Production method for positive electrode active material

Abstract

Provided is a production method for a novel positive electrode active material. This production method for a positive electrode active material includes: forming a cobalt compound by reacting a cobalt aqueous solution with an alkaline aqueous solution; mixing the cobalt compound with a lithium compound; performing a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound including a first additive element; performing a second heat treatment to form a second composite oxide; mixing the second composite oxide with a compound including a second additive element; and performing a third heat treatment. The first heat treatment is performed at a temperature of 700-1100ºC. The second heat treatment is performed at a temperature of 700-1000ºC. The third heat treatment is performed at a temperature equal to or lower than the temperature for the second heat treatment.

Description

Method for producing positive electrode active material

[0001] One embodiment of the present invention relates to an object, a method, or a manufacturing method. One embodiment of the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, or an electronic device, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a positive electrode active material for a lithium-ion secondary battery and a manufacturing method thereof.

[0002] In recent years, demand for high-power, high-capacity lithium-ion secondary batteries has rapidly expanded, and they have become indispensable in modern society as a reusable energy source.

[0003] In particular, lithium ion secondary batteries for portable electronic devices are required to have a large discharge capacity per weight and excellent charge / discharge characteristics. To meet these requirements, improvements to the positive electrode active materials of lithium ion secondary batteries have been actively pursued (see, for example, Patent Document 1). Patent Document 1 discloses a positive electrode active material with high capacity and excellent charge / discharge characteristics.

[0004] WO2020 / 099978 publication

[0005] The above Patent Document 1 does not describe a method for producing a hydroxide containing an element M (cobalt is exemplified as M) as a raw material. Furthermore, the above Patent Document 1 exemplifies a case where pre-synthesized lithium cobalt oxide is purchased.

[0006] In order to manufacture a secondary battery having excellent charge / discharge characteristics, it is important to control the positive electrode active material from the starting material, but when using the method for manufacturing lithium cobalt oxide as described in Patent Document 1, it is difficult to control the positive electrode active material, and it has not been possible to control, for example, the shape or particle size of the lithium cobalt oxide. Furthermore, it has not been possible to grasp the impurities contained in the lithium cobalt oxide.

[0007] In view of the above, an object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material that can solve at least one of the above problems.

[0008] Another object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material having a large discharge capacity.Another object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material that can withstand high charge / discharge voltages.Another object of one embodiment of the present invention is to provide a method for manufacturing a positive electrode active material that is less likely to deteriorate.Another object of one embodiment of the present invention is to provide a novel positive electrode active material.

[0009] Another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery including the above-described positive electrode active material. That is, another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery having a large discharge capacity. Another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery that can withstand high charge / discharge voltages. Another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery that is less susceptible to deterioration. Another object of one embodiment of the present invention is to provide a method for manufacturing a secondary battery with a long life. Another object of one embodiment of the present invention is to provide a novel method for manufacturing a secondary battery.

[0010] Another object of one embodiment of the present invention is to provide a positive electrode active material or a secondary battery obtained by the above manufacturing method.

[0011] Note that the description of the above-mentioned problems does not preclude the existence of other problems. Furthermore, problems other than the above-mentioned problems can be extracted from the description of the specification, drawings, and claims. One embodiment of the present invention does not necessarily solve all of the above-mentioned problems, but solves at least one of the above problems.

[0012] As a result of intensive research into the above-mentioned problems, the present inventors have discovered a method for producing a cobalt compound by reacting an aqueous solution containing cobalt ions (hereinafter referred to as a cobalt aqueous solution) with an aqueous solution exhibiting basicity (hereinafter referred to as a basic aqueous solution). A typical example of the basic aqueous solution is an aqueous solution exhibiting alkalineity (hereinafter referred to as an alkaline aqueous solution). Thus, one embodiment of the present invention is a method for producing a positive electrode active material, which includes reacting a cobalt aqueous solution with an alkaline aqueous solution to form a cobalt compound, mixing the cobalt compound with a lithium compound, performing a first heat treatment to form a first composite oxide, mixing the first composite oxide with a compound having a first additive element, performing a second heat treatment to form a second composite oxide, mixing the second composite oxide with a compound having a second additive element, and performing a third heat treatment, wherein the first heat treatment is performed at a temperature of 700° C. to 1100° C., the second heat treatment is performed at a temperature of 700° C. to 1000° C., and the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

[0013] Another embodiment of the present invention is a method for producing a positive electrode active material, the method including: reacting a cobalt aqueous solution, an alkaline aqueous solution, and a chelating agent to form a cobalt compound; mixing the cobalt compound with a lithium compound; performing a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element; performing a second heat treatment to form a second composite oxide; mixing the second composite oxide with a compound having a second additive element; and performing a third heat treatment, wherein the first heat treatment is performed at a temperature of 700° C. or higher and 1100° C. or lower; the second heat treatment is performed at a temperature of 700° C. or higher and 1000° C. or lower; and the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

[0014] Another embodiment of the present invention is a method for producing a positive electrode active material, comprising the steps of: reacting a first mixed solution containing a cobalt aqueous solution and a first chelating agent with a second mixed solution containing an alkaline aqueous solution and a second chelating agent to form a cobalt compound; mixing the cobalt compound with a lithium compound; performing a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element; performing a second heat treatment to form a second composite oxide; mixing the second composite oxide with a compound having a second additive element; and performing a third heat treatment, wherein the first heat treatment is performed at a temperature of 700° C. to 1100° C.; the second heat treatment is performed at a temperature of 700° C. to 1000° C.; and the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

[0015] Another embodiment of the present invention is a method for producing a positive electrode active material, the method including: reacting a first mixed solution containing a cobalt aqueous solution and a first chelating agent with an alkaline aqueous solution and a second chelating agent to form a cobalt compound; mixing the cobalt compound with a lithium compound; performing a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element; performing a second heat treatment to form a second composite oxide; mixing the second composite oxide with a compound having a second additive element; and performing a third heat treatment, wherein the first heat treatment is performed at a temperature of 700° C. to 1100° C.; the second heat treatment is performed at a temperature of 700° C. to 1000° C.; and the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

[0016] In another embodiment of the present invention, a complexing agent or a chelating agent can be used, and it is preferable to use ammonia as the complexing agent and glycine, oxine, 1-nitroso-2-naphthol or 2-mercaptobenzothiazole as the chelating agent.

[0017] In another embodiment of the present invention, a complexing agent or a chelating agent can be used. It is preferable to use ammonia as the first complexing agent and ammonia as the second complexing agent, or to use glycine, oxine, 1-nitroso-2-naphthol or 2-mercaptobenzothiazole as the first chelating agent and glycine, oxine, 1-nitroso-2-naphthol or 2-mercaptobenzothiazole as the second chelating agent.

[0018] In another aspect of the present invention, the first chelating agent preferably has the same material as the second chelating agent.

[0019] In another aspect of the present invention, it is preferable that the first additional element includes Mg or F, and the second additional element includes Ni or Al.

[0020] In another embodiment of the present invention, it is preferable to mix the second composite oxide with a compound having a second additional element to form a mixture, mix the mixture with a compound having a third additional element, and perform a third heat treatment.

[0021] In another aspect of the present invention, it is preferable that the first additional element includes Mg or F, the second additional element includes Ni, and the third additional element includes Zr or Al.

[0022] In another embodiment of the present invention, it is preferable to form a second composite oxide by performing a second heat treatment after crushing the first composite oxide.

[0023] According to one embodiment of the present invention, it is possible to control the shape or particle size of the positive electrode active material from the starting material. Furthermore, according to one embodiment of the present invention, it is possible to grasp the impurities contained in the positive electrode active material.

[0024] According to another embodiment of the present invention, a method for producing a positive electrode active material having a large discharge capacity can be provided. Alternatively, according to another embodiment of the present invention, a method for producing a positive electrode active material that can withstand high charge / discharge voltages can be provided. Alternatively, according to another embodiment of the present invention, a method for producing a positive electrode active material that is less susceptible to deterioration can be provided. Alternatively, according to another embodiment of the present invention, a novel positive electrode active material can be provided.

[0025] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0026] FIG. 1 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 2 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 3 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 4 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 5 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 6 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 7 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 8 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 9 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 10 is a flow chart showing a manufacturing process for a cathode active material according to one embodiment of the present invention. FIG. 11 is a diagram showing a coprecipitation synthesis apparatus according to one embodiment of the present invention. FIG. 12 is a diagram showing a coprecipitation synthesis apparatus according to one embodiment of the present invention. FIG. 13 is a diagram illustrating a change in the crystalline structure of a cathode active material. FIG. 14 is a diagram illustrating a change in the crystalline structure of a conventional cathode active material. FIG. 15 is a diagram showing an XRD pattern calculated from the crystal structure. FIG. 16 is a diagram showing an XRD pattern calculated from the crystal structure. FIGS. 17A to 17D are cross-sectional views illustrating an example of a positive electrode of a secondary battery. FIG. 18A is an exploded perspective view of a coin-type secondary battery, FIG. 18B is a perspective view of the coin-type secondary battery, and FIG. 18C is a cross-sectional perspective view thereof. FIG. 19A is a diagram showing an example of a cylindrical secondary battery, FIG. 19B is a diagram showing an example of a cylindrical secondary battery, and FIG. 19C is a diagram showing an example of a plurality of cylindrical secondary batteries. FIGS. 20A and 20B are diagrams illustrating an example of a secondary battery, and FIG. 20C is a diagram showing the internal state of the secondary battery. FIGS. 21A to 21C are diagrams illustrating an example of a secondary battery. FIGS. 22A and 22B are diagrams showing the external appearance of a secondary battery. FIGS. 23A to 23C are diagrams illustrating a method for manufacturing a secondary battery. Fig. 24A is a diagram showing the appearance of a battery pack, Fig. 24B is a diagram showing an example of the configuration of a battery pack, and Fig. 24C is a diagram showing an example of the configuration of a battery pack. Figs. 25A and 25B are diagrams explaining an example of a secondary battery. Figs. 26A to 26C are diagrams explaining an example of a secondary battery. Figs. 27A and 27B are diagrams explaining an example of a secondary battery.FIG. 28A is a perspective view of a battery pack illustrating one embodiment of the present invention, FIG. 28B is a block diagram of the battery pack, and FIG. 28C is a block diagram of a vehicle having a motor. FIGS. 29A to 29D are diagrams illustrating an example of a transportation vehicle. FIGS. 30A and 30B are diagrams illustrating a power storage device according to one embodiment of the present invention. FIG. 31A is a diagram illustrating an electric bicycle, FIG. 31B is a diagram illustrating a secondary battery of the electric bicycle, and FIG. 31C is a diagram illustrating an electric motorcycle. FIGS. 32A to 32C are diagrams illustrating an example of an electronic device. FIG. 33A shows an example of a wearable device, FIG. 33B is a perspective view of a wristwatch-type device, and FIG. 33C is a diagram illustrating a side view of the wristwatch-type device. FIGS. 34A and 34B are diagrams illustrating an example of an electronic device. FIGS. 35A to 35E are diagrams illustrating an example of an electronic device. FIGS. 36A to 36H are diagrams illustrating an example of an electronic device. FIGS. 37A to 37C are diagrams illustrating an example of an electronic device. FIG. 38 is a diagram illustrating an example of an electronic device. Fig. 39 is a diagram showing the results of XRD analysis. Fig. 40 is a planar SEM image of the positive electrode active material. Fig. 41 is a graph showing the results of a cycle test using a coin cell. Figs. 42A and 42B are graphs showing the results of a cycle test using a coin cell. Figs. 43A and 43B are graphs showing the results of a cycle test using a coin cell. Fig. 44 is a diagram showing the results of XRD analysis. Fig. 45 is a planar SEM image of the positive electrode active material.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0028] Embodiment 1 In this embodiment, a method for manufacturing a positive electrode active material according to one embodiment of the present invention will be described.

[0029] 1 , a cobalt aqueous solution is prepared as aqueous solution 890, and an alkaline aqueous solution is prepared as aqueous solution 892. These are reacted to produce a cobalt compound 880. This reaction may be referred to as a neutralization reaction, an acid-base reaction, or a coprecipitation reaction, and the cobalt compound 880 may be referred to as a precursor of lithium cobalt oxide.

[0030] <Cobalt aqueous solution> As the cobalt aqueous solution, cobalt sulfate (for example, CoSO ４ etc.), cobalt chloride (e.g., CoCl ２ etc.) or cobalt nitrate (e.g., Co(NO ３ ) ２ etc.), cobalt acetate (e.g., C ４ H ６ CoO ４ Examples of suitable cobalt solutions include aqueous solutions containing cobalt alkoxides, organic cobalt complexes, or hydrates thereof. For example, aqueous solutions prepared by dissolving these in pure water can be used. Because cobalt aqueous solutions are acidic, they can be referred to as acidic aqueous solutions. Furthermore, cobalt aqueous solutions can be referred to as a cobalt source in the manufacturing process of a positive electrode active material.

[0031] <Alkaline aqueous solution> Examples of alkaline aqueous solutions include aqueous solutions containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia. For example, aqueous solutions in which these are dissolved in pure water can be used. An aqueous solution in which multiple types selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia are dissolved in pure water may also be used.

[0032] <Pure Water> The pure water suitable for use in the cobalt aqueous solution and alkaline aqueous solution is water having a resistivity of 1 MΩ cm or more, more preferably 10 MΩ cm or more, and even more preferably 15 MΩ cm or more. Water satisfying this resistivity requirement has high purity and contains very few impurities.

[0033] <Reaction Conditions> When reacting aqueous solution 890 and aqueous solution 892 according to the coprecipitation method, the pH of the reaction system is adjusted to 9.0 or more and 13.0 or less, preferably 9.8 or more and 12.5 or less. For example, when aqueous solution 892 is placed in a reaction tank (also referred to as a reaction vessel) and aqueous solution 890 is added dropwise to the reaction vessel, the pH of the aqueous solution in the reaction vessel should be maintained within the above-mentioned range. The reaction vessel can be a highly chemical-resistant container, such as a glass container or a stainless steel container. Examples of glass containers include beakers and flasks. Furthermore, "maintaining the range" refers to the fact that if the pH value of the aqueous solution in the reaction vessel fluctuates when aqueous solution 890 is added dropwise, the pH of the aqueous solution in the reaction vessel should satisfy the above-mentioned range after a certain period of time has elapsed. The certain period of time is 1 second or more and 5 seconds or less, preferably 1 second or more and 3 seconds or less. The same applies when aqueous solution 890 is placed in a reaction vessel and aqueous solution 892 is added dropwise to the reaction vessel. The dropping rate of the aqueous solution 890 or 892 is preferably 0.1 mL / min to 1.0 mL / min, more preferably 0.3 mL / min to 1.0 mL / min. A slow dropping rate is preferable because it is easier to control the pH conditions.

[0034] In the reaction vessel, it is preferable to use a stirring means to stir the aqueous solution 892 or 890. The stirring means can be a stirrer, and examples of stirrers include a magnetic stirrer. Alternatively, the stirring means can be mechanical, such as a stirring blade connected to a motor. The stirring blade can be a propeller blade or an inclined paddle blade, which can have two to six blades. For example, when using four blades, it is preferable to arrange them in a cross shape when viewed from above. The rotation speed of the stirring means is preferably 800 rpm to 1200 rpm.

[0035] The aqueous solution 890 or 892 in the reaction vessel is adjusted to a temperature of 40° C. or higher, preferably 50° C. to 90° C. Dropping of the aqueous solution may be started after the temperature has reached the appropriate level.

[0036] The inside of the reaction vessel is preferably kept in an inert atmosphere. For example, when a nitrogen atmosphere is used, nitrogen gas is preferably introduced at a flow rate of 0.5 L / min to 2 L / min.

[0037] The reaction vessel may also be equipped with a reflux condenser, which allows nitrogen gas to escape from the reaction vessel. Water produced by reflux cooling can be returned to the reaction vessel.

[0038] After the above reaction, a cobalt compound precipitates in the reaction vessel. Filtration is performed to recover the cobalt compound. Before filtration, the reaction product precipitated in the reaction vessel is preferably washed with pure water and then with an organic solvent with a low boiling point (e.g., acetone). Furthermore, the cobalt compound may be sieved before washing.

[0039] The filtered cobalt compound may be further dried, for example, in a vacuum atmosphere at 60° C. to 90° C. for 0.5 to 3 hours. In this manner, cobalt compound 880 can be obtained.

[0040] Cobalt Compound 880 is cobalt hydroxide (e.g., Co(OH) ２ Cobalt hydroxide after filtration is obtained as secondary particles formed by aggregation of primary particles. In this specification, primary particles refer to the smallest particle clusters that can be confirmed by observation at, for example, 5000x magnification using a scanning electron microscope (SEM). In other words, primary particles refer to the smallest particle unit surrounded by grain boundaries. In addition to grain boundaries that can be observed using the SEM, some grain boundaries are present within particles. Secondary particles refer to particles that are not easily separated (particles independent from others) because the primary particles aggregate to share part of the grain boundary (such as the outer periphery of the primary particle). In other words, secondary particles may have grain boundaries.

[0041] Next, a lithium compound 881 is prepared.

[0042] <Lithium Compound 881> As the lithium compound 881, lithium hydroxide (for example, LiOH), lithium carbonate (for example, Li ２ CO ３ etc.), or lithium nitrate (e.g., LiNO ３ etc.)

[0043] When cobalt hydroxide is obtained as the cobalt compound 880, it is preferable to use lithium hydroxide as the lithium compound 881.

[0044] It is preferable to use a high-purity material for the lithium compound 881. The lithium compound can be referred to as a lithium source. Specifically, the purity of the material is 4N (99.99%) or higher, preferably 4N5 (99.995%) or higher, and more preferably 5N (99.999%) or higher. The use of a high-purity material can improve the battery characteristics of the secondary battery.

[0045] The lithium compound 881 is preferably microparticulated. In order to improve battery characteristics, it is preferable that no unreacted lithium compound remains during synthesis, and microparticulation can enhance reactivity. When lithium hydroxide or lithium carbonate is used as the lithium compound, the particle size of both is preferably 1 μm or more and 5 μm or less, and preferably 1 μm or more and 3 μm or less. Here, the particle size is defined as the median diameter (D50).

[0046] <Mixture> The lithium compound 881 and the cobalt compound 880 are mixed to obtain a mixture 903. Mixing can be performed by dry or wet methods. A rotation-revolution type mixer may be used for mixing. Furthermore, a ball mill, a bead mill, or the like may be used as the mixing means. When using a ball mill, it is preferable to use zirconia balls as the medium. Furthermore, when using a ball mill, a bead mill, or the like, it is preferable to set the peripheral speed to 100 mm / sec or more and 2000 mm / sec or less in order to suppress contamination from the media or materials. The cobalt compound 880 and the lithium compound 881 may be pulverized simultaneously with mixing, but pulverization is not required.

[0047] Next, the mixture is heated 885. This step is sometimes referred to as a heating step, and sometimes referred to as a baking step. When heating is performed after this step, the heating of this step may be referred to as, for example, the first heating by adding an ordinal number.

[0048] <Heating Conditions> The heating temperature is preferably 700°C or higher and lower than 1100°C, more preferably 800°C or higher and 1000°C or lower, and even more preferably 800°C or higher and 950°C or lower. The heating step may be carried out multiple times; for example, heating may be carried out first at a temperature of 400°C or higher and 700°C or lower, and then heating may be carried out at the above-mentioned temperature of 700°C or higher and lower than 1100°C. The previous heating is sometimes referred to as pre-baking because it is a low temperature, but such heating is expected to release gas components in the starting material, and by using this starting material, a composite oxide with few impurities can be obtained.

[0049] The heating time can be, for example, from 1 hour to 100 hours, and preferably from 2 hours to 20 hours.

[0050] The heating atmosphere is preferably an oxygen-containing atmosphere or a so-called dry air (also referred to as dry air) atmosphere containing oxygen with little water (for example, a dew point of −50° C. or less, more preferably a dew point of −80° C. or less). The latter oxygen-containing atmosphere is referred to as a dry atmosphere. An oxygen-containing atmosphere with an oxygen content of 90% or more is preferred.

[0051] For example, when heating at 850°C for 10 hours, the temperature rise rate should be 150°C / hour or more and 250°C / hour or less. The flow rate of dry air that can constitute the drying atmosphere should be 1 L / min or more and 15 L / min or less, preferably 8 L / min or more and 15 L / min or less, and more preferably 5 L / min or more and 10 L / min or less. The temperature drop time is preferably 10 hours or more and 50 hours or less until the temperature drops from the specified temperature to room temperature, and the temperature drop rate can be calculated from the temperature drop time, etc.

[0052] The crucible, sagger, setter, or container used during heating is preferably made of a material that does not easily release impurities. For example, a crucible made of alumina with a purity of 99.9% is recommended. For mass production, it is recommended to use a mullite-cordierite sagger. A mullite-cordierite sagger is a sagger made from mullite and cordierite.

[0053] Furthermore, when recovering the material after heating, the material may be transferred from the crucible to a mortar, but at this time, impurities should not be mixed into the material. For this reason, it is recommended to use a mortar made of alumina with a purity of 90% or more, preferably 99% or more. Of course, a zirconia mortar can also be used.

[0054] The above steps allow for the production of a positive electrode active material 100 such as lithium cobalt oxide. The shape, particle size, and composition of the lithium cobalt oxide can be controlled more easily than with lithium cobalt oxide produced entirely by a solid-phase method. Lithium cobalt oxide may also be referred to as a cobalt compound or composite oxide.

