Method for producing positive electrode active material

Abstract

To provide a method for manufacturing a positive electrode active material of a lithium ion secondary battery.SOLUTION: A method for manufacturing a positive electrode active material includes: a first step of placing in a heating furnace, a first container in which a mixture of a lithium oxide, a fluoride and a magnesium compound is put; a second step of bringing the inside of the heating furnace into an oxygen containing atmosphere; and a third step of heating the inside of the heating furnace. The first step and the second step are executed and then, the third step is executed. It is preferable that the inside of the heating furnace is brought into the oxygen containing atmosphere before heating the inside of the heating furnace. It is more preferable that the fluoride is lithium fluoride and the magnesium compound is magnesium fluoride.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In this specification, the term "power storage device" refers to all elements and devices having a power storage function, including, for example, storage batteries (also called secondary batteries) such as lithium ion secondary batteries, lithium ion capacitors, all-solid-state batteries, and electric double layer capacitors.

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like. [Background technology]

[0004] In recent years, there has been active development of various power storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, as well as all-solid-state batteries. Demand for high-power, high-capacity lithium-ion secondary batteries has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, as they are used in a wide range of applications, including mobile phones, smartphones, laptop computers, and other portable information terminals, as well as portable music players, digital cameras, medical devices, and next-generation clean-energy vehicles, including hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs or PHEVs).

[0005] Therefore, improvements in the positive electrode active material have been investigated in order to improve the cycle characteristics and increase the capacity of lithium ion secondary batteries (Patent Documents 1 and 2).

[0006] Furthermore, the characteristics required of the power storage device include safety in various operating environments and improved long-term reliability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-018914 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-076454 [Non-patent literature]

[0008] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-patent document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2(0.0≦x≦1.0)”, Physical Review B, 80(16);165114 Summary of the Invention [Problem to be solved by the invention]

[0009] Lithium-ion secondary batteries and the cathode active materials used in them are expected to be improved in various aspects, such as capacity, cycle characteristics, charge / discharge characteristics, reliability, and safety. Therefore, the development of a lithium composite oxide, LiMO2, in which part of LiCoO2 is replaced with a different element, is underway. Furthermore, the development of a method for producing LiMO2 cheaply and quickly is also desired.

[0010] 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, a novel positive electrode active material, or a novel power storage device.

[0011] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims. [Means for solving the problem]

[0012] One embodiment of the present invention is a method for producing a positive electrode active material, which includes a first step of placing a first container containing a mixture of lithium oxide, fluoride, and a magnesium compound in a heating furnace, a second step of creating an oxygen-containing atmosphere inside the heating furnace, and a third step of heating the inside of the heating furnace, and the third step is performed after the first step and the second step.

[0013] Another embodiment of the present invention is a method for producing a positive electrode active material, which includes a first step of placing a first container containing a mixture of lithium oxide, fluoride, and a magnesium compound in a heating furnace, a second step of evacuating the inside of the heating furnace and then introducing oxygen gas, and a third step of heating the inside of the heating furnace, in which the third step is performed after the first step and the second step.

[0014] In the above structure, the fluoride is preferably lithium fluoride (LiF).

[0015] In the above configuration, it is preferable that the inside of the heating furnace is heated to 735°C or higher and 1000°C or lower.

[0016] In the above configuration, the magnesium compound is preferably magnesium fluoride (MgF2).

[0017] In the above configuration, it is preferable that the first container is covered with a lid. [Effects of the Invention]

[0018] According to one embodiment of the present invention, a manufacturing method of a positive electrode active material, novel positive electrode active material particles, and a novel power storage device can be provided. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 2] FIG. 2 is a diagram illustrating the results of DSC measurement of a mixture of LiF and MgF2. [Figure 3] 3A and 3B illustrate a method for manufacturing a positive electrode active material of one embodiment of the present invention. [Figure 4] 4A and 4B illustrate a method for manufacturing a positive electrode active material of one embodiment of the present invention. [Figure 5] 5A and 5B illustrate a method for manufacturing a positive electrode active material of one embodiment of the present invention. [Figure 6] FIG. 6 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 7] FIG. 7 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 8] FIG. 8 is a diagram illustrating an example of a method for producing a positive electrode active material. [Figure 9] FIG. 9 is a diagram illustrating the crystal structure and magnetism of the positive electrode active material. [Figure 10] FIG. 10 is a diagram illustrating the crystal structure and magnetism of a conventional positive electrode active material. [Figure 11] 11A and 11B are cross-sectional views of an active material layer in which a graphene compound is used as a conductive additive. [Figure 12] 12A and 12B are perspective views illustrating a coin-type secondary battery. [Figure 13] 13A is a perspective view illustrating a cylindrical secondary battery, FIG. 13B is an exploded perspective view, FIG. 13C is a perspective view of the cylindrical secondary battery, and FIG. 13D is a top view illustrating the cylindrical secondary battery. [Figure 14] 14A and 14B are diagrams illustrating an example of a secondary battery. [Figure 15] 15A, 15B, 15C, and 15D are perspective views illustrating examples of secondary batteries. [Figure 16] 16A and 16B are perspective views illustrating an example of a secondary battery. [Figure 17] 17A and 17B are perspective views illustrating an example of a secondary battery. [Figure 18] FIG. 18 is a perspective view illustrating an example of a secondary battery. [Figure 19] 19A, 19B, and 19C are perspective views illustrating a laminated secondary battery. [Figure 20] FIG. 20A is a top view illustrating a laminated secondary battery, and FIG. 20B is a cross-sectional view illustrating a laminated secondary battery. [Figure 21] FIG. 21 is a diagram showing the appearance of a secondary battery. [Figure 22] FIG. 22 is a diagram showing the appearance of a secondary battery. [Figure 23] 23A, 23B, and 23C are diagrams illustrating a method for manufacturing a secondary battery. [Figure 24] FIG. 24A is a top view of a bendable secondary battery, and FIGS. 24B, 24C, 24D, and 24E are cross-sectional views illustrating the secondary battery. [Figure 25] 25A and 25B are perspective views illustrating a bendable secondary battery. [Figure 26]Figures 26A and 26B are perspective views illustrating an example of an electronic device, Figure 26C is a perspective view of a secondary battery, Figure 26D is a diagram illustrating an example of an electronic device, Figure 26E is a perspective view of a secondary battery, and Figures 26F and 26G are diagrams illustrating an example of an electronic device. [Figure 27] 27A and 27B are top views illustrating an example of an electronic device, and FIG. 27C is a block diagram. [Figure 28] FIG. 28 is a diagram illustrating an example of an electronic device. [Figure 29] FIG. 29A is a perspective view of the vehicle, FIG. 29B is a perspective view showing the vehicle during charging, and FIG. 29C is a perspective view for explaining the electric motorcycle. [Figure 30] 30A and 30B are diagrams illustrating the alumina crucible used during annealing. [Figure 31] FIG. 31 is a diagram illustrating the cycle characteristics according to the example. [Figure 32] FIG. 32 is a diagram illustrating the cycle characteristics according to the example. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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.

[0021] In addition, in crystallography, crystal planes and directions are represented by numbers with a superscript bar, but in this specification and elsewhere, due to limitations on notation in applications, crystal planes and directions are represented by a minus sign (-) before the number instead of a bar above it. Also, individual directions indicating directions within a crystal are represented by [ ], collective directions indicating all equivalent directions are represented by < >, individual planes indicating crystal planes are represented by ( ), and collective planes with equivalent symmetry are represented by {}.

[0022] In this specification, the term "fluoride-containing atmosphere" refers to an atmosphere of a mixed gas containing fluoride as at least one of its constituent components.

[0023] (Embodiment 1) An example of a method for producing a lithium composite oxide LiMO2 (where M is two or more metals including Co, and there is no particular limitation on the substitution position of the metal) will be described using Figure 1. Below, we will explain an example of a positive electrode active material in which Mg is contained as a metal element other than Co in LiMO2.

[0024] First, a halogen source is prepared as a material for the mixture 902. Chloride, bromide, or iodide can be used as the halogen source, but fluoride is preferred. In this embodiment, LiF, a fluorine source, is prepared as the halogen source. LiF is preferred because it has a common cation with LiCoO. LiF can be used as both a lithium source and a fluorine source. LiF is also preferred because it has a relatively low melting point of 848°C and is easily melted in the annealing step described below. Similarly, MgF, which can also be used as a fluorine source, is preferred as a magnesium source for LiMO. LiCl and MgCl can also be used as the halogen source and magnesium source, respectively. A combination of a halogen source and a magnesium source having a eutectic point is preferred because the melting point depression described below can be utilized. The halogen source that can be used in one embodiment of the present invention is not limited to LiF and LiCl. The magnesium source that can be used in one embodiment of the present invention is not limited to MgF and MgCl.

[0025] As used herein, the term "eutectic point" refers to the point on the solid-liquid phase curve of two components where the two components completely melt and mix in the liquid state without forming a solid solution. For example, when two metal elements A and B melt together, A and B do not form a solid solution but form separate solid phases or form a molecular compound, and in the liquid phase, A and B completely melt together. If this occurs, the mixture of A and B will have a melting point lower than the melting points of A or B alone. A mixture with a certain concentration ratio of A and B will exhibit the lowest melting point, and this temperature is also referred to as the eutectic point, and this mixture is also referred to as a eutectic mixture. The eutectic point is not limited to two components, but may be three, four, or five or more components.

[0026] In this embodiment, LiF, which is a fluorine source, is prepared as the halogen source, and MgF2 is prepared as the fluorine source and magnesium source (Step S11 in FIG. 1). The molar ratio of LiF to MgF2 is preferably LiF:MgF2=u:1 (0≦u≦1.9), more preferably LiF:MgF2=u:1 (0.1≦u≦0.5), and even more preferably LiF:MgF2=u:1 (u=near 0.33).

[0027] If the subsequent mixing and grinding steps are performed wet, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, acetone is used (see step S11 in FIG. 1).

[0028] Next, the materials for the mixture 902 are mixed and pulverized (step S12 in FIG. 1). Mixing can be performed by either a dry or wet method, but a wet method is preferred because it allows for finer pulverization. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the medium. It is preferable to thoroughly perform this mixing and pulverization process to finely pulverize the mixture 902.

[0029] The mixed and crushed materials are collected (step S13 in FIG. 1) to obtain a mixture 902 (step S14 in FIG. 1).

[0030] The average particle size (D50) of the mixture 902 is preferably, for example, 600 nm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. Such a finely pulverized mixture 902 facilitates uniform adhesion of the mixture 902 to the surface of the composite oxide particles when mixed with a composite oxide containing lithium, transition metal, and oxygen, such as lithium cobalt oxide, in a subsequent process. Uniform adhesion of the mixture 902 to the surface of the composite oxide particles is preferable because it facilitates thorough distribution of halogen and magnesium throughout the surface layer of the composite oxide particles after heating. If there are regions in the surface layer that do not contain halogen and magnesium, it may be difficult to form a pseudospinel-type crystal structure, as described below, in a charged state.

[0031] <Step S25> Next, a lithium source is prepared as shown in step S25. In step S25, a composite oxide containing lithium, a transition metal, and oxygen that has been synthesized in advance is used.

