a method for producing a positive electrode active material with a large charge-discharge capacity can be provided. Alternatively, according to one aspect of the present invention, a method for producing a secondary battery with high reliability or safety can be provided.

[0028] Furthermore, one aspect of the present invention can provide a positive electrode active material that is stable in high potential states and / or high temperature states. Alternatively, it can provide a positive electrode active material with excellent charge-discharge cycle characteristics. Alternatively, it can provide a positive electrode active material with a large charge-discharge capacity. Alternatively, it can provide a secondary battery with high reliability or safety.

[0029] Furthermore, one aspect of the present invention can provide novel materials, active material particles, electrodes, secondary batteries, energy storage devices, or methods for producing the same. Also, one aspect of the present invention can provide a method for producing a secondary battery having one or more characteristics selected from high purity, high performance, and high reliability, or a secondary battery.

[0030] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0031] Figure 1 is a flowchart showing the process for producing a positive electrode active material according to one aspect of the present invention. Figure 2 is a flowchart showing the process for producing a positive electrode active material according to one embodiment of the present invention. Figures 3A to 3F are flowcharts showing the process for producing a positive electrode active material according to one embodiment of the present invention. Figures 4A1 to 4C2 are cross-sectional views of the positive electrode active material. Figure 5 illustrates the charging depth and crystal structure of a positive electrode active material according to one embodiment of the present invention. Figure 6 shows the XRD pattern calculated from the crystal structure. Figure 7 illustrates the charging depth and crystal structure of the positive electrode active material in the comparative example. Figure 8 shows the XRD pattern calculated from the crystal structure. Figure 9A is an exploded perspective view of a coin-type rechargeable battery, Figure 9B is a perspective view of a coin-type rechargeable battery, and Figure 9C is a cross-sectional perspective view thereof. Figure 10A shows an example of a cylindrical secondary battery. Figure 10B shows an example of a cylindrical secondary battery. Figure 10C shows an example of multiple cylindrical secondary batteries. Figure 10D shows an example of an energy storage system with multiple cylindrical secondary batteries. Figures 11A and 11B illustrate examples of secondary batteries, while Figure 11C shows the inside of a secondary battery. Figures 12A to 12C illustrate an example of a secondary battery. Figures 13A and 13B show the external appearance of a secondary battery. Figures 14A to 14C illustrate the method for manufacturing a secondary battery. Figures 15A to 15C show examples of battery pack configurations. Figures 16A and 16B are cross-sectional views of the active material layer when a graphene compound is used as the conductive material. Figures 17A and 17B illustrate an example of a secondary battery. Figures 18A to 18C illustrate an example of a secondary battery. Figures 19A and 19B illustrate an example of a secondary battery. Figure 20A is a perspective view of a battery pack showing one embodiment of the present invention, Figure 20B is a block diagram of the battery pack, and Figure 20C is a block diagram of a vehicle having a motor. Figures 21A to 21E illustrate an example of a mobile body. Figures 22A and 22B illustrate an energy storage device according to one embodiment of the present invention. Figure 23A shows an electric bicycle, Figure 23B shows the secondary battery of an electric bicycle, and Figure 23C illustrates an electric motorcycle. Figures 24A to 24D illustrate an example of an electronic device. Figure 25A shows an example of a wearable device, Figure 25B shows a perspective view of a wristwatch-type device, and Figure 25C is a diagram illustrating the side view of a wristwatch-type device. Figure 25D is a diagram illustrating an example of wireless earphones. Figures 26A and 26B are SEM images of the embodiment. Figures 27A and 27B are SEM images of the embodiment. Figures 28A and 28B are SEM images of the embodiment. Figures 29A and 29B are graphs showing the cycle characteristics of the half-cells in the embodiment. [Modes for carrying out the invention]

[0032] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0033] In this specification, the term "complex oxide" refers to an oxide that contains multiple types of metal elements in its structure.

[0034] Furthermore, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a bar above the number, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a bar above the number. In addition, individual orientations indicating directions within a crystal are indicated by [ ], collective orientations indicating all equivalent directions are indicated by < >, individual planes indicating crystal planes are indicated by ( ), and collective planes having equivalent symmetry are indicated by {}. Furthermore, for trigonal and hexagonal crystals, including R-3m, (hkl) as well as (hkil) may be used for Miller indices, where i is -(h+k).

[0035] Furthermore, 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 ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are arranged regularly to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Also, strictly speaking, a layered rock salt-type crystal structure may have a distorted lattice structure of the rock salt-type crystal.

[0036] Furthermore, in this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. Note that there may be vacancies of cations or anions in part of the crystal structure.

[0037] In this specification, the active material may be referred to as active material particles, but its shape is diverse and not limited to particulate. For example, the shape of the active material (active material particles) in a cross-section may be other than circular, such as elliptical, rectangular, trapezoidal, triangular, square with rounded corners, or asymmetrical.

[0038] In this specification, a smooth surface of an active material can be defined as having a surface roughness of at least 10 nm or less, when the surface irregularities information of a cross-section of the active material is quantified from measurement data.

[0039] In this specification, a cross-section is, for example, a cross-section obtained when observing with a scanning transmission electron microscope (STEM).

[0040] Furthermore, the theoretical capacity of the positive electrode active material refers to the amount of electric charge when all the insertable and detachable lithium in the positive electrode active material has been detached. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 275 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0041] Furthermore, the extent to which insertable and detachable lithium remains in the positive electrode active material is determined by x in the composition formula, for example, Li x x in CoO2, or Li x Indicated by x in MO2 (where M is a transition metal element). Li in this specification. x CoO2 contains Li as appropriate. x This can be interpreted as MO2. In the case of the positive electrode active material in a secondary battery, x can also be written as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2 mAh / g, Li 0.2 It can be expressed as CoO2 or x=0.2. x A small x in CoO2 means, for example, 0.1 <x≦0.24をいう。

[0042] When lithium cobalt oxide approximately satisfies the stoichiometric ratio, it is LiCoO2, and the Li occupancy rate of the lithium sites is x=1. Similarly, a secondary battery that has finished discharging is also LiCoO2, and it can be said that x=1. Discharge completion here refers to the state where, for example, with a current of 100mA / g, the voltage falls below 2.5V (counter electrode lithium). In lithium-ion secondary batteries, when the lithium occupancy rate of the lithium sites becomes x=1 and no more lithium can be added, the voltage drops sharply. At this point, discharge can be said to have finished. Generally, in lithium-ion secondary batteries using LiCoO2, the discharge voltage drops sharply before reaching 2.5V, so discharge is considered to have finished under the above conditions.

[0043] Li x The charging and / or discharging capacities used to calculate x in CoO2 should preferably be measured under conditions where there is little or no influence from short circuits and / or electrolyte decomposition. For example, data from secondary batteries that have experienced a sudden change in capacity, which may be attributed to a short circuit, should not be used to calculate x.

[0044] (Embodiment 1) This embodiment describes a method for producing a positive electrode active material, which is one embodiment of the present invention.

[0045] Method for preparing positive electrode active material 1 <Step S11> In step S11 shown in Figure 1, lithium sources (Li sources) and transition metal sources (M sources) are prepared as the starting materials, lithium and transition metals, respectively.

[0046] As a lithium source, it is preferable to use a lithium-containing compound, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. The lithium source should preferably have high purity; for example, a material with a purity of 99.99% or higher is preferable.

[0047] The transition metal can be selected from elements listed in groups 3 through 11 of the periodic table, for example, at least one of manganese, cobalt, and nickel. The transition metal may be cobalt only, nickel only, cobalt and manganese, cobalt and nickel, or cobalt, manganese, and nickel. When cobalt only is used, the resulting positive electrode active material contains lithium cobalt oxide (LCO). When cobalt, manganese, and nickel are used, the resulting positive electrode active material contains nickel-cobalt-lithium manganese oxide (NCM).

[0048] As a transition metal source, it is preferable to use a compound having the above-mentioned transition metal. For example, oxides of the metals exemplified above as transition metals, or hydroxides of the exemplified metals, etc., can be used. As a cobalt source, cobalt oxide, cobalt hydroxide, etc., can be used. As a manganese source, manganese oxide, manganese hydroxide, etc., can be used. As a nickel source, nickel oxide, nickel hydroxide, etc., can be used. As an aluminum source, aluminum oxide, aluminum hydroxide, etc., can be used.

[0049] The transition metal source should preferably have high purity; for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher should be used. By using a high-purity material, impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and / or the reliability of the secondary battery is improved.

[0050] In addition, it is preferable that the transition metal source has high crystallinity, for example, that it has single crystal grains. The crystallinity of the transition metal source can be evaluated by TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. The above methods for evaluating crystallinity can be applied not only to transition metal sources but also to the evaluation of other materials.

[0051] Furthermore, when using two or more transition metal sources, it is preferable to prepare them in a ratio (mixing ratio) such that the resulting composite oxide can adopt a layered rock salt-type crystalline structure.

[0052] <Step S12> Next, as shown in step S12 in Figure 1, the lithium source and the transition metal source are crushed and mixed to prepare a mixed material. Crushing and mixing can be done dry or wet. Wet crushing is preferred because it allows for finer crushing. If wet crushing is used, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal source with dehydrated acetone with a purity of 99.5% or higher, with a water content of 10 ppm or less, and then crush and mix them. By using dehydrated acetone of such purity as described above, the amount of impurities that may be introduced can be reduced.

[0053] A ball mill or bead mill can be used for mixing and other processes. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they produce less impurity. Also, when using a ball mill or bead mill, the peripheral speed should be set to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0054] <Step S13> Next, as step S13 shown in Figure 1, the mixed material is heated. This step may be called firing or first heating to distinguish it from later heating steps. The heating temperature is preferably 700°C to 1200°C, and more preferably 800°C to 1100°C. For example, the heating temperature is more preferably 900°C to 1000°C, and even more preferably around 950°C. Or 1000°C to 1200°C is preferable. If the temperature is too low, the decomposition and melting of the lithium source and transition metal source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to the evaporation or sublimation of lithium from the lithium source and / or the excessive reduction of the metal used as the transition metal source. Such defects include, for example, when cobalt is used as the transition metal, excessive reduction can cause the cobalt to change from trivalent to divalent, inducing oxygen defects.

[0055] The heating time should ideally be between 1 hour and 100 hours, and preferably between 2 hours and 20 hours.

[0056] The heating rate depends on the target temperature, but a rate between 80°C / h and 250°C / h is generally recommended. For example, when heating to 1000°C for 10 hours, a heating rate of 200°C / h is appropriate.

[0057] Heating is preferably carried out in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of -50°C or lower, more preferably an atmosphere with a dew point of -80°C or lower. In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. In order to suppress impurities that may be mixed into the material, the concentrations of impurities such as CH4, CO, CO2, and H2 in the heating atmosphere should be kept below 5 ppb (parts per billion) each.

[0058] An atmosphere containing oxygen is preferred as the heating atmosphere. For example, one method is to continuously introduce dry air into the reaction chamber. In this case, the flow rate of the dry air is preferably 2 L / min or more and 10 L / min or less. The method of continuously supplying oxygen to the reaction chamber and having oxygen flow within the reaction chamber is called flow.

[0059] When the heating atmosphere is an oxygen-containing atmosphere, it is also acceptable to avoid supplying oxygen to the reaction chamber. For example, one can reduce the pressure in the reaction chamber, then fill it with oxygen, and prevent the oxygen from entering or leaving the chamber; this is called purging. For example, if the pressure in the reaction chamber is controlled by a differential pressure gauge, one can reduce the pressure to -970 hPa and then fill it with oxygen up to 50 hPa.

[0060] After heating, natural cooling is acceptable, but it is preferable that the cooling time from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary; it is sufficient if it cools to a temperature acceptable for the next step.

[0061] Heating in this process may be carried out using a rotary kiln or a roller hearth kiln. When using a rotary kiln, heating can be performed while stirring, whether in a continuous or batch system.

[0062] A crucible can be used as the container for heating, and alumina is preferred as the material of the container. Alumina crucibles are made of a material that does not easily release impurities. In this embodiment, a crucible of alumina with a purity of 99.9% is used. It is preferable to place a lid on the crucible before heating. This prevents evaporation or sublimation of the material. Alternatively, a flat-bottomed container called a sheath or setter may be used instead of a crucible. Mullite (Al2O3-SiO2 ceramic) may also be used as the material of the container.

[0063] After heating is complete, the material may be crushed and sieved as needed. When collecting the heated material, it may be transferred from the crucible to a mortar before collection. It is preferable to use an alumina mortar. Alumina mortars are made of a material that does not easily release impurities. Specifically, an alumina mortar with a purity of 90% or higher, preferably 99% or higher, should be used. In addition, the same heating conditions as in step S13 can be applied to the heating processes described later, other than step S13.

[0064] <Step S14> Through the above process, a composite oxide containing a transition metal (LiMO2) can be obtained in step S14 as shown in Figure 1. The composite oxide only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. When cobalt is used as the transition metal, for example, lithium cobaltate can be obtained, which is represented as LiCoO2. The composition is not strictly limited to Li:Co:O=1:1:2.

[0065] Although examples of producing composite oxides by solid-phase methods have been shown as in steps S11 to S14, composite oxides may also be produced by coprecipitation or by hydrothermal methods.

[0066] <Step S19> In step S19 shown in Figure 1, additive elements X and Y may be added to the composite oxide to the extent that it can take on a layered rock salt type crystal structure. Details of the steps for obtaining the additive element X source (X source) and the additive element Y source (Y source) shown in Figure 1 will be explained using Figures 3A to 3D.

[0067] <Step S22> In step S22 shown in Figure 3A, an X source to be added to the composite oxide is prepared. If the added element X is barium (Ba), a barium source (Ba source) can be prepared as the X source. A fluorine source (F source) may also be provided as the X source. Figure 3A shows an example in which a Ba source and an F source are prepared in step S22.

[0068] For example, barium fluoride (BaF2), barium oxide (BaO), barium hydroxide (Ba(OH)2), barium nitrate (Ba(NO3)2), barium sulfate (BaSO4), or barium carbonate (BaCO3) can be used as a source of barium.

[0069] As a source of fluorine, for example, 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), cerium fluoride (CeF2), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3AlF6) can be used. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later.

[0070] When the X source includes both a Ba source and an F source, it is preferable to use barium fluoride as the Ba source and lithium fluoride as the F source because they have a eutectic point.

[0071] <Step S23a / S23b> Next, the Ba source and F source prepared in step S22 are crushed. The Ba source and F source may be crushed independently, as shown in step S23a of Figure 3A, or they may be crushed while being mixed, as shown in step S23b of Figure 3B. The crushing, or crushing and mixing, can be performed by selecting from the crushing and mixing conditions described in step S12 of Figure 1. Note that if only the Ba source is used as the X source, crushing for the X source does not need to be performed.

[0072] <Step S24a / S24b> Next, in step S24a shown in Figure 3A or step S24b shown in Figure 3B, the material that has been crushed or crushed and mixed above can be recovered to obtain the X source. Note that an X source having multiple starting materials can be called a mixture.

[0073] For obtaining the X source, either the steps shown in Figure 3A or the steps shown in Figure 3B may be used.

[0074] <Step S25> In step S25, shown in Figures 3C and 3D, a Y source to be added to the composite oxide is prepared. It is desirable to have a fluorine source (F source) as the Y source. Figures 3C and 3D show an example in step S25 in which a magnesium source (Mg source) and a fluorine source (F source) are prepared.

[0075] As the additive element Y, one or more can be selected from magnesium, calcium, fluorine, aluminum, nickel, cobalt, manganese, titanium, zirconium, yttrium, vanadium, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, and boron.

[0076] When magnesium is selected as the additive element Y, the Y source can be called a magnesium source. Suitable magnesium sources include magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate. Multiple magnesium sources may also be used.

[0077] When fluorine is selected as the additive element Y, the Y source can be called a fluorine source. Examples of suitable fluorine sources include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), cerium fluoride (CeF2), lanthanum fluoride (LaF3), or sodium aluminum hexafluoride (Na3AlF6). Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating process described later.

[0078] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source.

[0079] The fluorine source may also be a gas, such as fluorine (F2), carbon fluoride, sulfur fluoride, or oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), which may be mixed into the atmosphere during the heating process described later. Multiple fluorine sources may also be used.