[0055] Furthermore, lithium cobalt oxide is preferable because it contains few impurities. However, when sulfate is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particles of the positive electrode active material using a glow discharge mass spectrometer (GD-MS), an inductively coupled plasma mass spectrometer (ICP-MS), or the like.

[0056] 2, a cobalt aqueous solution is prepared as an aqueous solution 890, an alkaline aqueous solution is prepared as an aqueous solution 892, and a chelating agent is prepared as an aqueous solution 891. The other configurations are the same as those of the above-mentioned manufacturing method 1.

[0057] <Chelating Agent> Examples of materials constituting the chelating agent include glycine, oxine, 1-nitroso-2-naphthol, 2-mercaptobenzothiazole, and EDTA (ethylenediaminetetraacetic acid). It is also possible to use a plurality of types selected from glycine, oxine, 1-nitroso-2-naphthol, and 2-mercaptobenzothiazole. An aqueous solution of these dissolved in pure water serves as the chelating agent. A chelating agent is a complexing agent that forms a chelate compound, and is preferable to general complexing agents. Of course, complexing agents other than chelating agents may also be used, and ammonia water may be used as the complexing agent.

[0058] The use of a chelating agent is preferable because it can suppress the generation of unnecessary crystal nuclei and promote the crystal growth of primary particles. Suppressing the generation of unnecessary nuclei suppresses the generation of fine particles, thereby enabling the production of complex oxides with a good particle size distribution. Furthermore, the use of a chelating agent can slow the acid-base reaction, allowing the reaction to proceed gradually, resulting in the production of secondary particles that are nearly spherical. The use of a chelating agent is also preferable because it makes it easier to control the pH of the reaction vessel when obtaining the cobalt compound 880. Glycine has the effect of maintaining a constant pH value at or near a pH of 9.0 to 10.0. Therefore, using a glycine aqueous solution as a chelating agent is preferable because it makes it easier to control the pH of the reaction vessel when obtaining the cobalt compound 880. Furthermore, the glycine concentration of the glycine aqueous solution in the aqueous solution 891 is preferably 0.05 mol / L to 0.1 mol / L.

[0059] The above steps allow the production of a positive electrode active material 100 such as lithium cobalt oxide. The shape, particle size, or composition of the lithium cobalt oxide can be controlled in comparison with that produced entirely by a solid-phase method.

[0060] Furthermore, lithium cobalt oxide is preferable because it contains few impurities. However, when sulfate is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particles of the positive electrode active material using GD-MS, ICP-MS, etc.

[0061] 3 , a cobalt aqueous solution is prepared as aqueous solution 890, an alkaline aqueous solution is prepared as aqueous solution 892, and chelating agents are prepared as aqueous solutions 893 and 894. Aqueous solution 893 is mixed with aqueous solution 890 to produce mixed solution 901. Aqueous solution 894 is mixed with aqueous solution 892 to produce mixed solution 902. Then, mixed solution 901 and mixed solution 902 are reacted to obtain cobalt compound 880. The other configurations are the same as those of the above-mentioned manufacturing method 1.

[0062] The use of a chelating agent is preferable because it can suppress the generation of unnecessary crystal nuclei and promote the crystal growth of primary particles. Suppressing the generation of unnecessary nuclei suppresses the generation of fine particles, thereby enabling the production of complex oxides with a good particle size distribution. Furthermore, the use of a chelating agent can slow the acid-base reaction, allowing the reaction to proceed gradually, resulting in the production of secondary particles that are nearly spherical. The use of a chelating agent is also preferable because it makes it easier to control the pH of the reaction vessel when obtaining cobalt compound 880. Glycine has the effect of maintaining a constant pH value at or around 9.0 to 10.0. Therefore, using a glycine aqueous solution as a chelating agent is preferable because it makes it easier to control the pH of the reaction vessel when obtaining the cobalt compound 880. Furthermore, the glycine concentration of the glycine aqueous solution is preferably 0.05 mol / L to 0.1 mol / L in aqueous solution 893 or aqueous solution 894.

[0063] The above steps allow the production of a positive electrode active material 100 such as lithium cobalt oxide. The shape, particle size, or composition of the lithium cobalt oxide can be controlled in comparison with that produced entirely by a solid-phase method.

[0064] Furthermore, lithium cobalt oxide is preferable because it contains few impurities. However, when sulfate is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particles of the positive electrode active material using GD-MS, ICP-MS, etc.

[0065] 4 , a cobalt aqueous solution is prepared as aqueous solution 890, an alkaline aqueous solution is prepared as aqueous solution 892, and chelating agents are prepared as aqueous solutions 893 and 894. Aqueous solution 893 is mixed with aqueous solution 890 to produce mixed solution 901. Furthermore, aqueous solutions 894 and 892 are not mixed in advance, but are reacted with mixed solution 901 to obtain cobalt compound 880. Specifically, aqueous solution 894 is placed in a reaction vessel, and mixed solution 901 and aqueous solution 892 are added dropwise to the reaction vessel. The other configurations are the same as those of Production Method 1 above.

[0066] The use of a chelating agent is preferable because it can suppress the generation of unnecessary crystal nuclei and promote the crystal growth of primary particles. Suppressing the generation of unnecessary nuclei suppresses the generation of fine particles, thereby enabling the production of complex oxides with a good particle size distribution. Furthermore, the use of a chelating agent can slow the acid-base reaction, allowing the reaction to proceed gradually, resulting in the production of secondary particles that are nearly spherical. The use of a chelating agent is also preferable because it makes it easier to control the pH of the reaction vessel when obtaining cobalt compound 880. Glycine has the effect of maintaining a constant pH value at or around 9.0 to 11.0. Therefore, using a glycine aqueous solution as a chelating agent is preferable because it makes it easier to control the pH of the reaction vessel when obtaining the cobalt compound 880. Furthermore, the glycine concentration of the glycine aqueous solution is preferably 0.05 mol / L to 0.1 mol / L in aqueous solution 893 or aqueous solution 894.

[0067] The above steps allow the production of a positive electrode active material 100 such as lithium cobalt oxide. The shape, particle size, or composition of the lithium cobalt oxide can be controlled in comparison with that produced entirely by a solid-phase method.

[0068] Furthermore, lithium cobalt oxide is preferable because it contains few impurities. However, when sulfate is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particles of the positive electrode active material using GD-MS, ICP-MS, etc.

[0069] <Manufacturing Method 5> A method for adding an additive element to the cathode active material 100 obtained by any of the above manufacturing methods 1 to 4 will be described with reference to Fig. 5. In Fig. 5, the cathode active material 100 obtained according to the above manufacturing method 4 is referred to as composite oxide 904, and a method for adding an additive element to the composite oxide 904 is illustrated. Specifically, the method enclosed by the dashed line in Fig. 5 is a method similar to the above manufacturing method 4. Note that the methods similar to the above manufacturing methods 1 to 3 may also be applied to the methods enclosed by the dashed line in Fig. 5.

[0070] First, an additive element source 905 is prepared to be added to the composite oxide 904. A lithium source may be prepared together with the additive element source 905.

[0071] <Additive Element> The additive element source 905 contains an additive element X. The additive element X is added to the composite oxide 904. For example, the additive element X can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. Alternatively, the additive element X can be one or more selected from bromine and beryllium. However, because bromine and beryllium are toxic to living organisms, it is more preferable to use the elements described above.

[0072] When magnesium is selected as the additive element X, the additive element source 905 can be called a magnesium source. The magnesium source can be magnesium fluoride (e.g., MgF ２ etc.), magnesium oxide (e.g., MgO etc.), magnesium hydroxide (e.g., Mg(OH) ２ etc.), or magnesium carbonate (e.g., MgCO ３ In addition, a plurality of the above-mentioned magnesium sources may be used.

[0073] When fluorine is selected as the additive element X, the additive element source can be called a fluorine source. Examples of the fluorine source include lithium fluoride (e.g., LiF), magnesium fluoride (e.g., MgF ２ etc.), aluminum fluoride (e.g., AlF ３ etc.), titanium fluoride (e.g., TiF ４ etc.), cobalt fluoride (e.g., CoF ２ , CoF ３ etc.), nickel fluoride (e.g., NiF ２ etc.), zirconium fluoride (e.g., ZrF ４ etc.), vanadium fluoride (e.g., VF ５ etc.), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (e.g., ZnF ２ etc.), calcium fluoride (e.g., CaF ２etc.), sodium fluoride (e.g., NaF etc.), potassium fluoride (e.g., KF etc.), barium fluoride (e.g., BaF ２ etc.), cerium fluoride (e.g., CeF ２ etc.), lanthanum fluoride (e.g., LaF ３ etc.), or sodium aluminum hexafluoride (e.g., Na ３ AlF ６ Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0074] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as both a fluorine source and a lithium source. Another lithium source is lithium carbonate.

[0075] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0076] When lithium fluoride and magnesium fluoride are crushed and mixed to prepare the additive element source 905, the molar ratio of lithium fluoride to magnesium fluoride is LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x:1 (x = 0.33 or its vicinity) is more preferable. Note that "x = 0.33 or its vicinity" refers to a value that is greater than 0.9 times and less than 1.1 times the value.

[0077] The crushing of the additive element source 905 and the mixing when two or more types are used can be carried out by a dry method or a wet method. The wet method is preferred because it allows for smaller crushing. When the wet method is used, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not react easily with lithium. It is preferable to use dehydrated acetone with a purity of 99.5% or higher. Using dehydrated acetone with the above purity can reduce possible impurities.

[0078] A mortar, ball mill, bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they emit less impurities. Furthermore, when using a ball mill or bead mill, it is preferable to set the rotation speed to 300 rpm or more and 500 rpm or less to suppress contamination from the media.

[0079] Although the above example shows the case where two kinds of additive element sources are prepared, the additive element sources may be one kind or three or more kinds.

[0080] When recovering the mixed and pulverized additive element source 905, the mixed and pulverized additive element source 905 may be classified using a sieve having an opening diameter of 250 μm or more and 350 μm or less. When a wet method is used, it is advisable to dry the solvent before carrying out the sieving.

[0081] The additive element X can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like.

[0082] A solid-phase method is exemplified. First, a mixture 906 of an additive element source 905 and a composite oxide 904 is produced. The mixture 906 can be mixed by a dry method or a wet method. The dry and wet methods and the means for mixing, etc., refer to the mixing of the additive element source. However, the rotation speed for mixing, etc., should be set to 100 rpm or more and 200 rpm or less to prevent the composite oxide 904 from collapsing.

[0083] Next, the mixture 906 is subjected to a second heating 886. The second heating 886 can be performed under conditions selected from the conditions for the first heating 885.

[0084] Here, a supplementary note about the heating temperature will be provided. The second heating 886 must be performed at a temperature at which the reaction between the composite oxide 904 and the additive element source 905 proceeds or higher. The temperature at which the reaction proceeds may be any temperature at which mutual diffusion between the composite oxide 904 and the additive element source 905 occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, and the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ Therefore, the heating temperature of the second heating 886 may be 500° C. or higher.

[0085] Of course, the reaction is easily promoted at a temperature equal to or higher than the temperature at which the composite oxide 904 and the additive element source 905 are partially melted. For example, LiF and MgF are used as the additive element source 905. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the second heating 886 is preferably at 700°C or higher, so that the temperature is 742°C or higher.

[0086] Also, LiCoO ２ :LiF:MgF ２ When the mixture 906 is obtained by mixing the components so that the molar ratio is 100:0.33:1, an endothermic peak is observed around 830° C. in differential scanning calorimetry (DSC measurement). Therefore, it is more preferable that the second heating 886 be performed at 830° C. or higher.

[0087] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0088] The heating temperature was the decomposition temperature of the composite oxide 904 (LiCoO ２ The decomposition temperature of the composite oxide 904 is set to be less than 1130°C. At temperatures close to the decomposition temperature, there is a concern that the composite oxide 904 may decompose, albeit only slightly. Therefore, the temperature is more preferably 1000°C or less, even more preferably 950°C or less, and even more preferably 900°C or less.

[0089] In consideration of these, the heating temperature of the second heating 886 is preferably 500°C or higher and 1130°C or lower, more preferably 700°C or higher and 1000°C or lower, even more preferably 700°C or higher and 950°C or lower, and even more preferably 700°C or higher and 900°C or lower. Also, it is preferably 742°C or higher and 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, it is preferably 800°C or higher and 1100°C or lower, or 830°C or higher and 1130°C or lower, more preferably 830°C or higher and 1000°C or lower, even more preferably 830°C or higher and 950°C or lower, and even more preferably 830°C or higher and 900°C or lower.

[0090] Furthermore, when the mixture 906 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0091] In the manufacturing method described in this embodiment, LiF, which is a fluorine source, may function as a flux, which allows the temperature of the second heating 886 to be lower than the decomposition temperature of the composite oxide 904, for example, to a temperature between 742°C and 950°C, thereby distributing the additive element X, such as magnesium, in the surface layer, and producing a positive electrode active material with good characteristics.

[0092] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF may sublime when heated, and if it sublimes, the amount of LiF in the mixture 906 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the sublimation of LiF. Note that even if LiF is not used as the fluorine source, Li on the surface of the composite oxide 904 may react with F in a fluorine source other than LiF, resulting in the generation of LiF, which may then sublimate. Therefore, even if a fluoride with a higher melting point than LiF is used as a fluorine source other than LiF, it is still necessary to suppress sublimation.

[0093] Therefore, in the second heating 886, it is preferable to heat the mixture 906 in an atmosphere containing LiF, that is, to heat the mixture 906 in a state where the partial pressure of LiF is high in the heating furnace. By such heating, it is possible to suppress the sublimation of LiF in the mixture 906.

[0094] The second heating is preferably performed so as not to cause adhesion between particles of the mixture 906. If the particles of the mixture 906 adhere to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the additive element (e.g., fluorine) diffuses is blocked, which may result in poor distribution of the additive element (e.g., magnesium) in the surface layer.

[0095] It is also believed that if the additive element (e.g., fluorine) is uniformly distributed in the surface layer, a smooth positive electrode active material with few irregularities can be obtained.

[0096] Furthermore, when heating is performed using a rotary kiln, it is preferable to control the inflow and outflow of oxygen so that the kiln has an oxygen-containing atmosphere. For example, one method is to restrict the inflow and outflow of oxygen after the oxygen-containing atmosphere has been created, that is, to reduce the flow rate of oxygen. Specifically, it is preferable to first introduce oxygen into the kiln, and then not introduce (flow) oxygen after the kiln has an oxygen-containing atmosphere. Flowing oxygen into the kiln may cause the fluorine source to sublimate, which is undesirable in terms of maintaining surface smoothness.

[0097] When heating is performed using a roller hearth kiln, the mixture 906 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 906 .

[0098] The material obtained by heating the mixture 906 is recovered and crushed as necessary to obtain a composite oxide 907. At this time, it is preferable to further sieve the recovered material. It is preferable to use a sieve with an opening diameter of 40 μm or more and 60 μm or less.

[0099] The additive element may be added in two or more batches. Based on this, in manufacturing method 5, a method of adding an additive element source 908 to a composite oxide 907 will be described.

[0100] First, an additive element source 908 to be added to the composite oxide 907 is prepared under the same conditions as those used in preparing the additive element source 905 .

[0101] The additive element source 908 contains an additive element Y. The additive element Y is added to the composite oxide 907. The additive element Y can be any of the elements described above as the additive element X, and may be different from the additive element X. As with the additive element X, the additive element Y can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD method, a PLD method, or the like.

[0102] When a solid phase method is used as a method for adding the additive element Y, a hydroxide is prepared as the additive element source 908. Examples include nickel hydroxide and aluminum hydroxide. When using two or more additive element sources, it is advisable to mix the additive element sources together first. In this case, the additive element sources may be pulverized in a mixed state or while being mixed. The heated state may also be used as the additive element source 908.

[0103] When the sol-gel method is used as a method for adding the additive element Y, a metal alkoxide can be used as the additive element source 908. In addition to the metal alkoxide, a solvent to be used in the sol-gel method is prepared. Alcohol can be used as the solvent. For example, when adding aluminum, aluminum isopropoxide can be used as the metal source, and isopropanol (2-propanol) can be used as the solvent. Furthermore, when adding zirconium, for example, zirconium (IV) tetrapropoxide can be used as the metal source, and isopropanol can be used as the solvent.

[0104] Furthermore, when a plurality of elements are used as the additive element source 908, they may be prepared independently. For example, nickel hydroxide may be prepared as the nickel source, aluminum isopropoxide as the aluminum source, and isopropanol may be prepared as the solvent.

[0105] In the solid phase method, a mixture 909 of an additive element source 908 and a composite oxide 907 is first prepared. The mixture 909 can be obtained in the same manner as the method for preparing the mixture 906. However, the rotation speed for mixing, etc., is preferably set to 50 rpm or more and 150 rpm or less so that the composite oxide 907 does not break down.

[0106] Next, the mixture 909 is subjected to a third heating 887. The third heating 887 can be performed under conditions selected from the conditions for the first heating 885.

[0107] Here, a supplementary note regarding the heating temperature will be provided. The heating temperature of the third heating 887 is preferably the same as or slightly lower than the heating temperature of the second heating 886. Specifically, the heating temperature is preferably 450°C or higher and 1130°C or lower, more preferably 450°C or higher and 1000°C or lower, even more preferably 450°C or higher and 950°C or lower, and even more preferably 450°C or higher and 900°C or lower. Also, the heating temperature is preferably 692°C or higher and 1130°C or lower, more preferably 692°C or higher and 1000°C or lower, even more preferably 692°C or higher and 950°C or lower, and even more preferably 692°C or higher and 900°C or lower. Also, the heating temperature is preferably 750°C or higher and 1000°C or lower, more preferably 780°C or higher and 1130°C or lower, even more preferably 780°C or higher and 1000°C or lower, even more preferably 780°C or higher and 950°C or lower, and even more preferably 780°C or higher and 900°C or lower. The heating time is, for example, preferably 3 hours or more and 50 hours or less, and more preferably 5 hours or more and 15 hours or less.

[0108] Next, the heated material is crushed in a mortar to make the particle size uniform, and then recovered, in the same manner as the composite oxide 907. Furthermore, in the same manner as the composite oxide 907, it may be classified using a sieve.

[0109] In this way, the positive electrode active material 100 to which the additive element is added can be obtained.

[0110] <Production Method 6> A case where the composite oxide 907 obtained by the above-mentioned Production Method 5 is used as the positive electrode active material 100 will be described with reference to Fig. 6. In this case, the description of Fig. 5 may be cited.

[0111] 6, the positive electrode active material 100 obtained according to the above-described manufacturing method 4 is referred to as a composite oxide 904, and illustrates a method of adding an additive element to the composite oxide 904. Specifically, the method enclosed by the dashed line in FIG. 6 is a method similar to the above-described manufacturing method 4. Note that the methods enclosed by the dashed line in FIG. 6 may be similar to the above-described manufacturing methods 1 to 3.

[0112] The positive electrode active material 100 can be obtained in the same manner as in the above-described manufacturing method 5. The sintered product may be crushed in a mortar to disintegrate it or to make the particle size uniform, and then recovered. Furthermore, classification may be performed using a sieve. The other steps may be the same as in the manufacturing method 5.

[0113] <Manufacturing Method 7> A manufacturing method in which the additive element source 905 is added at a timing different from that of the manufacturing method 5 will be described with reference to Fig. 7. In this case, the description of Fig. 5 may be referred to.

[0114] 7, an additive element source 905 is added at the same time as mixing the lithium compound 881 and the cobalt compound 880. When hydroxides are used as the lithium compound 881 and the cobalt compound 880, it is preferable to use a hydroxide containing the additive element X as the additive element source 905.

[0115] Adding the additive element source 905 at the above timing makes it easier for the additive element X to exist inside (bulk) of the cobalt oxide that becomes the positive electrode active material. After the addition, the first heating 885 may be performed.

[0116] Thereafter, when the additive element source 908 is added, the additive element Y is more likely to be present in the surface layer of the cobalt oxide. After the addition, a second heating 886 may be performed.

[0117] In the manufacturing method 7, the additive element source 908 does not have to be added.

[0118] The positive electrode active material 100 can be obtained in the same manner as in the above-described manufacturing method 5. The sintered product may be crushed in a mortar to disintegrate it or to make the particle size uniform, and then recovered. Furthermore, classification may be performed using a sieve. The other steps may be the same as in the manufacturing method 5.

[0119] <Manufacturing Method 8> A method of adding an additive element to the cathode active material obtained by the above manufacturing methods 1 to 4 will be described with reference to Fig. 8. In Fig. 8, the cathode active material 100 obtained according to the above manufacturing method 4 is referred to as composite oxide 904-1, and a method of adding an additive element to the composite oxide 904-1 is illustrated. Specifically, the method surrounded by a dashed line in Fig. 8 is a method similar to the above manufacturing method 4. Note that the methods similar to the above manufacturing methods 1 to 3 may also be applied to the methods surrounded by dashed lines in Fig. 8.

[0120] First, the composite oxide 904-1 is crushed. Crushing can be performed by either a dry method or a wet method. A wet method is preferred because it allows for crushing into smaller particles. When performing the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not easily react with lithium. It is preferable to use dehydrated acetone with a purity of 99.5% or higher. Using dehydrated acetone with the above purity can reduce impurities that may be mixed in.

[0121] A mortar, ball mill, bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they emit less impurities. Furthermore, when using a ball mill or bead mill, it is preferable to set the rotation speed to 300 rpm or more and 500 rpm or less to suppress contamination from the media.