[0032] When using a pre-synthesized composite oxide containing lithium, transition metals, and oxygen, it is preferable to use one with few impurities. In this specification, the main components of the composite oxide containing lithium, transition metals, and oxygen, and the positive electrode active material, are lithium, cobalt, nickel, manganese, aluminum, and oxygen, and elements other than the main components are considered impurities. For example, when analyzed by glow discharge mass spectrometry (GD-MS), the total impurity concentration is preferably 10,000 ppm wt or less, more preferably 5000 ppm wt or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppm wt or less, more preferably 1500 ppm wt or less.

[0033] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as pre-synthesized lithium cobalt oxide. This lithium cobalt oxide has an average particle diameter (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry shows that the magnesium and fluorine concentrations are 50 ppm wt or less, the calcium, aluminum, and silicon concentrations are 100 ppm wt or less, the nickel concentration is 150 ppm wt or less, the sulfur concentration is 500 ppm wt or less, the arsenic concentration is 1100 ppm wt or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppm wt or less.

[0034] The composite oxide containing lithium, a transition metal, and oxygen in step S25 preferably has a layered rock-salt crystal structure with few defects and strain. Therefore, a composite oxide with few impurities is preferred. If the composite oxide containing lithium, a transition metal, and oxygen contains a large amount of impurities, it is likely to have a crystal structure with many defects or strains.

[0035] Next, the mixture 902 is mixed with a composite oxide containing lithium, a transition metal, and oxygen (step S31 in FIG. 1). The ratio of the number of transition metal atoms TM in the composite oxide containing lithium, a transition metal, and oxygen to the number of magnesium atoms MgMix1 in the mixture 902 is preferably TM:MgMix1=1:v (0.005≦v≦0.05), more preferably TM:MgMix1=1:v (0.007≦v≦0.04), and even more preferably about TM:MgMix1=1:0.02.

[0036] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the composite oxide particles. For example, the mixing conditions are preferably lower in rotation speed or shorter in time than those in step S12. It can also be said that dry mixing conditions are milder than wet mixing. For example, a ball mill, bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the media.

[0037] The mixed materials are collected (step S32 in FIG. 1) to obtain a mixture 903 (step S33 in FIG. 1).

[0038] Next, mixture 903 is heated (step S34 in FIG. 1). This step is sometimes called annealing. By performing annealing, LiMO2 is produced. Therefore, the conditions for performing step S34, such as the temperature, time, atmosphere, and weight of mixture 903 to be annealed, are important. In this specification, annealing also means heating mixture 903 or at least heating a heating furnace in which mixture 903 is placed.

[0039] If the conditions for S34 are not appropriate, a positive electrode active material with good properties may not be obtained. Furthermore, the processing time for step S34 is often longer than that for other steps. Therefore, shortening the processing time for step S34 would enable the production of a positive electrode active material in a shorter time. Therefore, a technology for shortening the processing time for step S34 is needed.

[0040] The present inventors have found that a positive electrode active material with favorable characteristics can be manufactured by performing annealing in an atmosphere containing fluoride (LiF in this embodiment) contained in the mixture 903. They have also found that the annealing time can be shortened according to one embodiment of the present invention.

[0041] [Effect of annealing in a fluoride-containing atmosphere] The annealing temperature is preferably equal to or higher than the temperature at which mixture 902 melts. It is believed that when mixture 903 is annealed, mixture 902 melts. For example, it is believed that a mixture of MgF2 (melting point 1263°C) and LiF (melting point 848°C) melts and distributes in the surface layer of the composite oxide particles. It is believed that the melting of MgF2 promotes a reaction with LiCoO2, resulting in the production of LiMO2. Therefore, it is preferable that the fluoride and magnesium source be combined to form a eutectic mixture.

[0042] Furthermore, it is more preferable that the annealing temperature is equal to or higher than the temperature at which the mixture 903 melts. It is believed that the formation of LiMO2 is promoted by the fluoride (e.g., LiF), the magnesium source (e.g., MgF2), and the lithium oxide (e.g., LiCoO2) forming a covalent mixture.

[0043] The annealing temperature must be equal to or lower than the decomposition temperature of LiCoO2 (1130°C), so it is preferable to heat the material at a temperature equal to or higher than the eutectic point of the fluoride and the magnesium source, but equal to or lower than 1130°C.

[0044] As will be described later, the eutectic point of LiF and MgF2 is around 735°C. Furthermore, LiF, MgF2, and LiCoO2 exhibit endothermic peaks around 820°C in differential scanning calorimetry (DSC). Therefore, the annealing temperature is preferably 735°C or higher, more preferably 820°C or higher. Furthermore, the decomposition temperature of LiCoO2 is 1130°C, and there is concern that LiCoO2 may decompose, albeit in trace amounts, at temperatures around that temperature. Therefore, the annealing temperature is preferably 1130°C or lower, and more preferably 1000°C or lower.

[0045] Therefore, the annealing temperature is preferably 735° C. or higher and 1130° C. or lower, and more preferably 735° C. or higher and 1000° C. or lower. Also, the annealing temperature is preferably 820° C. or higher and 1130° C. or lower, and more preferably 820° C. or higher and 1000° C. or lower.

[0046] Here, we will explain the DSC measurement of a mixture of LiF and MgF2.

[0047] The measurement device used is ThermoplusEV02 manufactured by Rigaku Co., Ltd. The temperature range is from 25°C to 1000°C, and the temperature is increased at a rate of 20°C / min.

[0048] Figure 2 shows the results of DSC measurement of a mixture of LiF and MgF2 (LiF / MgF2 = 0.33 mol%). Figure 2 shows an endothermic peak observed near 735°C. Therefore, the mixture of LiF and MgF2 has a eutectic point near 735°C.

[0049] In addition, in this embodiment, it is believed that LiF, which is a fluoride, functions as a flux. Therefore, if LiF evaporates and the amount of LiF in the mixture 903 decreases, it is expected that MgF2 will become difficult to melt, and the generation of LiMO2 will be suppressed. Therefore, it is preferable to heat the mixture while suppressing the evaporation of LiF.

[0050] Therefore, by heating mixture 903 in an atmosphere containing LiF, that is, by heating mixture 903 in a state where the partial pressure of LiF is high in the heating furnace, the vaporization of LiF in mixture 903 can be suppressed and the generation of LiMO2 can be efficiently promoted. As a result, a positive electrode active material with good properties can be produced and the annealing time can also be shortened.

[0051] Here, the weight loss rate can be investigated experimentally when a mixture of LiF and MgF2 (LiF / MgF2 = 0.33 mol%) is heated at a predetermined temperature. The experimental method is to heat the mixture of LiF and MgF2 at 200°C / h to a predetermined temperature and hold it at that temperature for 10 hours. The temperature is then lowered over a period of 10 hours or more. The mixture is heated while oxygen is flowing at a flow rate of 2.5 L / min. The results of the weight loss rate measurement are shown in Table 1. In Table 1, the weight loss rate (%) is calculated by dividing the weight difference of the mixture before and after heating by the weight of the mixture before heating x 100.

[0052] [Table 1]

[0053] As shown in Table 1, a weight loss was observed in the mixture of LiF and MgF2 at least at 700°C. This indicates that at temperatures above 700°C, the components of LiF and MgF2 are vaporized and lost from the reaction system.

[0054] In this specification, a heating furnace is a facility used to heat-treat (anneal) a substance or mixture, and has a heater unit and an inner wall that can withstand a fluoride-containing atmosphere and at least 600° C. The heating furnace may also be equipped with a pump that has the function of at least one of reducing and increasing the pressure inside the furnace.

[0055] [Annealing in a fluoride-containing atmosphere] An example of a method for annealing in a heating furnace with an atmosphere containing a fluoride will be described with reference to FIGS. 3A and 3B.

[0056] 3A and 3B includes a furnace space 102, a hot plate 104, a heater unit 106, and a heat insulator 108. FIG. 3A shows a state in which a container 116 containing a mixture 903 is placed in the furnace space 102. The mixture 903 contains fluoride. Therefore, by heating the mixture 903 and vaporizing a portion of the fluoride contained in the mixture 903, the mixture 903 can be heated in an atmosphere containing fluoride.

[0057] Here, the valence of Co (cobalt) in LiMO2 produced according to one embodiment of the present invention is preferably trivalent. Co can be divalent or trivalent. Therefore, in order to suppress the reduction of Co, the atmosphere in the heating furnace space 102 preferably contains oxygen, and more preferably the ratio of oxygen to nitrogen in the atmosphere in the heating furnace space 102 is equal to or higher than that of the air atmosphere, and even more preferably the oxygen concentration in the atmosphere in the heating furnace space 102 is equal to or higher than that of the air atmosphere. Therefore, it is necessary to introduce an oxygen-containing atmosphere into the heating furnace space.

[0058] One possible method for introducing an oxygen-containing atmosphere into the heating furnace space 102 is to perform annealing while flowing oxygen gas from the outside. However, the molecular weight of oxygen (O2) is approximately 32, and the molecular weight of lithium fluoride (LiF) is approximately 26, so gaseous LiF is lighter than oxygen gas. Therefore, if annealing is performed while flowing oxygen gas, LiF vaporized by heating is likely to be expelled outside the heating furnace space 102, and annealing in a LiF atmosphere may not be possible.

[0059] Therefore, in one embodiment of the present invention, as shown in Figures 3A and 3B, annealing is performed in an atmosphere containing fluoride, either without flowing oxygen gas or with a lid 118 placed on the container 116, or both.

[0060] To perform annealing without flowing oxygen gas, the steps of creating an oxygen-containing atmosphere in the heating furnace space 102 and placing the container 116 containing the mixture 903 in the heating furnace space 102 are performed before heating. By performing these steps in this order, the mixture 903 can be annealed in an atmosphere containing oxygen and fluoride. Furthermore, the heating furnace space 102 is sealed during annealing to prevent gas from being transported to the outside.

[0061] Alternatively, as shown in FIG. 3B, annealing is performed with a lid 118 placed on the container 116. This configuration allows the space 119 enclosed by the container 116 and the lid 118 to be filled with a fluoride-containing atmosphere. Because the volume of the space 119 is smaller than the furnace space 102, a small amount of fluoride is vaporized, creating an atmosphere containing fluoride. That is, the reaction system can be filled with a fluoride-containing atmosphere without significantly reducing the amount of fluoride contained in the mixture 903. Therefore, LiMO2 can be efficiently produced. Furthermore, the use of the lid 118 allows the mixture 903 to be annealed in a fluoride-containing atmosphere simply and inexpensively.

[0062] By providing the lid 118, it is possible to perform annealing in an atmosphere containing a sufficient amount of fluoride without sealing the space 102 inside the heating furnace. Therefore, when the lid 118 is provided, annealing can be performed by flowing oxygen gas. In particular, it is preferable to provide the lid 118 on a deep container 116a as shown in FIGS. 3A and 3B. The deep container 116a has a relatively larger space 119a relative to the amount of mixture 903 than the shallow container 116, when the mixture 903 is placed to the same depth. Therefore, an atmosphere containing a sufficient amount of fluoride can be maintained.

[0063] It is more preferable to perform annealing without flowing oxygen gas and with the lid 118 in place.