[0080] In one example of the Y source in this embodiment, lithium fluoride (LiF) is prepared as the fluorine source and magnesium fluoride (MgF2) is prepared as the magnesium source. The effect of lowering the melting point is greatest 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 will be in excess and the cycle characteristics will deteriorate. For this reason, 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 (x=0.33 and near 0.33). In this specification, "near" means a value greater than 0.9 times and less than 1.1 times the value.

[0081] For obtaining the Y source, either the steps shown in Figure 3C or the steps shown in Figure 3D may be used.

[0082] Furthermore, the molar ratio of barium fluoride (BaF2) contained in additive element X in step S19 to magnesium fluoride (MgF2) contained in additive element Y is preferably 0.5 ≤ y ≤ 10, more preferably 3 ≤ y ≤ 10, and even more preferably 3 ≤ y ≤ 5, when MgF2:BaF2 = y:1. Also, the molar ratio of lithium fluoride (LiF) contained in additive elements X and Y in step S19 to barium fluoride (BaF2) contained in additive element X is preferably 3 ≤ z ≤ 7, more preferably 4 ≤ z ≤ 7, and even more preferably 4 ≤ z ≤ 4.6, when LiF:BaF2 = z:1.

[0083] Within the above range, it is preferable that 3≦y≦10 and 4≦z≦7, more preferably 3≦y≦5 and 4≦z≦4.6, as this is expected to improve battery characteristics. Within the above range, if 0.5≦y≦1.5 and 3≦z≦3.6, it is expected to have the effect of lowering the heating temperature in step S33 described later.

[0084] <Step S26a / S26b> Next, the Mg source and F source prepared in step S25 are ground. The Mg source and F source may be ground independently, as shown in step S26a of Figure 3C, or they may be ground together, as shown in step S26b of Figure 3D. The grinding, or grinding and mixing, can be carried out by selecting from the grinding and mixing conditions described in step S12 of Figure 1.

[0085] A heating step may be performed after step S26b if necessary. The heating step can be performed by selecting from the heating conditions described in step S13. The heating time is preferably 2 hours or more, and the heating temperature is preferably 800°C to 1100°C.

[0086] <Step S27a / S27b> Next, in step S27a shown in Figure 3C or step S27b shown in Figure 3D, the material that has been crushed or crushed and mixed above can be recovered to obtain a Y source. A Y source having multiple starting materials can be called a mixture.

[0087] The particle size of the mixture from step S24a or step S24b and the mixture from step S27a or step S27b is preferably such that the D50 (median diameter) is 50 nm or more and 10 μm or less, and more preferably 100 nm or more and 3 μm or less. Even when using only one material as the additive element source, the D50 (median diameter) is preferably such that it is 50 nm or more and 10 μm or less, and more preferably 100 nm or more and 3 μm or less.

[0088] Such finely powdered mixtures (including those with only one additive element) are preferable because they allow for uniform adhesion of the mixture to the surface of the composite oxide particles when mixed with the composite oxide in a later step. Uniform adhesion of the mixture to the surface of the composite oxide is preferable because it facilitates the uniform distribution or diffusion of barium and magnesium to the surface layer of the composite oxide after heating. The region where barium and magnesium are distributed can also be called the surface layer. If there are regions in the surface layer that do not contain barium and magnesium, it may be difficult to form the O3' type crystal structure described later in the charged state.

[0089] <Step S31> Next, in step S31 shown in Figure 1, the composite oxide, the X source, and the Y source are mixed.

[0090] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter time than the mixing in step S12. Also, dry mixing is considered milder than wet mixing. For mixing, for example, a ball mill, bead mill, or kneader can be used. When using a ball mill, it is preferable to use zirconia balls as the media. Furthermore, the mixing should be carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0091] <Step S32> Next, in step S32 of Figure 1, the materials mixed above are recovered to obtain mixture 903. During recovery, if necessary, crushing and sieving may be performed. In mixture 903, the molar ratio of barium fluoride (BaF2) contained in additive element X in step S19 to magnesium fluoride (MgF2) contained in additive element Y is maintained. Also in mixture 903, the molar ratio of lithium fluoride (LiF) contained in additive elements X and Y in step S19 to barium fluoride (BaF2) contained in additive element X is maintained.

[0092] <Step S33> Next, in step S33 shown in FIG. 1, the mixture 903 is heated. It can be carried out by selecting from the heating temperatures described in step S13. The heating time is preferably 2 hours or more. This step may be referred to as the second heating.

[0093] Here, a supplement about the heating temperature is made. The lower limit of the heating temperature in step S33 needs to be at least the temperature at which the reaction between the composite oxide (LiMO2) and the X source and the Y source proceeds. The temperature at which the reaction proceeds may be any temperature at which mutual diffusion of the elements possessed by LiMO2, the X source, and the Y source occurs, and it may be lower than the melting temperature of these materials. Taking oxides as an example, it is known that solid-phase diffusion occurs from 0.757 times the melting temperature T m (Tammann temperature T d ). Therefore, the heating temperature in step S33 may be 500°C or higher.

[0094] Of course, when the temperature is at least the temperature at which at least a part of the mixture 903 melts, the reaction proceeds more easily. For example, when the X source includes LiF and BaF2, the eutectic point of LiF and BaF2 is around 765°C, so the lower limit of the heating temperature in step S33 is preferably 765°C or higher. Also, for example, when the Y source includes LiF and MgF2, the eutectic point of LiF and MgF2 is around 742°C, so the lower limit of the heating temperature in step S33 is preferably 742°C or higher. Also, for example, when the X source and the Y source include LiF, BaF2, and MgF2, the eutectic point of LiF, BaF2, and MgF2 is around 654°C, so it is preferably 654°C or higher. Therefore, the heating temperature in step S33 is preferably 654°C or higher, more preferably 742°C or higher, and even more preferably 775°C or higher.

[0095] A higher heating temperature makes the reaction proceed more easily, requires a shorter heating time, and is preferable for high productivity.

[0096] The upper limit of the heating temperature should be below the decomposition temperature of LiMO2 (the decomposition temperature of LiCoO2 is 1130°C). At temperatures near the decomposition temperature, there is a concern that LiMO2 may decompose, albeit in small amounts. Therefore, it is more preferable to be 1000°C or lower, even more preferable to be 950°C or lower, and even more preferable to be 900°C or lower.

[0097] Based on these considerations, the heating temperature in step S33 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, 654°C to 1130°C is preferred, more preferably 654°C to 1000°C, even more preferably 654°C to 950°C, and even more preferably 654°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 765°C to 1130°C is preferred, more preferably 765°C to 1000°C, even more preferably 765°C to 950°C, and even more preferably 765°C to 900°C. The heating temperature in step S33 should be lower than that in step S13.

[0098] Furthermore, when heating the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride, caused by the fluorine source, etc., within an appropriate range in the heating furnace or heating container such as a crucible.

[0099] In the manufacturing method described in this embodiment, some materials, such as the lithium source LiF, may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of the composite oxide (LiMO2), for example, between 654°C and 950°C, enabling the distribution of additive elements, including barium and magnesium, to the surface layer and the production of a positive electrode active material with good properties.

[0100] However, since LiF is lighter than oxygen in its gaseous state, heating may cause LiF to evaporate or sublimate, which would reduce the amount of LiF in mixture 903. This would weaken its function as a flux. Therefore, heating is necessary while suppressing the evaporation or sublimation of LiF. Even if LiF is not used as a lithium source, Li on the surface of LiMO2 may react with F from a fluorine source to produce LiF, which may then evaporate or sublimate. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress evaporation or sublimation is necessary.

[0101] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the evaporation or sublimation of LiF in the mixture 903.

[0102] In this step, heating is preferably carried out in a way that prevents the particles of mixture 903 from sticking together. If the particles of mixture 903 stick together during heating, the contact area with oxygen in the atmosphere decreases, and the diffusion pathways of additive elements X and Y (e.g., barium, magnesium, and fluorine) are obstructed, which may prevent the additive elements X and Y (e.g., barium, magnesium, and fluorine) from being uniformly distributed in the surface layer. Therefore, in order to achieve a smooth surface in this step, it is preferable that the particles do not stick together.

[0103] Furthermore, it is believed that a smooth positive electrode active material with few irregularities can be obtained if the additive elements X and Y (e.g., barium, magnesium, and fluorine) are uniformly distributed on the surface. Therefore, in order to maintain or further improve the smooth surface after heating in step S13 of this process, it is preferable that the particles do not adhere to each other.

[0104] Furthermore, when heating with a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere inside the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to purge the atmosphere initially and then not supply oxygen after introducing the oxygen atmosphere into the kiln. If oxygen is supplied and flows through the above atmosphere, the fluorine source may evaporate or sublimate, which is undesirable for achieving a smooth surface.

[0105] When heating by roller hearth kiln, for example, the mixture 903 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 903.

[0106] A note regarding heating time: The heating time varies depending on conditions such as the heating temperature, the size of the LiMO2 particles in step S14, and their composition. When the particles are small, a lower temperature or shorter time may be preferable than when the particles are large.

[0107] When the median diameter (D50) of the composite oxide (LiMO2) in step S14 of Figure 1 is approximately 12 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0108] On the other hand, if the median diameter (D50) of the composite oxide (LiMO2) in step S14 is about 5 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0109] <Step S34> Next, the material heated in step S33 is recovered to obtain a composite oxide having additive elements X and Y. This is also called the second composite oxide to distinguish it from the composite oxide of step S14.

[0110] <Step S40> In step S40 shown in Figure 1, the additive element Z source is added. An example of using nickel and aluminum as the additive element Z will be explained with reference to Figures 3E and 3F.

[0111] As the additive element Z, one or more can be selected from magnesium, calcium, fluorine, aluminum, nickel, cobalt, manganese, titanium, zirconium, yttrium, vanadium, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, and boron.

[0112] When nickel and aluminum are selected as the additive element Z, nickel sources such as nickel oxide and nickel hydroxide can be used. Aluminum sources such as aluminum oxide and aluminum hydroxide can be used.

[0113] <Step S41> In step S41, shown in Figures 3E and 3F, a nickel source (Ni source) and an aluminum source (Al source) are prepared.

[0114] <Step S42a / S42b> Next, the Ni source and Al source prepared in step S41 are ground. The Ni source and Al source may be ground independently, as shown in step S42a of Figure 3E, or they may be ground together, as shown in step S42b of Figure 3F.

[0115] <Step S43a / S43b> Next, in step S43a shown in Figure 3E or step S43b shown in Figure 3F, the material that has been crushed or crushed and mixed above is recovered to obtain the additive element Z source (Z source).

[0116] For obtaining the additive element Z source, either the steps shown in Figure 3E or the steps shown in Figure 3F may be used.

[0117] <Steps S51 to S53> Next, steps S51 to S53 shown in Figure 1 can be carried out under the same conditions as steps S31 to S34. The mixture 904 from step S52 is heated in step S53. At this time, the heating conditions in step S53 may be lower in temperature and shorter in duration than in step S33. The heating in step S53 may be referred to as a third heating. Through the above steps, a positive electrode active material 100 of one embodiment of the present invention can be obtained in step S54.

[0118] Method for preparing positive electrode active material (2) Furthermore, a method for producing a positive electrode active material, which is another embodiment of the present invention, will be explained with reference to Figure 2. Steps S11 to S14 can be carried out in the same manner as described in "Method for Producing a Positive Electrode Active Material 1".

[0119] <Step S20> Within the range in which a layered rock salt-type crystalline structure can be obtained, additive elements X, Y, and Z may be added to the composite oxide obtained in step S14. In this method for producing a positive electrode active material, unlike method 1 for producing a positive electrode active material, additive elements X, Y, and Z are added to the composite oxide simultaneously.

[0120] The steps for obtaining the additive element X source and the additive element Y source can be carried out in the same manner as described in "Method for Preparing Cathode Active Material 1". For the step of obtaining the additive element X source, either the step shown in Figure 3A or the step shown in Figure 3B may be used. For the step of obtaining the additive element Y source, either the step shown in Figure 3C or the step shown in Figure 3D may be used.

[0121] The step of obtaining the additive element Z source, as shown in Figure 2, can be carried out in the same way as the step of obtaining the additive element Z source described in "Method for Preparing Cathode Active Material 1". For the step of obtaining the additive element Z source, either the step shown in Figure 3E or the step shown in Figure 3F may be used.

[0122] The molar ratio of barium fluoride (BaF2) contained in the additive element X source in step S19 to magnesium fluoride (MgF2) contained in the additive element Y source, and the molar ratio of lithium fluoride (LiF) contained in the additive element Y in step S19 to barium fluoride (BaF2) contained in the additive element X, should be set in the same way as the molar ratios described in "Method for Preparing Positive Electrode Active Material 1".

[0123] <Step S31> Next, in step S31 shown in Figure 2, the composite oxide is mixed with the X source, the Y source, and the Z source.

[0124] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or shorter time than the mixing in step S12. Also, dry mixing is considered milder than wet mixing. For mixing, for example, a ball mill, bead mill, or kneader can be used. When using a ball mill, it is preferable to use zirconia balls as the media. Furthermore, the mixing should be carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0125] <Step S32> Next, in step S32 of Figure 2, the materials mixed above are recovered to obtain mixture 905. During recovery, if necessary, the materials may be crushed and then sieved.

[0126] <Step S33> Next, in step S33 shown in Figure 2, the mixture 905 is heated. This can be performed at a temperature selected from those described in step S13. A heating time of 2 hours or more is preferable.

[0127] Let me add some information about the heating temperature here. The lower limit of the heating temperature in step S33 must be above the temperature at which the reaction between the composite oxide (LiMO2) and the X, Y, and Z sources proceeds. The temperature at which the reaction proceeds is the temperature at which the elemental interdiffusion between LiMO2 and the X, Y, and Z sources occurs, and it may be lower than the melting temperature of these materials. Let me explain using an oxide as an example, but the melting temperature T m 0.757 times (Tammann temperature T) d It is known that solid-phase diffusion occurs from ). Therefore, the heating temperature in step S33 should be 500°C or higher.

[0128] Of course, the reaction proceeds more easily if the temperature is above the melting point of at least a portion of the mixture 905. For example, if LiF and BaF2 are used as the X source, the eutectic point of LiF and BaF2 is around 765°C, so it is preferable to set the lower limit of the heating temperature in step S33 to 765°C or higher. Also, for example, if LiF and MgF2 are used as the Y source, the eutectic point of LiF and MgF2 is around 742°C, so it is preferable to set the lower limit of the heating temperature in step S33 to 742°C or higher. Also, for example, if LiF, BaF2 and MgF2 are used as the X and Y sources, the eutectic point of LiF, BaF2 and MgF2 is around 654°C, so it is preferable to set the temperature to 654°C or higher. Therefore, the heating temperature in step S33 is preferably 654°C or higher, more preferably 742°C or higher, and more preferably 775°C or higher.

[0129] A higher heating temperature is preferable because it facilitates the reaction, shortens the heating time, and increases productivity.

[0130] The upper limit of the heating temperature should be below the decomposition temperature of LiMO2 (the decomposition temperature of LiCoO2 is 1130°C). At temperatures near the decomposition temperature, there is a concern that LiMO2 may decompose, albeit in small amounts. Therefore, it is more preferable to be 1000°C or lower, even more preferable to be 950°C or lower, and even more preferable to be 900°C or lower.

[0131] Based on these considerations, the heating temperature in step S33 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, 654°C to 1130°C is preferred, more preferably 654°C to 1000°C, even more preferably 654°C to 950°C, and even more preferably 654°C to 900°C. Also, 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, 765°C to 1130°C is preferred, more preferably 765°C to 1000°C, even more preferably 765°C to 950°C, and even more preferably 765°C to 900°C.

[0132] Furthermore, when heating the mixture 905, it is preferable to control the partial pressure of fluorine or fluoride caused by the fluorine source, etc., within an appropriate range in the heating furnace or heating container such as a crucible.

[0133] In the manufacturing method described in this embodiment, some materials, such as LiF, which is a Li source, may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of the composite oxide (LiMO2), for example, between 654°C and 950°C, enabling the distribution of additive elements, including barium and magnesium, to the surface layer and the production of a positive electrode active material with good properties.