[0122] <Initial Heating> Then, a second heating 889 is performed. This heating is referred to as the initial heating because it is the first heating of the composite oxide. After the initial heating, the surface of the composite oxide becomes smooth. A smooth surface means that the surface of the composite oxide has few irregularities, is rounded overall, and has rounded corners. Furthermore, a state in which there is little foreign matter adhering to the surface is referred to as smooth. Foreign matter is thought to be a cause of irregularities, so it is preferable that it does not adhere to the surface.

[0123] Initial heating is performed after the composite oxide is completed, and initial heating for the purpose of smoothing the surface may reduce deterioration after charge and discharge. Initial heating for smoothing the surface does not require the preparation of a lithium source.

[0124] Alternatively, the initial heating to smooth the surface does not require the provision of a source of the additive element.

[0125] Alternatively, initial heating to smooth the surface does not require the use of a fluxing agent.

[0126] The initial heating may be referred to as preheating or pretreatment.

[0127] The lithium source may contain impurities, but the impurities can be reduced from the composite oxide by initial heating.

[0128] The heating conditions for the initial heating may be any conditions that result in a smooth surface of the composite oxide. For example, the heating conditions may be selected from those described for the first heating. For example, heating may be performed at a temperature of 700°C or higher but lower than 1000°C for 2 hours or longer. In addition to the heating conditions, the heating temperature for the initial heating may be lower than the first heating temperature in order to maintain the crystalline structure of the composite oxide. Furthermore, the heating time for the initial heating may be shorter than the first heating time in order to maintain the crystalline structure of the composite oxide.

[0129] When a composite oxide with a smooth surface is used as a positive electrode active material, deterioration during charge and discharge in a secondary battery is reduced, and cracking of the positive electrode active material can be prevented.

[0130] The smooth surface of a composite oxide can be expressed as a surface roughness of at least 10 nm or less when surface irregularity information is quantified from measurement data at a cross section of the composite oxide. The cross section is, for example, a cross section obtained when observing with a scanning transmission electron microscope (STEM).

[0131] After the second heating 889, a composite oxide 904-2 can be obtained.

[0132] Next, an additive element source (X source) 905 to be added to the composite oxide 904-2 is prepared. A lithium source may be prepared together with the additive element source.

[0133] <Additive Element> The additive element source (X source) 905 contains an additive element X. The additive element X is added to the composite oxide 904-2. For example, the additive element X can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. Alternatively, the additive element X can be one or more selected from bromine and beryllium. However, because bromine and beryllium are toxic to living organisms, it is more preferable to use the elements described above.

[0134] When magnesium is selected as the additional element X, the additional element source (X source) can be referred to as a magnesium source. Examples of the magnesium source include magnesium fluoride (e.g., MgF ２ etc.), magnesium oxide (e.g., MgO etc.), magnesium hydroxide (e.g., Mg(OH) ２ etc.), or magnesium carbonate (e.g., MgCO ３ In addition, a plurality of the above-mentioned magnesium sources may be used.

[0135] When fluorine is selected as the additive element X, the additive element source can be referred to as a fluorine source. Examples of the fluorine source include lithium fluoride (e.g., LiF), magnesium fluoride (e.g., MgF ２ etc.), aluminum fluoride (e.g., AlF ３ etc.), titanium fluoride (e.g., TiF ４ etc.), cobalt fluoride (e.g., CoF ２ , CoF ３ etc.), nickel fluoride (e.g., NiF ２ etc.), zirconium fluoride (e.g., ZrF ４ etc.), vanadium fluoride (e.g., VF ５etc.), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (e.g., ZnF ２ etc.), calcium fluoride (e.g., CaF ２ etc.), sodium fluoride (e.g., NaF etc.), potassium fluoride (e.g., KF etc.), barium fluoride (e.g., BaF ２ etc.), cerium fluoride (e.g., CeF ２ etc.), lanthanum fluoride (e.g., LaF ３ etc.), or sodium aluminum hexafluoride (e.g., Na ３ AlF ６ Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0136] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as both a fluorine source and a lithium source. Another lithium source is lithium carbonate.

[0137] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O ４ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0138] When lithium fluoride and magnesium fluoride are crushed and mixed to produce an additive element source (X source), the molar ratio of lithium fluoride to magnesium fluoride is LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x:1 (x = 0.33 or its vicinity) is more preferable. Note that "x = 0.33 or its vicinity" refers to a value that is greater than 0.9 times and less than 1.1 times the value.

[0139] When the additive element source (X source) 905 is pulverized or two or more kinds are used, the additive element sources are mixed together first. There are two methods for mixing, one in which the raw materials are pulverized while being mixed, and the other in which the raw materials are mixed without being pulverized. Therefore, two or more additive element sources may be pulverized while being mixed.

[0140] The crushing of the additive element source (X source) 905 and the mixing when two or more types are used can be carried out by a dry method or a wet method. The wet method is preferred because it allows for smaller crushing. When the wet method is used, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not easily react with lithium. It is preferable to use dehydrated acetone with a purity of 99.5% or higher. Using dehydrated acetone with the above purity can reduce potential impurities.

[0141] A ball mill, a bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, it is preferable to set the rotation speed to 300 rpm or more and 500 rpm or less to suppress contamination from the media.

[0142] Although the above example shows the case where two kinds of additive element sources are prepared, the additive element sources may be one kind or three or more kinds.

[0143] When the mixed and pulverized additive element source (X source) 905 is recovered, it may be classified using a sieve with an opening diameter of 250 μm or more and 350 μm or less.

[0144] The additive element X can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like.

[0145] A solid-phase method is exemplified. First, a mixture 906 of an additive element source (X source) 905 and a composite oxide 904-2 is produced. The mixture 906 can be mixed by dry or wet methods. The dry and wet methods and mixing means refer to the mixing of the additive element source. However, the rotation speed for mixing, etc., is preferably 100 rpm or more and 200 rpm or less to prevent the composite oxide 904-2 from collapsing.

[0146] Next, the mixture 906 is subjected to a third heating 895. The third heating 895 can be performed under conditions selected from the conditions for the first heating 885.

[0147] Here, a supplementary note about the heating temperature will be provided. The third heating 895 must be performed at a temperature at which the reaction between the composite oxide 904-2 and the additive element source (X source) 905 proceeds or higher. The temperature at which the reaction proceeds may be any temperature at which interdiffusion between the composite oxide 904-2 and the additive element source (X source) occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, and the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ Therefore, the heating temperature of the third heating 895 may be 500° C. or higher.

[0148] Of course, the reaction is easily promoted at a temperature equal to or higher than the temperature at which the composite oxide 904-2 and the additive element source (X source) 905 are partially melted. For example, LiF and MgF are used as the additive element source (X source). ２ When LiF and MgF ２ Since the eutectic point of the alloy is around 742°C, the third heating 895 is preferably performed at 700°C or higher, so that the temperature is 742°C or higher.

[0149] Also, LiCoO ２ :LiF:MgF ２ When the mixture 906 is obtained by mixing the components so that the molar ratio is 100:0.33:1, an endothermic peak is observed around 830° C. in differential scanning calorimetry (DSC measurement). Therefore, it is more preferable that the third heating 895 be performed at 830° C. or higher.

[0150] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0151] The heating temperature was the decomposition temperature of the composite oxide 904-2 (LiCoO ２ The decomposition temperature of the composite oxide 904-2 is set to be less than 1130°C. At temperatures close to the decomposition temperature, there is a concern that the composite oxide 904-2 may decompose, albeit only slightly. Therefore, the temperature is more preferably 1000°C or less, even more preferably 950°C or less, and even more preferably 900°C or less.

[0152] In consideration of these, the heating temperature of the third heating 895 is preferably 500°C or higher and 1130°C or lower, more preferably 700°C or higher and 1000°C or lower, even more preferably 700°C or higher and 950°C or lower, and even more preferably 700°C or higher and 900°C or lower. Also, it is preferably 742°C or higher and 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, it is preferably 800°C or higher and 1100°C or lower, more preferably 830°C or higher and 1130°C or lower, even more preferably 830°C or higher and 1000°C or lower, even more preferably 830°C or higher and 950°C or lower, and even more preferably 830°C or higher and 900°C or lower.

[0153] Furthermore, when the mixture 906 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0154] In the manufacturing method described in this embodiment, LiF, which is a fluorine source, may function as a flux, which allows the temperature of the third heating 895 to be lower than the decomposition temperature of the composite oxide 904-2, for example, to a temperature between 742°C and 950°C, thereby distributing the additive element X, such as magnesium, in the surface layer portion, and producing a positive electrode active material with good characteristics.

[0155] However, because LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF may sublime when heated, and if it sublimes, the amount of LiF in the mixture 906 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the sublimation of LiF. Note that even if LiF is not used as the fluorine source, Li on the surface of the composite oxide 904-2 may react with F in a fluorine source other than LiF, resulting in the generation of LiF, which may then sublimate. Therefore, even if a fluoride with a higher melting point than LiF is used as a fluorine source other than LiF, it is still necessary to suppress sublimation.

[0156] Therefore, it is preferable to heat the mixture 906 in an atmosphere containing LiF, that is, to heat the mixture 906 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the sublimation of LiF in the mixture 906.

[0157] The third heating 895 is preferably performed so as not to cause particles of the mixture 906 to stick together. If the particles of the mixture 906 stick together during heating, the contact area with oxygen in the atmosphere decreases, and a route for the added element (for example, fluorine) to diffuse is blocked, which may result in a poor distribution of the added element (for example, magnesium) in the surface layer portion.

[0158] It is also believed that if the additive element (for example, fluorine) is uniformly distributed in the surface layer, a smooth positive electrode active material with few irregularities can be obtained.

[0159] Furthermore, when heating is performed using a rotary kiln, it is preferable to control the inflow and outflow of oxygen so that the kiln has an oxygen-containing atmosphere. For example, one method is to restrict the inflow and outflow of oxygen after the oxygen-containing atmosphere has been created, that is, to reduce the flow rate of oxygen. Specifically, it is preferable to first introduce oxygen into the kiln, and then not introduce (flow) oxygen after the kiln has an oxygen-containing atmosphere. Flowing oxygen into the kiln may cause the fluorine source to sublimate, which is undesirable in terms of maintaining surface smoothness.

[0160] When heating is performed using a roller hearth kiln, the mixture 906 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 906 .

[0161] The mixture 906 is heated and recovered, and crushed as necessary to obtain a composite oxide 907. At this time, it is preferable to further sieve the recovered material.

[0162] The additive element may be added in two or more batches. Based on this, in manufacturing method 8, a method of adding an additive element source (Y source) to the composite oxide 907 will be described.

[0163] First, a second additive element source (Y source) 908 is prepared to be added to the composite oxide 907. A lithium source may be prepared together with the second additive element source.

[0164] The second additive element source (Y source) 908 contains an additive element Y. The additive element Y is added to the composite oxide 907. The additive element Y can be any of the elements described above as the additive element X, and may be different from the additive element X. As with the additive element X, the additive element Y can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD method, a PLD method, or the like.

[0165] When a solid phase method is used as a method for adding the additive element Y, a hydroxide is prepared as a second additive element source (Y source). Examples include nickel hydroxide and aluminum hydroxide. When using two or more additive element sources, the additive element sources are first mixed together. Mixing can be done by mixing the raw materials while pulverizing them, or by mixing them without pulverizing them. Therefore, the additive element source may be pulverized while being mixed. The heated state may also be used as the second additive element source (Y source) 908.

[0166] When the sol-gel method is used as a method for adding the additional element Y, a metal alkoxide can be used as the second additional element source (Y source). In addition to the metal alkoxide, a solvent to be used in the sol-gel method is prepared. Alcohol can be used as the solvent. For example, when adding aluminum, aluminum isopropoxide can be used as the metal source, and isopropanol (2-propanol) can be used as the solvent. Furthermore, when adding zirconium, for example, zirconium (IV) tetrapropoxide can be used as the metal source, and isopropanol can be used as the solvent.

[0167] In addition, when the second additive element source (Y source) contains a plurality of elements, each element may be prepared independently. For example, nickel hydroxide may be prepared as the nickel source, and aluminum isopropoxide and isopropanol may be prepared as the aluminum source.

[0168] A solid phase method is exemplified, and first a mixture 909 of a second additive element source (Y source) 908 and a composite oxide 907 is produced. The composite oxide 907 can be obtained by a method similar to that for producing the mixture 906. However, the rotation speed for mixing, etc., is preferably set to 50 rpm or more and 150 rpm or less so that the composite oxide 907 does not collapse.

[0169] Next, the mixture 909 is subjected to a fourth heating 896. The fourth heating 896 can be performed under conditions selected from the conditions for the first heating 885. In addition to the heating conditions, taking into account the melting point of the additive element source (Y source) 908, the fourth heating 896 is preferably performed at a temperature equal to or lower than the heating temperature for the third heating 895.

[0170] The above steps allow the production of a positive electrode active material 100 such as lithium cobalt oxide. The shape, particle size, or composition of the lithium cobalt oxide can be controlled in comparison with that produced entirely by a solid-phase method.

[0171] Furthermore, lithium cobalt oxide is preferable because it contains few impurities. However, when sulfate is used as the starting material, sulfur may be detected in the lithium cobalt oxide. The sulfur concentration can be measured by performing elemental analysis of the entire particles of the positive electrode active material using GD-MS, ICP-MS, etc.

[0172] <Manufacturing Method 9> A method of adding an additive element to cathode active material 100 obtained by any of the above manufacturing methods 1 to 4 will be described with reference to Fig. 9. In Fig. 9, cathode active material 100 obtained according to the above manufacturing method 4 is referred to as composite oxide 904, and a method of adding an additive element to composite oxide 904 is illustrated. Specifically, the method enclosed by the dashed line in Fig. 9 is a method similar to the above manufacturing method 4. Note that the methods similar to the above manufacturing methods 1 to 3 may also be applied to the methods enclosed by the dashed line in Fig. 9.

[0173] First, an additive element source 905 is prepared to be added to the composite oxide 904. A lithium source may be prepared together with the additive element source 905.

[0174] <Additive Element> The additive element source 905 contains an additive element X. The additive element X is added to the composite oxide 904. For example, the additive element X can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. Alternatively, the additive element X can be one or more selected from bromine and beryllium. However, since bromine and beryllium are toxic to living organisms, it is more preferable to use the elements described above.

[0175] When magnesium is selected as the additive element X, the additive element source 905 can be called a magnesium source. The magnesium source can be magnesium fluoride (e.g., MgF ２ etc.), magnesium oxide (e.g., MgO etc.), magnesium hydroxide (e.g., Mg(OH) ２ etc.), or magnesium carbonate (e.g., MgCO ３In addition, a plurality of the above-mentioned magnesium sources may be used.

[0176] When fluorine is selected as the additive element X, the additive element source can be called a fluorine source. Examples of the fluorine source include lithium fluoride (e.g., LiF), magnesium fluoride (e.g., MgF ２ etc.), aluminum fluoride (e.g., AlF ３ etc.), titanium fluoride (e.g., TiF ４ etc.), cobalt fluoride (e.g., CoF ２ , CoF ３ etc.), nickel fluoride (e.g., NiF ２ etc.), zirconium fluoride (e.g., ZrF ４ etc.), vanadium fluoride (e.g., VF ５ etc.), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (e.g., ZnF ２ etc.), calcium fluoride (e.g., CaF ２ etc.), sodium fluoride (e.g., NaF etc.), potassium fluoride (e.g., KF etc.), barium fluoride (e.g., BaF ２ etc.), cerium fluoride (e.g., CeF ２ etc.), lanthanum fluoride (e.g., LaF ３ etc.), or sodium aluminum hexafluoride (e.g., Na ３ AlF ６ Among these, lithium fluoride is preferred because it has a relatively low melting point of 848° C. and is easily melted in the heating step described below.

[0177] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as both a fluorine source and a lithium source. Another lithium source is lithium carbonate.

[0178] The fluorine source may also be gaseous, such as fluorine (F ２ ), fluorocarbon, sulfur fluoride, or oxygen fluoride (OF ２ , O ２ F ２ , O ３ F ２ , O４ F ２ , O ２ F) or the like may be used and mixed into the atmosphere in the heating step described below. Also, a plurality of the above-mentioned fluorine sources may be used.

[0179] When lithium fluoride and magnesium fluoride are crushed and mixed to prepare the additive element source 905, the molar ratio of lithium fluoride to magnesium fluoride is LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x:1 (x = 0.33 or its vicinity) is more preferable. Note that "x = 0.33 or its vicinity" refers to a value that is greater than 0.9 times and less than 1.1 times the value.

[0180] The crushing of the additive element source 905 and the mixing when two or more types are used can be carried out by a dry method or a wet method. The wet method is preferred because it allows for smaller crushing. When the wet method is used, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not react easily with lithium. It is preferable to use dehydrated acetone with a purity of 99.5% or higher. Using dehydrated acetone with the above purity can reduce possible impurities.

[0181] A mortar, ball mill, bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, it is preferable to use alumina balls or zirconia balls as the grinding media. Zirconia balls are preferable because they emit less impurities. Furthermore, when using a ball mill or bead mill, it is preferable to set the rotation speed to 300 rpm or more and 500 rpm or less to suppress contamination from the media.

[0182] Although the above example shows the case where two kinds of additive element sources are prepared, the additive element sources may be one kind or three or more kinds.

[0183] When the mixed and pulverized additive element source 905 is recovered, it may be classified using a sieve with an opening diameter of 250 μm or more and 350 μm or less.

[0184] The additive element X can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like.

[0185] A solid-phase method is exemplified. First, a mixture 906 of an additive element source 905 and a composite oxide 904 is produced. The mixture 906 can be mixed by a dry method or a wet method. The dry and wet methods and the means for mixing, etc., refer to the mixing of the additive element source. However, the rotation speed for mixing, etc., should be set to 100 rpm or more and 200 rpm or less to prevent the composite oxide 904 from collapsing.

[0186] Next, the mixture 906 is subjected to a second heating 886. The second heating 886 can be performed under conditions selected from the conditions for the first heating 885.

[0187] Here, a supplementary note about the heating temperature will be provided. The second heating 886 must be performed at a temperature at which the reaction between the composite oxide 904 and the additive element source 905 proceeds or higher. The temperature at which the reaction proceeds may be any temperature at which mutual diffusion between the composite oxide 904 and the additive element source 905 occurs, and may be lower than the melting temperature of these materials. An oxide will be used as an example for explanation, and the melting temperature T ｍ 0.757 times (Tammann temperature T ｄ Therefore, the heating temperature of the second heating 886 may be 500° C. or higher.

[0188] Of course, the reaction is easily promoted at a temperature equal to or higher than the temperature at which the composite oxide 904 and the additive element source 905 are partially melted. For example, LiF and MgF are used as the additive element source 905. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the second heating 886 is preferably at 700°C or higher, so that the temperature is 742°C or higher.

[0189] Also, LiCoO ２ :LiF:MgF ２When the mixture 906 is obtained by mixing the components so that the molar ratio is 100:0.33:1, an endothermic peak is observed around 830° C. in differential scanning calorimetry (DSC measurement). Therefore, it is more preferable that the second heating 886 be performed at 830° C. or higher.

[0190] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0191] The heating temperature was the decomposition temperature of the composite oxide 904 (LiCoO ２ The decomposition temperature of the composite oxide 904 is set to be less than 1130°C. At temperatures close to the decomposition temperature, there is a concern that the composite oxide 904 may decompose, albeit only slightly. Therefore, the temperature is more preferably 1000°C or less, even more preferably 950°C or less, and even more preferably 900°C or less.

[0192] In consideration of these, the heating temperature of the second heating 886 is preferably 500°C or higher and 1130°C or lower, more preferably 700°C or higher and 1000°C or lower, even more preferably 700°C or higher and 950°C or lower, and even more preferably 700°C or higher and 900°C or lower. Also, it is preferably 742°C or higher and 1130°C or lower, more preferably 742°C or higher and 1000°C or lower, even more preferably 742°C or higher and 950°C or lower, and even more preferably 742°C or higher and 900°C or lower. Also, it is preferably 800°C or higher and 1100°C or lower, more preferably 830°C or higher and 1130°C or lower, even more preferably 830°C or higher and 1000°C or lower, even more preferably 830°C or higher and 950°C or lower, and even more preferably 830°C or higher and 900°C or lower.

[0193] Furthermore, when the mixture 906 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0194] In the manufacturing method described in this embodiment, LiF, which is a fluorine source, may function as a flux, which allows the temperature of the second heating 886 to be lower than the decomposition temperature of the composite oxide 904, for example, to a temperature between 742°C and 950°C, thereby distributing the additive element X, such as magnesium, in the surface layer, and producing a positive electrode active material with good characteristics.

[0195] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF may sublime when heated, and if it sublimes, the amount of LiF in the mixture 906 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the sublimation of LiF. Note that even if LiF is not used as the fluorine source, Li on the surface of the composite oxide 904 may react with F in a fluorine source other than LiF, resulting in the generation of LiF, which may then sublimate. Therefore, even if a fluoride with a higher melting point than LiF is used as a fluorine source other than LiF, it is still necessary to suppress sublimation.

[0196] Therefore, it is preferable to heat the mixture 906 in an atmosphere containing LiF, that is, to heat the mixture 906 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the sublimation of LiF in the mixture 906.