[0064] 4A and 4B show detailed steps in the case where oxygen gas is not flowed in step S34 shown in FIG. 1. The order of the step of creating an oxygen-containing atmosphere in the heating furnace space 102 (step S34-1 in FIGS. 4A and 4B) and the step of placing the container 116 containing the mixture 903 in the heating furnace space 102 (step S34-2 in FIGS. 4A and 4B) is not particularly limited. As shown in FIG. 4B, the step of creating an oxygen-containing atmosphere in the heating furnace space 102 may be performed after placing the container 116 containing the mixture 903 in the heating furnace space 102. After these steps are performed, the step of heating the heating furnace 120 (S34-3 in FIGS. 4A and 4B) is performed.

[0065] There are no particular limitations on the method for creating an oxygen-containing atmosphere in the heating furnace space 102, but examples include a method of evacuating the heating furnace space 102 and then introducing an oxygen-containing gas such as oxygen gas or dry air, or a method of infusing an oxygen-containing gas such as oxygen gas or dry air for a certain period of time. Among these, it is preferable to evacuate the heating furnace space 102 and then introduce oxygen gas (oxygen substitution). Note that air may also be used as the oxygen-containing atmosphere.

[0066] The process of placing the container 116 containing the mixture 903 in the heating furnace space 102 is not particularly limited, but examples include a method of placing the container 116 directly in the heating furnace space 102, and a method of using an apparatus having a conveying mechanism as shown in Figure 5A and placing the container 116 in the heating furnace space 102 using the conveying mechanism.

[0067] There is no particular limitation on the process for heating the heating furnace 120. Heating may be performed using a heating mechanism provided in the heating furnace 120.

[0068] Furthermore, there are no particular limitations on how the mixture 903 is arranged when placed in the container 116, but it is preferable to arrange the mixture 903 so that the upper surface of the mixture 903 is flat with respect to the bottom surface of the container 116, in other words, so that the height of the upper surface of the mixture 903 is uniform, as shown in Figures 3A and 3B.

[0069] The annealing is preferably performed at an appropriate temperature and time. The appropriate temperature and time vary depending on conditions such as the size and composition of the composite oxide particles containing lithium, transition metal, and oxygen in step S25. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large.

[0070] For example, when the average particle size (D50) of the particles in step S25 is about 12 μm, the annealing time is preferably, for example, 3 hours or more, and more preferably 10 hours or more.

[0071] On the other hand, when the average particle size (D50) of the particles in step S25 is about 5 μm, the annealing time is preferably, for example, from 1 hour to 10 hours, and more preferably about 2 hours.

[0072] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0073] The annealed material is collected (Step S35 in FIG. 1) to obtain positive electrode active material 904 (Step S36 in FIG. 1).

[0074] An example of a heating furnace is shown in Figure 5. In Figure 5, parts having the same functions as those shown in Figure 3 are given the same hatch pattern, and the reference numerals may be omitted. Furthermore, parts having the same functions are given the same reference numerals, and detailed descriptions thereof may be omitted.

[0075] <Heating furnace configuration> The heating furnace used in one embodiment of the present invention is not particularly limited, and various heating furnaces can be used, such as batch-type and continuous-type heating furnaces, examples of which are shown in Figures 5A and 5B.

[0076] The heating furnace 130 shown in FIG. 5A is an example of a continuous heating furnace. The heating furnace 130 has a belt conveyor 132. Containers 134 containing mixture 903 are placed on the belt conveyor 132, and the mixture is treated in the heating furnace 130, allowing for continuous annealing. The annealing time can be adjusted by adjusting the speed of the belt conveyor. Furthermore, by placing fluoride 906 in one of the containers 134 and annealing it simultaneously with mixture 903, the space inside the heating furnace 102 can be filled with a fluoride atmosphere. It is preferable to cover the container 134, as in FIG. 3B. By annealing mixture 903 in the heating furnace 130, a positive electrode active material 904 can be obtained.

[0077] The heating furnace 140 shown in FIG. 5B is an example of a rotary heating furnace. The heating furnace 140 has a material input section 142, an atmosphere control section 144, and a recovery section 146. Mixture 903 is input from material input section 142 into the heating furnace interior space 102. The heating plate 104 has a mechanism for rotating, and furthermore, the heating plate 104 is inclined toward the recovery section 146. With this configuration, annealing can be performed while the mixture 903 is flowing. The annealing time can be adjusted by adjusting the inclination and rotation speed. The annealed mixture 903 is recovered in the recovery section 146, and positive electrode active material 904 can be obtained.

[0078] The atmosphere control unit 144 can also adjust the oxygen atmosphere and fluoride atmosphere in the heating furnace space 102 .

[0079] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0080] (Embodiment 2) An example of a method for producing LiMO2 will be described below. Below, a production method in which multiple metal elements are used as the metal element other than Co contained in LiMO2 will be described with reference to FIG.

[0081] <<Positive electrode active material production method 2>> FIG. 6 shows an example of a manufacturing process for LiMO2, a composite oxide containing Mg, Ni, and Al in addition to Co. In this manufacturing process, metal element sources other than Li and Co are separately mixed and pulverized, and then the pulverized metal element sources are mixed with lithium cobalt oxide and annealed. Steps S11 to S36 are the same as those described in Embodiment 1 and FIG. 1. In other words, in step S34, mixture 903-2 is preferably annealed in an atmosphere containing LiF. Positive electrode active material 904-2 can be obtained by the manufacturing process shown in FIG. 6.

[0082] <Steps S15, S16, and S17> Also, finely pulverized nickel hydroxide (Ni(OH)2) is prepared for mixing in step S31. The finely pulverized nickel hydroxide is previously subjected to step S15, in which nickel hydroxide is mixed with acetone, and step S16, in which the finely pulverized nickel hydroxide is recovered. Step S16 results in the finely pulverized nickel hydroxide (step S17).

[0083] <Steps S18, S19, and S20> Furthermore, finely pulverized aluminum hydroxide (Al(OH)3) is prepared for mixing in step S31. The finely pulverized aluminum hydroxide is previously subjected to step S18 in which aluminum hydroxide is mixed with acetone and step S19 in which it is collected. By step S19, finely pulverized aluminum hydroxide is obtained (step S20).

[0084] In the above steps S15 to S20, nickel hydroxide is used as the nickel (Ni) source and aluminum hydroxide is used as the aluminum (Al) source, but the nickel source and aluminum source are not limited to these. Oxides or halides containing the respective elements can also be used.

[0085] <<Positive electrode active material production method 3>> FIG. 7 shows an example of a process for producing a composite oxide containing Mg, Ni, and Al in addition to Co as LiMO2. In this production method, metal element sources other than Li and Co are simultaneously mixed (S21), pulverized, mixed with lithium cobalt oxide, and annealed. Steps S31 to S35 are the same as those described in Embodiment 1 and FIG. 1. That is, in step S34, it is preferable to anneal mixture 903-3 in an atmosphere containing LiF. Positive electrode active material 904-3 can be obtained by the production process shown in FIG. 7.

[0086] <Steps S22 to S24> As in steps S15 to S17 and steps S18 to S20 described above, finely pulverized MgF, Ni(OH), and Al(OH) are prepared. The finely pulverized aluminum hydroxide is previously subjected to step S22, in which the aluminum hydroxide is mixed with acetone, and step S23, in which the aluminum hydroxide is collected. Step S22 yields a finely pulverized mixture 902-3 (step S24).

[0087] <<Method 4 for preparing positive electrode active material>> FIG. 8 shows an example of a process for producing a composite oxide containing Mg, Ni, and Al as LiMO2 in addition to Co. In this production method, a composite oxide containing Mg, LiMO2, is produced, and then a Ni source and an Al source are added to produce a composite oxide containing Mg, Ni, and Al. Steps S11 to S14 and S31 to S36 are the same as those described in Embodiment 1 and FIG. 1. That is, in step S34, it is preferable to anneal mixture 903 in an atmosphere containing LiF. Steps S15 to S17 are as described with reference to FIG. 6. Positive electrode active material 904-4 can be obtained by the production process shown in FIG. 8.

[0088] As shown in step S50, positive electrode active material 904 and pulverized nickel hydroxide are mixed. Then, the mixed material is recovered (step S51). The pulverized nickel hydroxide is previously subjected to step S15 in which nickel hydroxide is mixed with acetone and step S16 in which it is recovered. By step S16, pulverized nickel hydroxide is obtained (step S17).

[0089] The materials mixed in step S50 are collected in step S51 to obtain a mixture 908 (step S52 in FIG. 8).

[0090] Next, Al is added through steps S53 to S55. Al can be added by a liquid phase method such as a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, or the like.

[0091] As shown in Fig. 8, first, in step S52, a metal source is prepared. If a sol-gel method is used, a solvent to be used in the sol-gel method is prepared. Examples of Al sources that can be used include Al alkoxide, Al hydroxide, and Al oxide. The aluminum concentration in the metal source should be 0.001 to 0.02 times the number of cobalt atoms in lithium cobalt oxide, which is 1.

[0092] Here, as an example, a sol-gel method is applied, and an example is shown in which aluminum isopropoxide is used as the metal source and 2-propanol is used as the solvent.

[0093] Next, aluminum alkoxide is dissolved in 2-propanol, and the mixture 905 is further mixed (step S53 in FIG. 8).

[0094] The amount of metal alkoxide required varies depending on the particle size of the lithium cobalt oxide. For example, when aluminum isopropoxide is used and the particle size (D50) of the lithium cobalt oxide is about 20 μm, it is preferable to add aluminum isopropoxide so that the concentration of aluminum in the lithium cobalt oxide is 0.001 to 0.02 times the number of cobalt atoms in the lithium cobalt oxide.

[0095] Next, the mixture of the alcohol solution of the metal alkoxide and the lithium cobalt oxide particles is stirred in a moist atmosphere. Stirring can be performed, for example, using a magnetic stirrer. The stirring time is sufficient to cause hydrolysis and polycondensation reactions between the water and metal alkoxide in the atmosphere, and can be performed, for example, for 4 hours at 25°C and 90% RH (relative humidity). Stirring can also be performed in an atmosphere without humidity or temperature control, such as in the air in a draft chamber. In such cases, a longer stirring time is preferable, for example, 12 hours or more at room temperature.

[0096] By reacting the metal alkoxide with moisture in the atmosphere, the sol-gel reaction can proceed more slowly than when liquid water is added. Furthermore, by reacting the metal alkoxide with water at room temperature, the sol-gel reaction can proceed more slowly than when, for example, heating is performed at a temperature above the boiling point of the solvent alcohol. Proceeding the sol-gel reaction slowly allows the formation of a high-quality coating layer with a uniform thickness.

[0097] A precipitate is recovered from the mixed solution after the above treatment (step S54 in FIG. 8). Recovery methods that can be used include filtration, centrifugation, and evaporation to dryness. The precipitate can be washed with the same alcohol as the solvent in which the metal alkoxide was dissolved. When evaporation to dryness is used, it is not necessary to separate the solvent and the precipitate in this step; for example, the precipitate can be recovered in the drying process of the next step (step S54).

[0098] Next, the collected residue is dried to obtain a mixture 909 (Step S55 in FIG. 8). The drying process can be performed, for example, by vacuum or ventilation drying at 80° C. for 1 hour to 4 hours.