[0134] However, since LiF is lighter than oxygen in its gaseous state, heating may cause LiF to evaporate or sublimate, which reduces the amount of LiF in mixture 905. This weakens its function as a flux. Therefore, heating is necessary while suppressing the evaporation or sublimation of LiF. Even if LiF is not used as a lithium source, Li on the surface of LiMO2 may react with F from a fluorine source to produce LiF, which may then evaporate or sublimate. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress evaporation or sublimation is necessary.

[0135] Therefore, it is preferable to heat the mixture 905 in an atmosphere containing LiF, that is, to heat the mixture 905 while the partial pressure of LiF in the heating furnace is high. Such heating can suppress the evaporation or sublimation of LiF in the mixture 905.

[0136] In this step, heating is preferably carried out in a way that prevents the particles of mixture 905 from sticking together. If the particles of mixture 905 stick together during heating, the contact area with oxygen in the atmosphere decreases, and the diffusion pathways of additive elements X and Y (e.g., barium, magnesium, and fluorine) are obstructed, which may prevent the additive elements X and Y (e.g., barium, magnesium, and fluorine) from being uniformly distributed in the surface layer. Therefore, in order to achieve a smooth surface in this step, it is preferable that the particles do not stick together.

[0137] Furthermore, it is believed that a smooth positive electrode active material with few irregularities can be obtained if the additive elements X and Y (e.g., barium, magnesium, and fluorine) are uniformly distributed on the surface.

[0138] Furthermore, when heating with a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere inside the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to purge the atmosphere initially and then not supply oxygen after introducing the oxygen atmosphere into the kiln. If oxygen is supplied and flows through the above atmosphere, the fluorine source may evaporate or sublimate, which is undesirable for achieving a smooth surface.

[0139] When heating by roller hearth kiln, for example, the mixture 905 can be heated in an atmosphere containing LiF by placing a lid on the container containing the mixture 905.

[0140] A note regarding heating time: The heating time varies depending on conditions such as the heating temperature, the size of the LiMO2 particles in step S14, and their composition. When the particles are small, a lower temperature or shorter time may be preferable than when the particles are large.

[0141] When the median diameter (D50) of the composite oxide (LiMO2) in step S14 of Figure 2 is approximately 12 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0142] On the other hand, if the median diameter (D50) of the composite oxide (LiMO2) in step S14 is about 5 μm, the heating temperature is preferably, for example, 600°C to 950°C. The heating time is preferably, for example, 1 hour to 10 hours, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours to 50 hours.

[0143] <Step S34> Next, the material heated in step S33 is recovered to obtain the positive electrode active material 100.

[0144] In addition, while methods 1 and 2 for preparing the positive electrode active material described above show examples in which the material of the additive element source is pulverized when adding the additive element source, the additive element source may be added without pulverizing part or all of the material.

[0145] Furthermore, in the above-described methods 1 and 2 for preparing the positive electrode active material, the F source was added as part of the X source and part of the Y source, but the F source may also be added as either the X source or the Y source.

[0146] When a composite oxide contains cobalt as a transition metal, it can be rephrased as a composite oxide containing cobalt.

[0147] This embodiment can be used in combination with other embodiments.

[0148] (Embodiment 2) In this embodiment, a positive electrode active material according to one aspect of the present invention will be described with reference to Figures 4 to 8.

[0149] [Cathode active material] Figures 4A1 and 4A2 are cross-sectional views of a positive electrode active material 100 according to one embodiment of the present invention. Figures 4B1 and 4B2 show enlarged views of the area around AB in Figure 4A1. Figures 4C1 and 4C2 show enlarged views of the area around CD in Figure 4A1.

[0150] As shown in Figures 4A1 to 4C2, the positive electrode active material 100 has a surface layer 100a and an interior layer 100b. In these figures, the boundary between the surface layer 100a and the interior layer 100b is indicated by a dashed line. In Figure 4A2, a part of the grain boundary 101 is shown by a dashed line. Also in Figure 4A2, the embedded parts 102 of the positive electrode active material 100, such as recesses, cracks, depressions, and V-shaped cross-sections, are shown. Furthermore, Figure 4A2 shows the unevenly distributed parts 103. The unevenly distributed parts 103 are regions in the positive electrode active material 100 where the additive elements (additive element X, additive element Y, and / or additive element Z) are unevenly distributed.

[0151] In this specification, the surface layer 100a of the positive electrode active material 100 refers to, for example, the region within 50 nm from the surface toward the interior, more preferably within 35 nm from the surface toward the interior, even more preferably within 20 nm from the surface toward the interior, and most preferably within 10 nm from the surface toward the interior. Surfaces formed by cracks and / or fissures may also be considered the surface. The surface layer 100a may also be called the vicinity of the surface or the vicinity of the surface. Furthermore, the region deeper than the surface layer 100a of the positive electrode active material is called the interior 100b. The interior 100b may also be called the interior region.

[0152] It is preferable that the surface layer 100a has a higher concentration of the additive elements (additive elements X, Y, and Z) described later than the interior layer 100b. It is also preferable that the additive elements (additive elements X, Y, and Z) have a concentration gradient. Furthermore, if there are multiple additive elements (additive elements X, Y, and Z), it is preferable that the depth of the concentration peak from the surface differs for each additive element.

[0153] For example, it is preferable that additive elements X and Y have a concentration gradient that increases from the interior 100b towards the surface, as shown by the gradient in Figure 4B1. Examples of additive elements X and Y that are preferable to have such a concentration gradient include barium, magnesium, fluorine, titanium, silicon, phosphorus, boron, and calcium.

[0154] Another additive element Z preferably has a concentration gradient, as shown in the gradient in Figure 4B2, and has a concentration peak in a region deeper than that shown in Figure 4B1. The concentration peak may be located in the surface layer 100a or deeper than the surface layer 100a. For example, additive element Z preferably has a peak in a region of 5 nm to 50 nm from the surface inward. Examples of additive elements Z that preferably have such a concentration gradient include aluminum and manganese.

[0155] Furthermore, it is preferable that the crystal structure of the positive electrode active material 100 changes continuously from the interior 100b toward the surface due to the aforementioned concentration gradient of the added elements (added element X, added element Y, and added element Z) present in the positive electrode active material 100.

[0156] <Contained elements> The positive electrode active material 100 comprises lithium, a transition metal M, oxygen, additive element X, additive element Y, and additive element Z. The positive electrode active material 100 has a structure in which the additive elements are added to a composite oxide represented by LiMO2. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented by LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. Furthermore, a positive electrode active material with added additive elements may also be referred to as a composite oxide.

[0157] As the transition metal M in the positive electrode active material 100, it is preferable to use a metal that can form a layered rock salt type composite oxide that belongs to space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, as the transition metal M in the positive electrode active material 100, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. In other words, the positive electrode active material 100 can have composite oxides containing lithium and a transition metal M, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is substituted with manganese, lithium cobalt oxide in which part of the cobalt is substituted with nickel, and nickel-manganese-lithium cobalt oxide. Layered rock salt type composite oxides have a two-dimensional lithium ion diffusion pathway and are suitable for lithium ion insertion / desorption reactions.

[0158] In particular, using cobalt as the transition metal M in the positive electrode active material 100 in an amount of 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics. Furthermore, if nickel is included in addition to cobalt within the above range as the transition metal M, the displacement of the layered structure consisting of octahedra of the transition metal and oxygen may be suppressed. Therefore, the crystal structure may become more stable, especially in the charged state at high temperatures, which is preferable.

[0159] Furthermore, the transition metal M does not necessarily have to contain manganese. By using a cathode active material 100 that is substantially free of manganese, the above advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics may be even greater. The weight of manganese contained in the cathode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0160] On the other hand, if nickel is used as the transition metal M in the positive electrode active material 100 in an amount of 33 atomic percent or more, preferably 60 atomic percent or more, and more preferably 80 atomic percent or more, the raw materials may be cheaper compared to the case where cobalt is abundant, and the charge / discharge capacity per unit weight may increase, which is preferable.

[0161] Furthermore, the transition metal M does not necessarily have to contain nickel. By using a positive electrode active material 100 that is substantially nickel-free, the above advantages such as being relatively easy to synthesize, easy to handle, and having excellent cycle characteristics may be even greater. The weight of nickel contained in the positive electrode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.

[0162] It is preferable to use at least one of the following as the additive elements (additive element X, additive element Y, and additive element Z) in the positive electrode active material 100: barium, magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. These additive elements may further stabilize the crystal structure of the positive electrode active material 100, as will be described later. In other words, the positive electrode active material 100 can include lithium cobalt oxide with barium, magnesium, and fluorine, lithium cobalt oxide with barium, magnesium, and aluminum, lithium nickel-cobalt oxide with barium, magnesium, and fluorine, lithium cobalt-aluminate with barium, magnesium, and nickel, lithium nickel-cobalt-aluminate with barium, magnesium, and fluorine, lithium nickel-manganese-cobalt oxide with barium, magnesium, and fluorine, and the like. In this specification, additive elements may also be referred to as mixtures, part of raw materials, or impurity elements.

[0163] Furthermore, the additive elements do not necessarily have to include magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, or boron.

[0164] In one embodiment of the present invention, in the positive electrode active material 100, even if lithium is removed from the positive electrode active material 100 due to charging, the layered structure consisting of octahedra of transition metal M and oxygen is not destroyed, as is reinforced by an additive element in the surface layer 100a, i.e., the outer periphery of the particles. For this reason, it is preferable that the concentration of the additive element be high in the surface layer 100a.

[0165] Furthermore, it is preferable that the concentration gradient of the additive elements (additive element X, additive element Y, and additive element Z) in the positive electrode active material 100 be similar throughout the entire surface layer 100a of the positive electrode active material 100. It can also be said that it is preferable that the reinforcement resulting from the high concentration of the additive elements is uniformly present in the surface layer 100a. Even if there is reinforcement in a part of the surface layer 100a, if there are parts without reinforcement, stress may concentrate in those parts. If stress concentrates in a part of the particles, defects such as cracks may occur from there, which may lead to cracking of the positive electrode active material and a decrease in charge / discharge capacity.

[0166] In this specification, homogeneity refers to the phenomenon in which, in a solid composed of multiple elements (e.g., A, B, C), a certain element (e.g., A) is distributed in a specific region with similar characteristics. It is sufficient that the elemental concentrations in the specific regions are substantially the same. For example, the difference in elemental concentrations between specific regions should be within 10%. Examples of specific regions include the surface, surface layer, convex areas, concave areas, and interior.

[0167] However, the concentration gradient of the additive elements (additive element X, additive element Y, and additive element Z) present in the positive electrode active material 100 does not necessarily have to be homogeneous across the entire surface layer 100a of the positive electrode active material 100. An example of the distribution of additive elements X and Y near CD in Figure 4A1 is shown in Figure 4C1. An example of the distribution of additive element Z near CD is shown in Figure 4C2.

[0168] Here, the region near CD has a layered rock salt crystal structure of R-3m, and the surface is (001) oriented. The (001) oriented surface may have a different distribution of additive elements (additive element X, additive element Y, and additive element Z) than other surfaces. For example, as shown in Figures 4C1 and 4C2, the (001) oriented surface and its surface layer 100a may have at least one of the additive elements X, Y, and Z remaining in a shallower portion from the surface compared to other orientations. Alternatively, the (001) oriented surface and its surface layer 100a may have a lower concentration of at least one of the additive elements X, Y, and Z compared to other orientations. Alternatively, the (001) oriented surface and its surface layer 100a may have at least one of the additive elements X, Y, and Z below the detection limit.

[0169] In the layered rock salt crystal structure of R-3m, cations are arranged parallel to the (001) plane. This indicates a structure in which MO2 layers, consisting of octahedrons of transition metal M and oxygen, and lithium layers are alternately stacked parallel to the (001) plane. Therefore, the diffusion pathways for lithium ions also exist parallel to the (001) plane.

[0170] The MO2 layer, consisting of an octahedron of transition metal M and oxygen, is relatively stable; therefore, the (001) plane on which the MO2 layer exists is also relatively stable. The (001) plane does not expose the diffusion pathway of lithium ions.

[0171] On the other hand, the lithium ion diffusion pathways are exposed on surfaces other than those oriented in the (001) direction. Therefore, the surfaces and surface layer 100a other than those oriented in the (001) direction are important regions for maintaining the lithium ion diffusion pathways, but at the same time, they are prone to instability because they are the regions where lithium ions first desorb. For this reason, reinforcing the surfaces and surface layer 100a other than those oriented in the (001) direction is preferable in order to maintain the overall crystal structure of the positive electrode active material 100.

[0172] Therefore, in another embodiment of the positive electrode active material 100 of the present invention, it is preferable that the distribution of additive elements (additive element X, additive element Y, and additive element Z) on surfaces other than (001) and its surface layer 100a is as shown in Figures 4B1 and 4B2. On the other hand, on the (001) surface and its surface layer 100a, the peak position of the additive elements may be shallow, the concentration of the additive elements may be low, or there may be no additive elements at all, as described above.

[0173] In the manufacturing method described in the previous embodiment, in which high-purity LiMO2 is produced and then the additive elements are mixed in and heated afterward, the additive elements (additive elements X, Y, and Z) spread mainly through the diffusion pathway of lithium ions, making it easier to achieve a favorable distribution of the additive elements (additive elements X, Y, and Z) on surfaces other than (001) and their surface layer 100a.

[0174] ≪Grain boundary≫ In one aspect of the present invention, when the positive electrode active material 100 has a grain boundary 101, it is more preferable that, in addition to the distribution described above, a portion of the additive elements (additive element X, additive element Y, and additive element Z) are segregated at and near the grain boundary 101.

[0175] More specifically, it is preferable that the barium concentration, magnesium concentration, and / or aluminum concentration at and near the grain boundary 101 of the positive electrode active material 100 are higher than those in other regions of the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundary 101 is higher than that in other regions of the interior 100b.

[0176] The grain boundary 101 is a type of surface defect. Therefore, like the grain surface, it is prone to instability and easily initiates changes in the crystal structure. For this reason, if the barium, magnesium, and / or aluminum concentrations are high at and near the grain boundary 101, changes in the crystal structure can be suppressed more effectively.

[0177] Furthermore, if the barium, magnesium, aluminum, and / or fluorine concentrations are high at and near the grain boundaries, even if cracks occur along the grain boundaries 101 of the particles of the positive electrode active material 100 according to one embodiment of the present invention, the barium, magnesium, aluminum, and / or fluorine concentrations will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid and the like can be improved even in the positive electrode active material after cracks have occurred.

[0178] In this specification, the vicinity of grain boundary 101 refers to the region extending approximately 50 nm from the grain boundary. A grain boundary is a plane where the arrangement of atoms changes and can be observed in an electron microscope image. Specifically, it refers to a region in an electron microscope image where the angle between repeating bright and dark lines changes by more than 5 degrees, or where the crystal structure can no longer be observed.

[0179] The positive electrode active material 100 may have depressions, cracks, pits, or V-shaped cross-sections. These are defects, and repeated charging and discharging may lead to the leaching of transition metal M, collapse of the crystal structure, cracking of the main body, and desorption of oxygen. However, if there are embedded portions 102 that fill these defects, the leaching of transition metal M and other defects can be suppressed. Therefore, a positive electrode active material 100 with excellent reliability and cycle characteristics can be obtained.

[0180] Furthermore, the positive electrode active material 100 may have a region where the additive elements (additive element X, additive element Y, and / or additive element Z) are unevenly distributed, which is a region 103. The uneven distribution region 103 may be convex in shape.

[0181] As mentioned above, if the additive elements (additive elements X, Y, and Z) in the positive electrode active material 100 are in excess, they may adversely affect the insertion and removal of lithium. Furthermore, when used in a secondary battery, this may lead to increased internal resistance and decreased charge / discharge capacity. On the other hand, if there are insufficient additive elements, they may not be distributed throughout the entire surface layer 100a, resulting in insufficient suppression of crystal structure degradation. Thus, the additive elements (also called impurity elements) in the positive electrode active material 100 need to be at an appropriate concentration, but adjusting this concentration is not easy.