[0197] The second heating 886 is preferably performed so as not to cause particles of the mixture 906 to stick together. If the particles of the mixture 906 stick together during heating, the contact area with oxygen in the atmosphere decreases, and a route for the added element (e.g., fluorine) to diffuse is blocked, which may result in a poor distribution of the added element (e.g., magnesium) in the surface layer.

[0198] It is also believed that if the additive element (e.g., fluorine) is uniformly distributed in the surface layer, a smooth positive electrode active material with few irregularities can be obtained.

[0199] Furthermore, when heating is performed using a rotary kiln, it is preferable to control the inflow and outflow of oxygen so that the kiln has an oxygen-containing atmosphere. For example, one method is to restrict the inflow and outflow of oxygen after the oxygen-containing atmosphere has been created, that is, to reduce the flow rate of oxygen. Specifically, it is preferable to first introduce oxygen into the kiln, and then not introduce (flow) oxygen after the kiln has an oxygen-containing atmosphere. Flowing oxygen into the kiln may cause the fluorine source to sublimate, which is undesirable in terms of maintaining surface smoothness.

[0200] When heating is performed using a roller hearth kiln, the mixture 906 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 906 .

[0201] The material obtained by heating the mixture 906 is recovered and crushed as necessary to obtain a composite oxide 907. At this time, it is preferable to further sieve the recovered material. It is preferable to use a sieve with an opening diameter of 40 μm or more and 60 μm or less.

[0202] Next, a method for adding the additive element source 908 to the composite oxide 907 will be described.

[0203] First, an additive element source 908 to be added to the composite oxide 907 is prepared under the same conditions as those used in preparing the additive element source 905 .

[0204] The additive element source 908 contains an additive element Y. The additive element Y is added to the composite oxide 907. The additive element Y can be any of the elements described above as the additive element X, and may be different from the additive element X. As with the additive element X, the additive element Y can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD method, a PLD method, or the like.

[0205] When a solid phase method is used as a method for adding the additive element Y, a hydroxide is prepared as the additive element source 908. For example, nickel hydroxide can be used. When two or more types of additive element sources are used, the additive element sources are mixed together first. At this time, the additive element sources may be mixed and then pulverized.

[0206] In the solid phase method, a mixture 909 of an additive element source 908 and a composite oxide 907 is first prepared. The mixture 909 can be obtained in the same manner as the method for preparing the mixture 906. However, the rotation speed for mixing, etc., is preferably set to 50 rpm or more and 150 rpm or less so that the composite oxide 907 does not break down.

[0207] The mixture 909 is recovered and crushed as necessary, and at this time, it is preferable to further sieve the recovered material.

[0208] The additive element may be added in two or more batches. Based on this, in this embodiment, a method of adding an additive element source 910 to the mixture 909 will be described. At this time, it is not necessary to heat the mixture 909. Of course, the mixture 909 may be heated.

[0209] First, an additive element source 910 to be added to the mixture 909 is prepared under the same conditions as those used for preparing the additive element source 905 .

[0210] The additive element source 910 contains an additive element Z. The additive element Z is added to the mixture 909. The additive element Z can be any of the elements described above as the additive element X, and may be different from the additive elements X and Y. As with the additive element X, the additive element Z can be added by a solid phase method, a liquid phase method such as a sol-gel method, a sputtering method, a vapor deposition method, a CVD method, a PLD method, or the like.

[0211] When the sol-gel method is used as a method for adding the additive element Z, a metal alkoxide can be used as the additive element source 910. In addition to the metal alkoxide, a solvent to be used in the sol-gel method is prepared. Alcohol can be used as the solvent. For example, when adding aluminum, aluminum isopropoxide can be used as the metal source, and isopropanol (2-propanol) can be used as the solvent. Furthermore, when adding zirconium, for example, zirconium (IV) tetrapropoxide can be used as the metal source, and isopropanol can be used as the solvent.

[0212] Next, for example, the zirconium (IV) tetrapropoxide isopropanol solution and the aluminum isopropoxide isopropanol solution are stirred to form a mixed solution, and the mixture 909 is added to the mixed solution and stirred. Stirring can be performed, for example, with a magnetic stirrer. The stirring time may be long enough to cause hydrolysis and polycondensation reactions between the water in the atmosphere and the zirconium (IV) tetrapropoxide, and can be performed for, for example, 60 hours at room temperature.

[0213] The mixture is recovered from the mixed solution after the above treatment. As a recovery method, filtration, centrifugation, evaporation to dryness, etc. can be applied. In this embodiment, the mixture is recovered by evaporation to dryness to obtain a mixture 911. In this embodiment, the mixture is dried by ventilation at 95°C.

[0214] Next, the mixture 911 is subjected to a third heating 887. The third heating 887 can be performed under conditions selected from the conditions for the first heating 885.

[0215] Here, a supplementary note regarding the heating temperature will be provided. The heating temperature of the third heating 887 is preferably the same as or slightly lower than the heating temperature of the second heating 886. Specifically, the heating temperature is preferably 450°C or higher and 1130°C or lower, more preferably 450°C or higher and 1000°C or lower, even more preferably 450°C or higher and 950°C or lower, and even more preferably 450°C or higher and 900°C or lower. Also, the heating temperature is preferably 692°C or higher and 1130°C or lower, more preferably 692°C or higher and 1000°C or lower, even more preferably 692°C or higher and 950°C or lower, and even more preferably 692°C or higher and 900°C or lower. Also, the heating temperature is preferably 750°C or higher and 1000°C or lower, more preferably 780°C or higher and 1130°C or lower, even more preferably 780°C or higher and 1000°C or lower, even more preferably 780°C or higher and 950°C or lower, and even more preferably 780°C or higher and 900°C or lower. The heating time is, for example, preferably 3 hours or more and 50 hours or less, and more preferably 5 hours or more and 15 hours or less.

[0216] Next, the heated material is crushed in a mortar to make the particle size uniform, and then recovered, in the same manner as the composite oxide 907. Furthermore, in the same manner as the composite oxide 907, it may be classified using a sieve.

[0217] In this way, the positive electrode active material 100 to which the additive element is added can be obtained.

[0218] <Manufacturing Method 10> A manufacturing method different from Manufacturing Method 5 described above, for example, a method in which composite oxide 904 is obtained, crushed, and then subjected to a second heat treatment (second heating 889), will be described using FIG. 10 . In this case, the description of Manufacturing Method 8 described above may be cited. Also, in FIG. 10 , positive electrode active material 100 obtained according to Manufacturing Method 4 described above is referred to as composite oxide 904, and a method of adding an additive element to composite oxide 904 is illustrated. Specifically, the method surrounded by a dashed line in FIG. 10 is a method similar to Manufacturing Method 4 described above. Note that methods similar to Manufacturing Methods 1 to 3 described above may also be applied to the methods surrounded by dashed lines in FIG. 10 .

[0219] The second heating 889 is sometimes called initial heating because it is the first heating of the composite oxide. After initial heating, the surface of the composite oxide becomes smooth. A smooth surface means that the surface of the composite oxide has few irregularities, is rounded overall, and has rounded corners. Furthermore, a smooth surface means that there is little foreign matter adhering to the surface. Foreign matter is thought to be a cause of irregularities, so it is preferable that it does not adhere to the surface.

[0220] Initial heating is performed after the composite oxide is completed, and initial heating for the purpose of smoothing the surface may reduce deterioration after charge and discharge. Initial heating for smoothing the surface does not require the preparation of a lithium source.

[0221] Alternatively, the initial heating to smooth the surface does not require the provision of a source of the additive element.

[0222] Alternatively, initial heating to smooth the surface does not require the use of a fluxing agent.

[0223] The initial heating is sometimes called preheating or pretreatment.

[0224] The prepared lithium source may contain impurities, but the impurities can be reduced from the composite oxide by initial heating.

[0225] The cobalt source may also contain impurities, but the impurities can be reduced from the composite oxide by initial heating.

[0226] The heating conditions for the initial heating may be any conditions that result in a smooth surface of the composite oxide. For example, the heating conditions may be selected from those described for the first heating. Regarding the heating conditions, the heating temperature for the initial heating should be lower than the temperature for the first heating in order to maintain the crystalline structure of the composite oxide. Furthermore, the heating time for the initial heating should be shorter than the time for the first heating in order to maintain the crystalline structure of the composite oxide. For example, heating at a temperature of 700°C or higher and 1000°C or lower for 2 hours or longer is recommended.

[0227] When a composite oxide with a smooth surface is used as a positive electrode active material, deterioration during charge and discharge in a secondary battery is reduced, and cracking of the positive electrode active material can be prevented.

[0228] The smooth surface of a composite oxide can be expressed as a surface roughness of at least 10 nm or less when surface irregularity information is quantified from measurement data at a cross section of the composite oxide. The cross section is, for example, a cross section obtained when observing with a scanning transmission electron microscope (STEM).

[0229] The other steps may be the same as those in manufacturing method 8.

[0230] This embodiment can be used in combination with other embodiments.

[0231] In this embodiment, a synthesis apparatus for coprecipitation (coprecipitation synthesis apparatus) will be described. Note that the case where a cobalt compound 880 is produced using the mixed solution 901 (containing a cobalt aqueous solution), the aqueous solution 892 (alkaline aqueous solution), and the aqueous solution 894 (chelating agent) in the above-described production method 4 will be exemplified.

[0232] The coprecipitation synthesis apparatus 170 shown in FIG. 11 has a reaction vessel 171. A separable flask is preferably used in the lower part of the reaction vessel, and a separable cover is preferably used in the upper part. The separable flask may be cylindrical or round. In the case of a cylindrical type, the separable flask has a flat bottom. The atmosphere inside the reaction vessel 171 can be controlled using at least one inlet of the separable cover. For example, the atmosphere preferably contains nitrogen.

[0233] First, an aqueous solution 894 (chelating agent) is placed in the reaction vessel 171, and then the mixed solution 901 and the aqueous solution 892 (alkaline aqueous solution) are added dropwise to the reaction vessel 171. The aqueous solution 192 in Fig. 11 shows the state at which the addition has started. The aqueous solution 894 may also be referred to as a "filling liquid." The "filling liquid" may also be referred to as an "adjusting liquid," and may refer to the aqueous solution before the reaction, i.e., the aqueous solution in its initial state inside the reaction vessel.

[0234] Other components of the coprecipitation synthesis apparatus 170 shown in Figure 11 will be described. The coprecipitation synthesis apparatus 170 includes a stirring unit 172, a stirring motor 173, a thermometer 174, a tank 175, a pipe 176, a pump 177, a tank 180, a pipe 181, a pump 182, a tank 186, a pipe 187, a pump 188, and a control device 190. As shown in Figure 12, the coprecipitation synthesis apparatus 170 may also include a reflux condenser 191. The reflux condenser 191 is connected to at least one inlet of the separable cover, and can discharge atmospheric gas, such as nitrogen, from the reaction vessel 171 and return water to the reaction vessel 171. The other components in Figure 12 are the same as those in Figure 11.

[0235] The stirring unit 172 can stir the aqueous solution 192 in the reaction vessel 171, and further has a stirring motor 173 as a power source for rotating the stirring unit 172. The stirring unit 172 has paddle-shaped stirring blades (referred to as paddle blades), and the paddle blades may have two to six blades, and the blades may have an inclination of 40 degrees to 70 degrees.

[0236] The thermometer 174 can measure the temperature of the aqueous solution 192. The reaction vessel 171 can be controlled using a thermoelectric element so that the temperature of the aqueous solution 192 is constant. An example of a thermoelectric element is a Peltier element. Although not shown, a pH meter is also placed in the reaction vessel 171 so as to be in contact with the aqueous solution 192, and can measure the pH of the aqueous solution 192.

[0237] Each tank can store a different aqueous raw material solution. For example, each tank can be filled with a mixed solution 901 and an aqueous solution 892. A tank filled with an aqueous solution 894 that functions as a filler liquid may also be prepared. Each tank is provided with a pump, and by using this pump, the aqueous raw material solution can be dripped into the reaction vessel 171 through the pipe. Each pump can control the amount of aqueous raw material solution dripped, i.e., the amount of solution sent. In addition to the pump, a valve may be provided in the pipe 176 to control the amount of aqueous raw material solution dripped, i.e., the amount of solution sent.

[0238] The control device 190 is electrically connected to the stirring motor 173, the thermometer 174, the pump 177, the pump 182, and the pump 188, and can control the rotation speed of the stirring unit 172, the temperature of the aqueous solution 192, the amount of each raw aqueous solution dropped, etc.

[0239] The rotation speed of the stirring unit 172, specifically the rotation speed of the paddle blades, is preferably, for example, 800 rpm to 1200 rpm. The stirring is preferably performed while heating the aqueous solution 192 to 50°C to 90°C. During this process, the mixed solution 901 and the like are preferably dripped into the reaction vessel 171 at a constant rate. Of course, the rotation speed of the paddle blades is not limited to a constant value and can be adjusted as appropriate. For example, the rotation speed can be changed depending on the amount of liquid in the reaction vessel 171. Furthermore, the dripping speed of the mixed solution 901 and the like can also be adjusted. The dripping speed can be adjusted to maintain a constant pH in the reaction vessel 171. Alternatively, the dripping speed can be controlled so that the mixed solution 901 is dripped first, and then the aqueous solution 892 is dripped when the pH value deviates from the desired value. The pH value is preferably set to 9.0 to 13.0, preferably 9.8 to 12.5.

[0240] After the above steps, a reaction product is precipitated in the reaction vessel 171. The reaction product contains a cobalt compound. This reaction can be referred to as coprecipitation, and this step may be referred to as a coprecipitation step.

[0241] This embodiment can be used in combination with other embodiments.

[0242] Embodiment 3 In this embodiment, a crystal structure of a positive electrode active material according to one embodiment of the present invention will be described. The case of lithium cobalt oxide will be described with reference to FIGS.

[0243] In the present embodiment and the like, crystal planes and crystal directions are expressed using Miller indices. Individual planes indicating crystal planes are expressed using ( ). In crystallography, crystal planes, crystal directions, and space groups are expressed by adding a superscript bar to the number, but in this specification and the like, due to formatting restrictions, they may be expressed by adding a - (minus sign) before the number instead of adding a bar above the number.

[0244] <Crystal structure> <Li ｘ CoO ２ When x is 1 in the positive electrode active material 100 of one embodiment of the present invention is in a discharged state, that is, Li ｘ CoO ２ When x = 1 in the formula, it is preferable to have a layered rock-salt type crystal structure belonging to the space group R-3m. Layered rock-salt type composite oxides have high discharge capacity, have two-dimensional lithium ion diffusion paths, are suitable for lithium ion insertion / extraction reactions, and are excellent as positive electrode active materials for secondary batteries. In Figure 13, the layered rock-salt type crystal structure when x = 1 is shown with the abbreviation R-3m O3.

[0245] <Li ｘ CoO ２ State in which x is small in the positive electrode active material 100 of one embodiment of the present invention contains the above-described additive element in a discharged state, and thus, ｘ CoO ２ The crystal structure when x is small is different from that of conventional positive electrode active materials. Here, "small x" means 0.1<x≦0.24.

[0246] The positive electrode active material shown in FIG. 14 is a conventional lithium cobalt oxide (LiCoO ２ ) In Figure 14, R-3m O3 is added to Li ｘ CoO ２ The crystal structure of lithium cobalt oxide with x=1 in Fig. 1 shows that lithium occupies octahedral sites and CoO２ There are three layers. Therefore, this crystal structure is sometimes called an O3 type crystal structure. ２ The layer is defined as a structure in which octahedral structures in which oxygen is six-coordinated to cobalt are connected in a plane with edge sharing. This is sometimes called a layer consisting of cobalt and oxygen octahedra.

[0247] It is also known that conventional lithium cobalt oxide has a crystal structure that has high lithium symmetry when x is about 0.5 and belongs to the monoclinic space group P2 / m. This structure has CoO ２ There is one layer, so it is sometimes called O1 type or monoclinic O1 type.

[0248] When x = 0, the positive electrode active material has a crystal structure of the trigonal space group P-3m1, and also contains CoO ２ There is one layer. Therefore, this crystal structure is sometimes called O1 type or trigonal O1 type. In addition, when the trigonal crystal is converted into a composite hexagonal lattice, it is sometimes called hexagonal O1 type.

[0249] Furthermore, when x is about 0.12, conventional lithium cobalt oxide has a crystal structure of the space group R-3m. This structure is similar to CoO, such as trigonal O1 type. ２ and LiCoO such as R-3m O ２ It can also be said that the structure of and are stacked alternately. Therefore, this crystal structure is sometimes called an H1-3 crystal structure. Note that, since actual lithium insertion and extraction can be uneven, the H1-3 crystal structure is experimentally observed from about x = 0.25. In fact, the number of cobalt atoms per unit cell in the H1-3 crystal structure is twice that of other structures. However, in Figure 14 and other parts of this specification, to make it easier to compare with other crystal structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0250] As an example of the H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed as Co (0,0,0.42150±0.00016), O1 (0,0,0.27671±0.00045), and O2 (0,0,0.11535±0.00045). O1 and O2 are each oxygen atoms. Which unit cell should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of an X-ray diffraction (XRD) pattern. In this case, it is sufficient to adopt a unit cell that results in a small GOF (goodness of fit) value.

[0251] Li ｘ CoO ２ When charging and discharging are repeated so that x in the formula is 0.24 or less, conventional lithium cobalt oxide undergoes repeated changes in crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0252] However, these two crystal structures are different from CoO ２ As shown by the dotted lines and arrows in FIG. 14, in the H1-3 type crystal structure, CoO ２ The layer is significantly different from the R-3m O3 in the discharged state. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0253] Furthermore, the difference in volume between these two crystal structures is large: per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the discharged R-3mO3 crystal structure is greater than 3.5%, typically 3.9% or more.

[0254] In addition, the H1-3 type crystal structure has CoO like the trigonal O1 type. ２ A structure with continuous layers is likely to be unstable.

[0255] Therefore, when charging and discharging is repeated so that x becomes 0.24 or less, the crystal structure of conventional lithium cobalt oxide collapses. This collapse of the crystal structure causes a deterioration in cycle characteristics. This is because the collapse of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0256] On the other hand, in the positive electrode active material 100 of one embodiment of the present invention shown in FIG. ｘ CoO ２ The change in the crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less is smaller than that of conventional positive electrode active materials. More specifically, the change in the crystal structure between the discharge state where x is 1 and the state where x is 0.24 or less is smaller than that of conventional positive electrode active materials. ２ The layer misalignment can be reduced. Furthermore, the change in volume per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to lose its crystal structure even when repeatedly charged and discharged so that x is 0.24 or less, and excellent cycle characteristics can be achieved. Furthermore, the positive electrode active material 100 of one embodiment of the present invention is less likely to lose its crystal structure even when repeatedly charged and discharged so that x is 0.24 or less. ｘ CoO ２ When x is 0.24 or less, the positive electrode active material 100 can have a more stable crystal structure than conventional positive electrode active materials. ｘ CoO ２ When the value of x in the formula (1) is kept at 0.24 or less, short circuits are unlikely to occur. In such a case, the safety of the secondary battery is further improved, which is preferable.

[0257] Li ｘ CoO ２ The crystal structure of the inside of the positive electrode active material 100 when x is about 1 or 0.2 is shown in FIG. 13. The inside occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge. ２ The most problematic areas are layer misalignment and volume changes.

[0258] When x=1, the positive electrode active material 100 has the same crystal structure of R-3m O3 as conventional lithium cobalt oxide.

[0259] However, when x is 0.24 or less, for example, about 0.2 or about 0.12, at which point conventional lithium cobalt oxide has an H1-3 crystal structure, the positive electrode active material 100 has a crystal structure different from the H1-3 crystal structure.

[0260] The positive electrode active material 100 according to one embodiment of the present invention when x is about 0.2 has a crystal structure belonging to the trigonal space group R-3m. ２ The symmetry of the layers is the same as that of O3. Therefore, this crystal structure is called an O3'-type crystal structure. This crystal structure is shown in Figure 13 with the notation R-3m O3'.

[0261] In the O3'-type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. Furthermore, the lattice constant of the unit cell is preferably 0.2797≦a≦0.2837 (nm), more preferably 0.2807≦a≦0.2827 (nm), typically a=0.2817 (nm). The c-axis is preferably 1.3681≦c≦1.3881 (nm), more preferably 1.3751≦c≦1.3811 (nm), typically c=1.3781 (nm).

[0262] In the O3' type crystal structure, ions of cobalt, nickel, magnesium, etc. occupy the hexacoordinated oxygen positions. Light elements such as lithium may occupy the tetracoordinated oxygen positions.

[0263] As shown by the dotted line in FIG. 13, the difference between the R-3m O3 in the discharged state and the O3′-type crystal structure is ２ There is almost no layer misalignment.

[0264] The difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.

[0265] As described above, in the positive electrode active material 100 according to one embodiment of the present invention, Li ｘ CoO ２When x is small, i.e., when a large amount of lithium is released, the change in crystal structure is suppressed compared to conventional positive electrode active materials. Furthermore, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material 100 does not easily collapse in crystal structure even when repeatedly charged and discharged so that x is 0.24 or less. Therefore, the positive electrode active material 100 suppresses the decrease in charge / discharge capacity during charge / discharge cycles. Furthermore, because more lithium can be stably utilized than in conventional positive electrode active materials, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be fabricated.

[0266] The positive electrode active material 100 is Li ｘ CoO ２ It has been confirmed that when x is 0.15 or more and 0.24 or less, it may have an O3' type crystal structure, and it is presumed that even when x is more than 0.24 and 0.27 or less, it has an O3' type crystal structure. However, the crystal structure is ｘ CoO ２ The range of x is not necessarily limited to the above range, since it is affected not only by the x in the formula but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc.

