Method for producing positive electrode active material

Abstract

One aspect of the present invention provides a method for producing a positive electrode active material having a stoichiometric composition as designed. Said one embodiment of the present invention is a method for producing a positive electrode active material including lithium, a transition metal, and oxygen. The method involves accommodating positive electrode active material particles containing lithium in a heat-resistant container with a lid, and placing and heating the positive electrode active material particles in a state where the particles are in contact with the inner wall of the heat-resistant container containing a plurality of metal elements, thereby selectively mixing at least one of the plurality of metal elements contained in the inner wall of the heat-resistant container with the positive electrode active material particles. The heat-resistant container is preferably made of an alloy material having high heat resistance. Specifically, one or more of nickel, manganese, titanium, and iron are used as the alloy material.

Description

Method for preparing positive electrode active material

[0001] This invention relates to an apparatus for producing oxides that can be used as positive electrode active materials, and a firing container that can be used in said apparatus. It also relates to a method for producing positive electrode active materials.

[0002] In recent years, there has been a great deal of development on various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries. In particular, the demand for lithium-ion secondary batteries, which offer high output and high capacity, has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable as a source of rechargeable energy in today's information society.

[0003] With the expansion of demand, there is a need to improve the productivity of lithium-ion batteries and their materials. As part of this effort, development is underway to efficiently produce positive electrode active materials, which are one of the materials used in lithium-ion batteries. For example, Patent Document 1 discloses a method for producing positive electrode active materials using a rotary kiln capable of continuous processing.

[0004] International Publication No. WO2021 / 116819 Brochure

[0005] The positive electrode active material for lithium-ion secondary batteries is manufactured by calcining lithium-containing raw material powder. When calcining lithium-containing raw material powder, it is common practice to place the powder in a container such as a crucible and calcine it.

[0006] The material of the container used for firing must be highly heat-resistant to withstand the firing temperature and have low reactivity with the raw material powder to be fired at high temperatures. Taking these factors into consideration, containers with aluminum oxide as the main component (also called alumina containers) are used.

[0007] However, it has been confirmed that when raw material powder containing lithium is calcined using a container mainly composed of aluminum oxide, the raw material components diffuse into the inner wall of the container, causing the white surface of the inner wall to change color.

[0008] In particular, when the stoichiometric composition of the positive electrode active material is accurately calculated and the amounts of the powder materials are weighed and mixed, the amount of lithium or the like decreases due to the reaction between the powder and the surface layer of the inner wall of the container, and the positive electrode active material as designed cannot be obtained, and the characteristics of the secondary battery using the positive electrode active material may deteriorate.

[0009] One aspect of the present invention aims to provide a method for producing a positive electrode active material with its stoichiometric composition as designed.

[0010] One aspect of the present invention aims to provide a method for producing a positive electrode active material with low production costs. Alternatively, one aspect of the present invention aims to provide a manufacturing apparatus capable of producing a positive electrode active material with low production costs. Alternatively, one aspect of the present invention aims to provide a method for producing a positive electrode active material whose crystal structure is hardly broken even when charge and discharge are repeated. Alternatively, one aspect of the present invention aims to provide a method for producing a positive electrode active material with excellent charge-discharge cycle characteristics. Alternatively, one aspect of the present invention aims to provide a method for producing a positive electrode active material with a large charge-discharge capacity. Alternatively, one aspect of the present invention aims to provide a secondary battery with high reliability or safety.

[0011] Note that the description of these problems does not prevent the existence of other problems. Note that one aspect of the present invention does not need to solve all of these problems. Note that it is possible to extract other problems from the descriptions in the specification, drawings, and claims.

[0012] One example of a production method of LiMO ２ (where M is one or more metals including Co, and there is no particular limitation on the substitution position of the metal) will be described.

[0013] In some cases, certain heat-treated materials, such as LiF (a fluorine source), can function as a flux when placed in a heat-resistant container with a lid to produce positive electrode active material (e.g., lithium cobalt oxide). This function allows the heating temperature to be lowered to below the decomposition temperature of lithium cobalt oxide, for example, between 742°C and 950°C. When additive elements, such as magnesium, are distributed on the surface of the positive electrode active material particles, positive electrode active material with good properties can be produced. For example, the presence of additive elements such as magnesium on the surface can suppress excessive reactions between the positive electrode active material and the electrolyte during the charge-discharge cycle, or it can suppress the release of oxygen from the positive electrode active material.

[0014] However, when heating in an oxygen atmosphere, LiF has a lower specific gravity in its gaseous state than oxygen, so there is a possibility that LiF will volatilize during heating. If it volatilizes, the amount of LiF in the material being heated will decrease. This weakens its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, LiMO ２ The Li on the surface may react with the fluorine source F to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is necessary.

[0015] Therefore, it is preferable to heat the material to be treated in an atmosphere containing fluoride, that is, to heat the material with a lid on the container.

[0016] Furthermore, if the particles of the material being heated adhere to each other during heating, the contact area with oxygen in the atmosphere decreases, and the diffusion pathway of the added elements is obstructed, which may worsen the distribution of added elements (e.g., magnesium) to the surface layer of the positive electrode active material. Therefore, it is preferable to stir the material to prevent the particles of the material being heated from adhering to each other during heating.

[0017] To stir the material being heated during the heating process, it is preferable to use a rotary kiln having a rotating drum or a cylindrical furnace tube, which can suppress the adhesion of particles. It is also preferable to use a rotary kiln in which the material to be heated is placed in cylindrical heat-resistant containers, covered, and then heated while the multiple heat-resistant containers are continuously moved through a cylindrical furnace tube having a diameter larger than that of the heat-resistant containers.

[0018] Furthermore, the heat-resistant container is preferably made of a highly heat-resistant alloy material. Specifically, one or more of nickel, manganese, titanium, magnesium, or iron can be used as the alloy material. Transition metals can be used for the heat-resistant container material, but chromium is excluded. If chromium is mixed into the positive electrode active material particles, it will degrade the characteristics of the secondary battery.

[0019] One aspect of the present invention is a method for producing a positive electrode active material, which involves placing positive electrode active material particles having lithium, a transition metal, and oxygen, along with a fluoride, in a heat-resistant container with a lid containing multiple metal elements, and mixing at least one of the multiple metal elements with the positive electrode active material particles by heating the heat-resistant container.

[0020] The transition metal can be one or more selected from cobalt, nickel, and manganese.

[0021] Because the heat-resistant container is made of an alloy, its thermal conductivity is higher than that of ceramic materials such as aluminum oxide, allowing heat to be transferred to the interior in a short time. Furthermore, it can prevent lithium from diffusing into the heat-resistant container more effectively than ceramic materials such as aluminum oxide. The heat-resistant container is cylindrical with a lid, and is heated while rotating with the lid on. Because it is stirred while rotating, the heating time can be shortened. The heating temperature can be between 800°C and 900°C, and the heating time can be between 1 hour and 3 hours.

[0022] Also, when at least one of the plurality of metal elements contained in the inner wall of the heat-resistant container is to be selectively mixed with the positive electrode active material particles, nickel or titanium can be mixed with the positive electrode active material particles in a trace amount. Thus, the battery characteristics can also be improved by mixing nickel oxide and titanium oxide from the inner wall of the heat-resistant container with the positive electrode active material particles. It is also possible to prepare a heat-resistant container with a higher ratio of the element to be selectively mixed from the heat-resistant container.

[0023] Further, when producing the positive electrode active material with the stoichiometric composition designed, nickel oxide and titanium oxide released from the inner wall of the heat-resistant container can be separated from the positive electrode active material particles using a sieve or the like. Since the colors of nickel oxide and titanium oxide are different from those of the positive electrode active material particles, it is easy to confirm whether they can be separated.

[0024] Conventionally, a container made of a ceramic material mainly composed of aluminum oxide or the like was used, so the thermal conductivity was low and a heating time of 10 hours or more was required. However, with this configuration, the positive electrode active material can be produced in a short time. In this specification and the like, when it is described that a certain material is included as the main component, it means that the content of the material is the largest among other components. Or, it means that the material is contained in the range of 50% by weight or more and less than 100% by weight, preferably 70% by weight or more and less than 100% by weight, more preferably 90% by weight or more and less than 100% by weight.