[0182] Therefore, if the positive electrode active material 100 has regions where the additive elements are unevenly distributed, some of the excess additive elements can be removed from the interior 100b of the positive electrode active material 100, and an appropriate concentration of additive elements can be achieved in the interior 100b. This makes it possible to suppress an increase in internal resistance and a decrease in charge / discharge capacity when used as a secondary battery. The ability to suppress an increase in the internal resistance of a secondary battery is an extremely desirable characteristic, especially in high-rate charge / discharge, such as charge / discharge at 2C or higher. Furthermore, when barium, magnesium, and fluorine are used as additive elements X and Y, BaMg2F6, LiBaF3, BaO, MgO, BaF2, and MgF2 may be detected in regions where the additive elements are unevenly distributed.

[0183] Furthermore, in positive electrode active material 100 having regions where the additive elements are unevenly distributed, it is permissible to mix the additive elements in excess to some extent during the manufacturing process. This is preferable because it widens the margin in production.

[0184] In this specification, "non-uniformity" refers to a situation where the concentration of an element in one region differs from that in other regions. It may also be described as segregation, precipitation, heterogeneity, bias, high concentration, or low concentration.

[0185] Furthermore, in a positive electrode active material 100 having additive element X, additive element Y, and / or additive element Z in the surface layer 100a of one aspect of the present invention, the surface layer 100a, i.e., the outer periphery of the particle, is reinforced so that even if lithium is removed from the positive electrode active material 100 by charging, the layered structure consisting of octahedra of transition metal and oxygen is not destroyed. It is desirable that the surface layer 100a with high concentrations of additive element X, additive element Y, and / or additive element Z is provided in at least a part of the surface layer of the particle, preferably more than half of the surface layer of the particle, and more preferably the entire surface layer of the particle.

[0186] Furthermore, in the positive electrode active material 100 according to one embodiment of the present invention, it is desirable that the concentration gradient region of additive element X, additive element Y and / or additive element Z be provided in at least a part of the surface layer of the particle, preferably more than half of the surface layer of the particle, and more preferably the entire surface layer of the particle. This is because even if a part of the surface layer 100a is reinforced, if there is a part without reinforcement, stress may concentrate in the part without reinforcement, which is undesirable. If stress concentrates in a part of the particle, defects such as closed cracks and fissures may occur from there, which may lead to a decrease in charge-discharge capacity.

[0187] Aluminum, gallium, boron, and indium are trivalent and can be present at transition metal sites in layered rock salt-type crystal structures. Gallium, aluminum, boron, and indium can suppress the elution of surrounding transition metals. Furthermore, gallium, aluminum, boron, and indium can suppress cation mixing of surrounding transition metals (migration of transition metals to lithium sites). In addition, because gallium, aluminum, boron, and indium have a strong bonding force with oxygen, they can suppress the desorption of oxygen from around them. Therefore, by having one or more of gallium, aluminum, boron, and indium as the additive element Z, a positive electrode active material 100 can be made that is less prone to crystal structure collapse even after repeated charging and discharging.

[0188] Magnesium is divalent and is more stable in lithium sites than transition metal sites in layered rock salt crystal structures, thus readily occupying lithium sites. The presence of magnesium at an appropriate concentration in the lithium sites of the surface layer 100a facilitates the maintenance of the layered rock salt crystal structure. Furthermore, magnesium has a strong binding affinity for oxygen, which can suppress the desorption of oxygen from its surroundings. At appropriate concentrations, magnesium is preferable as it does not adversely affect lithium insertion and desorption during charging and discharging. However, excessive magnesium may adversely affect lithium insertion and desorption.

[0189] Fluorine is a monovalent anion, and if some of the oxygen in the surface layer 100a is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of cobalt ions associated with lithium desorption differs depending on the presence or absence of fluorine. For example, without fluorine, the valence changes from trivalent to tetravalent, while with fluorine, it changes from divalent to trivalent, resulting in a different oxidation-reduction potential for cobalt ions. Therefore, if some of the oxygen in the surface layer 100a of the positive electrode active material 100 is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. This is preferable because it improves charge-discharge characteristics, rate characteristics, etc., when used in a secondary battery.

[0190] Titanium oxide is known to be superhydrophilic. Therefore, by using a positive electrode active material 100 having titanium oxide in its surface layer 100a, it is possible to improve wettability with highly polar solvents. When used as a secondary battery, good contact at the interface between the positive electrode active material 100 and the highly polar electrolyte may be achieved, potentially suppressing an increase in resistance. In this specification, the term "electrolyte" may be read as "electrolyte solution".

[0191] As the charging voltage of a secondary battery increases, the voltage at the positive electrode generally rises. The positive electrode active material according to one aspect of the present invention has a stable crystal structure even at high voltages. The stability of the crystal structure of the positive electrode active material in the charged state suppresses the decrease in capacity associated with repeated charging and discharging.

[0192] Furthermore, a short circuit in a secondary battery can not only cause malfunctions in the charging and / or discharging operations of the secondary battery, but also lead to overheating and ignition. To realize a safe secondary battery, it is preferable that the short-circuit current is suppressed even at high charging voltages. The positive electrode active material 100 in one aspect of the present invention suppresses the short-circuit current even at high charging voltages. Therefore, it is possible to create a secondary battery that achieves both high capacity and safety.

[0193] A secondary battery using the positive electrode active material 100 according to one embodiment of the present invention preferably satisfies high capacity, excellent charge-discharge cycle characteristics, and safety simultaneously.

[0194] The concentration gradient of additive elements can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX). EDX can be used in combination with scanning electron microscopes (SEM) or satellite microscopes (STEM). In EDX measurements, evaluation along a line segment connecting two points is sometimes called EDX line analysis. In EDX measurements, measurement while scanning within a rectangular or other area and evaluating the area in two dimensions is sometimes called EDX surface analysis. Furthermore, when data from a linear region is extracted from EDX surface analysis and the distribution of atomic concentrations within the positive electrode active material is also sometimes called EDX line analysis. In EDX surface analysis and EDX line analysis, the point where the characteristic X-ray detection value of a certain element is maximum is sometimes called the concentration peak.

[0195] EDX surface analysis (e.g., elemental mapping) allows for the quantitative analysis of the concentrations of additive elements in the surface layer 100a, interior 100b, and near grain boundaries of the positive electrode active material 100. Furthermore, EDX radiation analysis allows for the analysis of peak concentrations of additive elements.

[0196] When EDX radiation analysis is performed on the positive electrode active material 100, the point where the characteristic X-ray detection value of barium and / or magnesium in the surface layer 100a is maximum is preferably located within a depth of 50 nm from the surface toward the center of the positive electrode active material 100, more preferably within a depth of 30 nm, and even more preferably within a depth of 20 nm. The point where the characteristic X-ray detection value of a certain element reaches its maximum is sometimes referred to as the peak concentration of that element.

[0197] Furthermore, it is preferable that the distribution of aluminum in the positive electrode active material 100 overlaps with the distribution of barium and / or magnesium. Therefore, when EDX radiation analysis is performed, the point where the characteristic X-ray detection value of aluminum in the surface layer 100a is maximum is preferably located within a depth of 50 nm from the surface toward the center of the positive electrode active material 100, more preferably within a depth of 40 nm, and even more preferably within a depth of 30 nm.

[0198] Furthermore, it is preferable that the distribution of barium, magnesium, and aluminum in the positive electrode active material 100 has regions where the concentration peaks overlap in a manner that differs. For example, as shown in Figures 4A1 to 4C2, it is preferable that the concentration peaks of barium and magnesium are located closer to the surface of the positive electrode active material 100 than the concentration peak of aluminum, and that there are regions where the distributions of barium, magnesium, and aluminum overlap. In other words, in the surface layer 100a, it is preferable that the points where the characteristic X-ray detection value of barium is maximum and the points where the characteristic X-ray detection value of magnesium is maximum are located closer to the surface of the positive electrode active material 100 than the point where the characteristic X-ray detection value of aluminum is maximum, and that there are regions where characteristic X-rays of barium, magnesium, and aluminum are detected.

[0199] [Crystal structure] Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiMO2.

[0200] It is known that the Jahn-Teller effect in transition metal compounds differs in strength depending on the number of electrons in the d orbitals of the transition metal.

[0201] In nickel-containing compounds, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the effect of the Jahn-Teller effect is suggested to be smaller, and it may have better resistance to high-voltage charging and discharging, making it preferable.

[0202] The crystal structure of the positive electrode active material will be explained using Figures 5 to 8. Figures 5 to 8 describe the case where cobalt is used as the transition metal M in the positive electrode active material.

[0203] [Conventional positive electrode active material] The positive electrode active material shown in Figure 7 is lithium cobalt oxide (LiCoO2) that substantially lacks additive elements X, Y, and Z. The crystal structure of the lithium cobalt oxide shown in Figure 7 changes depending on the depth of charge. In other words, Li x When expressed as CoO2, the crystal structure changes depending on the lithium occupancy rate x of the lithium sites.

[0204] In this specification, the depth of charge is a value that indicates how much capacity has been charged to the positive electrode active material, relative to its theoretical capacity; in other words, how much lithium has been released from the positive electrode. For example, lithium cobalt oxide (LiCoO2) and lithium nickel-cobalt-manganate (LiNi x Co y Mn zIn the case of a positive electrode active material with a layered rock salt structure such as O2(x+y+z=1), using the theoretical capacity of 274 mAh / g as a reference, a charge depth of 0 means that no lithium has been detached from the positive electrode active material, a charge depth of 0.5 means that lithium equivalent to 137 mAh / g has been detached from the positive electrode, and a charge depth of 0.8 means that lithium equivalent to 219.2 mAh / g has been detached from the positive electrode. x When expressed as CoO2(0≦x≦1), if the charging depth is 0, it is written as LiCoO2 with x = 1, and if the charging depth is 0.5, it is written as Li with x = 0.5. 0.5 It is written as CoO2, and when the charging depth is 0.8, x is 0.2 Li 0.2 It is written as CoO2.

[0205] As shown in Figure 7, lithium cobalt oxide at a charge depth of 0 (discharge state, x=1) has a region with a crystal structure of space group R-3m, where lithium occupies octahedral sites, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3 type crystal structure. The CoO2 layer refers to a structure in which octahedral structures, in which oxygen atoms are 6-coordinated to cobalt, are continuous in a plane with shared edges.

[0206] Furthermore, conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when x=0.5, as the symmetry of lithium increases. In this structure, one CoO2 layer exists in the unit cell. For this reason, it is sometimes called a monoclinic O1 type crystal structure. Also, at a charging depth of 1 (x=0), it has a crystal structure of the trigonal space group P-3m1, with one CoO2 layer in the unit cell. For this reason, this crystal structure is sometimes called a trigonal O1 type crystal structure.

[0207] Furthermore, lithium cobalt oxide at x=0.12 has a crystal structure of space group R-3m. This structure can be described as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 type crystal structure. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 7, the c-axis of the H1-3 type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0208] As an example, the H1-3 type crystal structure can be represented by the coordinates of cobalt and oxygen in a unit cell as follows: Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are oxygen atoms, respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygen atoms. On the other hand, as will be described later, the O3' type crystal structure in one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' structure and the H1-3 type structure, and that the O3' structure shows less variation from the O3 structure compared to the H1-3 type structure. The choice of which unit cell is preferable to represent the crystal structure of the positive electrode active material can be made, for example, by selecting the unit cell that results in a smaller GOF (goodness of fit) value in Rietveld analysis of the XRD pattern.

[0209] When high-voltage charging occurs, where the charging voltage is 4.6V or higher relative to the oxidation-reduction potential of lithium metal, or when deep charging occurs, where the charging depth is 0.8 or higher (x=less than 0.2), and discharging is repeated, lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0210] However, these two crystal structures exhibit a large displacement of the CoO2 layer. As shown by the dotted line and arrow in Figure 7, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m(O3). Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0211] Furthermore, the volume difference is also significant. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

[0212] In addition, the H1-3 type crystal structure, which consists of continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0213] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to break down. This breakdown of the crystalline structure leads to a deterioration of the cycle characteristics. As the crystalline structure breaks down, the number of sites where lithium can exist stably decreases, and lithium insertion and removal becomes more difficult.

[0214] The positive electrode active material 100 according to one aspect of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charging and discharging. Furthermore, it can reduce the change in volume. Therefore, the positive electrode active material according to one aspect of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material according to one aspect of the present invention can adopt a stable crystal structure in a high-voltage charged state. Therefore, the positive electrode active material according to one aspect of the present invention may be less prone to short circuits when a high-voltage charged state is maintained. In such cases, safety is further improved, which is preferable.

[0215] In one embodiment of the present invention, the change in crystal structure and the difference in volume per unit of the same number of transition metal M atoms are small between a fully discharged state and a high-voltage charged state.

[0216] Figure 5 shows the crystal structure of the positive electrode active material 100 before and after charging and discharging. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal M, and oxygen. In addition to the above, it is preferable to have barium as an additive element X and magnesium as an additive element Y. It is also preferable to have fluorine as an additive element Y.

[0217] The crystal structure at charge depth 0 (discharge state, x=1) in Figure 5 is R-3m(O3), the same as in Figure 7. On the other hand, the interior 100b of the positive electrode active material 100 has a crystal structure different from the H1-3 type crystal structure when it is fully charged. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium occupy the oxygen 6 coordination positions. Furthermore, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, in this specification, this structure is called the O3' type crystal structure. In both the O3 type crystal structure and the O3' type crystal structure, it is preferable that magnesium is present dilutely between the CoO2 layers, i.e., at the lithium sites. It is also preferable that halogens such as fluorine are present randomly and dilutely at the oxygen sites.

[0218] In addition, in the O3' type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate position, and in this case as well, the arrangement of ions has a symmetry similar to that of the spinel type.

[0219] Furthermore, the O3' type crystal structure can be said to be similar to the CdCl2 type crystal structure, although it has lithium randomly placed between the layers. This CdCl2 type-like crystal structure is observed when lithium nickelate is charged to a depth of charge of 0.94 (x=0.06) (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0220] In one embodiment of the present invention, the change in crystal structure when charged at high voltage and a large amount of lithium is desorbed is suppressed compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 5, there is almost no displacement of the CoO2 layer in these crystal structures.

[0221] More specifically, the positive electrode active material 100 according to one embodiment of the present invention exhibits high crystal structure stability even at high charging voltages. For example, in conventional positive electrode active materials, there is a range of charging voltages in which the R-3m(O3) crystal structure can be maintained even at a charging voltage that results in an H1-3 type crystal structure, for example, a voltage of about 4.6V relative to the potential of lithium metal. Furthermore, there is a region in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of 4.65V to 4.7V relative to the potential of lithium metal. Only when the charging voltage is increased even further may an H1-3 type crystal be observed. In addition, in secondary batteries, for example, when graphite is used as the negative electrode active material, there is a range of charging voltages in which the R-3m(O3) crystal structure can be maintained even when the voltage of the secondary battery is 4.3V to 4.5V. Furthermore, there is a region in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of 4.35V to 4.55V relative to the potential of lithium metal.

[0222] Therefore, in the positive electrode active material 100 of one aspect of the present invention, the crystal structure is less likely to collapse even when repeatedly charged and discharged at high voltage.

[0223] Furthermore, in the positive electrode active material 100, the difference in volume per unit cell between the O3-type crystal structure at a charging depth of 0 (x=1) and the O3'-type crystal structure at a charging depth of 0.8 (x=0.2) is 2.5% or less, more specifically 2.2% or less.

[0224] Furthermore, the O3' type crystal structure can be represented by showing the coordinates of cobalt and oxygen in the unit cell as follows: Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25.

[0225] Additive elements Y, such as magnesium, which are randomly and dilutely present between CoO2 layers, i.e., at lithium sites, have the effect of suppressing the displacement of the CoO2 layers. Therefore, when magnesium is present between CoO2 layers, an O3' type crystal structure is more likely to be formed. For this reason, it is desirable that magnesium be present in at least a portion of the surface layer of the particles of the positive electrode active material 100 according to one embodiment of the present invention, preferably in more than half of the surface layer of the particles, and more preferably in the entire surface layer of the particles. Furthermore, in order to distribute magnesium throughout the entire surface layer of the particles, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 100 according to one embodiment of the present invention.

[0226] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the likelihood that the added element Y, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site does not help maintain the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation of lithium.

[0227] Therefore, it is preferable to add a fluorine compound to lithium cobalt oxide before the heat treatment to distribute magnesium throughout the entire surface layer. Adding a fluorine compound lowers the melting point of lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute magnesium throughout the entire surface layer of the particles at a temperature at which cation mixing is less likely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0228] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of transition metal M atoms, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. Alternatively, 0.001 times or more and less than 0.04 times is preferred. Alternatively, 0.01 times or more and 0.1 times or less is preferred. The magnesium concentration shown here may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material blend during the process of manufacturing the positive electrode active material.