[0267] Therefore, the positive electrode active material 100 is Li ｘ CoO ２ When x is greater than 0.1 and equal to or less than 0.24, the entire interior of the positive electrode active material 100 does not have to have the O3′-type crystal structure, but may contain other crystal structures, or may be partially amorphous.

[0268] Also Li ｘ CoO ２ To make the value of x small, it is generally necessary to charge at a high charging voltage. ｘ CoO ２The state where x is small can be rephrased as a state where the battery is charged at a high charging voltage. For example, when CC / CV charging is performed at a voltage of 4.6 V or higher relative to the potential of lithium metal in an environment of 25°C, a H1-3 crystal structure appears in conventional positive electrode active materials. Therefore, a charging voltage of 4.6 V or higher relative to the potential of lithium metal can be said to be a high charging voltage. Furthermore, in this specification and the like, unless otherwise specified, charging voltages will be expressed relative to the potential of lithium metal.

[0269] Therefore, in other words, the positive electrode active material 100 of one embodiment of the present invention is preferable because it can maintain a crystal structure with R-3m O symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or higher at 25° C. In other words, it is preferable because it can adopt an O 3′-type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or higher and 4.7 V or lower at 25° C.

[0270] In some cases, the H1-3 type crystal is finally observed when the charge voltage is further increased, even in the positive electrode active material 100. Furthermore, as described above, the crystal structure is affected by the number of charge / discharge cycles, the charge / discharge current, the electrolyte, and the like. Therefore, even when the charge voltage is lower, for example, even when the charge voltage is 4.5 V or higher but lower than 4.6 V at 25° C., the positive electrode active material 100 of one embodiment of the present invention may be able to adopt the O3′ type crystal structure.

[0271] In addition, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery decreases by the difference between the potential of the graphite and the potential of lithium metal. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystal structure is maintained at the voltage obtained by subtracting the potential of graphite from the above voltage.

[0272] In addition, in O3' of FIG. 13, lithium is shown to exist at all lithium sites with equal probability, but this is not limited to this. It may exist unevenly at some lithium sites, or, for example, in the monoclinic O1 (Li ０．５ CoO ２The distribution of lithium can be analyzed, for example, by neutron diffraction.

[0273] The O3' type crystal structure has random lithium between layers, but CdCl ２ It can be said that this crystal structure is similar to that of the CdCl type. ２ A similar crystal structure to the Li-type is lithium nickel oxide. ０．０６ NiO ２ The crystal structure is similar to that when charged to 1000V, but pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt usually have a CdCl ２ It is known that it does not have a typical crystal structure.

[0274] CoO ２ The additive element, for example, magnesium, which is randomly and dilutely present between the layers, i.e., at the lithium site, turns into CoO when charged at a high voltage. ２ This has the effect of suppressing layer misalignment. In other words, magnesium is preferably present at the lithium site. Therefore, CoO ２ When magnesium is present between layers, an O3'-type crystal structure is likely to be formed. Therefore, magnesium is preferably present in the surface layer portion of the positive electrode active material 100 of one embodiment of the present invention. Therefore, heat treatment is preferably performed in the manufacturing process of the positive electrode active material 100 of one embodiment of the present invention.

[0275] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that added elements, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site will not be effective in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0276] Therefore, it is preferable to add a fluorine compound to lithium cobalt oxide during or before the heat treatment for adding magnesium. The addition of the fluorine compound can lower the melting point of lithium cobalt oxide, making it easier to add magnesium at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of the fluorine compound is expected to improve corrosion resistance against hydrofluoric acid produced by decomposition of the electrolyte.

[0277] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the cathode active material 100 of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the transition metal M, more preferably more than 0.01 to less than 0.04 times, and even more preferably about 0.02 times. Alternatively, it is preferably 0.001 to 0.04 times. Alternatively, it is preferably 0.01 to 0.1 times. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the cathode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the production process of the cathode active material.

[0278] Lithium cobalt oxide may contain an additive element other than cobalt (hereinafter, metal Z), such as one or more metals selected from nickel, aluminum, manganese, titanium, zirconium, vanadium, and chromium. Adding one or more of nickel and aluminum is particularly preferred. Manganese, titanium, vanadium, and chromium may be stable and easily tetravalent, which may contribute significantly to structural stability. Adding metal Z to the cathode active material of one embodiment of the present invention may result in a more stable crystal structure, for example, in a charged state at a high voltage. In the cathode active material 100 of one embodiment of the present invention, metal Z is preferably added at a concentration that does not significantly change the crystallinity of the lithium cobalt oxide. For example, the amount is preferably such that the Jahn-Teller effect or the like is not exhibited.

[0279] As the magnesium concentration in the positive electrode active material 100 of one embodiment of the present invention increases, the charge / discharge capacity of the positive electrode active material may decrease. For example, this may be due to magnesium entering the lithium site, reducing the amount of lithium contributing to charge / discharge. Excess magnesium may also produce magnesium compounds that do not contribute to charge / discharge. When the positive electrode active material of one embodiment of the present invention contains nickel as the metal Z in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased. When the positive electrode active material of one embodiment of the present invention contains aluminum as the metal Z in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased. When the positive electrode active material of one embodiment of the present invention contains nickel and aluminum in addition to magnesium, the charge / discharge capacity per weight and per volume may be increased.

[0280] Hereinafter, the concentrations of elements such as magnesium and metal Z contained in the positive electrode active material of one embodiment of the present invention will be expressed in terms of the number of atoms.

[0281] The number of nickel atoms in the positive electrode active material 100 of one embodiment of the present invention is preferably more than 0% and 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, more than 0% and 4% or less are preferable. Alternatively, more than 0% and 2% or less are preferable. Alternatively, 0.05% to 7.5% or less are preferable. Alternatively, 0.05% to 2% or less are preferable. Alternatively, 0.1% to 7.5% or less are preferable. Alternatively, 0.1% to 4% or less are preferable. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0282] Nickel contained at the above concentration is likely to be uniformly dissolved throughout the positive electrode active material 100, thereby contributing particularly to the stabilization of the internal crystalline structure. Furthermore, the presence of divalent nickel within the positive electrode active material 100 may allow divalent additive elements, such as magnesium, present at the lithium site to exist more stably in the vicinity of the nickel. Therefore, magnesium elution can be suppressed even after high-voltage charging and discharging. Suppressing magnesium elution can improve charge-discharge cycle performance. Thus, combining the effects of nickel within the positive electrode active material 100 and magnesium, aluminum, titanium, fluorine, and the like in the surface layer is extremely effective in stabilizing the crystalline structure during high-voltage charging.

[0283] The number of aluminum atoms in the positive electrode active material 100 of one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 4% is preferable. The aluminum concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0284] The positive electrode active material 100 of one embodiment of the present invention preferably contains the element W, and preferably uses phosphorus as the element W. Furthermore, the positive electrode active material 100 of one embodiment of the present invention more preferably contains a compound containing phosphorus and oxygen.

[0285] When the positive electrode active material 100 of one embodiment of the present invention contains a compound containing the element W, short circuits can be suppressed in some cases when a charged state at high voltage is maintained.

[0286] When the positive electrode active material 100 of one embodiment of the present invention contains phosphorus as the element W, hydrogen fluoride generated by decomposition of the electrolyte solution may react with the phosphorus, resulting in a decrease in the hydrogen fluoride concentration in the electrolyte solution.

[0287] The electrolyte is LiPF ６In the case where the electrolyte contains PVDF, hydrogen fluoride may be generated by hydrolysis. Hydrogen fluoride may also be generated by a reaction between PVDF, which is used as a component of the positive electrode, and an alkali. By reducing the hydrogen fluoride concentration in the electrolyte, corrosion or peeling of the current collector may be suppressed. Furthermore, a decrease in adhesion due to gelation or insolubilization of PVDF may be suppressed.

[0288] When the positive electrode active material 100 of one embodiment of the present invention contains magnesium in addition to the element W, the stability in a charged state at a high voltage is extremely high. When the element W is phosphorus, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. Alternatively, 1% to 10% is preferred. Alternatively, 1% to 8% is preferred. Alternatively, 2% to 20% is preferred. Alternatively, 2% to 8% is preferred. Alternatively, 3% to 20% is preferred. Alternatively, 3% to 10% is preferred. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and more preferably 0.7% to 4%. Alternatively, 0.1% to 5% is preferred. Alternatively, 0.1% to 4% is preferred. Alternatively, 0.5% to 10% is preferred. Alternatively, 0.5% to 4% is preferred. Alternatively, the phosphorus and magnesium concentrations are preferably 0.7% or more and 10% or less. Alternatively, the phosphorus and magnesium concentrations are preferably 0.7% or more and 5% or less. The phosphorus and magnesium concentrations shown here may be values ​​obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on values ​​obtained by mixing raw materials in the process of producing the positive electrode active material.

[0289] <Analysis Method> Whether or not a positive electrode active material exhibits an O3'-type crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred in that it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery as is.

[0290] As described above, the cathode active material 100 of one embodiment of the present invention is characterized by minimal change in crystal structure between a high-voltage charged state and a discharged state. Materials in which a crystal structure that exhibits a large change between a high-voltage charged state and a discharged state accounts for 50 wt % or more are not preferable because they cannot withstand high-voltage charging and discharging. Furthermore, when the above material is charged at a predetermined voltage, the O3'-type crystal structure becomes nearly 100 wt %, and further increasing the predetermined voltage may result in the formation of an H1-3-type crystal structure. Therefore, to determine whether or not a material is the cathode active material 100 of one embodiment of the present invention, analysis such as XRD is recommended.

[0291] However, when the positive electrode active material 100 is charged or discharged at a high voltage, its crystal structure may change when exposed to the air. For example, the crystal structure may change from an O3'-type to an H1-3-type. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0292] <Charging Method> To understand the state of the positive electrode active material during high-voltage charging, for example, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) may be prepared using lithium metal as the counter electrode, charged, and then analyzed.

[0293] More specifically, a coin cell having a positive electrode in which a slurry containing the positive electrode active material, the conductive additive, and the binder is coated on an aluminum foil positive electrode current collector may be used, and lithium metal may be used as the counter electrode.

[0294] The coin cell contains an electrolyte solution, which is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7, with 2 wt% vinylene carbonate (VC). The electrolyte solution contains 1 mol / L lithium hexafluorophosphate (LiPF ６ ) can be used.

[0295] The coin cell has a separator, which can be made of polypropylene with a thickness of 25 μm.

[0296] The positive electrode can and the negative electrode can of the coin cell can be made of stainless steel (SUS).

[0297] The coin cell prepared under the above conditions is charged at a constant current of 0.5 C at an arbitrary voltage (for example, 4.6 V, 4.65 V, or 4.7 V), and then charged at a constant voltage until the current value reaches 0.01 C. Note that 1 C can be 137 mA / g or 200 mA / g. The temperature is 25°C.

[0298] After charging in this manner, the coin cell is disassembled in an argon-atmosphere glove box and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When various analyses are performed after this, it is preferable to seal the positive electrode active material in an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing the positive electrode active material in a sealed container in an argon atmosphere.

[0299] <<XRD>> The apparatus and conditions for XRD measurement are not particularly limited. For example, the measurement can be performed using the following apparatus and conditions. XRD apparatus: D8 ADVANCE manufactured by Bruker AXS X-ray source: CuKα １ Line output: 40 KV, 40 mA Slit width: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0300] If the measurement sample is a powder, it can be set by placing it in a glass sample holder or sprinkling the sample on a greased silicone anti-reflective plate, etc. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape and set to match the measurement surface required by the device.

[0301] The XRD pattern of the O3' type crystal structure is shown in Figure 15. For comparison, Figure 15 also shows the XRD pattern of LiCoO ２ The ideal XRD pattern calculated from the crystal structure of (O3) is also shown. Next, the CuKα pattern calculated from the model of the H1-3 type crystal structure is shown.１ The ideal XRD pattern of the powder by the X-ray is shown in Figure 16. For comparison, Figure 16 also shows LiCoO ２ (O3) and CoO at charge depth 1 ２ The ideal XRD pattern calculated from the crystal structure of LiCoO (O1) is also shown. ２ (O3) and CoO ２ The pattern of (O1) was created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The 2θ range was 15° to 75°, step size = 0.01, and wavelength λ = 1.540562 × 10 −１０ m and λ2 were not set, and the monochromator was single.

[0302] As shown in Figure 15, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 16, in the H1-3 type crystal structure and CoO ２ In (O1), no peaks appear at these positions. Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0303] As shown in FIG. 15, in the O3′ type crystal structure, diffraction peaks appear at 2θ=19.25±0.12° (19.13° or more and less than 19.37°) and 2θ=45.47±0.10° (45.37° or more and less than 45.57°).

[0304] However, as shown in FIG. 16, the H1-3 type crystal structure and CoO ２In (O1), no peaks appear at these positions. ｘ CoO ２ The appearance of diffraction peaks at 2θ = 19.25 ± 0.12° (19.13° or more and less than 19.37°) and 2θ = 45.47 ± 0.10° (45.37° or more and less than 45.57°) when x is small can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0305] This can also be said to be because the positions at which XRD diffraction peaks appear are close between the crystal structures of x = 1 and x ≦ 0.24. More specifically, for the main diffraction peaks of the crystal structures of x = 1 and x ≦ 0.24 that appear at 2θ of 42° or more and 46° or less, the difference in 2θ is 0.7° or less, more preferably 0.5° or less.

[0306] The positive electrode active material 100 according to one embodiment of the present invention is Li ｘ CoO ２ When x in the formula is small, the material has an O3'-type crystal structure, but not all of it needs to be an O3'-type crystal structure. It may contain other crystal structures, or a portion may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3'-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, it can be a positive electrode active material with sufficiently excellent cycle characteristics.

[0307] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type crystal structure is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more.

[0308] Furthermore, the sharpness of the diffraction peaks in the XRD pattern indicates the degree of crystallinity. Therefore, it is preferable that each diffraction peak after charging is sharp, i.e., the half-width is narrow. The half-width varies depending on the XRD measurement conditions or the value of 2θ, even for peaks arising from the same crystalline phase. Under the above-mentioned measurement conditions, for peaks observed at 2θ = 43° or more and 46° or less, the half-width is preferably 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of the crystalline phase is high. Such high crystallinity contributes to the stabilization of the crystal structure.

[0309] The crystallite size of the O3'-type crystal structure of the positive electrode active material 100 is ２ Therefore, even under the same XRD measurement conditions as the positive electrode before and after charging and discharging, the ｘ CoO ２ When x in the graph is small, a clear peak of the O3' type crystal structure can be confirmed. ２ In this case, even if a part of the crystal structure resembles the O3'-type crystal structure, the crystallite size will be small and the peak will be broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0310] The positive electrode active material may have cracks, and the presence of phosphorus, more specifically, a compound containing phosphorus and oxygen, inside the positive electrode active material with the cracks on the surface may inhibit the progression of the cracks.

[0311] This embodiment can be used in combination with other embodiments.

[0312] Embodiment 4 In this embodiment, a lithium-ion secondary battery including a positive electrode active material according to one embodiment of the present invention will be described. The secondary battery includes at least an outer casing, a current collector, an active material (a positive electrode active material or a negative electrode active material), a conductive additive, and a binder. The secondary battery also includes an electrolyte solution containing a lithium salt or the like dissolved therein. In the case of a secondary battery using an electrolyte solution, a positive electrode, a negative electrode, and a separator are provided between the positive electrode and the negative electrode.

[0313] The positive electrode active material layer preferably contains the positive electrode active material described in Embodiment 1, and may further contain a binder, a conductive additive, and the like.

[0314] FIG. 17A shows an example of a schematic cross-sectional view of a positive electrode.

[0315] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry onto the metal foil and drying it. After drying, the metal foil may be further pressed. The positive electrode is formed by forming a positive electrode active material layer on the current collector 550.

[0316] The slurry is a material liquid used to form a positive electrode active material layer on the current collector 550, and refers to a material containing at least a positive electrode active material, a binder, and a solvent, and preferably further mixed with a conductive additive. The slurry is also called an electrode slurry or an active material slurry, and a positive electrode slurry is used when forming a positive electrode active material layer, and a negative electrode slurry is used when forming a negative electrode active material layer.

[0317] The conductive additive, also called a conductivity-imparting agent or conductive material, is made of a carbon material. By attaching the conductive additive between multiple active materials, the active materials are electrically connected to each other, thereby increasing their conductivity. Note that "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covering part of the surface of the active material, the conductive additive fitting into the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0318] A typical carbon material used as a conductive additive is carbon black (furnace black, acetylene black, graphite, etc.).

[0319] 17A illustrates acetylene black 553 as a conductive additive. Also, FIG. 17A illustrates an example in which the positive electrode active material 100 has particles with different particle sizes. That is, the example illustrates a mixture of a first positive electrode active material 561 with a large particle size and a second positive electrode active material 562 with a small particle size. By mixing positive electrode active materials with different particle sizes, a high-density positive electrode active material layer can be obtained, and the charge / discharge capacity of the secondary battery can be increased.

[0320] A binder (resin) is mixed into the positive electrode of a secondary battery to bond the current collector 550, such as a metal foil, to the active material. The binder is also called a binding agent. The binder is a polymeric material, and adding too much binder reduces the proportion of active material in the positive electrode, thereby reducing the discharge capacity of the secondary battery. Therefore, the amount of binder is minimized. In Figure 17A, the areas not filled with the first positive electrode active material 561, the second positive electrode active material 562, and the acetylene black 553 represent voids or binder. While voids are necessary for the electrolyte to penetrate, too many voids reduce electrode density, while too few voids prevent the electrolyte from penetrating. If voids remain after the secondary battery is fabricated, the energy density decreases.

[0321] 17A shows an example in which first positive electrode active material 561 is spherical, but is not particularly limited thereto and may have various shapes. The cross-sectional shape of first positive electrode active material 561 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0322] 17B shows an example in which first positive electrode active material 561 has various shapes. FIG. 17B shows an example different from FIG. 17A.

[0323] In addition, in the positive electrode in FIG. 17B, graphene 554 is used as a carbon material used as a conductive additive.

[0324] In FIG. 17B , a positive electrode active material layer including a first positive electrode active material 561 , graphene 554 , and acetylene black 553 is formed over a current collector 550 .

[0325] In the step of mixing the graphene 554 and the acetylene black 553 to obtain electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of the graphene.

[0326] Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, acetylene black 553 exhibits excellent dispersion stability and is less likely to aggregate during slurry preparation. Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 553 as a conductive additive. Increasing the electrode density can increase the capacity per unit weight. Specifically, the density of the positive electrode active material layer measured by weight can be increased to more than 3.5 g / cc. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is within the above range, a synergistic effect can be expected in terms of increasing the capacity of the secondary battery, which is preferable.

[0327] By using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high density of the electrode and creation of appropriate gaps necessary for ion conduction, and the positive electrode can have high energy density and good output characteristics.

[0328] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive additive, rapid charging can be achieved by mixing graphene (a first carbon material) and acetylene black (a second carbon material that is different in shape and the like from the first carbon material) in the above range. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is in the above range, the secondary battery is more stable and can be expected to have a synergistic effect of being able to handle even faster charging, which is preferable. These features are effective for a secondary battery for vehicle use.

[0329] This structure is also effective in a portable information terminal, and the secondary battery can be miniaturized and have a high capacity by using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and by setting the mixture ratio of acetylene black and graphene in an optimal range. In addition, by setting the mixture ratio of acetylene black and graphene in an optimal range, the portable information terminal can be rapidly charged.

[0330] Note that in FIG. 17B, regions that are not filled with the first positive electrode active material 561, the graphene 554, or the acetylene black 553 indicate voids or binders.

[0331] By using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high density of the electrode and creation of appropriate gaps necessary for ion conduction, and a secondary battery having high energy density and good output characteristics can be obtained.

[0332] 17C illustrates an example of a positive electrode in which carbon nanotubes 555 are used instead of graphene. Fig. 17C shows an example different from Fig. 17B. The use of carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and improve dispersibility.

[0333] In FIG. 17C, the regions not filled with first positive electrode active material 561, carbon nanotubes 555, and acetylene black 553 indicate voids or binders.

[0334] 17D shows another example of a positive electrode. In FIG. 17D, carbon nanotubes 555 are used in addition to graphene 554. When both graphene 554 and carbon nanotubes 555 are used, aggregation of carbon black such as acetylene black 553 can be prevented and dispersibility can be further improved.

[0335] In FIG. 17D , regions that are not filled with first positive electrode active material 561 , carbon nanotubes 555 , graphene 554 , and acetylene black 553 indicate voids or binders.

[0336] A secondary battery can be produced by using any one of the positive electrodes shown in FIGS. 17A to 17D , placing a separator on the positive electrode, and placing the laminate obtained by placing the negative electrode on the separator in a container (such as an exterior body or a metal can) and filling the container with an electrolyte.

[0337] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0338] For example, a semi-solid battery or an all-solid battery can be manufactured using the positive electrode active material 100 described in Embodiment 1.

[0339] In this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. Here, semi-solid does not mean that the ratio of solid material is 50%. Semi-solid means that while having solid properties such as small volume change, it also has some liquid-like properties such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, a porous solid material may be impregnated with a liquid material.

[0340] In this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between a positive electrode and a negative electrode. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries. Polymer electrolyte secondary batteries may also be called semi-solid batteries.