[0099] Next, the resulting mixture is heated (Step S56 in FIG. 8).

[0100] The heating time is preferably set to a holding time within the heating temperature range of 1 hour to 80 hours.

[0101] The heating temperature is less than 1000°C, preferably 700°C or higher and 950°C or lower, and more preferably about 850°C.

[0102] The heating is preferably carried out in an atmosphere containing oxygen.

[0103] In this embodiment, the heating temperature is set to 850° C. and is maintained for two hours, the temperature is increased at 200° C. / h, and the oxygen flow rate is set to 10 L / min.

[0104] The heating temperature in step S56 is preferably lower than the heating temperature in step S34.

[0105] <Steps S57 and S58> Next, the cooled particles are collected (Step S57 in FIG. 8). Furthermore, it is preferable to sieve the particles. Through the above steps, positive electrode active material 904-4 can be produced (Step S58 in FIG. 8).

[0106] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0107] (Embodiment 3) In this embodiment, an example of a structure of a positive electrode active material manufactured by a manufacturing method of one embodiment of the present invention will be described.

[0108] [Positive electrode active material structure] Materials having a layered rock salt-type crystal structure such as lithium cobalt oxide (LiCoO₂) are known to have a high discharge capacity and be excellent as a positive electrode active material for secondary batteries. Examples of materials having a layered rock salt-type crystal structure include composite oxides represented by LiMO₂. Examples of the element M include one or more selected from Co or Ni. Further, examples of the element M include one or more selected from Al and Mg in addition to one or more selected from Co and Ni.

[0109] It is known that the Jahn-Teller effect in transition metal compounds varies in strength depending on the number of electrons in the d orbitals of the transition metal.

[0110] In compounds having nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charging and discharging at a high voltage in LiNiO₂, there is a concern that the crystal structure may collapse due to distortion. It is suggested that the influence of the Jahn-Teller effect is small in LiCoO₂, and it may be more excellent in resistance to charging and discharging at a high voltage, which is preferable.

[0111] The positive electrode active material will be described using FIGS. 9 and 10. FIGS. 9 and 10 describe the case where cobalt is used as the transition metal included in the positive electrode active material.

[0112] For the positive electrode active material produced in one aspect of the present invention, the shift of the CoO₂ layer can be reduced in repeated charging and discharging at a high voltage. Further, the volume change can be reduced. Therefore, the compound can achieve excellent cycle characteristics. Further, the compound can have a stable crystal structure in a charged state at a high voltage. Therefore, when the compound maintains a charged state at a high voltage, a short circuit is less likely to occur. In such a case, since the safety is further improved, it is preferable.Especially, for the compound represented by the chemical formula Li (1-x-y) Co (1-a-b) Ni (x+a) Mg (y+b) O₂, it is preferable because the characteristics are good when 0 < x + a ≤ 0.015 and 0 < y + b ≤ 0.06.

[0113] In this compound, the change in crystal structure and the difference in volume between a fully discharged state and a high-voltage charged state are small when compared per the same number of transition metal atoms.

[0114] The crystal structure of positive electrode active material 904 before and after charge and discharge is shown in Figure 9. Positive electrode active material 904 is a composite oxide containing lithium, cobalt, and oxygen. In addition to the above, it preferably contains magnesium. It also preferably contains halogen such as fluorine or chlorine. It also preferably contains aluminum and nickel.

[0115] The crystal structure at a charge depth of 0 (discharged state) in Figure 9 is the same as that in Figure 10, R-3m(O3). On the other hand, when the positive electrode active material 904 is fully charged, it has a crystal structure different from the H1-3 crystal structure. This structure belongs to the space group R-3m. Although it is not a spinel crystal structure, ions such as cobalt and magnesium occupy the oxygen hexacoordination sites, and the cation arrangement has a symmetry similar to that of a spinel structure. Therefore, this structure is referred to as a pseudo-spinel crystal structure in this specification. In the pseudo-spinel crystal structure shown in Figure 9, lithium is omitted to explain the symmetry of the cobalt atoms and the oxygen atoms. However, in reality, lithium is present between the CoO2 layers at, for example, 20 atomic % or less relative to cobalt. In both the O3 crystal structure and the pseudo-spinel crystal structure, magnesium is preferably present in a dilute form between the CoO2 layers, i.e., at the lithium sites. Furthermore, halogens such as fluorine may be present randomly and dilutely at the oxygen sites.

[0116] In addition, in the pseudospinel crystal structure, light elements such as lithium may occupy the oxygen tetracoordination site, and in this case too, the arrangement of ions has a symmetry similar to that of the spinel structure.

[0117] It can also be said that the pseudospinel crystal structure has random Li between the layers, but is similar to the CdCl2 crystal structure. This CdCl2-like crystal structure was observed when lithium nickel oxide was charged to a depth of charge of 0.94 (Li 0.06 The crystal structure is similar to that of lithium cobaltate (NiO2), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0118] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in pseudospinel crystals also have a cubic close-packed structure. When these crystals contact, there are crystal planes where the cubic close-packed structures formed by the anions are aligned. However, the space group of layered rock salt crystals and pseudospinel crystals is R-3m, which is different from the space groups of rock salt crystals, Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and pseudospinel crystals and rock salt crystals. In this specification, when the cubic close-packed structures formed by the anions are aligned in layered rock salt crystals, pseudospinel crystals, and rock salt crystals, the crystal orientations may be said to be approximately aligned.

[0119] In positive electrode active material 904, when a large amount of lithium is released during high-voltage charging, the change in the crystal structure is suppressed more than in positive electrode active material 100C, which will be described later. For example, as shown by the dotted line in Figure 9, there is almost no displacement of the CoO layers in these crystal structures.

[0120] More specifically, the cathode active material 904 exhibits high structural stability even at high charging voltages. For example, the cathode active material 100C exhibits a charging voltage range where the R-3m(O3) crystal structure can be maintained even at charging voltages where the H1-3 crystal structure is formed, e.g., at approximately 4.6 V relative to the potential of lithium metal. Furthermore, even at higher charging voltages, e.g., at voltages of approximately 4.65 V to 4.7 V relative to the potential of lithium metal, a pseudo-spinel crystal structure can be formed. Furthermore, the H1-3 crystal structure may only be observed at higher charging voltages. In a secondary battery, for example, when graphite is used as the anode active material, a charging voltage range where the R-3m(O3) crystal structure can be maintained exists even at secondary battery voltages of 4.3 V to 4.5 V, and a pseudo-spinel crystal structure can be formed even at higher charging voltages, e.g., at voltages of 4.35 V to 4.55 V relative to the potential of lithium metal.

[0121] Therefore, the crystal structure of the positive electrode active material 904 is not easily broken even when charging and discharging are repeated at a high voltage.

[0122] The pseudospinel crystal structure can be expressed by the coordinates of cobalt and oxygen in the unit cell being Co(0,0,0.5), O(0,0,x), with 0.20≦x≦0.25.

[0123] Magnesium, which is present randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, has the effect of suppressing the displacement of the CoO2 layers. Therefore, the presence of magnesium between the CoO2 layers tends to form a pseudo-spinel crystal structure. Therefore, it is preferable that magnesium be distributed throughout the particles of the positive electrode active material 100A-1. In addition, to distribute magnesium throughout the particles, it is preferable to perform a heat treatment during the production process of the positive electrode active material 100A-1.

[0124] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that magnesium will enter the cobalt site. If magnesium is present at the cobalt site, it will no longer be effective in maintaining the R-3m structure. Furthermore, if the heat treatment temperature is too high, there are concerns that adverse effects such as cobalt being reduced to a divalent state and lithium evaporating may occur.

[0125] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment to distribute magnesium throughout the particles. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium throughout the particles at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0126] Note that increasing the magnesium concentration above a desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the positive electrode active material prepared according to one embodiment of the present invention is preferably 0.001 to 0.1 times the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably approximately 0.02. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the preparation of the positive electrode active material.

[0127] The number of nickel atoms in the positive electrode active material 904 is preferably 7.5% or less of the number of cobalt atoms, preferably 0.05% to 4%, and more preferably 0.1% to 2%. 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, ICP-MS or the like, or may be based on a value of the composition of raw materials in the process of producing the positive electrode active material.

[0128] ≪Particle size≫ If the particle size of the positive electrode active material 904 is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte occur. Therefore, the average particle size (D50: also referred to as median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0129] <Analysis method> Whether a certain positive electrode active material exhibits a pseudospinel crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred because it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0130] As mentioned above, the positive electrode active material 904 is characterized by minimal change in its crystal structure between the high-voltage charged and discharged states. Materials with a crystal structure that exhibits significant changes between the high-voltage charged and discharged states at 50 wt% or more are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that the desired crystal structure may not be achieved simply by adding impurity elements. For example, even if both materials share the common feature of being lithium cobalt oxide containing magnesium and fluorine, there are cases in which the pseudo-spinel crystal structure accounts for 60 wt% or more and cases in which the H1-3 crystal structure accounts for 50 wt% or more when charged at a high voltage. Furthermore, at a certain voltage, the pseudo-spinel crystal structure may be nearly 100 wt%, and further increasing the voltage may result in the H1-3 crystal structure. Therefore, it is preferable to analyze the crystal structure of the positive electrode active material 904 using XRD or other methods.

[0131] However, when positive electrode active materials are charged or discharged at high voltage, their crystal structure may change when exposed to air. For example, they may change from a pseudospinel crystal structure to an H1-3 crystal structure. Therefore, it is recommended that all samples be handled in an inert atmosphere, such as an argon-containing atmosphere.

[0132] <Comparative Example Positive Electrode Active Material 100C> The positive electrode active material 100C shown in Fig. 10 is lithium cobalt oxide (LiCoO) to which no halogen or magnesium is added using a manufacturing method described later. As described in Non-Patent Documents 1 and 2, the crystal structure of the lithium cobalt oxide shown in Fig. 10 changes depending on the depth of charge.

[0133] As shown in Figure 10, lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, with three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is six-coordinated with oxygen, and the layers are connected in a plane with edge sharing.

[0134] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0135] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.88 has a crystal structure of the space group R-3m. This structure can be described as a structure in which a CoO2 structure such as P-3m1(O1) and a LiCoO2 structure such as R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes referred to as an H1-3 crystal structure. In reality, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 10 and other parts of this specification, for ease of comparison with other structures, the c-axis of the H1-3 crystal structure is shown as half the unit cell.

[0136] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 type crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the pseudospinel type crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the pseudospinel structure and the H1-3 type structure, and that the pseudospinel structure changes less from the O3 structure than the H1-3 type structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (goodness of fit) value is smaller in Rietveld analysis of XRD.

[0137] When lithium cobalt oxide is repeatedly charged and discharged at a high voltage of 4.6 V or higher, based on the redox potential of lithium metal, or at a deep charge depth of 0.8 or higher, the crystal structure of the lithium cobalt oxide changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0138] However, these two crystal structures have a large deviation in the CoO2 layers. As shown by the dotted lines and arrows in Figure 10, in the H1-3 type crystal structure, the CoO2 layers are significantly deviated from the R-3m(O3) structure. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0139] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the O3 crystal structure in the discharged state is more than 3.0%.