[0025] The material of the positive electrode active material is not particularly limited. As the material of the positive electrode active material, LiM represented by lithium cobalt oxide ｘ O ｙ (x > 0 and y > 0, more specifically, for example, y = 2 and 0.8 < x < 1.2) is not limited to lithium composite oxides represented by, and LiNi ｘ Co １−ｘ O ２ (0 < x < 1) represented by the NiCo system, LiM ｘ O ｙ As lithium composite oxides represented by, for example, LiNi ｘ Mn １−ｘ O ２It can also be used as a positive electrode active material for NiMn systems represented by (0 < x < 1), etc. ｘ Co ｙ Mn ｚ O ２ It can also be applied to NiCoMn systems (also called NCM) represented by (x>0, y>0, 0.8<x+y+z<1.2). Specifically, for example, it is preferable that 0.1x<y<8x and 0.1x<z<8x are satisfied. As an example, it is preferable that x, y, and z satisfy x:y:z=1:1:1 or values ​​close to it. Or as an example, it is preferable that x, y, and z satisfy x:y:z=5:2:3 or values ​​close to it. Or as an example, it is preferable that x, y, and z satisfy x:y:z=8:1:1 or values ​​close to it. Or as an example, it is preferable that x, y, and z satisfy x:y:z=6:2:2 or values ​​close to it. Or as an example, it is preferable that x, y, and z satisfy x:y:z=1:4:1 or values ​​close to it. Furthermore, lithium iron phosphate (LiFePO) is used as the positive electrode active material. ４ ) may be used. Lithium iron phosphate is a positive electrode active material also known as LFP.

[0026] The heat-resistant container can be heated with its lid closed to minimize gas leakage. Heating the powdered material while stirring allows for efficient heat treatment. By covering the container to prevent heat loss and rotating it for stirring, the total heating time can be shortened. After heating, the container can be stored with the lid closed, maintaining quality for extended periods without exposure to the atmosphere, making it suitable for use as a storage container for positive electrode active materials.

[0027] According to one aspect of the present invention, a method for producing a positive electrode active material with low production costs can be provided. By using a heat-resistant container, the stoichiometric composition of the positive electrode active material can be produced as designed. As a result, secondary batteries using this positive electrode active material have high discharge capacity and good cycle characteristics, allowing for long-term use over extended periods.

[0028] Figure 1A is an example of a cross-sectional view of a heat-resistant container and a manufacturing apparatus using the same, which represent one embodiment of the present invention, and Figure 1B is a schematic diagram showing a cross-section of the furnace core tube and the container. Figures 2A and 2B are diagrams illustrating an example of a method for producing a positive electrode active material. Figure 3 is a diagram illustrating an example of a method for producing a positive electrode active material. Figure 4 is a diagram illustrating an example of a method for producing a positive electrode active material. Figure 5 is a diagram showing the external appearance of a secondary battery. Figures 6A, 6B, and 6C are diagrams illustrating a method for producing a secondary battery. Figures 7A, 7B, 7C, and 7D are diagrams illustrating an example of an electronic device. Figures 8A, 8B, and 8C are diagrams illustrating an example of an electronic device. Figures 9A, 9B, and 9C are diagrams illustrating an example of a vehicle. Figures 10A and 10B are diagrams illustrating an example of an electric bicycle. Figure 11 is a graph showing the cycle characteristics of this embodiment.

[0029] 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.

[0030] In this specification, the terms "first" and "second" may be used for convenience to understand the technical content or to identify each component. Therefore, the terms "first" and "second" do not limit the number of each component. Nor do the terms "first" and "second" limit the order of each component. Furthermore, the terms "first" and "second" or identification codes used in this specification may not correspond to the terms or identification codes in the claims of this patent.

[0031] (Embodiment 1) In this embodiment, an example of performing heat treatment in a rotary kiln apparatus using a lid and a heat-resistant container is shown below.

[0032] The heat-resistant container shall be cylindrical in shape and made of an alloy material, specifically one or more of nickel, manganese, titanium, or iron. The lid shall also be made of the same alloy material, with a coefficient of thermal expansion equal to that of the heat-resistant container, so that no gaps are created before and after heat treatment.

[0033] Figure 1A shows an example of a cross-sectional view of a rotary kiln apparatus. The manufacturing apparatus shown in Figure 1A is suitable for producing positive electrode active materials (LCO, NCM, LFP, etc.). Specifically, lithium cobaltate is mixed with additive materials (such as materials containing magnesium) as a composite oxide having lithium and cobalt, then placed in a heat-resistant container, and heat treatment is performed under an oxygen gas atmosphere while the heat-resistant container is rotated to stir the material to be heated. By covering the container, the inflow and outflow of gas during the heat treatment can be limited to the flow of oxygen gas between the outside and inside of the heat-resistant container. Furthermore, since it is not completely sealed, the inside of the heat-resistant container does not become abnormally high pressure, making it safe. The mixture contains at least a fluoride, for example, lithium fluoride (LiF) and magnesium fluoride (MgF). ２ A mixture of ) is used.

[0034] When the melting point of fluorides, including lithium fluoride, is lower than that of other additive element sources, they can function as fluxes (also called fluxing agents) that lower the melting point of the other additive element sources. Fluorides include LiF and MgF. ２ If LiF and MgF are present, ２ Since the eutectic point P is around 742°C, it is preferable to set the heating temperature to 742°C or higher during the heat treatment after mixing the added elements.

[0035] Figure 1A shows a schematic cross-sectional view of a manufacturing apparatus 110 according to one embodiment of the present invention.

[0036] The manufacturing apparatus 110 includes a rotating furnace tube 111, a heating means 112, a vibrating means 119, and a stage 118. The manufacturing apparatus 110 also includes a rotation drive device 115 for the furnace tube 111, a gas supply means 116a, and a gas discharge means 116b. A heat-resistant container 120a containing the material is placed inside the furnace tube 111.

[0037] The furnace core tube 111 is a cylinder with an outer radius larger than that of the heat-resistant container, with one end being the supply port and the other end being the discharge port. The furnace core tube 111 rotates to agitate the material to be processed, i.e., the material to be heated, contained in the heat-resistant container 120a.

[0038] The heating means 112 is divided into three sections and arranged around the furnace core tube 111, and has the function of heating to a temperature of 700°C or higher and 1200°C or lower. As the heating means 112, for example, a silicon carbide heater, a carbon heater, a metal heater, or a molybdenum disilide heater can be used.

[0039] The gas supply means 116a has the function of controlling the atmosphere inside the furnace core tube 111 (also called the processing chamber). An example of the gas supply means 116a is a gas introduction line. The gas introduced is oxygen. When replacing the atmosphere inside the furnace core tube 111, which is the kiln body, the internal gas can be exhausted by the gas discharge means 116b, and then oxygen gas can be supplied from the gas supply means 116a to create the desired oxygen atmosphere. Alternatively, the oxygen gas may be heated before being supplied into the furnace core tube from the gas supply means 116a.

[0040] Furthermore, although not shown in the figures, the gas discharge means 116b may also include a pump for discharging gas from inside the furnace core tube 111, a valve for preventing backflow, and a detoxification device (combustion detoxification device or plasma detoxification device) for rendering the gas harmless before releasing it into the outside air.

[0041] In Figure 1A, for simplification, nothing is shown at both ends of the furnace tube 111, but gate valves, glove boxes, load chambers, unload chambers, or quartz lids are provided. Gate valves or the like are provided at both ends of the furnace tube 111 to maintain the cleanliness of the internal space of the furnace tube 111 and to create an oxygen atmosphere. After creating an oxygen atmosphere, the heating treatment may be performed with the ends of the furnace tube 111 closed off without supplying oxygen. The oxygen atmosphere inside the furnace tube 111 can be controlled based on an oxygen concentration meter.

[0042] In the diagram, the axis (central axis) of the furnace tube 111 is not inclined with respect to the horizontal plane. However, the axis of the furnace tube 111 may be inclined with respect to the horizontal plane (or the plane of the stage 118), and the container insertion side may be raised to facilitate the movement of the container inside the furnace tube. The inclination angle of the furnace tube axis can be changed by the operator as appropriate. Increasing the rotation speed of the furnace tube can also stir the material inside the heat-resistant container, but if the rotation speed is increased too much, the container will move inside the furnace tube because the axis of the furnace tube is inclined, shortening the time it takes to reach the area without a heater and preventing sufficient heating. Furthermore, if the rotation speed is increased too much, the material may become unevenly distributed against the inner wall of the container due to centrifugal force, and may not be stirred. Therefore, it is preferable for the operator to adjust the rotation speed of the furnace tube and the inclination angle of the axis as appropriate to ensure sufficient heating time.