[0229] As shown in the legend in Figure 5, transition metals such as nickel and manganese, as well as gallium, aluminum, boron, and indium, are preferably present at the cobalt site, and although some may be present at the lithium site, only in small amounts. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0230] Furthermore, by including barium as additive element X, the structure of the surface layer 100a of the positive electrode active material 100 is stabilized, as shown in the calculations concerning barium mentioned above, and it is expected that stability in the high-voltage charging state will be enhanced. Therefore, due to the synergistic effect of including additive elements X, Y, and Z, the positive electrode active material of one embodiment of the present invention becomes a positive electrode active material that is less prone to degradation at high charge and discharge voltages.

[0231] In one embodiment of the present invention, the capacity of the positive electrode active material 100 may decrease as the content of additive elements X, Y, and Z increases. For example, the presence of gallium, aluminum, boron, or indium at the transition metal sites may prevent nearby lithium ions from contributing to charging and discharging. Additionally, the presence of barium or magnesium at the lithium sites may reduce the amount of lithium contributing to charging and discharging. Furthermore, excess barium may produce barium compounds that do not contribute to charging and discharging, or excess magnesium may produce magnesium compounds that do not contribute to charging and discharging.

[0232] As is evident from the oxygen atoms indicated by arrows in Figure 5, the symmetry of oxygen atoms differs slightly between the O3-type and O3'-type crystal structures. Specifically, in the O3-type crystal structure, oxygen atoms are aligned along the dotted line, whereas in the O3'-type crystal structure, oxygen atoms are not strictly aligned. This is because, in the O3'-type crystal structure, the amount of tetravalent cobalt increases with decreasing lithium, leading to a larger Jahn-Teller strain and distortion of the octahedral structure of CoO6. The increased repulsion between oxygen atoms in the CoO2 layer due to the decrease in lithium also plays a role.

[0233] Thus, it is preferable that the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention has a different composition from the interior 100b, with a higher concentration of the additive element Y, such as magnesium and fluorine. Furthermore, it is preferable that the composition adopts a crystalline structure that is stable at room temperature (25°C). For this reason, the surface layer 100a may have a different crystalline structure from the interior 100b. For example, at least a part of the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention may have a rock salt type crystalline structure. Also, if the surface layer 100a and the interior 100b have different crystalline structures, it is preferable that the orientation of the crystals in the surface layer 100a and the interior 100b is approximately the same.

[0234] Layered rock salt crystals, and the anions in rock salt crystals, adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3'-type crystals adopt a cubic close-packed structure.

[0235] In this specification, a structure in which anions are stacked in three layers with offsets from each other, such as ABCABC, will be referred to as a cubic close-packed structure. Therefore, the anions do not need to be strictly cubic in shape. At the same time, since real crystals always have defects, the analytical results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) patterns such as electron diffraction patterns or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said that it adopts a cubic close-packed structure.

[0236] When layered rock salt crystals are in contact with other rock salt crystals, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned.

[0237] Alternatively, it can be explained as follows: The anions in the (111) plane of the cubic crystal structure have a triangular lattice. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic (111) plane has a similar atomic arrangement to the hexagonal lattice of the (0001) plane of the layered rock salt type. The consistency between the two lattices can be described as the orientation of the cubic close-packed structure being aligned.

[0238] However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space group Fm-3m (the space group of typical rock salt crystals) and Fd-3m of rock salt crystals. Therefore, the Miller indices of crystal planes that satisfy the above conditions are different for layered rock salt crystals and O3'-type crystals compared to rock salt crystals. In this specification, it is sometimes said that the crystal orientations are roughly the same when the orientations of the cubic close-packed structure composed of anions are aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals.

[0239] The approximate agreement of crystal orientation in two regions can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron diffraction patterns, FFT patterns of TEM images, etc. XRD (X-ray Diffraction) and neutron diffraction can also be used as indicators.

[0240] However, if the surface layer 100a consists only of MgO, or only of a solid solution of MgO and CoO(II), lithium insertion and removal becomes difficult. Therefore, the surface layer 100a must contain at least cobalt, and in the discharge state, it must also contain lithium and have pathways for lithium insertion and removal. Furthermore, it is preferable that the concentration of cobalt is higher than that of magnesium.

[0241] Furthermore, it is preferable that the additive element X is located on the surface layer 100a of the particles of the positive electrode active material 100 according to one aspect of the present invention. For example, the positive electrode active material 100 according to one aspect of the present invention may be covered with a coating having the additive element X.

[0242] Grain boundaries are also surface defects. Therefore, like crystal surfaces, they tend to be unstable and prone to initiating changes in crystal structure. For this reason, increasing the concentration of additive elements X and / or Y at and near the grain boundaries can more effectively suppress changes in crystal structure.

[0243] Further, when the concentrations of additive element X, additive element Y, and / or additive element Z at the grain boundaries and in the vicinity thereof are high, even when cracks occur along the grain boundaries of the particles of the positive electrode active material 100 according to one aspect of the present invention, the concentrations of additive element X, additive element Y, and / or additive element Z become high in the vicinity of the surface generated by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be enhanced even in the positive electrode active material after cracks occur.

[0244] [High-voltage charged state of positive electrode active material] Whether the positive electrode active material is the positive electrode active material 100 according to one aspect of the present invention that exhibits an O3'-type crystal structure when charged at a high voltage can be determined by analyzing the positively charged electrode using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like. In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, can compare the crystallinity and crystal orientation, can analyze the periodic strain of the lattice and the crystallite size, and can obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery as it is.

[0245] The positive electrode active material 100 according to one aspect of the present invention has the characteristic that there is little change in the crystal structure between the state charged at a high voltage and the discharged state as described above. A material in which a crystal structure with a large change from the discharged state occupies 50 wt% or more in the state charged at a high voltage is not preferable because it cannot withstand high-voltage charge and discharge. It should be noted that the desired crystal structure may not be obtained only by adding additive elements. For example, even in the case of lithium cobaltate having magnesium and fluorine, there are cases where the O3'-type crystal structure is 60% or more and cases where the H1-3 type crystal structure occupies 50% or more in the state charged at a high voltage. Also, at a predetermined voltage, the O3'-type crystal structure may become almost 100%, and when the predetermined voltage is further increased, the H1-3 type crystal structure may occur. Therefore, in order to determine whether it is the positive electrode active material 100 according to one aspect of the present invention, analysis of the crystal structure including XRD is necessary.

[0246] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they may change from an O3' type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0247] ≪Charging method≫ High-voltage charging to determine whether a certain composite oxide is the positive electrode active material 100 according to one aspect of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) with lithium as the counter electrode and then charging it.

[0248] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry of a mixture of positive electrode active material, conductive material, and binder.

[0249] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode will differ. In this specification, the voltage and potential refer to the potential of the positive electrode unless otherwise specified.

[0250] The electrolyte in the electrolyte solution may be 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7, and vinylene carbonate (VC) at 2 wt%.

[0251] A 25 μm thick porous polypropylene film can be used as the separator.

[0252] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0253] The coin cell prepared under the above conditions is charged with a constant current of 0.5C at an arbitrary voltage (e.g., 4.6V, 4.65V, or 4.7V), and then charged with a constant voltage until the current value becomes 0.01C. Note that 1C can be 137mA / g or 200mA / g. If the weight of the positive electrode active material in one coin cell is 10mg and 1C is 137mA / g, then 0.5C corresponds to charging at 0.685mA. It is desirable to charge at such a small current value to observe the phase change of the positive electrode active material. The temperature is 25°C. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere, and the positive electrode is removed to obtain a positive electrode active material with a deep charge depth. When performing various analyses afterward, it is preferable to seal the cell under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the cell in a sealed container under an argon atmosphere. Furthermore, it is preferable to remove the positive electrode promptly after charging is complete and subject it to analysis. Specifically, it is preferable to do this within one hour of the charging completion, and more preferably within 30 minutes.

[0254] ≪XRD≫ The equipment and conditions for XRD measurement are not particularly limited. For example, measurements can be taken using the following equipment and conditions. XRD system: Bruker AXS D8 ADVANCE X-ray source:CuKα1 ray Output: 40KV, 40mA Slit width: Div.Slit, 0.5° Detector: LynxEye Scanning method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0255] Figure 6 shows the ideal powder XRD pattern calculated using CuKα1 lines from a model of the O3' type crystal structure. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) at a charging depth of 0 (x=1) and CoO2(O1) at a charging depth of 1 (x=0) are also shown. Figure 8 shows the ideal powder XRD pattern calculated using CuKα1 lines from a model of the H1-3 type crystal structure. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) at x=1 and CoO2(O1) at x=0 are also shown. The patterns for LiCoO2(O3) and CoO2(O1) were created using the Reflex Powder Diffraction module in Materials Studio (BIOVIA) from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The 2θ range was set to 15° to 75°, with a step size of 0.01 and a wavelength λ1 = 1.540562 × 10⁻¹⁰. -10 m and λ2 were not set, and the Monochromator was set to single. The H1-3 type crystal structure pattern was similarly created from the crystal structure information described in Non-Patent Literature 1. For the O3' type crystal structure pattern, the crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0256] As shown in Figure 6, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 8, these peaks do not appear in the H1-3 type crystal structure and CoO2 (P-3m1, O1). Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° when charged at high voltage is a characteristic feature of the positive electrode active material 100 in one embodiment of the present invention.

[0257] This also means that the crystal structure at a charging depth of 0 (x=1) and the crystal structure in a high-voltage charging state have similar positions where XRD diffraction peaks appear. More specifically, for two or more, more preferably three or more, of the main diffraction peaks of the two, the difference in the positions where the peaks appear is 2θ=0.7° or less, and more preferably 2θ=0.5° or less.

[0258] In one embodiment of the present invention, the positive electrode active material 100 has an O3' type crystal structure when charged with a high voltage, but not all particles have to have an O3' type crystal structure. Other crystal structures may be included, and some may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that 50% or more of the O3' type crystal structure is present, more preferably 60% or more, and even more preferably 66% or more. If 50% or more, more preferably 60% or more, and even more preferably 66% or more of the O3' type crystal structure is present, a positive electrode active material with sufficiently excellent cycle characteristics can be obtained.

[0259] Furthermore, even after more than 100 charge-discharge cycles from the start of measurement, it is preferable that the O3' type crystal structure accounts for 35% or more, more preferably 40% or more, and even more preferably 43% or more when Rietveld analysis is performed.

[0260] Also, the sharpness of the diffraction peaks in the XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, that is, has a narrow half-width. The half-width varies depending on the XRD measurement conditions and / or the value of 2θ, even for peaks arising from the same crystal phase. In the case of the measurement conditions described above, for peaks observed at 2θ = 43° or more and 46° or less, the half-width is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily need to satisfy this requirement. If some peaks satisfy this requirement, it can be said that the crystallinity of that crystal phase is high. Such high crystallinity contributes to the stabilization of the crystal structure after charging.

[0261] Also, the crystallite size of the O3'-type crystal structure possessed by the particles of the positive electrode active material only decreases to about 1 / 10 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as those of the positive electrode before charge and discharge, a clear peak of the O3'-type crystal structure can be confirmed in the high-voltage charged state. On the other hand, in the case of simple LiCoO2, even if a part has a structure similar to the O3'-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0262] In the positive electrode active material of one aspect of the present invention, as described above, it is preferable that the influence of the Jahn-Teller effect is small. The positive electrode active material of one aspect of the present invention preferably has a layered rock salt-type crystal structure and mainly has cobalt as a transition metal. Further, in the positive electrode active material of one aspect of the present invention, within a range where the influence of the Jahn-Teller effect is small, in addition to cobalt, it may have the above-described additive element X and / or additive element Y.

[0263] Furthermore, in a positive electrode active material according to one embodiment of the present invention, when XRD analysis is performed on the layered rock salt type crystal structure of the particles of the positive electrode active material in a state without charging or discharging, or in a discharged state, a first peak may be observed when 2θ is between 18.50° and 19.30°, and a second peak may be observed when 2θ is between 38.00° and 38.80°.

[0264] The peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100. The crystal structure of the surface layer 100a, grain boundaries 101, etc., can be analyzed by electron diffraction of the cross-section of the positive electrode active material 100.

[0265] [Surface roughness and specific surface area] In one embodiment of the present invention, the positive electrode active material 100 preferably has a smooth surface with few irregularities. A smooth surface with few irregularities indicates that the additive element Y source and the surface of the composite oxide melted during the manufacturing process of the positive electrode active material 100. Therefore, it is one factor indicating that the concentration distribution of the additive element Y in the surface layer 100a is uniform, or that the concentration gradient of the additive element Y is gentle.

[0266] The smoothness and minimal irregularities of the surface can be determined, for example, from a cross-sectional SEM image or TEM image of the positive electrode active material 100, or from the specific surface area of ​​the positive electrode active material 100.

[0267] For example, the surface smoothness of the positive electrode active material 100 can be quantified from a cross-sectional SEM image as shown below.

[0268] First, the positive electrode active material 100 is processed using FIB or the like to expose its cross-section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, protective agent, etc. Next, an SEM image of the interface between the protective film, etc. and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image using image processing software. For example, Gaussian blurring (σ=2) is performed, followed by binarization. Interface extraction is then performed using image processing software. Furthermore, the interface line between the protective film, etc. and the positive electrode active material 100 is selected using a tool such as Magic Hand, and the data is extracted into spreadsheet software, etc. Using the functions of the spreadsheet software, correction is performed from the regression curve (quadratic regression), parameters for roughness calculation are obtained from the slope-corrected data, and the root mean square (RMS) surface roughness is calculated by calculating the standard deviation. This surface roughness is the surface roughness of the positive electrode active material at least at 400 nm from the outer circumference of the particle.

[0269] In this embodiment, the particle surface of the positive electrode active material 100 preferably has a root mean square (RMS) surface roughness of less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0270] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited, but for example, "ImageJ" can be used. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

[0271] For example, the actual specific surface area A measured by the gas adsorption method using the constant-volume method. R And the ideal specific surface area A i The surface smoothness of the positive electrode active material 100 can also be quantified from this ratio.

[0272] Ideal specific surface area A i This is calculated by assuming that all particles have the same diameter as D50, the same weight, and are ideal spheres.

[0273] The median diameter D50 can be measured using a particle size analyzer that employs laser diffraction and scattering methods. The specific surface area can be measured using a specific surface area measuring device that employs a gas adsorption method based on constant volume, for example.

[0274] In one embodiment of the present invention, the positive electrode active material 100 has an ideal specific surface area A (when assumed to be a perfect sphere) determined from the median diameter D50. i And the actual specific surface area A R Ratio A R / A i It is preferable that the value is between 1 and 2.

[0275] In one embodiment of the present invention, if the particle size of the positive electrode active material 100 is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if the particle size is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte. Therefore, the median diameter of the positive electrode active material 100 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.

[0276] This embodiment can be implemented in appropriate combination with other embodiments.

[0277] (Embodiment 3) In this embodiment, examples of multiple shapes of secondary batteries having a positive electrode active material 100 manufactured by the manufacturing method described in the previous embodiment will be explained.

[0278] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 9A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 9B is an external view, and Figure 9C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices. In this specification, the term "coin-type battery" includes button-type batteries.

[0279] Figure 9A is a schematic diagram to show the overlapping (vertical and positional) of the components for clarity. Therefore, Figures 9A and 9B are not perfectly identical corresponding diagrams.

[0280] In Figure 9A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 9A. The spacer 322 and washer 312 are used to protect the inside or to fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are pressed together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0281] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0282] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0283] Figure 9B is a perspective view of the completed coin-type rechargeable battery.

[0284] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0285] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side of the current collector.

[0286] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel and aluminum, etc., to prevent corrosion caused by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0287] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 9C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are pressed together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0288] The above configuration makes it possible to create a coin-type secondary battery 300 with high capacity, high charge / discharge capacity, and excellent cycle characteristics. Furthermore, if the secondary battery has a solid electrolyte layer between the negative electrode 307 and the positive electrode 304, the separator 310 can be omitted.