[0140] In addition, the continuous CoO2 layer structure, such as P-3m1(O1), which is contained in the H1-3 type crystal structure, is likely to be unstable.

[0141] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is thought to be because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0142] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0143] (Fourth embodiment) In this embodiment, examples of materials that can be used in a secondary battery including a positive electrode active material manufactured by a manufacturing method of one embodiment of the present invention will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an outer casing will be described as an example.

[0144] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector.

[0145] <Cathode active material layer> The positive electrode active material layer contains positive electrode active material particles and may also contain a conductive additive and a binder.

[0146] The positive electrode active material particles can be a positive electrode active material produced by a production method according to one embodiment of the present invention.

[0147] The conductive additive may be a carbon material, a metal material, a conductive ceramic material, or the like. Alternatively, a fibrous material may be used as the conductive additive. The content of the conductive additive relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, more preferably 1 wt% to 5 wt%.

[0148] The conductive additive can form an electrically conductive network in the electrode. The conductive additive can maintain an electrical conduction path between the positive electrode active materials. By adding the conductive additive to the active material layer, an active material layer with high electrical conductivity can be realized.

[0149] Examples of the conductive additive include natural graphite, artificial graphite such as mesocarbon microbeads, and carbon fibers. Examples of the carbon fibers that can be used include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Examples of the carbon fibers that can be used include carbon nanofibers and carbon nanotubes. Carbon nanotubes can be produced by, for example, vapor phase growth methods. Examples of the conductive additive include carbon materials such as carbon black (e.g., acetylene black (AB)), graphite particles, graphene, and fullerene. Examples of the conductive additive include metal powders and metal fibers such as copper, nickel, aluminum, silver, and gold, and conductive ceramic materials.

[0150] A graphene compound may also be used as the conductive additive.

[0151] Graphene compounds may have excellent electrical properties, such as high electrical conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds also have a planar shape. Graphene compounds enable surface contact with low contact resistance. Even when thin, they can have very high electrical conductivity, allowing a small amount to efficiently form a conductive path within the active material layer. Therefore, using graphene compounds as conductive additives is preferable because it increases the contact area between the active material and the conductive additive. It is also preferable because it can reduce electrical resistance. Here, graphene, multigraphene, or reduced graphene oxide (hereinafter, RGO) is particularly preferable as the graphene compound. Here, RGO refers to a compound obtained by reducing graphene oxide (GO).

[0152] When using active material particles with a small particle size, for example, active material particles of 1 μm or less, the specific surface area of ​​the active material particles is large, and more conductive paths connecting the active material particles are required. In such cases, it is particularly preferable to use a graphene compound that can efficiently form conductive paths even in a small amount.

[0153] As an example, a cross-sectional configuration example in which a graphene compound is used as a conductive additive in the active material layer 200 will be described below.

[0154] FIG. 11A shows a longitudinal cross-sectional view of an active material layer 200. FIG. 11B is an enlarged view of the area surrounded by the dotted line in FIG. 11A. The active material layer 200 includes a granular positive electrode active material 101, a graphene compound 201 as a conductive additive, and a binder (not shown). Here, graphene or multi-graphene may be used as the graphene compound 201. Here, the graphene compound 201 preferably has a sheet-like shape. Alternatively, the graphene compound 201 may be a sheet-like shape formed by partially overlapping a plurality of multi-graphenes and / or a plurality of graphenes.

[0155] 11A , in a longitudinal cross section of the active material layer 200, sheet-like graphene compounds 201 are dispersed approximately uniformly within the active material layer 200. In FIG. 11A , the graphene compounds 201 are schematically represented by thick lines, but in reality, they are thin films having a thickness corresponding to a single layer or multiple layers of carbon molecules. The plurality of graphene compounds 201 are formed so as to wrap around or cover the plurality of granular positive electrode active material 101 or to be attached to the surfaces of the plurality of granular positive electrode active material 101, and thus are in surface contact with one another.

[0156] Here, a plurality of graphene compounds are bonded together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When an active material is covered with a graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or no binder is required, and the ratio of the active material to the electrode volume or weight can be improved. In other words, the capacity of the power storage device can be increased.

[0157] Here, it is preferable to use graphene oxide as the graphene compound 201, mix it with an active material to form a layer that will become the active material layer 200, and then reduce it. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene compound 201, it is possible to disperse the graphene compound 201 approximately uniformly inside the active material layer 200. Since the solvent is removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compound 201 remaining in the active material layer 200 is dispersed to the extent that it partially overlaps and is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of the graphene oxide may be performed by, for example, heat treatment or using a reducing agent.

[0158] Therefore, unlike a granular conductive additive such as acetylene black that makes point contact with the active material, the graphene compound 201 enables surface contact with low contact resistance, and therefore can improve the electrical conductivity between the granular positive electrode active material 101 and the graphene compound 201 with a smaller amount than that of a typical conductive additive. Thus, the proportion of the positive electrode active material 101 in the active material layer 200 can be increased. This can increase the discharge capacity of the power storage device.

[0159] 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. Also, fluororubber can be used as the binder.

[0160] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of water-soluble polymers that can be used include polysaccharides. Examples of polysaccharides 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.

[0161] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, 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 as the binder.

[0162] The binder may be used in combination with two or more of the above.

[0163] For example, a material with 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 particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with particularly excellent viscosity adjusting effect. Furthermore, as water-soluble polymers with particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose derivatives such as regenerated cellulose, and starch may be used.

[0164] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium salts or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials and other components when preparing electrode slurry. In this specification, the cellulose and cellulose derivatives used as electrode binders also include their salts.

[0165] Water-soluble polymers stabilize viscosity by dissolving in water, and can stably disperse active materials and 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 groups and carboxyl groups. Because of these functional groups, the polymers are expected to interact with each other and widely cover the surface of the active material.

[0166] 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 have the effect of suppressing 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 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.

[0167] <Positive electrode current collector> The positive electrode 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 positive electrode 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, or expanded metal, as appropriate. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0168] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive additive and a binder.

[0169] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0170] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. For this reason, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions through alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called alloy-based materials.

[0171] 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.

[0172] 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.

[0173] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0174] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and a higher level of safety compared to lithium metal.

[0175] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0176] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0177] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0178] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 , sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0179] 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.

[0180] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0181] [Electrolyte] The electrolytic solution contains a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, or sultone, or any combination and ratio of two or more of these.

[0182] 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 rises due to an internal short circuit or overcharging of the electricity storage device. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0183] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these.

[0184] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular dust and 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.

[0185] The electrolyte may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0186] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0187] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0188] 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.

[0189] In addition, instead of an electrolyte solution, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymer materials such as polyethylene oxide (PEO) 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, there is no risk of leakage, dramatically improving safety.

[0190] Therefore, the cathode active material manufactured by the manufacturing method of one embodiment of the present invention can be applied to an all-solid-state battery. By applying the cathode active material to an all-solid-state battery, an all-solid-state battery with high safety and excellent characteristics can be obtained.

[0191] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0192] (Embodiment 5) In this embodiment, an example of the shape of a secondary battery including a positive electrode active material manufactured by the manufacturing method described in the previous embodiment will be described. The description in the previous embodiment can be referred to for the material used in the secondary battery described in this embodiment.

[0193] [Coin-type secondary battery] First, an example of a coin-type secondary battery will be described. Fig. 12A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 12B is a cross-sectional view thereof.

[0194] In a 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.

[0195] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0196] Positive electrode can 301 and 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, it is preferable to coat them with nickel, aluminum, or the like. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0197] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 12B, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via gasket 303 to produce coin-type secondary battery 300.

[0198] By using the positive electrode active material particles described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can be made less susceptible to deterioration and highly safe.

[0199] [Separator] The secondary battery preferably has a separator. Examples of the separator include fibers containing cellulose, such as paper, nonwoven fabrics, glass fibers, ceramics, and synthetic fibers made of nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably formed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0200] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0201] 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.

[0202] 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.

[0203] 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.

[0204] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Figures 13A to 13D. As shown in Figures 13A and 13B, a cylindrical secondary battery 600 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.

[0205] FIG. 13B is a schematic diagram showing the cross section of a cylindrical secondary battery. Inside a hollow cylindrical battery can 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. 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 that is corrosion-resistant to the electrolyte, such as nickel, aluminum, or titanium, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel). Furthermore, a coating of nickel, aluminum, or the like is preferable to prevent corrosion by the electrolyte. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The non-aqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0206] Because 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. 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 612, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO3) based semiconductor ceramics or the like can be used for the PTC element.

[0207] 13C , a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between conductive plates 613 and 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in series after being connected in parallel. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0208] FIG. 13D is a top view of a module 615. For clarity, the conductive plate 613 is shown with a dotted line. As shown in FIG. 13D, the module 615 may have conductive wires 616 that electrically connect the multiple secondary batteries 600. The conductive plate 613 can be provided by overlapping the conductive wires 616. A temperature control device 617 may also be provided between the multiple secondary batteries 600. When the secondary batteries 600 are overheated, they can be cooled by the temperature control device 617, and when the secondary batteries 600 are too cold, they can be heated by the temperature control device 617. This makes it less likely that the performance of the module 615 will be affected by the outside temperature.

[0209] By using the positive electrode active material manufactured by the manufacturing method described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 can be one that is less susceptible to deterioration and has high safety.

[0210] [Structure example of power storage device] Another structural example of the power storage device will be described with reference to FIGS.

[0211] 14A and 14B are diagrams showing the appearance of a power storage device. The power storage device has a circuit board 900 and a secondary battery 913. A label 910 is attached to the secondary battery 913. Furthermore, as shown in FIG. 14B, the power storage device has a terminal 951, a terminal 952, an antenna 914, and an antenna 915.

[0212] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to a terminal 951, a terminal 952, an antenna 914, an antenna 915, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0213] The circuit 912 may be provided on the back surface of the circuit board 900. The antennas 914 and 915 are not limited to being coil-shaped, and may be, for example, wire-shaped or plate-shaped. Also, antennas such as a planar antenna, an aperture antenna, a traveling-wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 or 915 may be a flat-plate conductor. This flat-plate conductor can function as one of the conductors for electric field coupling. In other words, the antenna 914 or 915 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.

[0214] The line width of the antenna 914 is preferably larger than the line width of the antenna 915. This allows the amount of power received by the antenna 914 to be increased.

[0215] The power storage device includes a layer 916 between the antenna 914, the antenna 915, and the secondary battery 913. The layer 916 has a function of shielding, for example, an electromagnetic field generated by the secondary battery 913. The layer 916 can be formed using, for example, a magnetic material.

[0216] The structure of the power storage device is not limited to that shown in FIG.

[0217] For example, as shown in Figures 15A and 15B, an antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 14A and 14B. Figure 15A is an external view of the pair of surfaces as seen from one side, and Figure 15B is an external view of the pair of surfaces as seen from the other side. Note that the description of the power storage device shown in Figures 14A and 14B can be used as appropriate for the same parts as those of the power storage device shown in Figures 14A and 14B.

[0218] 15A, an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 sandwiched therebetween, and as shown in Fig. 15B, an antenna 915 is provided on the other of the pair of surfaces of the secondary battery 913 with a layer 917 sandwiched therebetween. The layer 917 has a function of shielding, for example, an electromagnetic field caused by the secondary battery 913. The layer 917 can be made of, for example, a magnetic material.