[0341] When a semi-solid battery is manufactured using the positive electrode active material 100 described in Embodiment 1, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, the semi-solid battery can have a high charge / discharge voltage. Alternatively, a semi-solid battery with high safety or reliability can be realized.

[0342] The positive electrode active material described in the first embodiment may be mixed with another positive electrode active material.

[0343] Other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, LiFePO ４ , LiFeO ２, LiNiO ２ , LiMn ２ O ４ , V ２ O ５ , Cr ２ O ５ , MnO ２ The following compounds are exemplified:

[0344] Other positive electrode active materials include LiMn ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0345] In addition, as another positive electrode active material, the composition formula Li ａ Mn ｂ M ｃ O ｄA lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among lithium and manganese, or silicon or phosphorus, and more preferably nickel. Furthermore, when measuring the entire lithium-manganese composite oxide particle, it is preferable that 0<a / (b+c)<2, c>0, and 0.26≦(b+c) / d<0.5 are satisfied during discharge. The composition of metals, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured, for example, using an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen composition in the entire lithium-manganese composite oxide particle can be measured, for example, using energy dispersive X-ray spectroscopy (EDX). Furthermore, the composition can be determined by valence evaluation using fusion gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, phosphorus, and the like.

[0346] <Binder> As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Furthermore, as the binder, fluororubber can be used.

[0347] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0348] Alternatively, it is preferable to use, as the binder, materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose.

[0349] The binder may be used in combination with two or more of the above.

[0350] For example, a material with a particularly excellent viscosity adjusting effect may be used in combination with other materials. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with a particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with a particularly excellent viscosity adjusting effect. Furthermore, as a water-soluble polymer with a particularly excellent viscosity adjusting effect, the aforementioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, or starch may be used.

[0351] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials or other components when preparing electrode slurries. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0352] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials or other materials combined as binders, such as styrene-butadiene rubber, in aqueous solutions. Furthermore, their functional groups are expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups, such as hydroxyl or carboxyl groups, and the functional groups are expected to allow interactions between polymers, resulting in widespread coverage of the active material surface.

[0353] When the binder covering or contacting the surface of the active material forms a film, it is expected to function as a passive film and suppress the decomposition of the electrolyte. Here, the passive film is a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress the decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0354] <Positive Electrode Current Collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0355] <Negative Electrode Active Material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0356] As the negative electrode active material, an element capable of undergoing a charge-discharge reaction by alloying / de-alloying with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. These elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, a compound containing these elements may be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0357] In this specification and the like, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0358] Examples of carbonaceous materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0359] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is therefore preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0360] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), the graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋ This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety than metallic lithium.

[0361] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten oxide (WO ２ ), molybdenum oxide (MoO ２ ) and other oxides can be used.

[0362] In addition, as the negative electrode active material, a composite nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N ３ has a large charge / discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0363] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, can be used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the composite nitride of lithium and a transition metal can be used as the negative electrode active material, even when a material containing lithium ions is used as the positive electrode active material, by first removing the lithium ions contained in the positive electrode active material.

[0364] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0365] As the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0366] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0367] [Separator] A separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include those made of cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyimide, polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0368] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0369] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0370] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0371] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0372] [Electrolyte] The electrolyte contains a solvent and an electrolyte. The solvent for the electrolyte is preferably an aprotic organic solvent, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, and sultone, or any combination and ratio of two or more of these.

[0373] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature of the electricity storage device rises due to an internal short circuit, overcharging, or the like. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0374] The electrolyte to be dissolved in the solvent is, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (Li(C) ２ O ４ ) ２ , LiBOB), or two or more of these can be used in any combination and ratio.

[0375] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0376] The electrolyte may contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0377] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0378] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0379] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0380] In addition, instead of an electrolytic solution, a solid electrolyte containing an inorganic material such as a sulfide or oxide, or a solid electrolyte containing a polymer material such as a PEO (polyethylene oxide) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0381] Therefore, the positive electrode active material 100 obtained in the first and second embodiments can be applied to an all-solid-state battery. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and excellent characteristics can be obtained.

[0382] [Exterior Body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0383] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0384] Embodiment Mode 5 In this embodiment mode, examples of various shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0385] [Coin-Type Secondary Battery] An example of a coin-type secondary battery will be described. Fig. 18A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 18B is an external view, and Fig. 18C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0386] 18A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 18A and 18B are not completely identical corresponding views.

[0387] In Fig. 18A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed by a negative electrode can 302 and a positive electrode can 301. Note that a gasket for sealing is not shown in Fig. 18A. The spacer 322 and the washer 312 are used to protect the inside or to fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0388] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0389] To prevent short-circuiting between the positive electrode and the negative electrode, a separator 310 and a ring-shaped insulator 313 are arranged so as to cover the side and top surfaces of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0390] FIG. 18B is a perspective view of the completed coin-type secondary battery.

[0391] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be formed of lithium metal foil or a lithium-aluminum alloy foil.

[0392] In addition, in each of the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300, an active material layer may be formed on only one surface.

[0393] The positive electrode can 301 and the negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0394] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 18C , the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, thereby producing a coin-shaped secondary battery 300.

[0395] The above-described configuration allows the coin-type secondary battery 300 to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that, when a secondary battery having a solid electrolyte layer between the negative electrode 307 and the positive electrode 304 is used, the separator 310 may be unnecessary.

[0396] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be described with reference to Fig. 19A. As shown in Fig. 19A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0397] 19B is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 19B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0398] A battery element is provided inside a hollow cylindrical battery can 602, which includes a strip-shaped positive electrode 604 and a negative electrode 606 wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal, such as nickel, aluminum, or titanium, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel, aluminum, or the like to prevent corrosion by the electrolyte. Inside the battery can 602, the wound battery element, which includes the positive electrode, negative electrode, and separator, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is injected inside the battery can 602, which contains the battery element. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0399] Since the positive and negative electrodes used in cylindrical secondary batteries are wound, it is preferable to form active materials on both sides of the current collector.

[0400] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0401] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element is made of barium titanate (BaTiO ３ )-based semiconductor ceramics, etc. can be used.

[0402] 19C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrode of each secondary battery is in contact with and electrically connected to a conductor 624. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is electrically connected to the control circuit 620 via wiring 626. A charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging or overdischarging, can be used as the control circuit 620.

[0403] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes it difficult for the performance of the power storage system 615 to be affected by the outside air temperature.

[0404] [Another Structural Example of Secondary Battery] Another structural example of a secondary battery will be described with reference to FIGS. 20 and 21. FIG.

[0405] The secondary battery 913 shown in FIG. 20A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 20A , for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0406] 20B, the housing 930 shown in Fig. 20A may be formed of a plurality of materials. For example, the secondary battery 913 shown in Fig. 20B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0407] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0408] 20C shows the structure of the wound body 950. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 sandwiched therebetween, and the laminated sheet is wound. Note that multiple layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0409] Alternatively, a secondary battery 913 may be provided that has a wound body 950a as shown in Fig. 21A. The wound body 950a shown in Fig. 21A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0410] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 932, the secondary battery 913 can have a large capacity, a large charge / discharge capacity, and excellent cycle characteristics.

[0411] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

[0412] 21B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. The positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0413] 21C , wound body 950 a and the electrolyte are covered by casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of casing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0414] As shown in Fig. 21B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a allows the secondary battery 913 to have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 21A and 21B, the descriptions of the secondary battery 913 shown in Figs. 20A to 20C can be referred to.

[0415] 22A and 22B show examples of external views of a laminated secondary battery, which includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0416] 23A shows the external appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area or shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 23A .

[0417] <Method of Manufacturing Laminated Secondary Battery> Here, an example of a method of manufacturing the laminated secondary battery whose external view is shown in FIG. 22A will be described with reference to FIGS. 23B and 23C.

[0418] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 23B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0419] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0420] Next, as shown in Fig. 23C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0421] Next, an electrolyte solution (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0422] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 503, the secondary battery 500 can have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0423] [Example of Battery Pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be described with reference to FIG.

[0424] Fig. 24A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (also called a thick flat plate shape). Fig. 24B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is affixed to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0425] The interior of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0426] 24B , the secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to the terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one 551 of the positive electrode lead and the negative electrode lead of the secondary battery 513, and the other 552 of the positive electrode lead and the negative electrode lead of the secondary battery 513.

[0427] Alternatively, as shown in FIG. 24C, the device may have a circuit system 590 a provided on a circuit board 540 and a circuit system 590 b electrically connected to the circuit board 540 via a terminal 514 .

[0428] The antenna 517 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Furthermore, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may also be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0429] The secondary battery pack 531 includes a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 513. The layer 519 can be formed using, for example, a magnetic material.

[0430] This embodiment mode can be combined with other embodiment modes as appropriate.

[0431] Sixth Embodiment In this embodiment, an example of manufacturing an all-solid-state battery using the positive electrode active material 100 obtained in the first embodiment will be described.

[0432] As shown in FIG. 25A , a secondary battery 400 of one embodiment of the present invention includes a positive electrode 410 , a solid electrolyte layer 420 , and a negative electrode 430 .

[0433] Positive electrode 410 includes positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 includes positive electrode active material 411 and solid electrolyte 421. Positive electrode active material 100 obtained in Embodiments 1 and 2 is used for positive electrode active material 411, and positive electrode active material layer 414 may include a conductive additive and a binder.

[0434] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0435] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 25B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0436] The solid electrolyte 421 of the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0437] The sulfide-based solid electrolytes include thiolithium-based (Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ etc.), sulfide glass (70Li ２ S・30P ２ S ５ , 30Li ２ S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 50Li ２ S・50GeS ２ etc.), sulfide crystallized glass (Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0438] The oxide-based solid electrolyte includes a material having a perovskite crystal structure (La２／３−ｘ Li ３ｘ TiO ３ etc.), materials having a NASICON type crystal structure (Li １−Ｙ Al Ｙ Ti ２−Ｙ (P.O. ４ ) ３ etc.), materials having a garnet-type crystal structure (Li ７ La ３ Zr ２ O １２ etc.), materials having a LISICON type crystal structure (Li １４ ZnGe ４ O １６ etc.), LLZO (Li ７ La ３ Zr ２ O １２ ), oxide glass (Li ３ P.O. ４ -Li ４ SiO ４ , 50Li ４ SiO ４ ・50Li ３ BO ３ etc.), oxide crystallized glass (Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0439] Halide-based solid electrolytes include LiAlCl ４ , Li ３ InBr ６ , LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as the solid electrolyte.

[0440] Also, different solid electrolytes may be mixed and used.

[0441] Among them, Li having a NASICON type crystal structure１＋ｘ Al ｘ Ti ２−ｘ (P.O. ４ ) ３ Since (0[x[1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, a synergistic effect can be expected in improving cycle characteristics, which is preferable. In addition, productivity can be improved by reducing the number of steps. Note that in this specification and the like, the NASICON-type crystal structure refers to a structure in which M ２ (XO ４ ) ３ (M: transition metal, X: S, P, As, Mo, W, etc.), ６ Octahedron and XO ４ It refers to a structure in which tetrahedrons are arranged three-dimensionally with their vertices shared.

[0442] [Exterior Body and Shape of Secondary Battery] Various materials and shapes can be used for the exterior body of the secondary battery 400 of one embodiment of the present invention, but it is preferable that the exterior body has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0443] For example, FIG. 26 shows an example of a cell for evaluating materials for an all-solid-state battery.

[0444] 26A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw or wing nut 764 that fixes them together, and electrode plate 753 is pressed to fix the evaluation material by rotating a holding screw 763. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is also provided between upper member 762 and holding screw 763 to provide a tight seal.

[0445] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. Figure 26B is an enlarged perspective view of the evaluation material and its surroundings.

[0446] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 26C. Note that the same reference numerals are used for the same parts in Figs. 26A to 26C.

[0447] The electrode plate 751 and the lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and the upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0448] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0449] Fig. 27A is a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 26. The secondary battery in Fig. 27A has external electrodes 771 and 772 and is sealed in an exterior body having a plurality of package members.

[0450] An example of a cross section taken along the dashed line in Figure 27A is shown in Figure 27B. A laminate including a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed within a package member 770a having a flat plate with an electrode layer 773a, a frame-shaped package member 770b, and a package member 770c having a flat plate with an electrode layer 773b. The package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[0451] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0452] By using the positive electrode active material 100 obtained in the first embodiment, an all-solid-state secondary battery having a high energy density and good output characteristics can be realized.

[0453] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0454] Seventh Embodiment In this embodiment, an example of application to an electric vehicle (EV) will be described with reference to FIGS. 28A, 28B, and 28C.

[0455] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0456] The internal structure of the first battery 1301a may be a wound type shown in Fig. 20C or 21A or a stacked type shown in Fig. 22A or 22B. The first battery 1301a may use the all-solid-state battery of Embodiment 6. By using the all-solid-state battery of Embodiment 6 for the first battery 1301a, a high capacity can be achieved, safety can be improved, and the battery can be made smaller and lighter.

[0457] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0458] In addition, in a secondary battery for vehicle use, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a in order to cut off power from multiple secondary batteries.

[0459] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided for the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0460] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0461] The first battery 1301a will be described with reference to FIG. 28A.

[0462] FIG. 28A shows an example in which nine prismatic secondary batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by the fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that the vehicle will be subjected to external vibrations or shaking (e.g., from the road surface), it is preferable that the fixing portions 1413 and 1414 fix multiple secondary batteries to a battery housing box or the like. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0463] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0464] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein the element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a c-axis aligned crystalline oxide semiconductor (CAAC-OS) or a cloud-aligned composite oxide semiconductor (CAC-OS). CAAC-OS is an oxide semiconductor having multiple crystalline regions, each of which has a c-axis aligned in a specific direction. CAC-OS is a material in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof.

[0465] Furthermore, since the control circuit unit 1320 can be used in high-temperature environments, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from −40° C. to 150° C., and their characteristics change less when the secondary battery is heated than single-crystal Si transistors. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement regardless of temperature, whereas the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150° C., the off-current of a single-crystal Si transistor increases, and the current on / off ratio is not sufficiently large. The control circuit unit 1320 can improve safety. Furthermore, a synergistic effect on safety can be achieved by combining the positive electrode active material 100 obtained in Embodiments 1 and 2 with a secondary battery using the positive electrode. The secondary battery and control circuit unit 1320 using the positive electrode active material 100 obtained in the first and second embodiments for the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0466] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for the secondary battery to address causes of instability such as micro-short circuits. These functions include overcharge prevention, overcurrent prevention, overheat control during charging, cell balancing in the battery pack, over-discharge prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of deterioration, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for the secondary battery can be miniaturized.

[0467] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0468] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0469] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0470] FIG. 28B shows an example of a block diagram of the battery pack 1415 shown in FIG. 28A.

[0471] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range, and when the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging or overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0472] The switch portion 1324 can be configured by combining n-channel transistors or p-channel transistors. The switch portion 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch portion 1324 may be formed using a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, and therefore integration can be easily achieved. Furthermore, OS transistors can be manufactured using the same manufacturing equipment as Si transistors, and therefore can be manufactured at low cost. That is, the control circuit portion 1320 using OS transistors can be stacked on the switch portion 1324 and integrated into a single chip. The volume occupied by the control circuit section 1320 can be reduced, which allows for miniaturization.

[0473] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle devices, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle devices. Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Lead-acid batteries have the disadvantage of being more self-discharged than lithium-ion secondary batteries and being prone to deterioration due to a phenomenon called sulfation. Using a lithium-ion secondary battery as the second battery 1311 offers the advantage of being maintenance-free, but after prolonged use, e.g., three years or more, there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, even if the first batteries 1301a and 1301b still have remaining capacity, the second battery 1311 is charged to maintain a full charge state by supplying power from the first battery to the second battery.

[0474] In this embodiment, an example in which lithium ion secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown. A lead storage battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, high capacity can be achieved, and reductions in size and weight can be achieved.

[0475] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then sent from the motor controller 1303 or the battery controller 1302 via the control circuit unit 1321 to charge the second battery 1311. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be capable of rapid charging.

[0476] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0477] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The control circuit unit 1320 may also be provided in the connection cable or the charger's connection cable. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0478] External chargers installed at charging stations and the like are available with 100V or 200V outlets, or three-phase 200V and 50kW, etc. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0479] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0480] Moreover, the secondary battery of the present embodiment described above has a high-density positive electrode by using the positive electrode active material 100 obtained in Embodiment 1. Furthermore, by using graphene as a conductive additive, a secondary battery with significantly improved electrical characteristics can be realized, which suppresses capacity reduction and maintains high capacity even when the electrode layer is thickened and the amount of graphene supported is increased. This is particularly effective for secondary batteries used in vehicles, and a vehicle with a long cruising range, specifically, a cruising range of 500 km or more per charge, can be provided without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0481] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material 100 described in embodiment 1, and can increase the usable capacity as the charging voltage increases. Furthermore, by using the positive electrode active material 100 described in embodiment 1 for the positive electrode, a secondary battery for vehicles having excellent cycle characteristics can be provided.

[0482] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0483] 21C or 28A , next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, the secondary battery can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes or planetary probes, and spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0484] 29A to 29D illustrate examples of transportation vehicles using one embodiment of the present invention. The automobile 2001 shown in FIG. 29A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 4 is installed in one or more locations. The automobile 2001 shown in FIG. 29A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further include a charge control device electrically connected to the secondary battery module.

[0485] Furthermore, the automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging may be performed using a predetermined charging method or connector standard, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged using a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge an electric storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device, such as an AC-DC converter.

[0486] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0487] 29B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series for a maximum voltage of 170 V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 29A, and therefore a description thereof will be omitted.

[0488] FIG. 29C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, which is obtained by connecting in series one hundred or more secondary batteries with a nominal voltage of 3.0 V or more and 5.0 V or less. Therefore, a secondary battery with minimal characteristic variation is required. By using a secondary battery that uses the positive electrode active material 100 described in embodiment 1 as the positive electrode, a secondary battery with stable battery characteristics can be manufactured, and mass production at low cost is possible from the standpoint of yield. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the battery pack 2202 has the same functions as those shown in FIG. 29A , and therefore a description thereof will be omitted.

[0489] Fig. 29D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 29D has wheels for takeoff and landing, it can also be said to be part of a transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and the secondary battery module and a charge control device.

[0490] The secondary battery module of the aircraft 2004 has, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, the secondary battery module has the same functions as those shown in Fig. 29A, and therefore a description thereof will be omitted.

[0491] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0492] Embodiment 8 In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 30A and 30B.

[0493] The house illustrated in FIG. 30A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611 or the like. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The power obtained by the solar panel 2610 can be charged to the power storage device 2612. The power stored in the power storage device 2612 can be charged to a secondary battery included in the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0494] The power stored in the power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0495] 30B illustrates an example of a power storage device according to one embodiment of the present invention. As illustrated in FIG. 30B , a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. The power storage device 791 may be provided with the control circuit described in Embodiment 6. A synergistic effect on safety can be obtained by using a secondary battery in which the positive electrode active material 100 obtained in Embodiments 1 and 2 is used for the power storage device 791. The control circuit described in Embodiment 6 and the secondary battery in which the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode can greatly contribute to preventing accidents such as fires caused by the power storage device 791 including a secondary battery.

[0496] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to the distribution board 703, the power storage controller 705 (also called the control device), the display 706, and the router 709 by wiring.

[0497] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment portion 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via outlets (not shown).

[0498] The general load 707 is, for example, an electronic device such as a television or a personal computer, and the power storage load 708 is, for example, an electronic device such as a microwave oven, a refrigerator, or an air conditioner.

[0499] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during a day (e.g., from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791 based on the amount of power demand predicted by the prediction unit 712.

[0500] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electronic device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile information terminal such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electronic device, or the mobile information terminal.

[0501] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0502] Embodiment 9 In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

[0503] 31A illustrates an example of an electric bicycle using the power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 illustrated in FIG. 31A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0504] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state detached from the bicycle in FIG. 31B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. The control circuit 8704 may be provided with the small solid-state secondary battery shown in FIGS. 27A and 27B. By providing the small solid-state secondary battery shown in FIGS. 27A and 27B in the control circuit 8704, power can be supplied to retain data in a memory circuit included in the control circuit 8704 for a long period of time. Furthermore, a synergistic effect in terms of safety can be obtained by combining the positive electrode active material 100 obtained in Embodiment 1 with a secondary battery using the positive electrode active material 100 obtained in Embodiment 1. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and the control circuit 8704 can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0505] 31C illustrates an example of a two-wheeled vehicle using the power storage device of one embodiment of the present invention. An electric motorcycle (scooter) 8600 illustrated in FIG. 31C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602, which includes a plurality of secondary batteries each using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode, can have a high capacity, which can contribute to miniaturization.

[0506] 31C can store a power storage device 8602 in an under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0507] Embodiment 10 In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in one or both of an electronic device and a lighting device will be described. Examples of electronic devices in which a secondary battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), smartphones, portable game consoles, portable music players, personal digital assistants (PDAs), sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, mobile phones, and hair irons.

[0508] FIG. 32A illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 or 2 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time and is suitable as a secondary battery to be mounted on the unmanned aerial vehicle 2300.

[0509] Fig. 32B shows an example of a robot. A robot 6400 shown in Fig. 32B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0510] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0511] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0512] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. Furthermore, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0513] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 or 2 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as the secondary battery 6409 to be mounted on the robot 6400.