[0289] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 10A. As shown in Figure 10A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0290] Figure 10B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 10B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0291] Inside the hollow cylindrical battery casing 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of metals such as nickel, aluminum, and titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery casing 602 with nickel and aluminum, etc., to prevent corrosion by the electrolyte. Inside the battery casing 602, the battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and insulating plate 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0292] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector. Figures 10A to 10D illustrate a secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder, but the battery is not limited to this configuration. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder is also possible. Such a configuration allows for, for example, miniaturization of the secondary battery.

[0293] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0294] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0295] Figure 10C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a protective circuit to prevent overcharging or over-discharging, etc.

[0296] Figure 10D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0297] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0298] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0299] Furthermore, in Figure 10D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0300] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 11 and 12.

[0301] The secondary battery 913 shown in Figure 11A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 11A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0302] Furthermore, as shown in Figure 11B, the housing 930 shown in Figure 11A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 11B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0303] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0304] Furthermore, the structure of the wound body 950 is shown in Figure 11C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0305] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figures 12A to 12C. The wound body 950a shown in Figure 12A 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.

[0306] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 932, a secondary battery 913 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0307] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0308] As shown in Figure 12B, the negative terminal 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive terminal 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0309] As shown in Figure 12C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure to prevent the battery from rupturing.

[0310] As shown in Figure 12B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge and discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 12A and 12B can be referenced from the description of the secondary battery 913 shown in Figures 11A to 11C.

[0311] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 13A and 13B, which show an example of its external appearance. Figures 13A and 13B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0312] Figure 14A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 14A.

[0313] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 13A, will be explained using Figures 14B and 14C.

[0314] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 14B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0315] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0316] Next, as shown in Figure 14C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0317] Next, the electrolyte is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0318] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 503, a secondary battery 500 can be made that has high capacity, high charge / discharge capacity, and excellent cycle characteristics.

[0319] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which is capable of wireless charging using an antenna, will be explained with reference to Figures 15A to 15C.

[0320] Figure 15A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 15B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 has a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0321] The internal structure of the secondary battery 513 may have a wound structure or a laminated structure.

[0322] In the secondary battery pack 531, for example, as shown in Figure 15B, a control circuit 590 is located on the circuit board 540. The circuit board 540 is electrically connected to terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0323] Alternatively, as shown in Figure 15C, the system may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0324] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0325] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0326] Next, we will explain some examples of components of a secondary battery.

[0327] [Positive electrode] The positive electrode comprises a positive electrode active material layer 200 and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may also contain a conductive material and a binder. The positive electrode active material used is a positive electrode active material 100 manufactured using the manufacturing method described in the previous embodiment.

[0328] The following describes an example of a cross-sectional configuration when graphene or a graphene compound is used as the conductive material in the positive electrode active material layer 200. Graphene compounds will be discussed later.

[0329] Figure 16A shows a longitudinal cross-sectional view of the positive electrode active material layer 200. The positive electrode active material layer 200 includes granular positive electrode active material 100, graphene or graphene compound 201 as a conductive material, and a binder (not shown).

[0330] For secondary batteries requiring rapid charging and rapid discharging, using graphene compounds as a conductive material is particularly effective. For example, secondary batteries for two-wheeled or four-wheeled vehicles, and secondary batteries for drones, may require rapid charging and rapid discharging characteristics. Mobile electronic devices may also require rapid charging characteristics. Rapid charging and rapid discharging can also be described as high-rate charging and high-rate discharging. For example, this refers to charging and discharging at 1C, 2C, or 5C or higher.

[0331] In the longitudinal section of the positive electrode active material layer 200, as shown in Figure 16B, sheet-like graphene or graphene compound 201 is dispersed approximately uniformly within the positive electrode active material layer 200. In Figure 16B, graphene or graphene compound 201 is schematically represented by thick lines, but in reality, it is a thin film having a single or multilayer thickness of carbon molecules. Multiple layers of graphene or graphene compound 201 are formed to partially cover multiple granular positive electrode active materials 100, or to adhere to the surface of multiple granular positive electrode active materials 100, and are therefore in surface contact with each other.

[0332] Here, multiple graphenes or graphene compounds can bond together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or eliminated, thereby improving the ratio of active material to electrode volume or electrode weight. In other words, the charge and discharge capacity of the secondary battery can be increased.

[0333] Here, it is preferable to use graphene oxide as graphene or graphene compound 201, mix it with the active material to form a layer that becomes the positive electrode active material layer 200, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in a polar solvent, for the formation of graphene or graphene compound 201, the graphene or graphene compound 201 can be dispersed approximately uniformly within the positive electrode active material layer 200. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene or graphene compound 201 remaining in the positive electrode active material layer 200 partially overlaps and is dispersed to the extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent.

[0334] Therefore, unlike granular conductive materials such as acetylene black that make point contact with the active material, graphene or a graphene compound 201 enables surface contact with low contact resistance. Thus, the electrical conductivity between the granular positive electrode active material 100 and graphene or the graphene compound 201 can be improved with a smaller amount than that of ordinary conductive materials. Therefore, the ratio of the positive electrode active material 100 in the positive electrode active material layer 200 can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

[0335] Also, by using a spray dryer in advance, it is possible to form a graphene compound, which is a conductive material, as a film covering the entire surface of the active material, and further form a conductive path between the active materials with the graphene compound.

[0336] The positive electrode active material layer 200 may also be formed by mixing the positive electrode active material described in the previous embodiment with other positive electrode active materials.

[0337] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0338] Also, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0339] Also, as another positive electrode active material, a composition formula Li a Mn b M c O dA lithium manganese composite oxide can be used, which can be represented as follows: Here, element M is preferably a metallic element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particle of lithium manganese composite oxide, <a / (b+c)<2、かつc>it is preferable that the discharge is 0 0 and 0.26 ≤ (b+c) / d < 0.5. The composition of metals, silicon, phosphorus, etc., of the entire particle of lithium manganese composite oxide can be measured, for example, using ICP-MS (inductively coupled plasma mass spectrometry). The oxygen composition of the entire particle of lithium manganese composite oxide can be measured, for example, using EDX (energy dispersive X-ray spectrometry). It can also be determined by using molten gas analysis and valence evaluation of XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. Lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may also contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0340] <Conductive material> Conductive materials, also called conductive additives or conductive imparters, are typically made of carbon. By attaching a conductive material between multiple active materials, the active materials are electrically connected to each other, increasing conductivity. Note that "attachment" does not only refer to physical contact between the active materials and the conductive material, but also includes cases where covalent bonds are formed, bonds are formed by van der Waals forces, the conductive material covers part of the surface of the active material, the conductive material fits into surface irregularities of the active material, or where they are electrically connected even without physical contact.

[0341] A typical example of a carbon material used as a conductive material is carbon black (furnace black, acetylene black, graphite, etc.).

[0342] Graphene or graphene compounds may also be used as the conductive material.​

[0343] In this specification, the term "graphene compound" includes multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is defined as a material having carbon atoms, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. This two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a bent shape. Graphene compounds may also be rolled up to resemble carbon nanofibers.

[0344] In this specification, graphene oxide refers to a material having carbon and oxygen, having a sheet-like structure, and possessing functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0345] In this specification, reduced graphene oxide refers to a material having carbon and oxygen, having a sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. It may also be called a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be laminated together. It is preferable that reduced graphene oxide has a portion where the carbon concentration is greater than 80 atomic%, and the oxygen concentration is between 2 atomic% and 15 atomic%. By having such carbon and oxygen concentrations, it can function as a highly conductive material even in small quantities. Furthermore, it is preferable that reduced graphene oxide has a G / D intensity ratio of 1 or more in the Raman spectrum. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small quantities.

[0346] Graphene and graphene compounds may possess excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Furthermore, graphene and graphene compounds may have a sheet-like shape. Graphene and graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. They may also exhibit very high conductivity even when thin, allowing for the efficient formation of conductive paths within the active material layer with a small amount. Therefore, using graphene or graphene compounds as a conductive material can increase the contact area between the active material and the conductive material. It is preferable that the graphene or graphene compound covers 80% or more of the active material's surface area. It is also preferable that the graphene or graphene compound adheres to at least a portion of the active material particles. Furthermore, it is preferable that the graphene or graphene compound overlaps at least a portion of the active material particles. It is also preferable that the shape of the graphene or graphene compound matches at least a portion of the shape of the active material particles. The shape of the active material particles refers, for example, to the irregularities of a single active material particle or the irregularities formed by multiple active material particles. Furthermore, it is preferable that graphene or a graphene compound surrounds at least a portion of the active material particles. The graphene or graphene compound may also have pores.

[0347] When using active material particles with a small particle size, such as 1 μm or less, the specific surface area of ​​the active material particles is large, and more conductive paths are required to connect the active material particles. In such cases, it is preferable to use graphene or graphene compounds that can efficiently form conductive paths even in small amounts.

[0348] Due to the properties described above, graphene compounds are particularly effective as conductive materials in secondary batteries that require rapid charging and rapid discharging. For example, secondary batteries for two-wheeled or four-wheeled vehicles, and secondary batteries for drones, may require rapid charging and rapid discharging characteristics. Mobile electronic devices may also require rapid charging characteristics. Rapid charging and rapid discharging can also be described as high-rate charging and high-rate discharging. For example, this refers to charging and discharging at 1C, 2C, or 5C or higher.

[0349] Furthermore, graphene or a graphene compound may be mixed with materials used in forming graphene or a graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon dioxide (SiO2, SiO2). x Examples of particles include those having (x<2), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The median diameter (D50) of the particles is preferably 1 μm or less, and more preferably 100 nm or less.

[0350] <Binder> As a binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluororubber can also be used as a binder.

[0351] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0352] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose as the binder.

[0353] You may use a combination of several of the binders mentioned above.

[0354] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials, while possessing excellent adhesive and elastic properties, can be difficult to adjust in viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. As a material with particularly excellent viscosity-modifying properties, a water-soluble polymer may be used. As a water-soluble polymer with particularly excellent viscosity-modifying properties, the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, and starch can be used.

[0355] Furthermore, cellulose derivatives such as carboxymethylcellulose can be made more effective as viscosity modifiers by increasing their solubility, for example, by using salts such as sodium or ammonium salts of carboxymethylcellulose. Increased solubility also improves the dispersibility of the active material and other components when preparing the electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0356] Water-soluble polymers stabilize viscosity by dissolving in water and can stably disperse the active material and other materials used as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, because they possess functional groups, they are expected to be easily and stably adsorbed onto the surface of the active material. Additionally, cellulose derivatives such as carboxymethylcellulose often contain functional groups such as hydroxyl or carboxyl groups, and because of these functional groups, the polymers interact with each other, allowing them to broadly cover the surface of the active material.

[0357] When a binder covers or is in contact with the surface of the active material, it is expected to act as a passivation film, suppressing the decomposition of the electrolyte. Here, a passivation film is a film that does not conduct electricity, or has extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Furthermore, it is even more desirable for the passivation film to suppress electrical conductivity while still allowing lithium ions to conduct.

[0358] <Positive electrode current collector> As the current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the positive electrode potential. Aluminum alloys with added elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. Alternatively, it may be formed from a metallic element that reacts with silicon to form a silicide. Examples of metallic elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in various shapes, such as foil, plate, sheet, mesh, perforated metal, or expanded metal. The current collector should preferably have a thickness of 5 μm to 30 μm.

[0359] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a conductive material and a binder.

[0360] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. In this context, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0361] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO refers to SiO x It can also be expressed as follows. Here, x is preferably 1 or a value in its immediate vicinity. For example, x is preferably between 0.2 and 1.5, and preferably between 0.3 and 1.2.

[0362] Suitable carbon-based materials include graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0363] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spheroidal graphite having a spherical shape can be used as artificial graphite. For example, MCMB may have a spherical shape and is therefore preferable. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, which may also be preferable. Examples of natural graphite include flake graphite and spheroidized natural graphite.

[0364] When lithium ions are inserted into graphite (during the formation of lithium-graphite intercalation compounds), graphite exhibits a potential as low as that of lithium metal (0.05V to 0.3V vs. Li / Li). + This allows lithium-ion secondary batteries using graphite to exhibit a high operating voltage. Furthermore, graphite is preferable 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.

[0365] Furthermore, titanium dioxide (TiO2) and lithium titanium oxide (Li4Ti5O2) are used as negative electrode active materials. 12 ), lithium-graphite intercalation compound (Li x Oxides such as C6, niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.

[0366] Furthermore, as the negative electrode active material, a Li3N type structure is used, which is a lithium and transition metal binitride. 3-x M x N(M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 The N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm²). 3 ) indicates a preference.

[0367] Using a lithium-transition metal complex nitride is preferable because it contains lithium ions in the negative electrode active material, allowing it to be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode active material. Even when using a lithium-ion-containing material as the positive electrode active material, the lithium-transition metal complex nitride can be used as the negative electrode active material by pre-desorbing the lithium ions contained in the positive electrode active material.

[0368] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 Examples include 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.

[0369] Furthermore, lithium can be used as the negative electrode active material. When lithium is used as the negative electrode active material, foil-like lithium can be provided on the negative electrode current collector. Alternatively, lithium may be provided on the negative electrode current collector by vapor deposition or by vapor phase methods such as sputtering. In addition, lithium may be deposited on the negative electrode current collector by electrochemical methods in a solution containing lithium ions.

[0370] The conductive material and binder that the negative electrode active material layer can have can be the same materials as the conductive material and binder that the positive electrode active material layer can have.

[0371] Furthermore, in addition to the same materials as the positive electrode current collector, copper and other materials can also be used as the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0372] Furthermore, as another form of the negative electrode of the present invention, a negative electrode without a negative electrode active material can be used. In a secondary battery using a negative electrode without a negative electrode active material, lithium is deposited on the negative electrode current collector during charging, and the lithium on the negative electrode current collector can be dissolved during discharge. Therefore, except in a completely discharged state, the negative electrode current collector will have lithium on it.

[0373] When using a negative electrode without a negative electrode active material, a film may be provided on the negative electrode current collector to homogenize the deposition of lithium. As a film to homogenize the deposition of lithium, for example, a solid electrolyte having lithium ion conductivity can be used. As the solid electrolyte, sulfide particle-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes can be used. Among these, polymer-based solid electrolytes are suitable as a film to homogenize the deposition of lithium because it is relatively easy to form a uniform film on the negative electrode current collector.

[0374] Furthermore, when using a negative electrode without negative electrode active material, a negative electrode current collector with irregularities can be used. When using a negative electrode current collector with irregularities, the recesses in the negative electrode current collector become cavities where lithium can easily be deposited, thus suppressing the formation of dendrite-like shapes when lithium is deposited.

[0375] [Electrolyte] One form of electrolyte can be used, which includes a solvent and an electrolyte dissolved in the solvent. The solvent for the electrolyte is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these in any combination and ratio.

[0376] Furthermore, by using one or more flame-retardant and low-volatility ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the energy storage device from rupturing or catching fire even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0377] Furthermore, examples of electrolytes to be dissolved in the above solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10Cl 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, and lithium bis(oxalate)borate (Li(C2O4)2, LiBOB) can be used individually or in any combination and ratio of two or more of these salts.

[0378] It is preferable to use a highly purified electrolyte in which particulate matter or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities") are present in small amounts. Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0379] Furthermore, additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the solvent in which the electrolyte is dissolved.

[0380] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0381] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0382] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluorine-based polymer gels, etc., can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the polymer formed may have a porous structure.

[0383] [Separator] As separators, for example, those made from cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane can be used.

[0384] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. As ceramic materials, for example, aluminum oxide particles or silicon oxide particles can be used. It is also possible to use a glass-like material as a ceramic material, but unlike the glass used in electrodes, it is preferable that it has low electronic conductivity. As fluorine materials, for example, PVDF or polytetrafluoroethylene can be used. As polyamide materials, for example, nylon or aramid (meta-aramid, para-aramid) can be used.

[0385] 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 facilitates better adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thereby enhancing the safety of secondary batteries.

[0386] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0387] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0388] (Embodiment 4) This embodiment shows an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in the above-described embodiment.

[0389] As shown in Figure 17A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0390] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is the positive electrode active material 100 obtained in the above-described embodiment. The positive electrode active material layer 414 may also have a conductive material and a binder.