[0043] Furthermore, productivity is improved because multiple heat-resistant containers 120a can be added continuously and heated sequentially. Figure 1A shows an example where three heat-resistant containers 120a are arranged, but this is not limited to four or more. In addition, since alloy materials are used for the heat-resistant containers 120a and lids, an oxide film is formed on the surface of the heat-resistant containers and lids, and this oxide film reduces corrosion caused by the acid used during cleaning.

[0044] Furthermore, nickel oxide or titanium oxide can be generated from the inner wall of the heat-resistant container 120a during heat treatment and mixed in.

[0045] Although not shown in the diagram, the heat-resistant container 120a may also be moved through the furnace core tube by pushing out one end of the heat-resistant container 120a using a transport robot installed in the loading chamber. The movement of the heat-resistant container 120a within the furnace core tube is not limited to a constant speed; it may be moved to a position close to the heating means 112, then rotated in place to heat while stirring, and after sufficient heat treatment, pushed out to complete the heat treatment.

[0046] Figure 1A shows an example in which a vibration means 119 is provided in the vertical direction to vibrate the heat-resistant container, but it is not particularly limited, and if sufficient stirring can be achieved and the vibration means 119 is not necessary, it is not required to provide it.

[0047] The vibrating means 119 moves periodically during the heating process. The vibrating means 119 is installed in the gap of the heating means 112 surrounding the furnace core tube 111. A metal bar is used as the vibrating means 119, and the metal bar is moved up and down by its own weight and a lifting mechanism using a spring or airflow, thereby impacting the furnace core tube and causing the container in contact with the inner wall of the furnace core tube to vibrate.

[0048] Figure 1A also shows the outer radius R2 of the furnace core tube 111. The material of the furnace core tube 111 can be any heat-resistant material, and the same material as the heat-resistant container 120a described above (heat-resistant alloy or ceramics) can be used. Figure 1B shows a cross-sectional view of the furnace core tube 111 and the heat-resistant container 120a when they are cut in half, illustrating the direction of rotation. Figure 1B also shows the inner radius R1 of the furnace core tube 111. The outer diameter r2 of the heat-resistant container 120a should be between 1 / 2 and 9 / 10 of the inner radius R1 of the furnace core tube. If the furnace core tube is thick, the outer radius r2 of the heat-resistant container can be increased, and the closer it is to the inner radius R1 of the furnace core tube, the more material can be heated at once. Furthermore, the closer the outer radius r2 of the heat-resistant container is to the inner radius R1 of the furnace core tube, the more difficult it becomes for the heat-resistant container to rotate. Therefore, it is better to have sufficient internal space within the furnace core tube for adequate stirring. Taking the above into consideration, the outer diameter r2 of the heat-resistant container and the inner radius R1 of the furnace core tube should be within an optimal range.

[0049] By using the manufacturing apparatus 110 shown in Figure 1A or Figure 1B, the diffusion of lithium into the inner wall of the heat-resistant container is suppressed by heating the heat-resistant container with the powdered material 161 sealed with a lid, the stoichiometric composition of the positive electrode active material can be produced as designed, and a manufacturing apparatus that can obtain a large amount of positive electrode active material at once can be provided.

[0050] (Embodiment 2) Example 1 of method for producing positive electrode active material The method for producing the positive electrode active material 100 will be explained using Figures 2A, 2B, 3, and 4.

[0051] <Step S11> In step S11 shown in Figure 2A, a lithium source (Li source) and a cobalt source (Co source) are prepared as lithium and cobalt materials.

[0052] It is preferable to use a lithium-containing compound as the lithium source, for example, lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride can be used. The purity of the lithium source is preferably high, for example, a purity of 4N (99.99%) or higher is preferred. Multiple types of lithium sources may be used.

[0053] It is preferable to use a compound containing cobalt as the cobalt source, for example, cobalt oxide or cobalt hydroxide can be used. Multiple types of cobalt sources may be used. The purity of the cobalt source is preferably high, for example, 3N (99.9%) or higher is preferable, more preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and more preferably 5N (99.999%) or higher.

[0054] By using high-purity materials, the amount of impurities in the positive electrode active material can be reduced. As a result, the capacity of the secondary battery is increased, and / or the reliability of the secondary battery is improved.

[0055] In addition, it is preferable that the cobalt source has high crystallinity; for example, it is preferable that the cobalt source be a single crystal grain. The crystallinity of the cobalt source can be evaluated using TEM images, scanning transmission electron microscope (STEM) images, high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, annular bright-field scanning transmission electron microscope (ABF-STEM) images, X-ray diffraction (XRD), electron diffraction, or neutron diffraction. Multiple methods may be used to evaluate crystallinity. Note that the above methods for evaluating crystallinity can be applied not only to cobalt sources but also to the evaluation of crystallinity of other materials.

[0056] Furthermore, in step S11, a portion of the A source described later may be prepared. For example, a nickel source may be prepared as the A source. Nickel is expected to have the effect of suppressing the deterioration of the crystal structure during the charge-discharge cycle by being present inside the positive electrode active material 100. For this reason, it is preferable to prepare a nickel source at the same time as the cobalt source.

[0057] For example, nickel oxide or nickel hydroxide can be used as the nickel source. Multiple types of nickel sources may also be used.

[0058] <Step S12> Next, as shown in Step S12 in Figure 2A, the lithium source and cobalt source are crushed and mixed to prepare a mixed material. If a nickel source is prepared in Step S11, the nickel source is also added and the mixed material is prepared in the same manner. 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. As a solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. 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 cobalt source with dehydrated acetone with a purity of 99.5% or higher, with a water content of 10 ppm (parts per million) or less, and then crush and mix. By using dehydrated acetone of the purity described above, the amount of impurities that may be introduced can be reduced.

[0059] For grinding and mixing, a dry compounding apparatus (powder processing machine), a ball mill, or a bead mill can be used. When using a ball mill, it is preferable to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they produce less impurity. When using a ball mill or a 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 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0060] <Step S13> Next, as shown in step S13 in Figure 2A, the mixed material is subjected to heat treatment.

[0061] The heating rate in the heating process depends on the target temperature, but is preferably between 80°C / h and 250°C / h. For example, if the temperature in the temperature holding process is 1000°C, the heating rate should be 200°C / h.

[0062] It is preferable that the heating rate in the processing chamber of the heat treatment apparatus is within the aforementioned range. However, the heating rate set in the heat treatment apparatus and the heating rate in the processing chamber may not match. For example, the heating rate in the processing chamber may be lower than the set heating rate. In such cases, the set heating rate should be adjusted so that the heating rate in the processing chamber falls within the aforementioned range. If the temperature in the processing chamber cannot be measured, the heating rate set in the heat treatment apparatus should be within the aforementioned range. If the temperature of the object to be processed can be measured, it is even more preferable that the heating rate of the object to be processed is within the aforementioned range.

[0063] The temperature in the temperature holding process is preferably 800°C to 1100°C, more preferably 900°C to 1000°C, and even more preferably around 950°C. If the temperature is too low, the decomposition and melting of the lithium source and cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to the evaporation of lithium from the lithium source and / or excessive reduction of cobalt. For example, cobalt may change from trivalent to divalent, inducing oxygen vacancies.

[0064] It is preferable that the temperature in the processing chamber of the heating apparatus is within the aforementioned range. However, the temperature set in the heating apparatus and the temperature in the processing chamber may not match. For example, the temperature in the processing chamber may be lower than the set temperature. In such cases, the set temperature should be adjusted so that the temperature in the processing chamber falls within the aforementioned range. If the temperature in the processing chamber cannot be measured, the temperature set in the heating apparatus should be within the aforementioned range. If the temperature of the object to be processed can be measured, it is even more preferable that the temperature of the object to be processed is within the aforementioned range.

[0065] After the heating process, at the beginning of the temperature holding process, a phenomenon called overshoot may occur where the temperature inside the processing chamber becomes higher than the set temperature. Even when overshoot occurs, it is preferable to adjust the heating rate so that the temperature inside the processing chamber remains within the temperature range of the aforementioned temperature holding process. Multiple heating processes with different heating rates may be provided. For example, a first heating process and a second heating process after the first heating process can be provided, and the heating rate of the second heating process can be set lower than that of the first heating process. This can suppress the occurrence of overshoot. If the temperature temporarily falls outside the temperature range of the aforementioned temperature holding process due to overshoot, it is preferable that this period be short.