[0219] By using the above structure, the size of both the antenna 914 and the antenna 915 can be increased.

[0220] Alternatively, as shown in Figures 15C and 15D, a separate antenna may be provided on each of a pair of opposing surfaces of secondary battery 913 shown in Figures 14A and 14B. Figure 15C is an external view of the pair of surfaces as seen from one side, and Figure 15D is an external view of the pair of surfaces as seen from the other side. Note that the description of the power storage device shown in Figures 14A and 14B can be used as appropriate for the same parts as those of the power storage device shown in Figures 14A and 14B.

[0221] 15C , antennas 914 and 915 are provided on one of a pair of surfaces of secondary battery 913 with layer 916 sandwiched therebetween, and as shown in FIG. 15D , antenna 918 is provided on the other of the pair of surfaces of secondary battery 913 with layer 917 sandwiched therebetween. Antenna 918 has a function of, for example, performing data communication with an external device. For example, an antenna having a shape applicable to antennas 914 and 915 can be used as antenna 918. As a communication method between the power storage device and another device via antenna 918, a response method that can be used between the power storage device and another device, such as NFC, can be used.

[0222] 16A, a display device 920 may be provided on the secondary battery 913 shown in FIGS. 14A and 14B. The display device 920 is electrically connected to a terminal 911 via a terminal 919. Note that the label 910 does not need to be provided on the portion where the display device 920 is provided. Note that the description of the power storage device shown in FIGS. 14A and 14B can be used as appropriate for the same portions as those of the power storage device shown in FIGS. 14A and 14B.

[0223] The display device 920 may display, for example, an image indicating whether charging is in progress or an image indicating the amount of stored power. For example, electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used as the display device 920. For example, by using electronic paper, the power consumption of the display device 920 can be reduced.

[0224] 16B, a sensor 921 may be provided in the secondary battery 913 shown in FIGS. 14A and 14B. The sensor 921 is electrically connected to the terminal 911 via a terminal 922. Note that the description of the power storage device shown in FIGS. 14A and 14B can be used as appropriate for the same parts as those of the power storage device shown in FIGS. 14A and 14B.

[0225] The sensor 921 may have a function of measuring, for example, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared ray. By providing the sensor 921, for example, data indicating the environment in which the power storage device is placed (such as temperature) can be detected and stored in the memory in the circuit 912.

[0226] Furthermore, an example of the structure of the secondary battery 913 will be described with reference to FIGS.

[0227] A secondary battery 913 shown in Fig. 17A has a wound body 950 in which terminals 951 and 952 are provided inside a housing 930. The wound body 950 is impregnated with 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. 17A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (such as aluminum) or a resin material.

[0228] 17B, ​​the housing 930 shown in Fig. 17A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 17B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0229] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking by the housing 930a is small, antennas such as the antenna 914 and the antenna 915 may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0230] 18 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 a plurality of layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0231] 14 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG.

[0232] By using the positive electrode active material particles described in the above embodiment for the positive electrode 932, the secondary battery 913 can be less susceptible to deterioration and highly safe.

[0233] [Laminated secondary battery] Next, examples of laminated secondary batteries will be described with reference to Figures 19 to 24. If a laminated secondary battery has a flexible configuration, and is mounted in an electronic device having at least a flexible portion, the secondary battery can also be bent in accordance with deformation of the electronic device.

[0234] 19A to 19C, a laminated secondary battery 980 will be described. The laminated secondary battery 980 has a wound body 993 shown in FIG. 19A. The wound body 993 has a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950 described in FIG. 18, the wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 on top of each other with the separator 996 sandwiched therebetween, and winding the laminated sheet.

[0235] The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed depending on the required capacity and element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0236] 19B, a film 981 serving as an exterior body and a film 982 having a recess are bonded together by thermocompression or the like to form a space, and the above-described wound body 993 is stored in the space, thereby producing a secondary battery 980 as shown in Fig. 19C. The wound body 993 has lead electrodes 997 and 998, and is impregnated with an electrolyte solution between the film 981 and the film 982 having a recess.

[0237] For example, a metal material such as aluminum or a resin material can be used for film 981 and film 982 having recesses. If a resin material is used as the material for film 981 and film 982 having recesses, film 981 and film 982 having recesses can be deformed when an external force is applied, and a flexible secondary battery can be produced.

[0238] Although FIGS. 19B and 19C show an example in which two films are used, a space may be formed by folding one film, and the wound body 993 described above may be housed in that space.

[0239] By using the positive electrode active material particles described in the above embodiment for the positive electrode 995, the secondary battery 980 can be one that is less susceptible to deterioration and has high safety.

[0240] 19A to 19C illustrate an example of a secondary battery 980 having a wound body in a space formed by a film that serves as an outer casing. However, as shown in FIG. 20, the secondary battery may have a plurality of rectangular positive electrodes, separators, and negative electrodes in a space formed by a film that serves as an outer casing.

[0241] 20A includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolyte 508, and an exterior body 509. The separator 507 is disposed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. The exterior body 509 is filled with the electrolyte 508. The electrolyte solution described in Embodiment 2 can be used as the electrolyte solution 508.

[0242] 20A , the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged so as to be partially exposed to the outside from the exterior body 509. Alternatively, the positive electrode current collector 501 and the negative electrode current collector 504 may not be exposed to the outside from the exterior body 509, and a lead electrode may be used to ultrasonically bond the positive electrode current collector 501 or the negative electrode current collector 504 to the outside, thereby exposing the lead electrode to the outside.

[0243] In the laminated secondary battery 500, the exterior body 509 can be a three-layer laminate film having a highly flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and further having an insulating synthetic resin film made of polyamide-based resin, polyester-based resin, or the like provided on the metal thin film as the outer surface of the exterior body.

[0244] 20B shows an example of the cross-sectional structure of laminated secondary battery 500. For simplicity, Fig. 20A shows an example configured with two current collectors, but in reality, it is configured with multiple electrode layers.

[0245] In FIG. 20B, the number of electrode layers is 16 as an example. Note that even if the number of electrode layers is 16, the secondary battery 500 remains flexible. FIG. 20B shows a structure with a total of 16 layers, including eight layers of negative electrode current collectors 504 and eight layers of positive electrode current collectors 501. Note that FIG. 20B also shows a cross section of the negative electrode lead-out portion, in which eight layers of negative electrode current collectors 504 are ultrasonically bonded. Of course, the number of electrode layers is not limited to 16 and may be more or less. When the number of electrode layers is large, a secondary battery with a larger capacity can be obtained. Furthermore, when the number of electrode layers is small, a secondary battery can be made thinner and have excellent flexibility.

[0246] 21 and 22 show an example of an external view of a laminated secondary battery 500. The battery 500 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.

[0247] FIG. 23A shows an external view of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area and shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 23A.

[0248] [Method for manufacturing laminated secondary batteries] Here, an example of a method for manufacturing the laminated secondary battery whose external view is shown in FIG. 21 will be described with reference to FIGS. 23B and 23C.

[0249] First, the negative electrode 506, the separator 507, and the positive electrode 503 are stacked. FIG. 23B shows the stacked negative electrode 506, the separator 507, and the positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. 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 electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0250] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0251] Next, as shown in Fig. 23C, exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of exterior body 509 so that electrolyte 508 can be introduced later.

[0252] Next, electrolytic solution 508 is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. Introduction of electrolytic solution 508 is preferably performed under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, secondary battery 500, which is a laminated secondary battery, can be produced.

[0253] By using the positive electrode active material particles described in the above embodiment for the positive electrode 503, the secondary battery 500 can be one that is less susceptible to deterioration and has high safety.

[0254] [Bendable secondary battery] Next, an example of a bendable secondary battery will be described with reference to FIGS.

[0255] FIG. 24A shows a schematic top view of a bendable battery 250. FIGS. 24B, 24C, and 24D are schematic cross-sectional views taken along the lines C1-C2, C3-C4, and A1-A2 in FIG. 24A, respectively. The battery 250 has an exterior housing 251 and a positive electrode 211a and a negative electrode 211b housed inside the exterior housing 251. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior housing 251. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed in the area surrounded by the exterior housing 251.

[0256] The positive electrode 211a and the negative electrode 211b of the battery 250 will be described with reference to Fig. 25. Fig. 25A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 25B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0257] 25A, battery 250 has a plurality of rectangular positive electrodes 211a, a plurality of rectangular negative electrodes 211b, and a plurality of separators 214. Positive electrode 211a and negative electrode 211b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of positive electrode 211a in the portion other than the tab, and a negative electrode active material layer is formed on one surface of negative electrode 211b in the portion other than the tab.

[0258] The positive electrode 211a and the negative electrode 211b are stacked so that the surfaces of the positive electrode 211a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

[0259] Furthermore, a separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material layer is formed and the surface of the negative electrode 211b on which the negative electrode active material layer is formed. In Fig. 25, the separator 214 is indicated by a dotted line for ease of viewing.

[0260] 25B, the positive electrodes 211a and the lead 212a are electrically connected at a joint 215a, and the negative electrodes 211b and the lead 212b are electrically connected at a joint 215b.

[0261] Next, exterior body 251 will be described with reference to FIGS. 24B, 24C, 24D, and 24E.

[0262] The exterior body 251 has a film-like shape and is folded in two to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body 251 has a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b, and can also be called side seals. The sealing portion 263 has a portion that overlaps with the lead 212a and the lead 212b, and can also be called a top seal.

[0263] The exterior body 251 preferably has a wave shape in which ridge lines 271 and valley lines 272 are alternately arranged in the portions overlapping the positive electrode 211a and the negative electrode 211b. Furthermore, the seal portions 262 and 263 of the exterior body 251 are preferably flat.

[0264] Fig. 24B is a cross section taken at a portion overlapping with ridge line 271, and Fig. 24C is a cross section taken at a portion overlapping with valley line 272. Fig. 24B and Fig. 24C both correspond to widthwise cross sections of battery 250 and positive electrode 211a and negative electrode 211b.

[0265] Here, the distance between the widthwise end of the negative electrode 211b, i.e., the end of the negative electrode 211b, and the seal portion 262 is defined as the distance La. When the battery 250 is deformed, such as by bending, the positive electrode 211a and the negative electrode 211b are deformed so as to be displaced from each other in the longitudinal direction, as described below. In this case, if the distance La is too short, the exterior body 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, resulting in damage to the exterior body 251. In particular, if the metal film of the exterior body 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is made too large, the volume of the battery 250 increases.

[0266] Furthermore, it is preferable that the distance La between the negative electrode 211b and the seal portion 262 is increased as the total thickness of the stacked positive electrode 211a and negative electrode 211b increases.

[0267] More specifically, when the total thickness of the stacked positive electrode 211a and negative electrode 211b is thickness t, the distance La is preferably 0.8 to 3.0 times, more preferably 0.9 to 2.5 times, and even more preferably 1.0 to 2.0 times the thickness t. By setting the distance La in this range, a compact battery with high reliability against bending can be realized.