[0391] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0392] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive material and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form it into particles, so the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 17B. Using metallic lithium in the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0393] As the solid electrolyte 421 in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halogen-based solid electrolyte, etc., can be used.

[0394] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 Li 3.25 P 0.95 It contains S4, etc. Sulfide-based solid electrolytes have advantages such as the availability of materials with high conductivity, the ability to be synthesized at low temperatures, and their relatively soft nature which helps maintain conductive paths even after charging and discharging.

[0395] Oxide-based solid electrolytes include materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x Materials having a NASICON-type crystal structure (Li 1+Y Al Y Ti 2-Y (PO4)3 etc.) Materials having a garnet-type crystal structure (Li7La3Zr2O 12 Materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16etc.), 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.

[0396] 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.

[0397] Also, different solid electrolytes may be mixed and used.

[0398] 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.

[0399] 〔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.

[0400] For example, Figure 18 shows an example of a cell used to evaluate the materials of an all-solid-state battery.

[0401] Figure 18A is a schematic cross-sectional view of an evaluation cell. The evaluation cell has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 that secure them together. The evaluation material is fixed by pressing the electrode plate 753 by rotating the retaining screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762, both of which are made of stainless steel. An O-ring 765 is provided between the upper member 762 and the retaining screw 763 for sealing.

[0402] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and pressed from above by an electrode plate 753. Figure 18B is a magnified perspective view of the area around this evaluation material.

[0403] As an example of the evaluated material, an example of a stacked structure consisting of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in Figure 18C. Note that the same parts are referred to by the same symbols in Figures 18A to 18C.

[0404] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be considered to correspond to the positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be considered to correspond to the negative electrode terminal. Electrical resistance and other properties can be measured while applying pressure to the evaluation material via the electrode plates 751 and 753.

[0405] Furthermore, it is preferable to use a package with excellent airtightness for the outer casing of a secondary battery according to one embodiment of the present invention. For example, a ceramic package or a resin package can be used. Also, when sealing the outer casing, it is preferable to block out the outside air and perform the sealing in a sealed atmosphere, for example, inside a glove box.

[0406] Figure 19A shows a perspective view of a secondary battery according to one embodiment of the present invention, having a different exterior and shape from that shown in Figure 18. The secondary battery in Figure 19A has external electrodes 771 and 772 and is sealed with an exterior having a plurality of package members.

[0407] Figure 19B shows an example of a cross-section cut along the dashed line in Figure 19A. The laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a having an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c having an electrode layer 773b on a flat plate. Insulating materials, such as resin materials and ceramics, can be used for the package members 770a, 770b, and 770c.

[0408] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. The external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0409] By using the positive electrode active material 100 obtained in the above-described embodiment, an all-solid-state secondary battery with high energy density and good output characteristics can be realized.

[0410] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0411] (Embodiment 5) This embodiment is a different example from Figure 10D, which is a cylindrical secondary battery. Figure 20C shows an example of its application to an electric vehicle (EV).

[0412] Electric vehicles are equipped with a first battery 1301a and 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so its capacity is smaller than that of the first batteries 1301a and 1301b.

[0413] The internal structure of the first battery 1301a may be a wound type as shown in Figure 11A or Figure 12C, or a stacked type as shown in Figure 13A or Figure 13B. Alternatively, the first battery 1301a may use the all-solid-state battery of Embodiment 4. Using the all-solid-state battery of Embodiment 4 for the first battery 1301a allows for higher capacity, improved safety, and miniaturization and weight reduction.

[0414] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0415] Furthermore, in the vehicle-mounted secondary battery, a service plug or circuit breaker that can cut off high voltage without using tools is provided in order to interrupt the power from multiple secondary batteries, and this is installed in the first battery 1301a.

[0416] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0417] Furthermore, the second battery 1311 supplies power to 14V automotive components (such as audio equipment 1313, power windows 1314, and lights 1315) via the DC-DC circuit 1310.

[0418] Furthermore, the first battery 1301a will be explained using Figure 20A.

[0419] Figure 20A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0420] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a BTOS (Battery operating system or Battery oxide semiconductor).

[0421] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, tin, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium) is preferable. In particular, the In-M-Zn oxide that can be applied as the oxide is preferably CAAC-OS (C-Axis Aligned Crystalline Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. Furthermore, a crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region in which the lattice arrangement is aligned. In addition, CAAC-OS has regions in which multiple crystalline regions are connected in the ab-plane direction, and these regions may have distortion. Distortion refers to a point in a region in which multiple crystalline regions are connected where the orientation of the lattice arrangement changes between a region in which the lattice arrangement is aligned and another region in which the lattice arrangement is aligned. In other words, CAAC-OS is an oxide semiconductor that is c-axis oriented and does not have a clear orientation in the ab-plane direction. Furthermore, CAC-OS is a material in which, for example, the elements constituting the metal oxide are unevenly distributed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size. In the following, in a metal oxide, a state in which one or more metal elements are unevenly distributed, and the regions containing the metal elements are mixed in a size of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size, is also referred to as a mosaic or patchy state.

[0422] Furthermore, CAC-OS is a composite metal oxide having a mosaic-like structure formed by the separation of the material into a first region and a second region, with the first region distributed within the film (hereinafter also referred to as a cloud-like structure). In other words, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0423] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS of In-Ga-Zn oxide, the first region is the region where [In] is greater than the [In] in the composition of the CAC-OS film. The second region is the region where [Ga] is greater than the [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is the region where [In] is greater than the [In] in the second region, and [Ga] is smaller than the [Ga] in the second region. The second region is the region where [Ga] is greater than the [Ga] in the first region, and [In] is smaller than the [In] in the first region.

[0424] Specifically, the first region described above is a region whose main components are indium oxide, indium zinc oxide, etc. The second region described above is a region whose main components are gallium oxide, gallium zinc oxide, etc. In other words, the first region can be rephrased as a region whose main component is In. Similarly, the second region can be rephrased as a region whose main component is Ga.

[0425] Furthermore, a clear boundary may not be observed between the first region and the second region described above.

[0426] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) confirms that it has a structure in which regions mainly composed of In (first region) and regions mainly composed of Ga (second region) are unevenly distributed and mixed.

[0427] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulation due to the second region work complementaryly to give CAC-OS a switching function (on / off function). In other words, CAC-OS has conductive function in part of the material, insulating function in part of the material, and semiconductor function as a whole. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I) can be achieved. on ), high field-effect mobility (μ), and good switching operation can be achieved.

[0428] Oxide semiconductors can take on diverse structures, each possessing different properties. One embodiment of the present invention may include two or more of the following: amorphous oxide semiconductor, polycrystalline oxide semiconductor, a-like OS, CAC-OS, nc-OS (nanocrystalline oxide semiconductor), and CAAC-OS.

[0429] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range of -40°C to 150°C than single-crystal Si transistors, and the change in characteristics is smaller even when the secondary battery is heated compared to single-crystal Si transistors. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery that uses the positive electrode active material 100 obtained in the above embodiment as the positive electrode.

[0430] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address causes of instability such as micro-shorts. Functions to eliminate causes of secondary battery instability include overcharging prevention, overcurrent prevention, overheating control during charging, maintaining cell balance in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-shorts, and prediction of abnormalities related to micro-shorts. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0431] Furthermore, a micro-short refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short-circuit in a small area can cause a large voltage change, this abnormal voltage value may affect the estimation of the subsequent charging and discharging state of the secondary battery.

[0432] One of the causes of micro-short circuits is said to be that multiple charge-discharge cycles result in an uneven distribution of the positive electrode active material, causing localized current concentration in parts of the positive and negative electrodes, leading to areas where the separator malfunctions, or causing micro-short circuits due to the generation of by-reactants from side reactions.

[0433] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0434] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 20A is shown in Figure 20B.

[0435] The control circuit unit 1320 includes at least a switch unit 1324 that includes a switch to prevent over-discharge, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current and the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the recommended voltage range for use, and if it 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 over-discharge and overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0436] The switch section 1324 can be constructed by combining an n-channel transistor and a p-channel transistor. The switch section 1324 is not limited to a switch having a Si transistor using single-crystal silicon, but can also be made of, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO x The switch section 1324 may be formed using a power transistor having a gallium oxide (where x is a real number greater than 0) or the like. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, by stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip. Since the volume occupied by the control circuit section 1320 can be reduced, miniaturization becomes possible.

[0437] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle equipment, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle equipment.

[0438] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor. For example, the all-solid-state battery of Embodiment 4 may be used. By using the all-solid-state battery of Embodiment 4 for the second battery 1311, high capacity can be achieved, and the device can be made smaller and lighter.

[0439] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged to the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0440] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0441] Although not shown in the diagram, when an electric vehicle is connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some cases, a control circuit is provided in the charger, and the functions of the battery controller 1302 are not used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the charger's outlet or connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU or GPU.

[0442] External chargers installed at charging stations and other locations include 100V outlets, 200V outlets, and 3-phase 200V with 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0443] For rapid charging, a rechargeable battery capable of withstanding high-voltage charging is desired to achieve short charging times.

[0444] Furthermore, the secondary battery of this embodiment described above uses the positive electrode active material 100 obtained in the previously described embodiment. In addition, by using graphene as a conductive material, even if the electrode layer is thickened and the load is increased, the decrease in capacity is suppressed and high capacity is maintained, resulting in a secondary battery with significantly improved electrical characteristics as a synergistic effect. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide a vehicle with a long driving range, specifically a driving range of 500 km or more on a single charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0445] In particular, the secondary battery of this embodiment described above can achieve a higher operating voltage by using the positive electrode active material 100 described in the previous embodiment, and the usable capacity can be increased with increasing charging voltage. Furthermore, by using the positive electrode active material 100 described in the previous embodiment as the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0446] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0447] Furthermore, by mounting the secondary battery shown in any one of Figures 10D, 12C, and 20A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing and rotary-wing aircraft, rockets, satellites, space probes, planetary probes, and spacecraft. A secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, a secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0448] Figures 21A to 21E illustrate an example of a mobile device using one aspect of the present invention, such as a transport vehicle. The automobile 2001 shown in Figure 21A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on the vehicle, one or more examples of the secondary battery shown in Embodiment 3 are installed in one location. The automobile 2001 shown in Figure 21A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device electrically connected to the secondary battery module.

[0449] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the secondary battery it possesses. When charging, the charging method and connector specifications may be carried out as appropriate using a prescribed method such as CHAdeMO (registered trademark) or Combo. The charging device may be a charging station installed in a commercial facility or a household power supply. For example, the secondary battery installed in the automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0450] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and when it is in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0451] Figure 21B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a nominal voltage of 3.0V to 5.0V. The secondary battery module of the battery pack 2201 has the same functions as Figure 21A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0452] Figure 21C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, for example, by connecting 100 or more secondary batteries with a nominal voltage of 3.0V to 5.0V in series. By using secondary batteries with the positive electrode active material 100 described in the above embodiment as the positive electrode, it is possible to manufacture secondary batteries with good rate characteristics and charge / discharge cycle characteristics, which can contribute to the high performance and long lifespan of the transport vehicle 2003. Furthermore, the battery pack 2202 has the same functions as Figure 21A except for differences in the number of secondary batteries constituting the secondary battery module, so the explanation is omitted.

[0453] Figure 21D shows an example of an aircraft 2004 having a fuel-burning engine. Since the aircraft 2004 shown in Figure 21D has landing gear for takeoff and landing, it can also be considered part of a transport vehicle. The aircraft 2004 has a battery pack 2203 which includes a secondary battery module composed of multiple connected secondary batteries and a charge control device.

[0454] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functions as Figure 21A, except for the number of secondary batteries that make up the module, so the explanation will be omitted.

[0455] Figure 21E also shows an example of a satellite 8800. The satellite 8800 shown in Figure 21E has a secondary battery 8801. As the secondary battery 8801, one example of the secondary battery shown in Embodiment 3 can be used. Since the satellite 8800 will be used in the extremely cold environment of space, it is desirable that the secondary battery 8801 be mounted inside the satellite 8800 and covered with a heat-insulating material.

[0456] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0457] (Embodiment 6) In this embodiment, an example of implementing a secondary battery, which is one aspect of the present invention, in a building will be explained using Figures 22A and 22B.

[0458] The house shown in Figure 22A has a power storage device 2612 having 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 via wiring 2611, etc. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0459] The power stored in the energy storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

[0460] Figure 22B shows an example of an energy storage device according to one aspect of the present invention. As shown in Figure 22B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Furthermore, the energy storage device 791 may be equipped with the control circuit described in Embodiment 5, and by using a secondary battery with the positive electrode active material 100 obtained in the above embodiment as the positive electrode in the energy storage device 791, a long-life energy storage device 791 can be made.

[0461] The energy storage device 791 is equipped with a control device 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0462] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the energy storage device 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0463] General loads 707 are electrical equipment such as televisions and personal computers, while energy storage loads 708 are electrical equipment such as microwave ovens, refrigerators, and air conditioners.

[0464] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0465] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked on electrical equipment such as televisions and personal computers via the router 709. Furthermore, it can be checked on portable electronic devices such as smartphones and tablets via the router 709. Additionally, the amount of electricity demand for each time period (or hourly) predicted by the prediction unit 712 can be checked on the display unit 706, electrical equipment, and portable electronic devices.

[0466] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0467] (Embodiment 7) This embodiment shows an example of mounting an energy storage device according to one aspect of the present invention on a motorcycle or bicycle.

[0468] Furthermore, Figure 23A shows an example of an electric bicycle using a power storage device according to one embodiment of the present invention. The power storage device according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 23A. The power storage device according to one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0469] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 is also portable, and Figure 23B shows it detached from the bicycle. The power storage device 8702 also has multiple built-in batteries 8701, which are part of a power storage device according to one embodiment of the present invention, and the remaining battery level can be displayed on a display unit 8703. The power storage device 8702 also has a control circuit 8704 capable of controlling the charging of a secondary battery or detecting abnormalities, as exemplified in Embodiment 5. The control circuit 8704 is electrically connected to the positive and negative electrodes of the batteries 8701. A small solid-state secondary battery, as shown in Figures 19A and 19B, may also be provided in the control circuit 8704. By providing the small solid-state secondary battery shown in Figures 19A and 19B in the control circuit 8704, power can be supplied to hold data in the memory circuit of the control circuit 8704 for a long period of time. Furthermore, a synergistic effect on safety can be obtained by combining the positive electrode active material 100 obtained in the above-described embodiment with a secondary battery that uses it as the positive electrode. The secondary battery and control circuit 8704 that use the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0470] Furthermore, Figure 23C shows an example of a two-wheeled vehicle using a power storage device according to one embodiment of the present invention. The scooter 8600 shown in Figure 23C is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply electricity to the turn signals 8603. In addition, the power storage device 8602, which houses multiple secondary batteries using the positive electrode active material 100 obtained in the above embodiment as the positive electrode, can have a high capacity and contribute to miniaturization.

[0471] Furthermore, the scooter 8600 shown in Figure 23C can accommodate the power storage device 8602 in the under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0472] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0473] (Embodiment 8) This embodiment describes an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0474] Figure 24A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By providing a secondary battery 2107 that uses the positive electrode active material 100 described in the above embodiment as the positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0475] The mobile phone 2100 can run various applications such as making phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0476] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0477] Furthermore, the 2100 mobile phone is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.

[0478] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0479] The mobile phone 2100 preferably has sensors. For example, it is preferable that the sensor includes a human body sensor such as a fingerprint sensor, pulse sensor, or body temperature sensor, as well as a touch sensor, pressure sensor, acceleration sensor, etc.

[0480] Figure 24B 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 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery to be mounted on the unmanned aerial vehicle 2300.

[0481] Figure 24C shows an example of a robot. The robot 6400 shown in Figure 24C is equipped with a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0482] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0483] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the user's desired information on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be enabled.

[0484] The upper camera 6403 and the lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, the lower camera 6406 and the obstacle sensor 6407.

[0485] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0486] Figure 24D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0487] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that might become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component within its internal region. The secondary battery using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode has high energy density and high safety, allowing for safe use over long periods, making it suitable as a secondary battery 6306 for the cleaning robot 6300.

[0488] Figure 25A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0489] For example, a secondary battery according to one embodiment of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 25A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 with good weight balance and long continuous use time can be made. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0490] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. The secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0491] 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. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0492] 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. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0493] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply and receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. A secondary battery using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0494] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and the secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0495] The display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0496] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, and manage their health.