[0066] If the temperature holding process is too short, lithium cobalt oxide may not be synthesized, and if it is too long, productivity will decrease. For example, the time should ideally be between 1 hour and 100 hours, and even more preferably between 2 hours and 20 hours.

[0067] It is not necessary to strictly distinguish between the heating process, the temperature holding process, and the cooling process. In the heat treatment, it is sufficient that the length of the period during which the temperature is within the aforementioned range is within the aforementioned time range. Therefore, in this specification, the temperature in the temperature holding process may be referred to as the heat treatment temperature or heating temperature, and the time in the temperature holding process may be referred to as the heat treatment time or heating time.

[0068] The atmosphere during the heating process and the temperature holding process preferably contains fluoride gas and oxygen.

[0069] After the temperature holding step, the workpiece is cooled in a cooling step. The cooling step can be, for example, 15 minutes to 50 hours. The cooling step may be performed by natural cooling. Furthermore, it is not necessary to cool the workpiece to room temperature; it is sufficient to cool it to a temperature acceptable for the next step.

[0070] For heat treatment, it is preferable to use an alloy material of nickel, manganese, titanium, or iron for the heat-resistant container and lid. For the alloy material used for the crucible or sheath, it is preferable to use a material that does not easily diffuse lithium or transition metal M. It is preferable to heat the crucible or sheath after placing a lid on it, as this can prevent the volatilization of the material.

[0071] After the heat treatment, the heat-treated material may be crushed and then sieved if necessary. If nickel oxide or titanium oxide peels off from the inner wall of the heat-resistant container and mixes with the positive electrode active material after the heat treatment, these peeled materials can be separated by sieving if it is desired to remove them. When recovering the heat-treated material, it may be transferred from the crucible to a mortar before recovery. A mortar made of zirconium oxide or agate can be suitably used. In addition, the same procedure as in step S13 can be followed for heat treatments other than step S13.

[0072] <Step S14> In step S14, lithium cobalt oxide (LiCoO) is produced. ２ ) can be obtained.

[0073] Here, we have shown an example of preparing a composite oxide by a solid-phase method as in steps S11 to S14, but the composite oxide may also be prepared by a coprecipitation method. Alternatively, the composite oxide may be prepared by a hydrothermal method.

[0074] In step S14, pre-synthesized lithium cobaltate can also be prepared. The composite oxide obtained or prepared in step S14 may already contain additive elements. By further adding additive elements to the composite oxide containing additive elements using the steps described later (steps S20, and steps S31 to S34, etc.), a positive electrode active material can be produced in which, for example, the additive elements are suitably contained in the surface layer and the interior.

[0075] Furthermore, by omitting the initial heating after step S14, the manufacturing process can be simplified.

[0076] <Step S20> Next, the preparation of the additive element A source (A source) shown in Step S20 will be explained using Figures 2A, 2B, and 3.

[0077] First, we will explain step S20 shown in Figure 2A (steps S21 to S23 which are described in detail in Figure 2B).

[0078] <Step S21> In step S21 shown in Figure 2B, a source of additive element A (source A) to be added to lithium cobalt oxide is prepared. A lithium source may also be prepared together with the additive element source A.

[0079] The aforementioned additive elements can be used as additive element A. Specifically, one or more selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, niobium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium can be used as additive element A.

[0080] When magnesium is used as an additive element, the additive element source can be called a magnesium source. For example, magnesium fluoride, magnesium oxide, magnesium hydroxide, or magnesium carbonate can be used as the magnesium source. Multiple types of magnesium sources may also be used.

[0081] When fluorine is used as an additive element, the additive element source can be called a fluorine source. Examples of such fluorine sources include lithium fluoride (LiF) and magnesium fluoride (MgF).２ ), aluminum fluoride (AlF ３ ), Titanium Fluoride (TiF ４ ), cobalt fluoride (CoF ２ CoF ３ ), nickel fluoride (NiF ２ ), zirconium fluoride (ZrF ４ ), vanadium fluoride (VF ５ ), manganese fluoride, iron fluoride, niobium fluoride, zinc fluoride (ZnF ２ ), calcium fluoride (CaF ２ ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF) ２ ), cerium fluoride (CeF ３ CeF ４ ), lanthanum fluoride (LaF ３ ), or sodium aluminum hexafluoride (Na ３ AlF ６ ) can be used. Among them, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted by heat treatment. Note that multiple types of fluorine sources may be used.

[0082] Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source.

[0083] The fluorine source may be a gas. When using a gaseous fluorine source, the fluorine source is mixed into the atmosphere during the subsequent heat treatment, and the heat treatment is performed while stirring using the heat treatment apparatus shown in Figure 1. As a gaseous fluorine source, for example, fluorine (F ２ ), carbon fluoride, nitrogen fluoride (NF ３ ) gas, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ５ F ２ , O ６ F ２ , O ２ F) can be used. Note that multiple types of fluorine sources may be used.

[0084] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF) is prepared as both the fluorine source and the magnesium source. ２ Prepare the following: Lithium fluoride and magnesium fluoride are LiF:MgF ２ Mixing lithium fluoride and magnesium fluoride in a molar ratio of approximately 65:35 yields the greatest effect in lowering the melting point. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the cycle characteristics will deteriorate due to an excess of lithium. Therefore, the molar ratio of lithium fluoride to magnesium fluoride should be LiF:MgF ２ Preferably, the ratio is x:1 (0 ≤ x ≤ 1.9), and LiF:MgF ２ = x: 1 (0.1 ≤ x ≤ 0.5) is more preferable, and LiF: MgF ２ A more preferable value is x = 1 (near x = 0.33). In this specification, "nearby" means a value greater than 0.9 times the value and less than 1.1 times the value.

[0085] <Step S22> Next, in step S22 shown in Figure 3, the magnesium source and fluorine source prepared in step S21 are crushed and mixed. Since this step can be explained by referring to the description in step S12, a detailed explanation is omitted.

[0086] <Step S23> Next, in step S23 shown in Figure 2B, the material crushed and mixed in step S22 is recovered to obtain the additive element A source (A source). The additive element A source shown in step S23 has multiple materials and can be called a mixture.

[0087] The particle size of the above mixture is preferably such that the D50 (median diameter) is 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less. Even when one material is used as the additive element source, the D50 (median diameter) is preferably such that it is 600 nm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0088] When the mixture is finely powdered in this way (including cases where only one additive element is present), it is easier to uniformly adhere the mixture to the surface of the lithium cobalt oxide particles when mixed with lithium cobalt oxide in a later process. When the mixture is uniformly adhered to the surface of the lithium cobalt oxide particles, it is preferable because it is easier to uniformly distribute or diffuse the additive element to the surface layer of the composite oxide after heating.

[0089] Next, we will explain step S21 (steps S21 to S23) shown in Figure 3.

[0090] <Step S21> In step S21 shown in Figure 3, four types of additive element sources are prepared to be added to lithium cobalt oxide. In other words, Figure 3 differs from Figure 2B in the types of additive element sources. A lithium source may also be prepared along with the additive element sources.

[0091] Four types of additive element sources are prepared: a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source). The magnesium and fluorine sources can be selected from the compounds described in Figure 3. Nickel oxide or nickel hydroxide can be used as the nickel source. Multiple types of nickel sources may be used. Aluminum oxide or aluminum hydroxide can be used as the aluminum source. Multiple types of aluminum sources may be used.

[0092] Although four types of additive elements (Mg, F, Ni, and Al) have been used as examples in this explanation, the present invention is not limited to these. The number of types of additive elements is not particularly limited.

[0093] <Steps S22 and S23> Steps S22 and S23 shown in Figure 3 are the same as steps S22 and S23 described in Figure 2B. This makes it possible to obtain an additive element A source (A source) having four types of additive elements (Mg, F, Ni, and Al).

[0094] <Step S31> Next, in step S31 shown in Figure 2A, lithium cobalt oxide and additive element A source (A source) are mixed. The ratio of the number of cobalt atoms Co in lithium cobalt oxide to the number of magnesium atoms Mg in additive element A source is preferably Co:Mg = 100:y (0.1 ≤ y ≤ 6), and more preferably M:Mg = 100:y (0.3 ≤ y ≤ 3).

[0095] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, dry mixing is considered to be milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, for example, it is preferable to use zirconium oxide balls as the media.

[0096] In this embodiment, the mixture is dry-mixed at 150 rpm for 1 hour using a ball mill with zirconium oxide balls with a diameter of 1 mm. The mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower. By performing the mixing in a dry room, it is possible to suppress the adhesion of moisture to lithium cobalt oxide and additive element A source (A source).