[0514] 32C shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0515] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 or 2 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time and is suitable as the secondary battery 6306 to be mounted on the cleaning robot 6300.

[0516] 33A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0517] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 33A . The eyeglasses-type device 4000 includes a frame 4000 a and a display portion 4000 b. By mounting the secondary battery on temple portions of the curved frame 4000 a, the eyeglasses-type device 4000 can be lightweight, well-balanced in weight, and has a long continuous use time. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 for its positive electrode has a high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0518] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 or 2 as a positive electrode has high energy density and can realize a configuration that can accommodate space saving associated with miniaturization of the housing.

[0519] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. A secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0520] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. A secondary battery using the positive electrode active material 100 obtained in Embodiments 1 and 2 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0521] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an inner region of the belt portion 4006a. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 for its positive electrode has high energy density, and a configuration that can accommodate space saving associated with miniaturization of the housing can be realized.

[0522] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 includes a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided in the display portion 4005a or the belt portion 4005b. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 or 2 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0523] The display unit 4005a can display not only the time but also various other information such as incoming emails or phone calls.

[0524] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0525] FIG. 33B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0526] 33C shows a side view of the display device 4005. Fig. 33C shows a state in which a secondary battery 913 is built into the internal area. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and can be made high density and large capacity, and is small and lightweight.

[0527] Since the wristwatch-type device 4005 is required to be small and lightweight, the positive electrode active material 100 obtained in Embodiment 1 and Embodiment 2 can be used for the positive electrode of the secondary battery 913, thereby making it possible to provide a high-energy density and small-sized secondary battery 913.

[0528] FIG. 34A is a diagram showing a hair iron. In FIG. 34A , the hair iron 7700 includes a handle 7701, a power switch 7702, a temperature switch button 7703, a temperature lamp 7704, a plate 7705, and a secondary battery 7706. To enhance safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 7706 may be electrically connected to the secondary battery 7706. The hair iron 7700 also includes an external terminal for connection to a charging cord. A heater for heating the plate 7705 is provided inside the plate 7705. The power source for this heater is the secondary battery 7706. The secondary battery 7706 is preferably lightweight. The secondary battery of one embodiment of the present invention has a high capacity and favorable cycle characteristics, and therefore, a lightweight hair iron 7700 that can be used for a long period of time can be provided.

[0529] FIG. 34B is a diagram of a different type of hair iron from the hair iron shown in FIG. 34A . In FIG. 34B , the hair iron 7750 includes a handle 7751, a power switch 7752, a temperature switch button 7753, a temperature lamp 7754, a pipe 7755, an auxiliary bar 7756, a lever 7757, a secondary battery 7758, and a connection terminal (not shown). To enhance safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 7758 may be electrically connected to the secondary battery 7758. The hair iron 7750 also includes an external terminal for connection to a charging cord. A heater for heating the pipe 7755 is provided inside the pipe 7755. The power source for this heater is the secondary battery 7758. It is desirable that the secondary battery 7758 be lightweight. The secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, making it possible to provide a lightweight hair iron 7750 that can be used for a long period of time.

[0530] A personal computer 2800 shown in FIG. 35A includes a housing 2801, a housing 2802, a display unit 2803, a keyboard 2804, a pointing device 2805, and the like. A secondary battery 2807 is provided inside the housing 2801, and a secondary battery 2806 is provided inside the housing 2802. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 2807 may be electrically connected to the secondary battery 2807. A touch panel is also applied to the display unit 2803. As shown in FIG. 35B, the housings 2801 and 2802 can be removed from the personal computer 2800, and the personal computer 2800 can be used as a tablet terminal using only the housing 2802.

[0531] A large secondary battery obtained by the method for manufacturing a secondary battery according to one embodiment of the present invention can be used as one or both of the secondary battery 2806 and the secondary battery 2807. The shape of the secondary battery obtained by the method for manufacturing a secondary battery according to one embodiment of the present invention can be freely changed by changing the shape of the exterior body. For example, by forming the secondary batteries 2806 and 2807 to match the shapes of the housings 2801 and 2802, the capacity of the secondary battery can be increased and the usage time of the personal computer 2800 can be extended. Furthermore, the weight of the personal computer 2800 can be reduced.

[0532] A flexible display is applied to the display portion 2803 of the housing 2802. A large-sized secondary battery obtained by the manufacturing method of a secondary battery according to one embodiment of the present invention is used as the secondary battery 2806. A large-sized secondary battery obtained by the manufacturing method of a secondary battery according to one embodiment of the present invention can be made into a bendable secondary battery by using a flexible film for the exterior body. This allows the housing 2802 to be folded and used as shown in FIG. 35C . In this case, part of the display portion 2803 can also be used as a keyboard as shown in FIG. 35C .

[0533] The housing 2802 can be folded so that the display portion 2803 faces inward as shown in FIG. 35D, or can be folded so that the display portion 2803 faces outward as shown in FIG. 35E.

[0534] The secondary battery of one embodiment of the present invention can be applied to a bendable secondary battery and mounted in an electronic device. The secondary battery can also be incorporated along a curved surface of an interior or exterior wall of a house or building, or the interior or exterior of an automobile.

[0535] 36A shows an example of a mobile phone. The mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 includes a secondary battery 7407. By using the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 7407 may be electrically connected to the secondary battery 7407.

[0536] FIG. 36B shows the mobile phone 7400 in a bent state. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 installed therein is also bent. FIG. 36C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to the current collector. For example, the current collector is copper foil, and a portion of the current collector is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.

[0537] FIG. 36D shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. To enhance safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 7104 may be electrically connected to the secondary battery 7104. FIG. 36E also shows a bent secondary battery 7104. When the secondary battery 7104 is worn on a user's wrist in a bent state, the housing deforms, causing a partial or complete change in curvature of the secondary battery 7104. The degree of bending at any point on the curve, expressed as the radius of the corresponding circle, is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, a partial or complete change in the main surface of the housing or secondary battery 7104 occurs within a radius of curvature range of 40 mm to 150 mm. High reliability can be maintained if the radius of curvature of the main surface of the secondary battery 7104 is within a range of 40 mm to 150 mm. By using the secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0538] 36F shows an example of a wristwatch-type portable information terminal 7200. The portable information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input / output terminal 7206, and the like.

[0539] The portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0540] The display surface of the display portion 7202 is curved, and display can be performed along the curved display surface. The display portion 7202 also includes a touch sensor, and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be started by touching an icon 7207 displayed on the display portion 7202.

[0541] The operation button 7205 can have various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the portable information terminal 7200.

[0542] The portable information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is possible by communicating with a wirelessly enabled headset.

[0543] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal 7206. Note that charging may be performed by wireless power supply without using the input / output terminal 7206.

[0544] The display portion 7202 of the portable information terminal 7200 includes the secondary battery of one embodiment of the present invention. By using the secondary battery of one embodiment of the present invention, a lightweight portable information terminal with a long life can be provided. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery may be electrically connected to the secondary battery. For example, the secondary battery 7104 shown in FIG. 36E can be installed in a curved state inside the housing 7201 or in a bendable state inside the band 7203.

[0545] The portable information terminal 7200 preferably has a sensor. For example, a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is preferably mounted as the sensor.

[0546] 36G shows an example of a wristband-type display device. The display device 7300 includes a display portion 7304 and a secondary battery of one embodiment of the present invention. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery may be electrically connected to the secondary battery. The display device 7300 may also include a touch sensor in the display portion 7304 and function as a portable information terminal.

[0547] The display surface of the display portion 7304 is curved, and display can be performed along the curved display surface. The display state of the display device 7300 can be changed by short-range wireless communication according to a communication standard.

[0548] The display device 7300 also includes an input / output terminal, and can directly exchange data with another information terminal via a connector. Charging can also be performed via the input / output terminal. Note that charging may be performed by wireless power supply without using the input / output terminal.

[0549] By using the secondary battery of one embodiment of the present invention as the secondary battery included in the display device 7300, a lightweight display device with a long lifetime can be provided.

[0550] Furthermore, examples in which a secondary battery with good cycle characteristics according to one embodiment of the present invention is mounted on an electronic device will be described with reference to FIGS. 36H, 37, and 38. FIG.

[0551] By using the secondary battery of one embodiment of the present invention as a secondary battery in an electronic device, a lightweight product with a long life can be provided. For example, examples of daily electronic devices include an electric toothbrush, an electric shaver, and an electric beauty device. For the secondary battery of these products, a small, lightweight, and large-capacity stick-shaped secondary battery is desired for ease of holding by users.

[0552] FIG. 36H is a perspective view of a device also known as a tobacco-containing smoking device (electronic cigarette). In FIG. 36H, the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle or a sensor. To enhance safety, a protection circuit that prevents overcharging and / or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 36H has external terminals so that it can be connected to a charging device. Because the secondary battery 7504 is the tip portion when held, it is desirable that the total length be short and the weight be light. The secondary battery of one embodiment of the present invention has high capacity and good cycle characteristics, making it possible to provide a compact and lightweight electronic cigarette 7500 that can be used for a long period of time.

[0553] Next, an example of a foldable tablet terminal is shown in Figures 37A and 37B. The tablet terminal 7600 shown in Figures 37A and 37B includes a housing 7630a, a housing 7630b, a movable portion 7640 connecting the housings 7630a and 7630b, a display portion 7631 having display portions 7631a and 7631b, switches 7625 to 7627, a fastener 7629, and an operation switch 7628. Using a flexible panel for the display portion 7631 allows the tablet terminal to have a larger display area. Figure 37A shows the tablet terminal 7600 in an open state, and Figure 37B shows the tablet terminal 7600 in a closed state.

[0554] The tablet terminal 7600 also includes a power storage unit 7635 inside the housing 7630a and the housing 7630b. The power storage unit 7635 passes through the movable portion 7640 and is provided across the housing 7630a and the housing 7630b.

[0555] All or part of the display portion 7631 can be a touch panel area, and data can be input by touching an image including an icon, text, an input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display portion 7631a on the housing 7630a side, and information such as text and images may be displayed on the display portion 7631b on the housing 7630b side.

[0556] A keyboard may be displayed on the display portion 7631b of the housing 7630b, and information such as text and images may be displayed on the display portion 7631a of the housing 7630a. A keyboard display switch button of a touch panel may be displayed on the display portion 7631, and the keyboard may be displayed on the display portion 7631 by touching the button with a finger, a stylus, or the like.

[0557] In addition, touch input can be simultaneously performed on the touch panel area of ​​the display portion 7631a on the housing 7630a side and the touch panel area of ​​the display portion 7631b on the housing 7630b side.

[0558] Furthermore, the switches 7625 to 7627 may be interfaces capable of switching various functions in addition to interfaces for operating the tablet terminal 7600. For example, at least one of the switches 7625 to 7627 may function as a switch for turning the tablet terminal 7600 on and off. For example, at least one of the switches 7625 to 7627 may have a function for switching the display orientation, such as portrait or landscape, or a function for switching between black and white and color display. For example, at least one of the switches 7625 to 7627 may have a function for adjusting the brightness of the display unit 7631. The brightness of the display unit 7631 can be optimized depending on the amount of external light detected by an optical sensor built into the tablet terminal 7600 during use. The tablet terminal may also have built-in not only an optical sensor but also other detection devices, such as a gyroscope, an acceleration sensor, or other sensors for detecting tilt.

[0559] 37A shows an example in which the display areas of the display portion 7631a on the housing 7630a and the display portion 7631b on the housing 7630b are substantially the same, the display areas of the display portion 7631a and the display portion 7631b are not particularly limited, and the sizes of one and the other may be different, and the display qualities may also be different. For example, one display panel may be capable of displaying at a higher resolution than the other.

[0560] 37B shows a tablet terminal 7600 folded in half, and the tablet terminal 7600 includes a housing 7630, a solar cell 7633, and a charge / discharge control circuit 7634 including a DCDC converter 7636. In addition, a secondary battery of one embodiment of the present invention is used as a power storage unit 7635.

[0561] As described above, the tablet terminal 7600 can be folded in half, and thus can be folded so that the housing 7630a and the housing 7630b overlap when not in use. By folding, the display portion 7631 can be protected, thereby improving the durability of the tablet terminal 7600. Furthermore, the power storage unit 7635 using the secondary battery of one embodiment of the present invention has a high capacity and favorable cycle characteristics, and therefore the tablet terminal 7600 can be used for a long period of time. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery included in the power storage unit 7635 may be electrically connected to the secondary battery.

[0562] In addition, the tablet terminal 7600 shown in Figures 37A and 37B can have functions such as displaying various information (still images, videos, text images, etc.), displaying a calendar, date or time on the display unit, a touch input function for touch inputting or editing information displayed on the display unit, and controlling processing using various software (programs).

[0563] A solar cell 7633 attached to the surface of the tablet terminal 7600 can supply power to a touch panel, a display unit, a video signal processor, or the like. The solar cell 7633 can be provided on one or both surfaces of the housing 7630, and can be configured to efficiently charge the power storage unit 7635. Use of a lithium-ion battery as the power storage unit 7635 has the advantage of enabling miniaturization.

[0564] The configuration and operation of the charge / discharge control circuit 7634 shown in Fig. 37B are described with reference to a block diagram in Fig. 37C Fig. 37C shows a solar cell 7633, a power storage unit 7635, a DC / DC converter 7636, a converter 7637, switches SW1 to SW3, and a display unit 7631. The power storage unit 7635, the DC / DC converter 7636, the converter 7637, and switches SW1 to SW3 correspond to the charge / discharge control circuit 7634 shown in Fig. 37B.

[0565] First, an example of operation when power is generated by the solar cell 7633 using external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 7636 to a voltage for charging the power storage unit 7635. When power from the solar cell 7633 is used to operate the display unit 7631, a switch SW1 is turned on, and the converter 7637 steps up or steps down the voltage to a voltage required for the display unit 7631. When no display is to be performed on the display unit 7631, the switch SW1 may be turned off and the switch SW2 may be turned on to charge the power storage unit 7635.

[0566] Note that the solar cell 7633 is shown as an example of a power generation means, but is not particularly limited thereto, and a configuration in which the power storage unit 7635 is charged by other power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element) may be used. For example, a configuration in which a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be used.

[0567] FIG. 38 illustrates an example of another electronic device. In FIG. 38 , a display device 8000 is an example of an electronic device using a secondary battery 8004 according to one embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display portion 8002, a speaker portion 8003, a secondary battery 8004, and the like. To enhance safety, a protection circuit for preventing overcharging and / or overdischarging of the secondary battery 8004 may be electrically connected to the secondary battery 8004. The secondary battery 8004 according to one embodiment of the present invention is provided inside the housing 8001. The display device 8000 can receive power from a commercial power source or can use power stored in the secondary battery 8004. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power source.

[0568] The display portion 8002 can be a liquid crystal display device, a light-emitting device having a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a semiconductor display device such as a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), or an FED (Field Emission Display).

[0569] The display device includes all display devices for displaying information, such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

[0570] In FIG. 38 , a stationary lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to one embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 8103 may be electrically connected to the secondary battery 8103. FIG. 38 illustrates the case where the secondary battery 8103 is provided inside a ceiling 8104 on which the housing 8101 and the light source 8102 are installed; however, the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power from a commercial power source or can use power stored in the secondary battery 8103. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply.

[0571] Note that although Figure 38 illustrates an example of a stationary lighting device 8100 provided on the ceiling 8104, the secondary battery of one embodiment of the present invention can also be used in a stationary lighting device provided on a side wall 8105, a floor 8106, a window 8107, or the like other than the ceiling 8104, or can also be used in a tabletop lighting device.

[0572] Furthermore, an artificial light source that artificially obtains light using electric power can be used as the light source 8102. Specifically, examples of the artificial light source include a discharge lamp such as an incandescent lamp or a fluorescent lamp, an LED, and / or an organic EL element.

[0573] In FIG. 38 , an air conditioner including an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a housing 8201, an air outlet 8202, a secondary battery 8203, and the like. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 8203 may be electrically connected to the secondary battery 8203. Although FIG. 38 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may also be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power from a commercial power source or can use power stored in the secondary battery 8203. In particular, when a secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, the air conditioner can be used by using the secondary battery 8203 of one embodiment of the present invention as an uninterruptible power supply even when power cannot be supplied from a commercial power source due to a power outage or the like.

[0574] Note that although Figure 38 illustrates an example of a separate-type air conditioner including an indoor unit and an outdoor unit, a secondary battery according to one embodiment of the present invention can also be used in an integrated air conditioner in which the functions of the indoor unit and the outdoor unit are combined in a single housing.

[0575] In FIG. 38 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator compartment door 8302, a freezer compartment door 8303, a secondary battery 8304, and the like. To improve safety, a protection circuit that prevents overcharging and / or overdischarging of the secondary battery 8304 may be electrically connected to the secondary battery 8304. In FIG. 38 , the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator-freezer 8300 can receive power from a commercial power source or can use power stored in the secondary battery 8304. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, the electric refrigerator-freezer 8300 can be used by using the secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply.

[0576] Among the electronic devices described above, electronic devices such as microwave ovens and other high-frequency heating devices and electric rice cookers require a large amount of power for a short period of time. Therefore, by using a secondary battery according to one embodiment of the present invention as an auxiliary power source for supplementing the power that cannot be supplied by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0577] Furthermore, by storing power in the secondary battery during times when electronic devices are not in use, particularly during times when the ratio of the amount of power actually used to the total amount of power that can be supplied by the commercial power supplier (referred to as the power usage rate) is low, it is possible to prevent the power usage rate from increasing outside of these times. For example, in the case of an electric refrigerator-freezer 8300, power is stored in the secondary battery 8304 during the night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed. Then, during the day when the temperature is high and the refrigerator door 8302 and the freezer door 8303 are opened and closed, the secondary battery 8304 is used as an auxiliary power source, thereby keeping the daytime power usage rate low.

[0578] According to one embodiment of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be improved. Furthermore, according to one embodiment of the present invention, a high-capacity secondary battery can be obtained, and therefore the characteristics of the secondary battery can be improved, and therefore the secondary battery itself can be made smaller and lighter. Therefore, by incorporating the secondary battery according to one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and be lighter.

[0579] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0580] In this example, a positive electrode active material was prepared according to the preparation method described in the embodiment mode and the like, and the results of obtaining battery characteristics will be described.

[0581] <Preparation of Positive Electrode Active Material> Samples 1 to 3 were prepared with reference to the manufacturing method 4 shown in Embodiment 1 and Fig. 4. The preparation process will be described in detail below.

[0582] 4, cobalt sulfate dissolved in pure water was prepared as an aqueous solution 890 (cobalt aqueous solution), and first glycine was added thereto as a chelating agent to prepare a mixed solution 901. The concentrations of cobalt sulfate and first glycine were adjusted to 2 mol / L and 0.075 mol / L, respectively.

[0583] Next, sodium hydroxide dissolved in pure water was prepared as aqueous solution 892 (alkaline aqueous solution) shown in FIG. 4 . The sodium hydroxide was adjusted to 5 mol / L. Furthermore, an aqueous solution containing a second glycine dissolved in pure water was prepared as aqueous solution 894 (chelating agent). The second glycine was adjusted to have the same molar concentration as the first glycine. The aqueous solution containing the second glycine was placed in a reaction vessel in advance.

[0584] The mixed solution 901 and the sodium hydroxide aqueous solution were added dropwise to the second glycine aqueous solution. Nitrogen was flowed through the reaction vessel at a flow rate of 1 L / min to create a nitrogen-containing atmosphere. The stirring blade rotation speed was set to 1000 rpm, and the temperature of the aqueous solution in the reaction vessel was maintained at 70°C. The rate of addition of the sodium hydroxide aqueous solution was adjusted so that the pH of the aqueous solution in the reaction vessel was maintained at 10.3. A precipitate was then formed in the reaction vessel. The precipitate contained cobalt hydroxide.

[0585] To obtain cobalt hydroxide, the aqueous solution in the reaction vessel was filtered to remove unnecessary water. Before filtration, the precipitate was washed with pure water and then with acetone.

[0586] Next, a drying process was performed to remove moisture from the precipitate. The filtered precipitate was transferred to a petri dish, which was then placed in a bell jar-type vacuum device and depressurized until the differential pressure gauge reached -0.1 MPa. That is, a vacuum was created using the bell jar-type vacuum device, and the filtered precipitate was dried at 80°C for 1 hour under this vacuum. This was used as cobalt compound 880 and lithium hydroxide as lithium compound 881, and these were mixed to prepare mixture 903. Cobalt compound 880 and lithium hydroxide were weighed so that the Li / Co ratio was 1.01, and mixed to obtain mixture 903. A kneader (Thinky Corporation, planetary-rotation type mixer, Awatori Rentaro) was used for mixing.

[0587] <Heating Conditions for Samples 1 to 3> Next, the mixture 903 was heated. The heating temperatures were set to 750°C, 850°C, and 950°C, and these were designated as Samples 1 to 3, respectively. The common conditions for Samples 1 to 3 were that the heating time was 10 hours and the heating atmosphere was an oxygen atmosphere. Specifically, to create the oxygen atmosphere, oxygen gas was continuously flowed at 5 L / min.