[0497] Figure 25B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0498] A side view is also shown in Figure 25C. Figure 25C shows how the secondary battery 913 is built into the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 3. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, allowing for high density and high capacity, as well as being small and lightweight.

[0499] Since the wristwatch-type device 4005 is required to be small and lightweight, using the positive electrode active material 100 obtained in the above embodiment as the positive electrode of the secondary battery 913 makes it possible to create a secondary battery 913 that is both high in energy density and compact.

[0500] Figure 25D shows an example of wireless earphones. Here, wireless earphones with a pair of main units 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0501] The main units 4100a and 4100b have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. Preferably, they also have a circuit board with a wireless IC or the like, charging terminals, etc. They may also have a microphone.

[0502] The case 4110 contains a secondary battery 4111. Preferably, it also has a circuit board on which circuits such as a wireless IC and a charging control IC are mounted, and charging terminals. It may also have a display unit, buttons, etc.

[0503] The main units 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. This allows them to play audio data sent from other electronic devices. Furthermore, if the main units 4100a and 4100b have microphones, they can send sound acquired by the microphones to other electronic devices, process the audio data, and then send it back to the main units 4100a and 4100b for playback. This allows them to be used, for example, as a translation device.

[0504] Furthermore, the secondary battery 4103 in the main unit 4100a can be charged from the secondary battery 4111 in the case 4110. As the secondary battery 4111 and the secondary battery 4103, coin-type secondary batteries, cylindrical secondary batteries, etc., as in the previous embodiment can be used. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density, and by using it in the secondary battery 4103 and the secondary battery 4111, a configuration that can accommodate space saving due to the miniaturization of wireless earphones can be realized.

[0505] This embodiment can be implemented in appropriate combination with other embodiments. [Examples]

[0506] In this example, samples A to C were prepared as positive electrode active materials with reference to the manufacturing methods shown in Figures 2, 3C, and 3E, and their characteristics were analyzed.

[0507] <Sample A> The method for preparing Sample A will be explained. As LiMO2 in step S14 of Figure 2, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) was prepared, which has cobalt as the transition metal M and no particular additive elements.

[0508] In step S20 of Figure 2, BaF2, MgF2, and LiF were prepared as the X and Y sources. BaF2, MgF2, and LiF were weighed such that when the molar ratio of MgF2:BaF2=y:1, y=9, and when the molar ratio of LiF:BaF2=z:1, z=6.

[0509] The mixing in step S31 was carried out without grinding BaF2. After weighing, MgF2 and LiF were ground separately in a ball mill. Specifically, MgF2 and LiF were placed in separate zirconia pots, each containing a 1 mm diameter zirconia ball and dehydrated acetone, and ground by stirring at a rotation speed of 400 rpm for 12 hours. After that, the ground MgF2 and LiF were sieved separately through sieves with a mesh size of 300 μm to equalize the particle size of each.

[0510] Furthermore, Ni(OH)2 and Al(OH)3 were prepared as the Z source for step S20 in Figure 2. After weighing Ni(OH)2 and Al(OH)3 so that each amount was 0.5 mol% relative to LiCoO2, they were separately ground in a ball mill. Specifically, Ni(OH)2 and Al(OH)3, along with 1 mm diameter zirconia balls and dehydrated acetone, were placed in separate zirconia pots and stirred at a rotation speed of 400 rpm for 12 hours to grind them. After that, the ground Ni(OH)2 and Al(OH)3 were separately sieved through sieves with a mesh size of 300 μm to equalize the particle size of each. Then, the mixing in step S31 was carried out.

[0511] Next, BaF2, MgF2, and LiF were combined and weighed to 1.6 mol% with respect to LiCoO2. According to step S31 in FIG. 2, lithium cobalt oxide and all the additive element sources were mixed in a kneader (manufactured by Shinki Co., Ltd., a rotation-revolution type mixer, Awatori Renkatarou). At this time, stirring was performed for 3 minutes at a rotational speed of 2000 rpm for 2 cycles. Thereby, mixture A was obtained. In mixture A, the combined ratio of Ba, Mg, Al, and Ni with respect to cobalt is 2 at%.

[0512] Next, mixture A was heated. The heating conditions were 850 °C, 60 hours, and an oxygen atmosphere (5 L / min flow rate). When heating, a lid was placed on the crucible containing mixture A. The inside of the crucible was an atmosphere containing oxygen. By heating, LCO containing Ba, Mg, F, Ni, and Al was obtained. The positive electrode active material thus obtained was designated as sample A.

[0513] <Sample B> In step S20, a sample prepared in the same manner as sample A except that BaF2, MgF2, and LiF were weighed so that y = 4 when the molar ratio was MgF2:BaF2 = y:1 and z = 4.33 when LiF:BaF2 = z:1 was designated as sample B.

[0514] <Sample C> In step S20, a sample prepared in the same manner as sample A except that BaF2, MgF2, and LiF were weighed so that y = 1 when the molar ratio was MgF2:BaF2 = y:1 and z = 3.33 when LiF:BaF2 = z:1 was designated as sample C.

[0515] <SEM Observation> SEM observation was performed to analyze the prepared samples A, B, and C. Figures 26A and 26B are SEM images of sample A, with Figure 26B being a magnified portion of Figure 26A. Figures 27A and 27B are SEM images of sample B, with Figure 27B being a magnified portion of Figure 27A. Figures 28A and 28B are SEM images of sample C, with Figure 28B being a magnified portion of Figure 28A.

[0516] <Half-cell charge / discharge cycle characteristics> A half-cell was assembled using a positive electrode active material according to one embodiment of the present invention, and its cycle characteristics were evaluated. The performance of the positive electrode alone was determined by evaluating the cycle characteristics of the half-cell.

[0517] First, using samples A through C as positive electrode active materials, half-cells for charge / discharge rates of 0.5C and 1C were assembled as test cells for cycle characteristics. The conditions for the half-cells are described below.

[0518] The above-mentioned positive electrode active material was prepared, acetylene black (AB) was prepared as the conductive material, and polyvinylidene fluoride (PVDF) was prepared as the binder. A slurry was prepared by mixing the positive electrode active material:AB:PVDF in a weight ratio of 95:3:2, and this slurry was coated onto an aluminum current collector. NMP was used as the solvent for the slurry.

[0519] After coating the current collector with slurry, the solvent was evaporated. The positive electrode was obtained through these steps. The active material content of the positive electrode was approximately 7 mg / cm³. 2 That's what I decided.

[0520] The electrolyte consisted of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, with 2 wt% vinylene carbonate (VC) added as an additive. The electrolyte in the electrolyte solution was 1 mol / L lithium hexafluoride phosphate (LiPF6). Polypropylene was used as the separator.

[0521] A lithium metal was used as the counter electrode, and a coin-shaped half-cell equipped with the above-mentioned positive electrode was formed, and its cycle characteristics were measured.

[0522] This section explains the discharge rate and charge rate under cycle conditions. The discharge rate is the relative ratio of the discharge current 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 1C is X (A). If the battery is discharged with a current of 2X (A), it is said to have been discharged at 2C, and if it is discharged with a current of X / 5 (A), it is said to have been discharged at 0.2C. Similarly, the charge rate is also defined as follows: if the battery is charged with a current of 2X (A), it is said to have been charged at 2C, and if it is charged with a current of X / 5 (A), it is said to have been charged at 0.2C.

[0523] The cycle characteristics are shown in Figures 29A and 29B. When the charge / discharge rate was 0.5C, charging was performed at a constant current of 0.5C up to 4.60V, and then at a constant voltage until the current value became 0.05C. Discharging was performed at a constant current of 0.5C up to 2.5V. When the charge / discharge rate was 1C, charging was performed at a constant current of 1C up to 4.60V, and then at a constant voltage until the current value became 0.1C. Discharging was performed at a constant current of 1C up to 2.5V. Here, 1C was defined as 200mA / g. The temperature was set to 45℃. This charging and discharging cycle was repeated 50 times.

[0524] Figures 29A and 29B show the results of charge-discharge cycle tests conducted at a charging voltage of 4.60V and a measurement temperature of 45°C. Figure 29A shows the results at a charging voltage of 4.60V, a measurement temperature of 45°C, and a charge-discharge rate of 0.5C, while Figure 29B shows the results at a charging voltage of 4.60V, a measurement temperature of 45°C, and a charge-discharge rate of 1C. Both results are graphs showing the change in discharge capacity with respect to the number of cycles. The horizontal axis of the graph represents the number of cycles, and the discharge capacity retention rate (%: maximum discharge capacity during 50 cycles is set to 100%) is shown. As evaluation results of coin cells using samples A to C, Table 1 shows the maximum discharge capacity value, Table 2 shows the discharge capacity value after 50 cycles, and Table 3 shows the discharge capacity retention rate after 50 cycles.

[0525] [Table 1]

[0526] [Table 2]

[0527] [Table 3]

[0528] Table 2 shows the discharge capacity values ​​after 50 cycles, and Table 3 shows the discharge capacity retention rate after 50 cycles. Samples A and B showed good battery characteristics at both charge / discharge rates of 0.5C and 1C, with Sample B demonstrating particularly excellent battery characteristics. [Explanation of symbols]

[0529] 100: Positive electrode active material, 100a: Surface layer, 100b: Interior, 101: Crystal grain boundary, 102: Embedding part, 103: Uneven distribution part, 200: Positive electrode active material layer, 201: Graphene compound, 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 312: Washer, 313: Ring-shaped insulator, 322: Spacer, 400: Secondary battery, 410: Positive electrode, 411: Positive electrode active material, 413: Positive electrode current collector, 414: 420: Positive electrode active material layer, 421: Solid electrolyte layer, 430: Negative electrode, 431: Negative electrode active material, 433: Negative electrode current collector, 434: Negative electrode active material layer, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode current collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Separator, 509: Outer casing, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 513: Secondary battery, 514: Terminal, 515: Seal, 517: Antenna, 519: Layer, 529: Label, 531: Secondary battery pack, 540: Circuit board, 551: Positive electrode lead and one of the negative leads, 552: positive lead and the other of the negative leads, 590: control circuit, 590a: circuit system, 590b: circuit system, 601: positive cap, 602: battery can, 603: positive terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 613: safety valve mechanism, 614: conductive plate, 615: energy storage system, 616: secondary battery, 620: control circuit, 621: wiring, 622: wiring, 623: wiring, 624: conductor, 625: insulator, 626: wiring, 627: wiring, 6 28: Conductive plate, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display unit, 707: General load, 708: Energy storage system load, 709: Router, 710: Service drop mounting section, 711: Measurement section, 712: Prediction section, 713: Planning section, 750a: Positive electrode, 750b: Solid electrolyte layer, 750c: Negative electrode, 751: Electrode plate, 752: Insulating tube, 753: Electrode plate, 761: Lower component, 762: Upper component, 764: Wing nut, 765: O-ring, 766: Insulator, 770a: Package component, 770b: Package component, 770c: Package component,771: External electrode, 772: External electrode, 773a: Electrode layer, 773b: Electrode layer, 790: Control device, 791: Energy storage device, 796: Underfloor space, 799: Building, 903: Mixture, 904: Mixture, 905: Mixture, 911a: Terminal, 911b: Terminal, 913: Secondary battery, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer, 933: Separator, 950: Winding body, 950a: Winding body, 951: Terminal, 952: Terminal, 1300: Rectangular secondary battery, 1301a: Battery, 130 1b: Battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC-DC circuit, 1308: Heater, 1309: Defogger, 1310: DC-DC circuit, 1311: Battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tires, 1317: Rear motor, 1320: Control circuit section, 1321: Control circuit section, 1322: Control circuit, 1324: Switch section, 1325: External terminals, 1326: External terminals, 1413: Fixing section, 1414: Fixing part, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2100: Mobile phone, 2101: Housing, 2102: Display unit, 2103: Operation buttons, 2104: External connection port, 2105: Speaker, 2106: Microphone, 2107: Rechargeable battery, 2200: Battery pack, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2300: Unmanned aerial vehicle, 2301: Rechargeable battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 260 4: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Energy storage device, 4000: Glasses-type device, 4000a: Frame, 4000b: Display unit, 4001: Headset-type device, 4001a: Microphone unit, 4001b: Flexible pipe, 4001c: Earphone unit, 4002: Device, 4002a: Housing, 4002b: Rechargeable battery, 4003: Device, 4003a: Housing, 4003b: Rechargeable battery, 4005: Wristwatch-type device, 4005a: Display unit, 4005b: Belt unit, 4006: Belt-type device, 4006a: Belt unit,4006b: Wireless power supply / receiving unit, 4100a: Main unit, 4100b: Main unit, 4101: Driver unit, 4102: Antenna, 4103: Rechargeable battery, 4104: Display unit, 4110: Case, 4111: Rechargeable battery, 6300: Cleaning robot, 6301: Housing, 6302: Display unit, 6303: Camera, 6304: Brush, 6305: Operation buttons, 6306: Rechargeable battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: My Crossphone, 6403: Upper camera, 6404: Speaker, 6405: Display unit, 6406: Lower camera, 6407: Obstacle sensor, 6408: Movement mechanism, 6409: Secondary battery, 8600: Scooter, 8601: Side mirror, 8602: Energy storage device, 8603: Turn signal light, 8604: Under-seat storage, 8700: Electric bicycle, 8701: Battery, 8702: Energy storage device, 8703: Display unit, 8704: Control circuit, 8800: Artificial satellite, 8801: Secondary battery,

Claims

1. A step of preparing a first mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, and a fluorine source with a composite oxide containing lithium and cobalt, A step of heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more, A step of preparing a second mixture by mixing a nickel source and an aluminum source with the first mixture, The process includes the step of heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more. The molar ratio of magnesium fluoride to barium fluoride in the first mixture is MgF ２ : BaF ２ A method for producing a positive electrode active material such that, when y = 1, y satisfies the conditions of 0.5 to 10.

2. A step of preparing a first mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, and a fluorine source with a composite oxide containing lithium and cobalt, A step of heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more, A step of preparing a second mixture by mixing a nickel source and an aluminum source with the first mixture, The process includes the step of heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more. The molar ratio of lithium fluoride to barium fluoride in the first mixture is LiF:BaF ２ A method for producing a positive electrode active material such that when z = 1, z satisfies the conditions of 3 to 7.

3. A step of preparing a first mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, and a fluorine source with a composite oxide containing lithium and cobalt, A step of heating the first mixture at a temperature of 800°C to 1100°C for 2 hours or more, A step of preparing a second mixture by mixing a nickel source and an aluminum source with the first mixture, The process includes the step of heating the second mixture at a temperature of 800°C to 1100°C for 2 hours or more. The molar ratio of magnesium fluoride to barium fluoride in the first mixture is MgF ２ : BaF ２ When y = 1, y satisfies the condition of being between 0.5 and 10. The molar ratio of lithium fluoride to barium fluoride in the first mixture is LiF:BaF ２ A method for producing a positive electrode active material such that when z = 1, z satisfies the conditions of 3 to 7.

4. A step of preparing a mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide containing lithium and cobalt. The process includes a step of heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more. The molar ratio of magnesium fluoride to barium fluoride in the mixture is MgF ２ : BaF ２ A method for producing a positive electrode active material such that, when y = 1, y satisfies the conditions of 0.5 to 10.

5. A step of preparing a mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide containing lithium and cobalt. The process includes a step of heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more. When the molar ratio of lithium fluoride to barium fluoride in the mixture is LiF:BaF ２ = z:1, a method for producing a positive electrode active material, where z satisfies 3 or more and 7 or less.

6. A step of preparing a mixture containing barium fluoride, magnesium fluoride, and lithium fluoride by mixing a barium source, a magnesium source, a fluorine source, a nickel source, and an aluminum source with a composite oxide containing lithium and cobalt. The process includes a step of heating the mixture at a temperature of 800°C to 1100°C for 2 hours or more. The molar ratio of magnesium fluoride to barium fluoride in the mixture is MgF ２ : BaF ２ When y = 1, y satisfies the condition of being between 0.5 and 10. The molar ratio of lithium fluoride to barium fluoride in the mixture is LiF:BaF ２ A method for producing a positive electrode active material such that when z = 1, z satisfies the conditions of 3 to 7.

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