[0097] <Step S32> Next, in step S32 of Figure 2A, the materials mixed above are recovered to obtain mixture 903. During recovery, if necessary, the materials may be crushed and then sieved.

[0098] <Step S33> Next, as step S33 shown in Figure 2A, the mixture 903 is subjected to heat treatment. The heat treatment can be described in step S13. Alternatively, the heat treatment apparatus shown in Figure 1 or Figure 3 can be used for this heat treatment.

[0099] The heating time is preferably two hours or more. At this time, in order to increase the oxygen partial pressure in the processing chamber of the heating apparatus shown in Figure 1 or Figure 3, the pressure in the processing chamber may exceed atmospheric pressure. This is because if the oxygen partial pressure in the processing chamber is low, cobalt and the like may be reduced, and lithium cobalt oxide and the like may not be able to maintain the layered rock salt type crystal structure.

[0100] Here, let's add some information about the heating temperature. The heating temperature in step S33 must be above the temperature at which the reaction between lithium cobalt oxide and the additive element source proceeds. The temperature at which the reaction proceeds is the temperature at which mutual diffusion of elements between lithium cobalt oxide and the additive element source occurs, and it may be lower than the melting temperature of these materials. In the case of oxides, the temperature at which solid-phase diffusion occurs (Tammann temperature T) is the temperature at which solid-phase diffusion occurs. ｄ ) is the melting temperature T ｍ This is 0.757 times. Therefore, the heating temperature in step S33 should be 650°C or higher.

[0101] Of course, the reaction proceeds more easily if the temperature is above the melting point of one or more of the materials in mixture 903. For example, LiF and MgF can be used as additive element sources. ２ If LiF and MgF are present, ２ Since the eutectic point is around 742°C, it is preferable that the lower limit of the heating temperature in step S33 be 742°C or higher.

[0102] LiCoO ２ :LiF:MgF ２ Mixture 903, obtained by mixing in a molar ratio of 100:0.33:1, shows an endothermic peak around 830°C in differential scanning calorimetry (DSC). Therefore, a lower limit of the heating temperature of 830°C or higher is more preferable.

[0103] A higher heating temperature is preferable because it facilitates the reaction and allows for a shorter heating time, resulting in higher productivity.

[0104] The heating temperature should be below the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures near the decomposition temperature, there is a concern that lithium cobalt oxide may decompose, albeit in small amounts. Therefore, the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower.

[0105] Based on these considerations, the heating temperature in step S33 is preferably 650°C to 1130°C, more preferably 650°C to 1000°C, more preferably 650°C to 950°C, and more preferably 650°C to 900°C. It is also preferably 742°C to 1130°C, more preferably 742°C to 1000°C, more preferably 742°C to 950°C, and more preferably 742°C to 900°C. It is also preferably 800°C to 1100°C, more preferably 830°C to 1130°C, more preferably 830°C to 1000°C, more preferably 830°C to 950°C, and more preferably 830°C to 900°C. The heating temperature in step S33 should be higher than that in step S13.

[0106] The heating rate depends on the target temperature, but is preferably between 80°C / h and 250°C / h. For example, if the temperature in the temperature holding process is 1000°C, the heating rate should be 200°C / h.

[0107] Furthermore, during the heat treatment of the mixture 903, it is preferable to control the partial pressure of fluorine or fluoride, which may be caused by the fluorine source, to an appropriate range.

[0108] In the manufacturing method described in this embodiment, some materials, such as LiF, a fluorine source, may function as a flux. This function allows the heating temperature to be lowered to below the decomposition temperature of lithium cobalt oxide, for example, between 742°C and 950°C, enabling the distribution of additive elements, including magnesium, to the surface layer and producing a positive electrode active material with good properties.

[0109] However, since LiF is less dense than oxygen in its gaseous state, heating may cause LiF to volatilize, which would reduce the amount of LiF in mixture 903. This would weaken its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, LiCoO ２ The Li on the surface may react with the fluorine source F to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, the same need to suppress volatilization is necessary.

[0110] 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. It is also preferable to heat the mixture 903 while circulating fluoride gas and oxygen gas using the heating apparatus shown in Figure 1 or Figure 3. This type of heating can suppress the volatilization of LiF in the mixture 903.

[0111] In step S33, the heat treatment is preferably carried out while stirring to prevent the particles of the mixture 903 from sticking together. By using the heat treatment apparatus shown in Figure 1 or Figure 3, the particles do not stick together, which eliminates the need for the subsequent crushing step and improves productivity.

[0112] When the median diameter (D50) of the lithium cobalt oxide obtained in step S14 of Figure 2A is about 12 μm, the heating temperature is preferably, for example, 650°C to 950°C. The heating time is preferably, for example, 3 hours to 60 hours, more preferably 10 hours to 30 hours, and even more preferably about 20 hours.

[0113] On the other hand, if the median diameter (D50) of the lithium cobalt oxide obtained in step S14 is about 5 μm, the heating temperature is preferably, for example, 650°C to 950°C. The heating time is preferably, for example, 1 hour to 10 hours, and more preferably about 5 hours.

[0114] A positive electrode active material according to one aspect of the present invention can be manufactured using a manufacturing method that involves heating in an atmosphere containing fluorine gas and circulating it.

[0115] By using a method for producing a positive electrode active material according to one aspect of the present invention, the concentration distribution of additive elements such as magnesium in the depth direction can be made to be distributed narrowly in the surface layer.

[0116] In one embodiment of the present invention, a method for producing a positive electrode active material can be obtained by the effect of a flux, resulting in a positive electrode active material with a smooth surface and few irregularities. A positive electrode active material with a smooth surface is considered to be less prone to cracking and more durable, even when the cooling rate is increased.

[0117] In addition, to distinguish the material that has undergone the heat treatment shown in step S33 from the composite oxide in step S14, an ordinal number may be assigned to it. For example, the composite oxide in step S14 may be referred to as the first composite oxide, and the material that has undergone the heat treatment shown in step S33 may be referred to as the second composite oxide.

[0118] <Step S34> Next, in step S34 shown in Figure 2A, the material that has undergone heat treatment is recovered and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sift the recovered particles. By the above steps, one embodiment of the positive electrode active material 100 of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0119] A positive electrode active material 100 with a smooth surface may be more resistant to physical damage such as pressure than a positive electrode active material with a smooth surface. For example, in tests involving pressure, such as a nail-piercing test, the positive electrode active material 100 may be less likely to be damaged, potentially resulting in increased safety.

[0120] Although this document describes a method of adding additive elements after obtaining lithium cobalt oxide, the present invention is not limited to this method. Additive elements may be added at other times, or added in multiple steps. The timing of addition may vary depending on the additive element.

[0121] For example, the additive element source may be added to the lithium source and cobalt source at step S11, that is, at the stage of the starting materials for the composite oxide. Then, lithium cobalt oxide having the additive element can be obtained in step S13. In this case, it is not necessary to separate the processes of steps S11 to S14 from the processes of steps S21 to S23. This can be said to be a simple and highly productive method.

[0122] Lithium cobaltate containing some of the additive elements may be used. For example, if lithium cobaltate with magnesium and fluorine added is used, steps S11 to S14 and some steps in S20 can be omitted. This can be said to be a simple and highly productive method.

[0123] 《Example 2 of Method for Preparing the Positive Electrode Active Material》 A method for preparing a positive electrode active material that differs from Example 1 of the method described above will be explained using Figure 4.

[0124] An example of a method for producing a positive electrode active material described here is that in step S14, lithium cobalt oxide (LiCoO) ２ This method differs from the aforementioned Example 1 of the method for producing a positive electrode active material in that, after obtaining the lithium cobalt oxide and before mixing the additive element A source (A source) in step S31, a heat treatment (i.e., initial heating) is performed. By adding additive element A to lithium cobalt oxide that has undergone initial heating, additive element A can be added uniformly. Therefore, it is preferable to add additive element A after initial heating. Except for initial heating, the description in the aforementioned Example 1 of the method for producing a positive electrode active material can be referred to.

[0125] First, lithium cobalt oxide is obtained via steps S11 to S14, similar to Figure 2A.

[0126] <Step S15> Next, as shown in Step S15 in Figure 4, the lithium cobalt oxide is subjected to heat treatment. Since this is the first heat treatment for the lithium cobalt oxide, the heat treatment in Step S15 can be called initial heating. Alternatively, since this heat treatment is performed before Step S20, it may be called preheating or pretreatment.