[0268] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to make distance Lb sufficiently larger than the width of the positive electrode 211a and the negative electrode 211b (here, width Wb of the negative electrode 211b). This allows parts of the positive electrode 211a and the negative electrode 211b to shift in the width direction even if the positive electrode 211a and the negative electrode 211b come into contact with the exterior body 251 when the battery 250 is repeatedly deformed, such as by bending, so that rubbing between the positive electrode 211a and the negative electrode 211b and the exterior body 251 can be effectively prevented.

[0269] For example, it is preferable that the difference between the distance Lb between the pair of seal portions 262 and the width Wb of the negative electrode 211b is 1.6 to 6.0 times, preferably 1.8 to 5.0 times, and more preferably 2.0 to 4.0 times the thickness t of the positive electrode 211a and the negative electrode 211b.

[0270] In other words, it is preferable that the distance Lb, the width Wb, and the thickness t satisfy the relationship of the following mathematical formula 1.

[0271]

number

[0272] Here, a satisfies the range of 0.8 to 3.0, preferably 0.9 to 2.5, and more preferably 1.0 to 2.0.

[0273] 24D is a cross section including lead 212a, and corresponds to a cross section in the longitudinal direction of battery 250, positive electrode 211a, and negative electrode 211b. As shown in FIG. 24D, it is preferable that a space 273 be formed between exterior body 251 and the longitudinal ends of positive electrode 211a and negative electrode 211b at bent portion 261.

[0274] Figure 24E shows a schematic cross-sectional view of the bent battery 250. Figure 24E corresponds to the cross section taken along the cutting line B1-B2 in Figure 24A.

[0275] When the battery 250 is bent, a portion of the exterior body 251 located on the outside of the bend expands, and another portion located on the inside contracts. More specifically, the portion located on the outside of the exterior body 251 deforms so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the portion located on the inside of the exterior body 251 deforms so that the wave amplitude becomes larger and the wave period becomes smaller. In this way, the deformation of the exterior body 251 relieves the stress applied to the exterior body 251 due to bending, so the material that constitutes the exterior body 251 itself does not need to expand or contract. As a result, the battery 250 can be bent with a small force without damaging the exterior body 251.

[0276] 24E, when the battery 250 is bent, the positive electrodes 211a and the negative electrodes 211b are displaced relative to each other. At this time, because one end of each of the stacked positive electrodes 211a and negative electrodes 211b on the sealing portion 263 side is fixed by the fixing member 217, the amount of displacement increases toward the bending portion 261. This relieves stress on the positive electrodes 211a and negative electrodes 211b, and the positive electrodes 211a and negative electrodes 211b themselves do not need to expand or contract. As a result, the battery 250 can be bent without damaging the positive electrodes 211a and negative electrodes 211b.

[0277] Furthermore, by providing the space 273 between the positive electrode 211a and the negative electrode 211b and the exterior body 251, when the battery is bent, the positive electrode 211a and the negative electrode 211b located on the inside can be relatively displaced without coming into contact with the exterior body 251.

[0278] 24 and 25 is a battery that is resistant to damage to the exterior body, the positive electrode 211a, and the negative electrode 211b, etc., even when repeatedly bent and stretched, and the battery characteristics are also resistant to deterioration. By using the positive electrode active material particles described in the previous embodiment for the positive electrode 211a of the battery 250, it is possible to obtain a secondary battery that is even less susceptible to deterioration and is therefore safer.

[0279] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0280] (Embodiment 6) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on an electronic device will be described.

[0281] 26 shows an example of mounting the bendable secondary battery described in part of the fourth embodiment in an electronic device. Examples of electronic devices that use the bendable secondary battery include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, sound reproduction devices, and large game machines such as pachinko machines.

[0282] Furthermore, a secondary battery having a flexible shape can be incorporated into the inner or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0283] 26A shows an example of a mobile phone. The mobile phone 7400 includes a display unit 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 also includes a secondary battery 7407.

[0284] FIG. 26B 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 inside is also bent. FIG. 26C shows the state of the bent secondary battery 7407 at that time. The secondary battery 7407 is a thin secondary battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to a current collector.

[0285] FIG. 26D 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. FIG. 26E 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, changing the curvature of part or all 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, part or all of the main surfaces of the housing or secondary battery 7104 change 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 surfaces of the secondary battery 7104 is within a range of 40 mm to 150 mm.

[0286] 26F 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.

[0287] 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.

[0288] The display surface of the display portion 7202 is curved, and a display can be performed along the curved display surface. The display portion 7202 is also provided with 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.

[0289] The operation button 7205 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the mobile information terminal 7200.

[0290] The mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, hands-free conversation is also possible by communicating with a wirelessly enabled headset.

[0291] The portable information terminal 7200 also includes an input / output terminal 7206, and can directly exchange data with other information terminals 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.

[0292] The secondary battery of one embodiment of the present invention is included in the display portion 7202 of the mobile information terminal 7200. For example, the secondary battery 7104 shown in FIG. 26E can be incorporated into the housing 7201 in a curved state or into the band 7203 in a bendable state.

[0293] The portable information terminal 7200 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or other human body sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0294] 26G illustrates an example of an armband-type display device. The display device 7300 includes a display portion 7304 and the secondary battery of one embodiment of the present invention. The display device 7300 can also be provided with a touch sensor in the display portion 7304 and can function as a portable information terminal.

[0295] 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.

[0296] The display device 7300 also has an input / output terminal, allowing direct data exchange with other information terminals via a connector. Charging can also be performed via the input / output terminal. Note that charging may also be performed by wireless power supply without using the input / output terminal.

[0297] Next, an example of a foldable tablet terminal is shown in FIGS. 27A and 27B. The tablet terminal 9600 shown in FIGS. 27A and 27B includes a housing 9630a, a housing 9630b, a movable portion 9640 connecting the housings 9630a and 9630b, a display unit 9631, a display mode selector switch 9626, a power switch 9627, a power saving mode selector switch 9625, a fastener 9629, and an operation switch 9628. A flexible panel can be used for the display unit 9631 to provide a tablet terminal with a larger display area. FIG. 27A shows the tablet terminal 9600 in an open state, and FIG. 27B shows the tablet terminal 9600 in a closed state.

[0298] The tablet terminal 9600 also includes a power storage unit 9635 inside the housing 9630a and the housing 9630b. The power storage unit 9635 passes through the movable portion 9640 and is provided across the housing 9630a and the housing 9630b.

[0299] A part of the display portion 9631 can be a touch panel area, and data can be input by touching displayed operation keys. Furthermore, keyboard buttons can be displayed on the display portion 9631 by touching a position on the touch panel where a keyboard display switch button is displayed with a finger or a stylus.

[0300] Furthermore, a display mode switch 9626 can switch the display orientation between portrait and landscape, and can select between black and white and color display. A power saving mode switch 9625 can optimize the display brightness according to the amount of external light during use detected by an optical sensor built into the tablet terminal 9600. The tablet terminal may be equipped with not only an optical sensor but also other detection devices such as a gyroscope, an acceleration sensor, or other sensors that detect tilt.

[0301] 27B shows the tablet terminal in a closed state, and includes a housing 9630, a solar cell 9633, and a charge / discharge control circuit 9634 including a DC-DC converter 9636. As a power storage unit 9635, a secondary battery according to one embodiment of the present invention is used.

[0302] Note that the tablet terminal 9600 can be folded in half, and thus can be folded so that the housing 9630a and the housing 9630b overlap each other when not in use. By folding, the display portion 9631 can be protected, thereby improving durability of the tablet terminal 9600. Furthermore, the power storage unit 9635 using the secondary battery of one embodiment of the present invention has high capacity and favorable cycle characteristics, and therefore, a tablet terminal that can be used for a long period of time can be provided.

[0303] In addition, the tablet terminals shown in Figures 27A and 27B 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 operating or editing information displayed on the display unit by touch input, and controlling processing using various software (programs).

[0304] A solar cell 9633 attached to the surface of the tablet terminal can supply power to a touch panel, a display unit, a video signal processor, etc. The solar cell 9633 can be provided on one or both surfaces of the housing 9630, and can be configured to efficiently charge the power storage unit 9635.

[0305] The configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 27B will be described with reference to a block diagram in Fig. 27C. Fig. 27C shows a solar cell 9633, a power storage unit 9635, a DC-DC converter 9636, a converter 9637, switches SW1 to SW3, and a display unit 9631. The power storage unit 9635, the DC-DC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the charge / discharge control circuit 9634 shown in Fig. 27B.

[0306] First, an example of operation when power is generated by the solar cell 9633 using external light will be described. The power generated by the solar cell is stepped up or down by a DC-DC converter 9636 to a voltage for charging a power storage unit 9635. When power from the solar cell 9633 is used to operate the display unit 9631, a switch SW1 is turned on, and the converter 9637 steps up or steps down the voltage to a voltage required for the display unit 9631. When no display is to be performed on the display unit 9631, the switch SW1 is turned off and the switch SW2 is turned on to charge the power storage unit 9635.

[0307] Note that the solar cell 9633 is shown as an example of a power generating means, but is not particularly limited thereto, and the power storage unit 9635 may be charged by other power generating means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that transmits and receives power wirelessly (contactlessly) for charging, or a combination of other charging means may be used.

[0308] FIG. 28 illustrates an example of another electronic device. In FIG. 28, 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. 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.

[0309] The display unit 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).

[0310] 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.

[0311] 28 , 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. Although FIG. 28 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, 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.

[0312] Note that although Figure 28 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 in a place other than the ceiling 8104, such as a side wall 8105, a floor 8106, or a window 8107, or can also be used in a tabletop lighting device.

[0313] 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 discharge lamps such as incandescent lamps and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

[0314] 28 , 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 of 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. Although FIG. 28 illustrates the case where the secondary battery 8203 is provided in the indoor unit 8200, the secondary battery 8203 may 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 the 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.

[0315] Note that although FIG. 28 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 that has the functions of both the indoor unit and the outdoor unit in a single housing.

[0316] 28 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 of one embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 28 , 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 of one embodiment of the present invention as an uninterruptible power source.

[0317] Furthermore, by storing power in the secondary battery during time periods when electronic devices are not in use, particularly during time periods 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 time periods. For example, in the case of electric refrigerator-freezer 8300, power is stored in secondary battery 8304 during the night when the temperature is low and refrigerator door 8302 and freezer door 8303 are not opened or closed. Then, during the daytime when the temperature rises and refrigerator door 8302 and freezer door 8303 are opened and closed, secondary battery 8304 is used as an auxiliary power source, thereby making it possible to keep the daytime power usage rate low.

[0318] In addition to the electronic devices described above, the secondary battery of one embodiment of the present invention can be installed in various electronic devices. According to one embodiment of the present invention, a secondary battery with less deterioration and high safety can be obtained. Therefore, by installing the secondary battery of one embodiment of the present invention in the electronic device described in this embodiment, the electronic device can have a longer life and higher safety.

[0319] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0320] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle will be described.

[0321] By installing a secondary battery in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), or plug-in hybrid vehicles (PHVs or PHEVs) can be realized.

[0322] 29A illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention. An automobile 8400 shown in FIG. 29A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. By using the secondary battery according to one embodiment of the present invention, a vehicle with a long cruising distance can be realized. The automobile 8400 also includes a secondary battery. The secondary battery not only drives the electric motor 8406 but also can supply power to a light-emitting device such as a headlight 8401 or an interior light (not shown).