[0588] <XRD Analysis Results of Samples 1 to 3> XRD measurements were carried out on Samples 1 to 3. The conditions were as follows: X-ray source: CuKα １Line output: 40 KV, 40 mA Slit width: Div. Slit, 0.5° Detector: LynxEye Scan method: 2θ / θ continuous scan Measurement range (2θ): 15° to 90° Step width (2θ): 0.01° setting Counting time: 1 second / step Sample stage rotation: 15 rpm

[0589] The results of the XRD analysis are shown in Figure 39. In Figure 39, LiCoO ２ The results of XRD analysis of the crystal structure of R-3m are also shown. In Samples 1 to 3, peaks were observed at the same positions as in the reference. The positions of the peaks can be seen in Figure 39. In Sample 1, a peak was observed at the 2θ position indicated by an arrow (a peak at 2θ of 36.5° or more and less than 37°) that was not observed in the reference. Sample 1 had the lowest heating temperature, and cobalt hydroxide that did not react with the Li source thermally decomposed to produce tricobalt tetroxide (Co ３ O ４ ) occurs, and Co ３ O ４ It is believed that peaks corresponding to these were confirmed. No peaks not present in the reference were confirmed in Samples 2 and 3. Table 1 shows the lattice constants, the half-widths of the peaks at 2θ around 18° and 45°, and the crystallite sizes.

[0590]

[0591] The smaller the half-value width, the higher the crystallinity. Sample 3 had the smallest half-value width, indicating high crystallinity. Furthermore, since Sample 3 had a larger crystallite size than Samples 1 and 2, it was confirmed that the higher the heating temperature, the larger the crystallite size.

[0592] <SEM Observation of Samples 1 to 3> Next, planar SEM images of Samples 1 to 3 are shown in Figure 40. For reference, Figure 40 also shows a planar SEM image of cobalt hydroxide. The planar SEM images were acquired using a Hitachi High-Technologies S4800, with the acceleration voltage fixed at 5 kV and the magnifications set to 5,000x (5k) and 20,000x (20k). Secondary electron detectors used were one located above the stage (upper) and one located next to the stage (lower). The 20k observation region was the area marked with a square on the 5k SEM image.

[0593] It was confirmed that samples 1 to 3 were formed into secondary particles, and it was found that the shape of the secondary particles reflected the shape of the precursor cobalt hydroxide. The diameter of the secondary particles in samples 1 to 3 was about 20 μm. In sample 3, flat primary particles were confirmed. The thickness direction of the primary particles was LiCoO ２ It is believed that the direction of the primary particles is parallel to the c-axis of the sample, and samples 1 to 3 are believed to be secondary particles with many surfaces parallel to the c-axis (sometimes referred to as basal planes) located on the surface. Secondary batteries containing such secondary particles are expected to have improved rate characteristics. Furthermore, comparing samples 1 to 3, it is found that the diameter of the primary particles is larger in sample 3. In other words, it is found that the higher the heating temperature, the larger the diameter of the primary particles and the larger the diameter of the secondary particles.

[0594] <Cycle Test> A cycle test was performed using Samples 1 to 3. First, Samples 1 to 3 were prepared as the positive electrode active material, acetylene black was prepared as the conductive additive, PVdF was prepared as the binder, and NMP was prepared as the solvent. Then, the positive electrode active material, conductive additive, and binder were mixed in a weight ratio of 95:3:2 using a planetary mixer at 2000 rpm for 3 minutes to prepare a positive electrode slurry. This positive electrode slurry was applied to an aluminum positive electrode current collector and dried to prepare a positive electrode.

[0595] As a counter electrode, lithium metal was prepared.

[0596] Next, a coin-shaped cell was fabricated having the positive electrode and negative electrode fabricated by the above method, a separator interposed therebetween, and an electrolyte solution impregnated in the separator. The separator was made of polypropylene. The electrolyte solution was prepared by adding vinylene carbonate (VC) as an additive to a mixed organic solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC = 3:7, volume ratio) at a concentration of 2 wt % relative to the mixed organic solvent, and further adding 1 molar concentration of lithium hexafluorophosphate (LiPF ６ ) was dissolved in water.

[0597] Next, a cycle test was carried out on the coin-type cell fabricated by the above method.

[0598] The conditions for the cycle test were as follows: charging at 0.5 C up to an upper limit voltage (charge cut-off voltage) of 4.6 V under constant current / constant voltage (CC / CV) conditions at a measurement temperature of 25° C., constant voltage charging was continued until the current value reached 0.05 C, and then discharging at 0.5 C down to a lower limit voltage (discharge cut-off voltage) of 2.5 V under constant current (CC) conditions, and the discharge capacity was measured.

[0599] The charging and discharging cycle was repeated 50 times to obtain the discharge capacity. The higher the discharge capacity, the better the performance of the secondary battery.

[0600] The results of the discharge capacity of the cycle test are shown in Figure 41. It was confirmed from Figure 41 that the secondary battery using the positive electrode active material of Sample 3 had the best battery characteristics in terms of discharge capacity. The maximum discharge capacities were 193 (mAh / g) for Sample 1, 194 (mAh / g) for Sample 2, and 222 (mAh / g) for Sample 3.

[0601] In this example, positive electrode active materials were prepared according to the manufacturing methods described in the embodiments and the like, and the results of obtaining battery characteristics are shown. Samples 4 and 5 were newly prepared with reference to Manufacturing Method 4 shown in Embodiment 1 and FIG. 4 and the like. The manufacturing process is described in detail below.

[0602] <Samples 4 and 5> In order to examine the lithium source, Samples 4 and 5 were prepared using different materials for the lithium compound 881. For Sample 4, cobalt hydroxide obtained in the same manner as in Example 1 was mixed with lithium carbonate using a rotation-revolution mixer to obtain Mixture 903. For Sample 5, cobalt hydroxide obtained in the same manner as in Example 1 was mixed with lithium hydroxide to obtain Mixture 903.

[0603] Next, the mixture 903 was heated at a temperature of 950° C. for 10 hours in an oxygen atmosphere. To create the oxygen atmosphere, oxygen gas was continuously flowed at a rate of 5 L / min.

[0604] <Cycle Test> To conduct a cycle test using Samples 4 and 5, coin-type cells were fabricated under the same conditions as in Example 1 using Samples 4 and 5 as the positive electrode active material. A cycle test was performed on the coin-type cells fabricated by the above method. The cycle test involved charging at 0.5 C under constant current / constant voltage (CC / CV) conditions at a measurement temperature of 25°C to an upper voltage (end-of-charge voltage) of 4.4 V or 4.6 V, followed by constant voltage charging until the current value reached 0.05 C. After that, the cells were discharged at 0.5 C under constant current (CC) conditions to a lower voltage (end-of-discharge voltage) of 2.5 V, and the discharge capacity was measured.

[0605] The above charge and discharge cycles were repeated 50 times to obtain the discharge capacity. The higher the discharge capacity, the better the performance of the secondary battery.

[0606] 42A shows the results of the discharge capacity when the upper limit voltage was 4.4 V, and FIG. 42B shows the results of the discharge capacity when the upper limit voltage was 4.6 V. It can be seen from FIG. 42A and FIG. 42B that sufficient discharge capacity can be obtained with both the positive electrode active material formed using lithium carbonate such as Sample 4 and the positive electrode active material formed using lithium hydroxide such as Sample 5. It can be seen from FIG. 42A that the use of lithium carbonate increases the discharge capacity.

[0607] It has been confirmed that a secondary battery using such a positive electrode active material has excellent battery characteristics such as excellent discharge capacity.

[0608] In this example, positive electrode active materials were prepared according to the manufacturing methods described in the embodiments and the like, and the results of obtaining battery characteristics are shown. Samples 6 to 8 were newly prepared with reference to Manufacturing Method 4 shown in Embodiment 1 and FIG. 4 and the like. The manufacturing process will be described in detail below.

[0609] <Samples 6 to 8> In Samples 6 to 8, when lithium carbonate was used as the Li source, the amount of lithium carbonate mixed was varied to investigate the optimal Li / Co ratio. For Sample 6, lithium carbonate and cobalt hydroxide were weighed out so that the molar ratio (Li / Co ratio) of lithium in the lithium carbonate to cobalt in the cobalt hydroxide obtained in the same manner as in Example 1 was 1.01, and these were mixed to obtain Mixture 903. For Sample 7, lithium carbonate and cobalt hydroxide were weighed out so that the Li / Co ratio was 1.03, and these were mixed to obtain Mixture 903. For Sample 8, lithium carbonate and cobalt hydroxide were weighed out so that the Li / Co ratio was 1.05, and these were mixed to obtain Mixture 903. A kneader (Thinky Corporation, planetary-rotation type mixer, Awatori Rentaro) was used for mixing.

[0610] Next, the mixture 903 was heated at a temperature of 950° C. for 10 hours in an oxygen atmosphere. To create the oxygen atmosphere, oxygen gas was continuously flowed at a rate of 5 L / min.

[0611] <XRD Analysis Results of Samples 6 to 8> XRD measurements were carried out on Samples 6 to 8. The XRD measurement conditions were the same as those in Example 1.

[0612] The XRD analysis results are shown in Figure 44. Although not shown in Figure 44, the LiCoO ２ The results of XRD analysis of the crystal structure of R-3m can be referred to. In Samples 6 to 8, peaks were observed at the same positions as in the reference. The positions of the peaks can be seen in Figure 44. In Sample 6, a peak was observed at the 2θ position indicated by an arrow (a peak at 2θ of 36.5° or more and less than 37°) that was not observed in the reference. In Sample 6, cobalt hydroxide that did not react with the Li source thermally decomposed to produce tricobalt tetroxide (Co ３O ４ ) occurs, and Co ３ O ４ It is believed that peaks corresponding to these were confirmed. No peaks not present in the reference were confirmed in Samples 7 and 8. Table 2 shows the lattice constants, half-widths of the peaks at 2θ around 18° and 45°, and crystallite sizes.

[0613]

[0614] The smaller the half-value width, the higher the crystallinity. Sample 8 has a small half-value width, indicating high crystallinity. In addition, since Sample 8 has a larger crystallite size than Samples 6 and 7, it was confirmed that the crystallite size tends to increase as the Li / Co ratio increases.

[0615] <SEM Observation of Samples 6 to 8> Next, planar SEM images of Samples 6 to 8 are shown in Fig. 45. The planar SEM images were acquired using an S4800 manufactured by Hitachi High-Technologies Corporation, with the acceleration voltage fixed at 5 kV and the magnifications set to 5,000x (5k) and 20,000x (20k). The 20k observation region was the area marked with a square on the 5k SEM image.

[0616] It can be seen that the diameter of the secondary particles is about 20 μm in all of Samples 6 to 8. Furthermore, it can be seen from Samples 6 to 8 that the diameter of the primary particles and the diameter of the secondary particles increase as the Li / Co ratio increases.

[0617] <Cycle Test> To conduct a cycle test using Samples 6 to 8, coin-type cells were fabricated under the same conditions as in Example 1 using Samples 6 to 8 as the positive electrode active material. A cycle test was performed on the coin-type cells fabricated by the above method. The cycle test involved charging at 0.5 C to an upper voltage (end-of-charge voltage) of 4.4 V or 4.6 V under constant current / constant voltage (CC / CV) conditions at a measurement temperature of 25° C., constant voltage charging until the current value reached 0.05 C, and then discharging at 0.5 C to a lower voltage (end-of-discharge voltage) of 2.5 V under constant current (CC) conditions, and measuring the discharge capacity.

[0618] The above charge and discharge cycles were repeated 50 times to obtain the discharge capacity. The higher the discharge capacity, the better the performance of the secondary battery.

[0619] 43A shows the results of the discharge capacity when the upper limit voltage was 4.4 V, and Fig. 43B shows the results of the discharge capacity when the upper limit voltage was 4.6 V. From the results of Samples 6 to 8 in Fig. 42A and Fig. 42B, it can be seen that when lithium carbonate is used, the Li / Co ratio is preferably 1.01 or more and 1.05 or less, and more preferably 1.03 or around there.

[0620] It has been confirmed that a secondary battery using such a positive electrode active material has excellent battery characteristics such as excellent discharge capacity.

[0621] 100: Positive electrode active material, 170: Coprecipitation synthesis apparatus, 171: Reaction vessel, 172: Stirring unit, 173: Stirring motor, 175: Tank, 176: Pipe, 177: Pump, 180: Tank, 181: Pipe, 182: Pump, 186: Tank, 187: Pipe, 188: Pump, 190: Control device, 191: Reflux condenser, 192: Aqueous solution, 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 312: Wire shear, 313: ring-shaped insulator, 322: spacer, 400: secondary battery, 410: positive electrode, 411: positive electrode active material, 413: positive electrode current collector, 414: positive electrode active material layer, 420: solid electrolyte layer, 421: solid electrolyte, 430: negative electrode, 431: negative electrode active material, 433: negative electrode current collector, 434: negative electrode active material layer, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 509: outer casing, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 513: secondary battery, 5 14: terminal, 515: seal, 517: antenna, 519: layer, 529: label, 531: secondary battery pack, 540: circuit board, 550: current collector, 551: positive electrode lead or negative electrode lead, 552: negative electrode lead or positive electrode lead, 553: acetylene black, 554: graphene, 555: carbon nanotubes, 561: first positive electrode active material, 562: second positive electrode active material, 590a: circuit system, 590b: circuit system, 590: control circuit, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606 : negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 613: safety valve mechanism, 615: power storage system, 616: secondary battery, 620: control circuit, 623: wiring, 624: conductor, 626: wiring, 701: commercial power source, 703: distribution board, 705: power storage controller, 706: display, 707: general load, 708: power storage system load, 709: router, 710: drop line attachment part, 711: measurement part, 712: prediction part, 713: planning part, 750a: positive electrode, 750b: solid electrolyte layer, 750c: negative electrode, 751: electrode plate, 752: insulating tube,753: electrode plate, 761: lower member, 762: upper member, 763: holding screw, 764: wing nut, 765: O-ring, 766: insulator, 770a: packaging member, 770b: packaging member, 770c: packaging member, 771: external electrode, 772: external electrode, 773a: electrode layer, 773b: electrode layer, 790: control device, 791: power storage device, 796: underfloor space, 799: building, 880: cobalt compound, 881: lithium compound, 885: first heating, 886: second heating, 887: third heating, 889: second heating, 890: aqueous solution, 891: aqueous solution, 892: aqueous solution, 893: aqueous solution, 894: aqueous solution, 895: third heating, 896: fourth heating, 901: mixed solution, 902: mixed solution, 903: mixture, 904: composite oxide, 905: additional element source, 906: mixture, 907: composite oxide, 908: additional element source, 909: mixture, 910: additional element source, 911a: terminal, 911b: terminal, 911: mixture, 913: secondary battery, 930a: casing, 930b: casing, 930: casing, 931a: negative electrode active material layer, 931: negative electrode, 932a: positive electrode active material layer, 932: positive electrode, 933: separator, 950a : Winding body, 950: Winding body, 951: Terminal, 952: Terminal, 1300: Prismatic secondary battery, 1301a: First battery, 1301b: First battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DCDC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defogger, 1310: DCDC circuit, 1311: Second battery, 1312: Inverter, 1313: Audio, 1314: Power window, 1315: Lamps, 1316: Tire, 1317: Rear motor , 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 1324: switch section, 1413: fixed section, 1414: fixed section, 1415: battery pack, 1421: wiring, 1422: wiring, 2001: automobile, 2002: transport vehicle, 2003: transport vehicle, 2004: aircraft, 2200: battery pack, 2201: battery pack, 2202: battery pack, 2203: battery pack, 2300: unmanned aerial vehicle, 2301: secondary battery, 2302: rotor, 2303: camera, 2603: vehicle, 2604: charging device, 2610: solar panel, 2611: wiring,2612: Power storage device, 2800: Personal computer, 2801: Housing, 2802: Housing, 2803: Display unit, 2804: Keyboard, 2805: Pointing device, 2806: Secondary battery, 2807: Secondary battery, 4000a: Frame, 4000b: Display unit, 4000: Glasses-type device, 4001a: Microphone unit, 4001b: Flexible pipe, 4001c: Earphone unit, 4001: Headset-type device, 4002a: Housing, 4002b: Secondary battery, 4002: Device, 4003a: Housing, 4003b: Secondary battery, 4003: Device , 4005a: display unit, 4005b: belt unit, 4005: wristwatch type device, 4006a: belt unit, 4006b: wireless power supply receiving unit, 4006: belt type device, 6300: cleaning robot, 6301: housing, 6302: display unit, 6303: camera, 6304: brush, 6305: operation button, 6306: secondary 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: secondary battery, 7100: portable display device, 7101: housing, 7102: display unit, 7103: operation button, 7104: secondary battery, 7200: portable information terminal, 7201: housing, 7202: display unit, 7203: band, 7204: buckle, 7205: operation button, 7206: input / output terminal, 7207: icon, 7300: display device, 7304: display unit, 7400: mobile phone, 7401: housing, 7402: display unit, 7403: operation button, 7404: external connection port, 7405: speaker, 7406: microphone, 7407: secondary battery, 7500: power Dummy cigarette, 7501: atomizer, 7502: cartridge, 7504: secondary battery, 7600: tablet terminal, 7625: switch, 7627: switch, 7628: operation switch, 7629: fastener, 7630a: housing, 7630b: housing, 7630: housing, 7631a: display unit, 7631b: display unit, 7631: display unit, 7633: solar cell, 7634: charge / discharge control circuit, 7635: power storage unit, 7636: DCDC converter, 7637: converter, 7640: moving part, 7700: hair iron, 7701: handle, 7702: power switch,7703: temperature switching button, 7704: temperature lamp, 7705: plate, 7706: secondary battery, 7750: hair iron, 7751: handle, 7752: power switch, 7753: temperature switching button, 7754: temperature lamp, 7755: pipe, 7756: support bar, 7757: lever, 7758: secondary battery, 8000: display device, 8001: housing, 8002: display unit, 8003: speaker unit, 8004: secondary battery, 8100: lighting device, 8101: housing, 8102: light source, 8103: secondary battery, 810 4: ceiling, 8105: side wall, 8106: floor, 8107: window, 8200: indoor unit, 8201: housing, 8202: air outlet, 8203: secondary battery, 8204: outdoor unit, 8300: electric refrigerator-freezer, 8301: housing, 8302: refrigerator compartment door, 8303: freezer compartment door, 8304: secondary battery, 8600: scooter, 8601: side mirror, 8602: power storage device, 8603: turn signal light, 8604: under-seat storage, 8700: electric bicycle, 8701: storage battery, 8702: power storage device, 8703: display unit, 8704: control circuit,

Claims

1. reacting an aqueous cobalt solution with an aqueous alkaline solution to form a cobalt compound; mixing the cobalt compound and a lithium compound and carrying out a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element and performing a second heat treatment to form a second composite oxide; A method for producing a positive electrode active material, comprising mixing the second composite oxide with a compound having a second additive element and performing a third heat treatment, The first additional element includes Mg or F, The second additional element includes Ni or Al, The first heat treatment is performed at a temperature of 700° C. or more and 1100° C. or less, The second heat treatment is performed at a temperature of 700° C. or more and 1000° C. or less, The method for producing a positive electrode active material, wherein the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

2. reacting an aqueous cobalt solution with an alkaline aqueous solution and a chelating agent to form a cobalt compound; mixing the cobalt compound and a lithium compound and carrying out a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element and performing a second heat treatment to form a second composite oxide; A method for producing a positive electrode active material, comprising mixing the second composite oxide with a compound having a second additive element and performing a third heat treatment, The first additional element includes Mg or F, The second additional element includes Ni or Al, The first heat treatment is performed at a temperature of 700° C. or more and 1100° C. or less, The second heat treatment is performed at a temperature of 700° C. or more and 1000° C. or less, The method for producing a positive electrode active material, wherein the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

3. reacting a first mixed liquid having an aqueous cobalt solution and a first chelating agent with a second mixed liquid having an aqueous alkaline solution and a second chelating agent to form a cobalt compound; mixing the cobalt compound and a lithium compound and carrying out a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element and performing a second heat treatment to form a second composite oxide; A method for producing a positive electrode active material, comprising mixing the second composite oxide with a compound having a second additive element and performing a third heat treatment, The first additional element includes Mg or F, The second additional element includes Ni or Al, The first heat treatment is performed at a temperature of 700° C. or more and 1100° C. or less, The second heat treatment is performed at a temperature of 700° C. or more and 1000° C. or less, The method for producing a positive electrode active material, wherein the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

4. reacting a first mixture having an aqueous cobalt solution and a first chelating agent with an alkaline aqueous solution and a second chelating agent to form a cobalt compound; mixing the cobalt compound and a lithium compound and carrying out a first heat treatment to form a first composite oxide; mixing the first composite oxide with a compound having a first additive element and performing a second heat treatment to form a second composite oxide; A method for producing a positive electrode active material, comprising mixing the second composite oxide with a compound having a second additive element and performing a third heat treatment, The first additional element includes Mg or F, The second additional element includes Ni or Al, The first heat treatment is performed at a temperature of 700° C. or more and 1100° C. or less, The second heat treatment is performed at a temperature of 700° C. or more and 1000° C. or less, The method for producing a positive electrode active material, wherein the third heat treatment is performed at a temperature equal to or lower than the temperature of the second heat treatment.

5. In claim 2, The method for producing a positive electrode active material, wherein the chelating agent comprises glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole.

6. In claim 3 or claim 4, the first chelating agent comprises glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole; The method for producing a positive electrode active material, wherein the second chelating agent comprises glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole.

7. In claim 6, The method for producing a positive electrode active material, wherein the first chelating agent has the same material as the second chelating agent.

8. In any one of claims 1 to 7, the first composite oxide is crushed, and then the second heat treatment is performed to form the second composite oxide.