[0127] As described above, initial heating causes lithium to be released from a portion of the surface layer of lithium cobalt oxide. It is also expected to improve the crystallinity of the interior of the lithium cobalt oxide. Furthermore, the lithium source and / or cobalt source prepared in step S11, etc., may contain impurities. Initial heating can reduce impurities from the lithium cobalt oxide obtained in step S14.

[0128] By performing initial heating, the time required for subsequent heat treatment (for example, the time required for heat treatment in step S33) can be shortened. Furthermore, in one embodiment of the method for producing a positive electrode active material, the time required for the cooling process can be shortened. As a result, the total time required for heat treatment in the production process of the positive electrode active material 100 can be reduced, thereby improving productivity.

[0129] Furthermore, initial heating has the effect of smoothing the surface of lithium cobalt oxide. A smooth surface of lithium cobalt oxide means that there are few irregularities, the composite oxide is generally rounded, and the corners are also rounded. In addition, a state in which there are few foreign substances adhering to the surface is also called smooth. Foreign substances are thought to be a cause of irregularities, so it is preferable that they do not adhere to the surface.

[0130] For this initial heating, it is not necessary to prepare a lithium source, nor is it necessary to prepare an additive element source, nor is it necessary to prepare a material that functions as a flux.

[0131] If the initial heating time is too short, sufficient effects will not be obtained, but if it is too long, productivity will decrease. For initial heating, refer to the description in step S13, for example. More specifically, the initial heating temperature should be lower than the heating temperature in step S13 in order to maintain the crystal structure of the composite oxide. Also, the initial heating time should be shorter than the heating time in step S13 in order to maintain the crystal structure of the composite oxide. For example, the initial heating should be at 700°C to 1000°C for 2 to 20 hours.

[0132] The effect of increasing the internal crystallinity of lithium cobalt oxide is, for example, the effect of mitigating distortions, displacements, etc., that arise from differences in the shrinkage of lithium cobalt oxide caused by the heat treatment in step S13.

[0133] The heat treatment in step S13 can cause a temperature difference between the surface and the interior of lithium cobalt oxide. This temperature difference can induce a difference in shrinkage. It is thought that the difference in shrinkage occurs because the fluidity of the surface and the interior differs due to the temperature difference. The energy associated with the difference in shrinkage gives rise to a difference in internal stress in lithium cobalt oxide. This difference in internal stress is also called strain, and the energy associated with it is sometimes called strain energy. The internal stress is removed by the initial heating in step S15, or in other words, the strain energy is considered to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain of lithium cobalt oxide is relieved. Consequently, the surface of lithium cobalt oxide may become smoother. This is also referred to as the surface being improved. In other words, it is thought that after step S15, the difference in shrinkage that occurred in lithium cobalt oxide is relieved, and the surface of the composite oxide becomes smoother.

[0134] The difference in shrinkage can cause microscopic displacements in the lithium cobalt oxide, such as crystal displacement. This process is recommended to reduce such displacements. This process makes it possible to homogenize the displacement of the composite oxide. When the displacement is homogenized, the surface of the composite oxide may become smoother. This can also be described as the crystal grains being aligned. In other words, it is believed that step S15 alleviates the crystal displacements that have occurred in the composite oxide, resulting in a smoother surface.

[0135] Using lithium cobalt oxide, which has a smooth surface, as the positive electrode active material reduces degradation during charging and discharging in a secondary battery and prevents cracking of the positive electrode active material.

[0136] In addition, lithium cobalt oxide synthesized in advance may be used as step S14. In this case, steps S11 to S13 can be omitted. By performing step S15 on the lithium cobalt oxide synthesized in advance, lithium cobalt oxide with a smooth surface can be obtained.

[0137] Subsequently, steps S20 to S33 are performed in the same manner as in Figures 2A, 2B, and 3.

[0138] In addition, ordinal numbers may be assigned to distinguish between the composite oxide in step S14, the material after the heat treatment in step S15, and the material after the heat treatment in step S33. For example, the composite oxide in step S14 may be referred to as the first composite oxide, the material after the heat treatment shown in step S15 may be referred to as the second composite oxide, and the material after the heat treatment shown in step S33 may be referred to as the third composite oxide.

[0139] <Step S34> Next, in step S34, the material that has undergone heat treatment is recovered and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sift the recovered particles. By the above steps, one embodiment of the positive electrode active material 100 of the present invention can be produced. The positive electrode active material of one embodiment of the present invention has a smooth surface.

[0140] By undergoing the initial heating shown in step S15 of this embodiment, a positive electrode active material with a smooth surface can be obtained.

[0141] The initial heating described in this embodiment is performed on lithium cobalt oxide. Therefore, it is preferable that the initial heating is performed under conditions that are lower than the heating temperature required to obtain lithium cobalt oxide and shorter than the heating time required to obtain lithium cobalt oxide. The step of adding the additive elements to the lithium cobalt oxide is preferably performed after the initial heating. This addition step can be divided into two or more steps. Following this order of steps is preferable because it maintains the surface smoothness obtained during the initial heating.

[0142] Furthermore, this embodiment is not limited to lithium cobalt oxide; it can also be used to produce NCM and LFP in the production of positive electrode active materials. By performing heat treatment using a heat-resistant container mainly composed of nickel, the stoichiometric composition of NCM or LFP can be produced according to the user's design, and a manufacturing apparatus can be provided that can obtain a large amount of positive electrode active material at once.

[0143] This embodiment can be used in combination with other embodiments.

[0144] (Embodiment 3) An example of the external view of a laminate-type secondary battery 500 is shown in Figures 5 and 6. Figures 5 and 6 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. If the laminate-type secondary battery has a flexible structure, it can be bent in accordance with the deformation of the electronic device when mounted on an electronic device that has at least a part of a flexible component. An example of a method for manufacturing the laminate-type secondary battery will be explained using Figures 6A to 6C.

[0145] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. The negative electrode 506 has a negative electrode active material layer 505 on a negative electrode current collector 504, and the positive electrode 503 has a positive electrode active material layer 502 on a positive electrode current collector 501. Figure 6B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. 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, for example, ultrasonic welding may 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.

[0146] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0147] Next, as shown in Figure 6C, 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 an inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0148] Next, an electrolyte (not shown) is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0149] By using the method for producing the positive electrode active material 100 described in the previous embodiment for the positive electrode 503, a secondary battery 500 with high discharge capacity and excellent cycle characteristics can be obtained.

[0150] This embodiment can be used in appropriate combination with other embodiments.

[0151] (Embodiment 4) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device will be described with reference to Figures 7A to 8C.

[0152] Figure 7A shows an example of a wearable device. Wearable devices use rechargeable batteries that have a high total capacity and are lightweight as a power source. Furthermore, in order to enhance splash resistance, water resistance, and dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging with an exposed connector.

[0153] For example, a secondary battery according to one aspect of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 7A. 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 a long continuous usage time can be made. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0154] 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. A secondary battery with a high total capacity and light weight can be provided in the flexible pipe 4001b and / or the earphone section 4001c. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0155] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in a device 4002 that can be directly attached to the body. A secondary battery 4002b with high capacity per unit weight and light weight can be provided within the thin housing 4002a of the device 4002. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0156] Furthermore, a secondary battery according to one aspect of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b with high capacity per unit weight and light weight can be provided within the thin housing 4003a of the device 4003. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0157] 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 / receiving portion 4006b, and a secondary battery with high capacity per unit weight and light weight can be mounted inside the belt portion 4006a. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0158] 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 a secondary battery with high capacity per unit weight and light weight can be provided in either the display unit 4005a or the belt unit 4005b. By using a positive electrode active material according to one aspect of the present invention, a highly reliable configuration can be achieved.

[0159] The display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0160] 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.

[0161] Figure 7B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0162] A side view is also shown in Figure 7C. Figure 7C shows the internal structure with a secondary battery 913. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, and is small and lightweight.

[0163] Figure 7D shows an example of wireless earphones. Here, wireless earphones having a pair of main units 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0164] 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 on which a wireless IC or the like is mounted, charging terminals, etc. They may also have a microphone.

[0165] 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.

[0166] The main units 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. This allows them to play back 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.

[0167] Furthermore, the secondary battery 4103 in the main body 4100a can be charged from the secondary battery 4111 in the case 4110. Coin-type secondary batteries, cylindrical secondary batteries, etc., can be used as the secondary batteries 4111 and 4103. By using the positive electrode active material obtained in Embodiment 2, highly reliable secondary batteries 4103 and 4111 can be realized.

[0168] Figure 8A 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.

[0169] 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 aspect of the present invention and a semiconductor device or electronic components. By using the secondary battery 6306 according to one aspect of the present invention in the cleaning robot 6300, the total capacity of the secondary battery 6306 is increased, and the overall weight of the cleaning robot 6300 is reduced, making the cleaning robot 6300 an electronic device with a longer operating time. Additionally, by using a positive electrode active material according to one aspect of the present invention, a highly reliable secondary battery 6306 can be realized.

[0170] Figure 8B shows an example of a robot. The robot 6400 shown in Figure 8B 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 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0171] The microphone 6402 has the function of detecting the user's voice and ambient sounds. The speaker 6404 has the function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and speaker 6404.

[0172] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0173] 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.

[0174] 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 inside. By using the secondary battery according to one aspect of the present invention in the robot 6400, the entire robot 6400 can be made lighter and an electronic device with a longer operating time can be created. Furthermore, by using a positive electrode active material according to one aspect of the present invention, a highly reliable secondary battery 6409 can be realized.

[0175] Figure 8C shows an example of an aircraft (also called an unmanned aerial vehicle or drone). The aircraft 6500 shown in Figure 8C has a propeller 6501, a camera 6502, and a secondary battery 6503 on its airframe 6504, and is capable of autonomous flight. The aircraft 6500 can be used for transporting cargo, photographing subjects from above, and spraying pesticides. The propeller 6501 has a microcomputer as the motor control circuit for the motor that rotates it. The motor is powered by the secondary battery 6503. Although the aircraft in Figure 8C shows an example with one propeller 6501, it is not particularly limited, and may be a rotary-wing aircraft (multicopter) with two or more propellers.

[0176] For example, when the aircraft 6500 is used for photography, the image data captured by the camera 6502 is stored in a semiconductor device having a memory element. The semiconductor device can analyze the image data and detect the presence or absence of obstacles during movement. When the aircraft 6500 is remotely controlled, the aircraft 6500 has a wireless receiving circuit and receives instructions from a controller on the ground, controlling its flight direction and other parameters.

[0177] Furthermore, when the aircraft 6500 is used for transport, if the weight of the load is heavy, it becomes difficult to maintain balance in the air. Therefore, it is preferable to make the weight of the secondary battery, as well as the components of the aircraft 6504, lighter. The components of the aircraft 6504 can be made of lightweight materials, specifically resin materials, composite materials such as CFRP (Carbon Fiber Reinforced Plastics), or paper. The aircraft 6500 is equipped with a secondary battery 6503 according to one aspect of the present invention inside the aircraft 6504. By using a secondary battery according to one aspect of the present invention in the aircraft 6500, the secondary battery becomes lighter, and the total capacity can be increased, thus reducing the overall weight of the aircraft 6500 and enabling an aircraft 6500 with a longer flight distance and flight time. In addition, by using a positive electrode active material according to one aspect of the present invention, a highly reliable secondary battery 6503 can be realized.

[0178] This embodiment can be implemented in appropriate combination with other embodiments.

[0179] (Embodiment 5) This embodiment shows an example in which a secondary battery according to one aspect of the present invention is mounted on a vehicle.

[0180] By installing secondary batteries in vehicles, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs) can be realized.

[0181] Figure 9 illustrates a vehicle using a secondary battery, which is one embodiment of the present invention. The automobile 8400 shown in Figure 9A 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. By using one embodiment of the present invention, the secondary battery can be made lighter, and a vehicle with a long driving range can be realized. The automobile 8400 also has a secondary battery 8402. For example, modules of the secondary battery 8402 can be arranged and used in the floor area inside the vehicle. The secondary battery 8402 can not only drive the electric motor 8406 but also supply power to light-emitting devices such as headlights 8401 and room lights (not shown).

[0182] Furthermore, the secondary battery can supply power to display devices such as the speedometer and tachometer of the automobile 8400. The secondary battery can also supply power to semiconductor devices such as the navigation system of the automobile 8400.

[0183] The automobile 8500 shown in Figure 9B can be charged by receiving power from an external charging facility via a plug-in method and / or a contactless power supply method to the secondary battery of the automobile 8500. Figure 9B shows the state in which the secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022. 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 8021 may be a charging station installed in a commercial facility or a household power supply. For example, the secondary battery 8024 mounted on the automobile 8500 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 ADC converter.

[0184] 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 and / or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between vehicles. In addition, solar cells can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and / or in motion. For such wireless power supply, electromagnetic induction and / or magnetic resonance methods can be used.

[0185] Furthermore, Figure 9C shows an example of a two-wheeled vehicle using a secondary battery according to one embodiment of the present invention. The scooter 8600 shown in Figure 9C is equipped with a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0186] Furthermore, the scooter 8600 shown in Figure 9C can accommodate a secondary battery 8602 in the under-seat storage compartment 8604. The secondary battery 8602 can be stored in the under-seat storage compartment 8604 even if the compartment is small. By using a positive electrode active material according to one aspect of the present invention, a highly reliable secondary battery 8602 can be realized. The secondary battery 8602 is removable, and when charging, it can be carried indoors, charged, and then stored before driving.

[0187] According to one aspect of the present invention, the secondary battery can be made lighter and its discharge capacity can be increased. Therefore, since the capacity per unit weight can be increased, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made lighter, it will contribute to the weight reduction of the vehicle, and thus the driving range can be improved. In addition, the secondary battery installed in the vehicle can be used as a power supply source other than the vehicle. In this case, for example, it is possible to avoid using commercial power during peak power demand. If the use of commercial power during peak power demand can be avoided, it will contribute to energy saving and the reduction of carbon dioxide emissions.

[0188] Furthermore, Figure 10A shows an example of an electric bicycle using a secondary battery according to one aspect of the present invention. The secondary battery according to one aspect of the present invention can be applied to the electric bicycle 8700 shown in Figure 10A. The energy storage device according to one aspect of the present invention includes, for example, a plurality of secondary batteries and a charge / discharge control unit.

[0189] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to the motor (electric unit) that assists the rider. The power storage device 8702 is also portable and is shown detached from the bicycle in Figure 10B, and corresponds to a secondary battery unit. The power storage device 8702 also has multiple batteries 8701 built in, and the remaining battery level can be displayed on the display unit 8703. The remaining level is displayed on the display unit 8703. The power storage device 8702 also has a charge / discharge control unit 8704 that can control the charging of the secondary battery or detect abnormalities. The charge / discharge control unit 8704 is connected to the positive and negative electrodes of the battery 8701. The electric vehicle body unit of the electric bicycle 8700 is equipped with an operation unit 8712 on the handlebars. The operation unit 8712 has a display unit 8713, a power switch 8714, and a power storage device 8711.

[0190] This embodiment can be implemented in appropriate combination with other embodiments.

[0191] In this embodiment, the positive electrode active material is prepared according to the flow chart in Figures 2A and 2B. Lithium oxide (LiMO) ２ (M is one or more metals containing Co, and there are no particular limitations on the substitution position of the metal) Commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industrial Co., Ltd.) is used. Therefore, the process will start from step S14 in Figure 2A. When the particle size distribution of Cellseed C-10N was measured, the median diameter (D50) was found to be 12.5 μm.

[0192] Furthermore, as source A, magnesium fluoride (MgF) is used as the fluorine source and magnesium source in step S21 of Figure 2B. ２ Prepare the following: Lithium fluoride and magnesium fluoride are LiF:MgF ２Mixing lithium fluoride and magnesium fluoride in a molar ratio of approximately 65:35 yields the greatest effect in lowering the melting point. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will become excessive, worsening the charge-discharge cycle characteristics. Therefore, the molar ratio of lithium fluoride to magnesium fluoride should be LiF:MgF ２ Preferably, the ratio is 1:x (2≦x≦4), and LiF:MgF ２ = 1:x (2.5 ≤ x ≤ 3.5) is more preferable, and LiF:MgF ２ A more preferable value is 1:x (x = 3 or its vicinity). In this specification, a vicinity is defined as a value greater than 0.9 times the value and less than 1.1 times the value.

[0193] In this embodiment, LiF:MgF ２ The ratio was set to 1:3.

[0194] In step S22 shown in Figure 2B, the magnesium source and the fluorine source are crushed and mixed.

[0195] Next, in step S23 shown in Figure 2B, the material that has been crushed and mixed above is recovered to obtain source A. Source A shown in step S23 has multiple starting materials and can be called a mixture.

[0196] The particle size of the above mixture is preferably such that the D50 (median diameter) is 600 nm or more and 20 μm or less.

[0197] When the mixture is finely powdered in this way (including cases where only one additive element is present), it is easier to uniformly adhere the mixture to the surface of the lithium cobalt oxide particles when mixed with lithium cobalt oxide in a later process. When the mixture is uniformly adhered to the surface of the lithium cobalt oxide particles, it is preferable because it is easier to uniformly distribute or diffuse the additive element to the surface layer of the composite oxide after heating.

[0198] Next, in step S31 shown in Figure 2A, lithium cobalt oxide and source A are mixed. The ratio of the number of cobalt atoms Co in lithium cobalt oxide to the number of magnesium atoms Mg in source A is preferably Co:Mg = 100:y (0.1 ≤ y ≤ 6), and more preferably Co:Mg = 100:y (0.3 ≤ y ≤ 3).

[0199] In this example, the ratio of Co to Mg was set to 100:1.

[0200] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 in order to avoid destroying the shape of the lithium cobalt oxide particles. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, dry mixing is generally milder than wet mixing. For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconium oxide balls as the media.

[0201] In this example, the mixture was stirred for 10 minutes at a rotational speed of 3000 rpm using a Picobond (manufactured by Hosokawa Micron). A Novilta rotor was used for the Picobond. The mixing was carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.

[0202] Next, in step S32 of Figure 2A, the materials mixed above are recovered to obtain mixture 903. During recovery, if necessary, the materials may be crushed and then sieved.

[0203] Next, the mixture 903 is placed in a heat-resistant container, covered, and heated using the manufacturing apparatus shown in Figure 1. The manufacturing apparatus shown in Figure 1 is a device that rotates a cylindrical heat-resistant container to efficiently heat the mixture 903 while stirring it.

[0204] In this example, an alloy material containing nickel, manganese, and iron is used as the heat-resistant container.

[0205] In this embodiment, heating was performed at 900°C for 2 hours.

[0206] Then, in step S34 of Figure 2A, the heated material was recovered and crushed as necessary to obtain the positive electrode active material 100.

[0207] In this embodiment, the powder removed from the heat-resistant container was mixed with the oxidized and peeled-off inner wall of the container. Therefore, the positive electrode active material and other metal oxides were separated by sieving.

[0208] Then, a coin cell was fabricated using the positive electrode active material 100, and its cycle characteristics were measured.

[0209] When preparing the slurry, the positive electrode active material, binder, solvent, and conductive additive were mixed. Polyvinylidene fluoride (PVDF) was used as the binder, N-methyl-2-pyrrolidone (NMP) as the solvent, and acetylene black (AB) as the conductive additive. The mixing conditions were adjusted so that the ratio of positive electrode active material:AB:PVDF was 95:3:2. The slurry was coated onto an aluminum positive electrode current collector. NMP was used as the solvent for the slurry. After coating the positive electrode current collector with the slurry, the solvent was evaporated.

[0210] Through the above process, a positive electrode having positive electrode active material 100 was obtained. The amount of positive electrode active material supported was 7 mg / cm³. ２ I adjusted it to the appropriate degree.

[0211] Next, a half-cell was fabricated using the positive electrode described above.

[0212] In this embodiment, a coin cell (CR2032 type, 20 mm in diameter, 3.2 mm in height) was used as the test battery, and lithium metal was used for the counter electrode. The coin cell comprises an electrolyte, a separator, a positive electrode casing, and a negative electrode casing. When 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, voltage and potential refer to the potential of the positive electrode unless otherwise specified.

[0213] The electrolyte in the electrolyte solution contains 1 mol / L lithium hexafluoride phosphate (LiPF). ６ The electrolyte used was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7, with vinylene carbonate (VC) at 2 wt%.

[0214] A 25 μm thick porous polypropylene film was used as the separator.

[0215] The positive electrode and negative electrode cans were made of stainless steel (SUS).

[0216] The coin cell manufactured under the above conditions is charged with an arbitrary voltage (for example, 4.6V). The charging method is not particularly limited as long as it can be charged at an arbitrary voltage for a sufficient amount of time. For example, when charging with CCCV, the current in CC charging can be 20mA / g or more and 100mA / g or less. CV charging can be terminated at 2mA / g or more and 10mA / g or less.

[0217] The charge-discharge cycle test conditions were as follows: charging was performed under CCCV (constant current constant voltage) conditions (0.5C, approximately 4.6V, 0.05C cut), and discharging was performed under CC conditions (0.5C, 2.5V cut). Here, 1C was defined as 200mA / g. The ambient temperature for the measurement environment was 25°C. The post-charge pause time from the completion of charging to the start of discharging, and the post-discharge pause time from the completion of discharging to the start of charging, were both set to 10 minutes. In addition, a total termination time of 20 hours was set for both charging and discharging, in conjunction with the termination conditions described above.

[0218] The results of the charge-discharge cycle characteristics are shown in Figure 11. Figure 11 is a graph showing the results of the charge-discharge cycle test of the coin cell. The horizontal axis of the graph shows the number of charge-discharge cycles, and the vertical axis shows the discharge capacity in each cycle. Sample 1 shows the coin cell of this embodiment, with the heat-resistant container being used for the first time, while Sample 2 is the same process as Sample 1, but with the heat-resistant container being used for the second time.

[0219] Furthermore, Figure 11 shows a coin cell using a container made of aluminum oxide and a positive electrode active material that was processed using the same process as the heat-resistant container, as a comparative example.

[0220] As shown in Figure 11, the coin cell of this embodiment exhibited more favorable charge-discharge cycle characteristics than the comparative example in charge-discharge cycle tests under high charging voltage conditions. From the experimental results in Figure 11, it can be said that by using a heat-resistant container, the stoichiometric composition of the positive electrode active material could be fabricated as designed, more so than in the comparative example.

[0221] 100: Positive electrode active material, 110: Manufacturing apparatus, 111: Furnace core tube, 112: Heating means, 115: Rotary drive device, 116a: Gas supply means, 116b: Gas discharge means, 118: Stage, 119: Vibration means, 120a: Heat-resistant container, 161: Workpiece, 500: Secondary battery, 503: Positive electrode, 506: Negative electrode, 507: Separator, 509: Outer casing, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 903: Mixture, 913: Secondary battery, 4000: Eyeglass-type device, 4000a: Frame, 4000b: Display unit, 4001: Headset-type device Chair, 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 Part, 4110: Case, 4111: Rechargeable battery, 6300: Cleaning robot, 6301: Housing, 6302: Display unit, 6303: Camera, 6304: Brush, 6305: Operation button, 6306: Rechargeable battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: Speaker, 6405: Display unit, 6406: Lower camera, 6407: Obstacle sensor, 6408: Movement mechanism, 6409: Rechargeable battery, 6500: Flying body, 6501: Propeller, 6502: Camera, 6503: Two 6504: Secondary battery, 8021: Aircraft, 8022: Charging device, 8024: Cable, 8024: Secondary battery, 8400: Automobile, 8401: Headlight, 8402: Secondary battery, 8406: Electric motor, 8500: Automobile, 8600: Scooter, 8601: Side mirror, 8602: Secondary battery, 8603: Turn signal, 8604: Under-seat storage, 8700: Electric bicycle, 8701: Battery, 8702: Energy storage device, 8703: Display unit, 8704: Charge / discharge control unit, 8711: Energy storage device, 8712: Operation unit, 8713: Display unit, 8714: Power switch

Claims

A heat-resistant container with a lid containing multiple metal elements houses positive electrode active material particles and fluoride, which contain lithium, a transition metal, and oxygen. A method for producing a positive electrode active material, characterized by mixing at least one of the plurality of metal elements with the positive electrode active material particles by heating the heat-resistant container. 　 A method for producing a positive electrode active material, wherein at least nickel is present on the surface of the inner wall of the heat-resistant container, according to claim 1. 　 A method for producing a positive electrode active material, wherein the inner wall surface of the heat-resistant container contains at least nickel and titanium, according to claim 1. 　 The method for producing a positive electrode active material according to claim 1, wherein the heat-resistant container is cylindrical with a lid, and the container is heated while rotating with the lid on. 　 A method for producing a positive electrode active material according to claim 1, wherein the heating temperature is 800°C or higher and 900°C or lower, and the heating time is 1 hour or higher and 3 hours or lower. 　 A method for producing a positive electrode active material according to claim 1, wherein the plurality of metal elements are one or more of nickel, manganese, titanium, or iron.

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