[0323] The secondary battery can also supply power to display devices such as a speedometer and a tachometer included in the automobile 8400. The secondary battery can also supply power to semiconductor devices such as a navigation system included in the automobile 8400.

[0324] The automobile 8500 shown in FIG. 29B can charge its secondary battery 8024 by receiving power from an external charging facility using a plug-in method, a wireless power supply method, or the like. FIG. 29B shows a state in which a ground-mounted charging device 8021 charges the secondary battery 8024 mounted on the automobile 8500 via a cable 8022. The charging method and connector specifications may be determined appropriately using a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station installed in a commercial facility or a household power source. For example, plug-in technology can be used to charge the secondary battery 8024 mounted on the automobile 8500 using external power supply. Charging can be performed by converting AC power to DC power using a conversion device such as an AC-DC converter.

[0325] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground power transmitting device 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 vehicles. Furthermore, a solar cell 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.

[0326] 29C shows an example of a two-wheeled vehicle using the secondary battery of one embodiment of the present invention. A scooter 8600 shown in FIG. 29C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603. The secondary battery 8602 can supply electricity to the turn signal light 8603.

[0327] 29C, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0328] According to one embodiment of the present invention, a secondary battery with little deterioration and high safety can be obtained. Therefore, by installing the secondary battery in a vehicle, deterioration of cruising range, acceleration performance, and the like can be suppressed. Furthermore, a vehicle with high safety can be obtained. Furthermore, a secondary battery installed in a vehicle can also be used as a power supply source for purposes other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. Avoiding the use of a commercial power source during peak power demand can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, since a secondary battery with little deterioration and high safety can be used for a long period of time, the amount of rare metals used, such as cobalt, can be reduced.

[0329] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0330] In this embodiment, LiMO₂ prepared by the manufacturing method of one aspect of the present invention will be described. The manufacturing method will be described using FIGS. 1, 3B, and Table 2.

[0331] <Preparation of Each Sample of LiMO₂> First, a mixture 902 containing magnesium and fluorine was prepared (Steps S11 to S14). Lithium fluoride and magnesium fluoride were weighed so that the molar ratio of LiF:MgF₂ was 1:3, and acetone was added as a solvent, followed by wet mixing and pulverization. The mixing and pulverization were performed using a ball mill with zirconia balls at 400 rpm for 12 hours. The processed material was recovered to obtain the mixture 902.

[0332] Next, lithium cobaltate was prepared as a composite oxide containing lithium and cobalt. More specifically, Celsid C-10N manufactured by Nippon Chemical Industry Co., Ltd. was prepared (Step S25).

[0333] Next, in Step S31, the mixture 902 was weighed so that the atomic weight of magnesium in the mixture 902 was 0.5 mol% with respect to the atomic weight of cobalt in lithium cobaltate. The mixing was performed dry using a ball mill with zirconia balls at 150 rpm for 1 hour. Then, it was recovered (Step S32) to obtain a mixture 903 (Step S33).

[0334] Next, the mixture 903 was placed in an alumina crucible (aluminum oxide crucible) and annealed in a muffler furnace (step S34). The annealing conditions differed for each sample and were as shown in Table 2. The temperature increase was set at 200 °C / h, and the temperature decrease was carried out over 10 hours or more. The material after the heat treatment was recovered and sieved (step S35) to obtain each sample (comparative sample 1, comparative sample 2, and sample 3) (step S36). The actually used alumina crucible is shown in Fig. 30. Fig. 30A shows the state before covering the alumina crucible with a lid, and Fig. 30B shows the state when the alumina crucible was covered. As shown in Fig. 30B, the alumina crucible was covered to prepare sample 3.

[0335] Sample 3 was prepared by the production method of one aspect of the present invention. Comparative sample 1 and sample 3 differed in annealing time and O2 conditions. Comparative sample 2 and sample 3 differed in O2 conditions. Note that comparative sample 1 and comparative sample 2 were prepared under an O2 condition of "flow".

[0336]

Table 2

[0337] <Annealing method for each sample of LiMO2> Up to S33 was the same for all samples. The annealing method in S34 differed for each sample. The conceptual diagram when annealing was carried out is as shown in Fig. 3B.

[0338] In Table 2, "sample weight" is the weight of the annealed mixture 903.

[0339] In Table 2, "annealing temperature" is the temperature when annealing was carried out, and "annealing time" is the time for maintaining the annealing temperature.

[0340] In Table 2, "O2 conditions" refers to the method of introducing O2 into the space 102 inside the heating furnace, "flow" indicates that annealing was performed while introducing O2 at a flow rate of 10 L / min, and "purge" indicates that the space 102 inside the heating furnace was replaced with O2 before annealing, and then annealing was performed.

[0341] <Battery cell production> Next, the positive electrodes were fabricated using the above-obtained comparative samples 1, 2, and 3 as the positive electrode active material. The positive electrode active material, AB, and PVDF were mixed in a weight ratio of active material:AB:PVDF=95:3:2, and the slurry was coated onto a current collector. NMP was used as the solvent for the slurry.

[0342] After the slurry was applied to the current collector, the solvent was evaporated. Then, a pressure of 210 kN / m was applied, followed by a further pressure of 1467 kN / m. A positive electrode was obtained through these steps. The loading on the positive electrode was approximately 7 mg / cm. 2 The electrode density was set to >3.8 g / cc.

[0343] Using the prepared positive electrode, a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0344] Lithium metal was used as the counter electrode.

[0345] The electrolyte used in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6), and the electrolytic solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7. For the secondary batteries used to evaluate the charge / discharge efficiency, 2 wt% vinylene carbonate (VC) was added to the electrolytic solution.

[0346] The separator was made of polypropylene with a thickness of 25 μm.

[0347] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0348] <Measurement of Charge-Discharge Efficiency> The cycle characteristics of the battery cells fabricated using the obtained Comparative Sample 1, Comparative Sample 2, and Sample 3 were measured. The cycle characteristics were evaluated at 25°C with charging being CCCV (1.0C, 4.6V, termination current 0.1C) and discharging being CC (1.0C, 2.5V). The results are shown in Fig. 31.

[0349] From Fig. 31, it was found that Sample 3 fabricated according to one aspect of the present invention exhibited better cycle characteristics than Comparative Sample 2. Also, Sample 3 exhibited cycle characteristics equivalent to those of Comparative Sample 1. However, from Table 2, it can be seen that Sample 3 can fabricate the positive electrode active material with an annealing time one-third that of Comparative Sample 1. Therefore, it can be said that a positive electrode active material with good characteristics was fabricated in a short time with Sample 3. From the above, it was found that according to one aspect of the present invention, a positive electrode active material showing good characteristics can be fabricated in a short time. Also, it was found that Sample 3 can process a relatively large mass of 30 g at one time. Therefore, it was found that according to one aspect of the present invention, a large amount of positive electrode active material having good characteristics can be fabricated in a short time.

Example

[0350] In this example, LiMO2 fabricated by a fabrication method of one aspect of the present invention different from that of Example 1 will be described. The fabrication method will be described using Fig. 1, Fig. 3B, and Table 3.

[0351] <Fabrication of Each Sample of LiMO2> The mixture 902 was fabricated through steps S11 to S14 of Fig. 1. It was performed in the same manner as in Example 1 except that mixing and pulverization were performed dry. Subsequently, the cell seed C-10N and the mixture 902 were mixed in the same manner as steps S31 to S33 of Example 1 to obtain the mixture 903.

[0352] Next, the mixture 903 was placed in an alumina crucible and annealed in a muffle furnace (step S34). The annealing conditions varied depending on the sample, as shown in Table 3. The alumina crucible used in this example was a small, deep container as shown in container 116a in FIG. 3. 1.5 g of each sample was placed in this small, deep container, and 12 such containers were lined up in a muffle furnace and annealed. The other conditions were the same as in Example 1.

[0353] [Table 3]

[0354] <Battery cell production> Next, battery cells were fabricated in the same manner as in Example 1 using the comparative sample 4 and sample 5 obtained above.

[0355] <Charge / discharge efficiency measurement> The cycle characteristics of the resulting battery cells of Comparative Sample 4 and Sample 5 were measured. The cycle characteristics were evaluated at 25°C with charging as CCCV (0.2C, 4.6V, cut-off current 0.02C) and discharging as CC (0.2C, 2.5V). The results are shown in Figure 32.

[0356] As shown in Figure 32, Sample 5, which was annealed with the lid on, exhibited significantly better cycle characteristics than Comparative Sample 4, which was annealed without the lid on. This shows that even when the O2 conditions are "flow," it is possible to produce a positive electrode active material that exhibits good characteristics when the container is deep and the lid is on. [Explanation of symbols]

[0357] 101: positive electrode active material, 100A-1: positive electrode active material, 100C: positive electrode active material, 102: space inside heating furnace, 116: container, 116a: container, 119: space, 119a: space, 120: heating furnace, 130: heating furnace, 132: belt conveyor, 134: container, 140: heating furnace, 142: material input section, 144: atmosphere control section, 146: recovery section, 200: active material layer, 201: graphene compound, 211a: positive electrode, 211b: negative electrode, 212a: lead, 212b: lead, 214: separator, 215a: joint section, 215b: joint section, 217: fixing member, 250: battery, 251 : exterior body, 261: folded portion, 262: sealed portion, 263: sealed portion, 271: ridge line, 272: valley line, 273: space, 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, 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, 508: electrolyte, 509: exterior body, 510: Positive electrode lead electrode, 511: negative electrode lead electrode, 600: secondary battery, 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, 612: safety valve mechanism, 613: conductive plate, 614: conductive plate, 615: module, 616: conducting wire, 617: temperature control device, 900: circuit board, 902: mixture, 902-3: mixture, 903: mixture, 903-2: mixture, 903-3: mixture, 904: positive electrode active material, 904-2: positive electrode active material, 904 -3: positive electrode active material, 904-4: positive electrode active material, 905: mixture, 908: mixture, 909: mixture, 910: label, 911: terminal, 912: circuit, 913: secondary battery, 914: antenna, 915: antenna, 916: layer, 917: layer, 918: antenna, 919: terminal, 920: display device, 921: sensor, 922: terminal, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 932: positive electrode, 933: separator, 950: wound body, 951: terminal, 952: terminal, 980: secondary battery, 981: film, 982: film, 993: wound body,994: negative electrode, 995: positive electrode, 996: separator, 997: lead electrode, 998: lead electrode, 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, 74 00: Mobile phone, 7401: Housing, 7402: Display unit, 7403: Operation buttons, 7404: External connection port, 7405: Speaker, 7406: Microphone, 7407: Secondary battery, 8000: Display device, 8001: Housing, 8002: Display unit, 8003: Speaker unit, 8004: Secondary battery, 8021: Charging device, 8022: Cable, 8024: Secondary battery, 8100: Lighting device, 8101: Housing, 8102: Light source, 8103: Secondary battery, 81 04: 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 door, 8303: Freezer door, 8304: Secondary battery, 8400: Automobile, 8401: Headlight, 8406: Electric motor, 8500: Automobile, 8600: Scooter, 8601: Side mirror, 8602: Secondary battery, 8603: Turn signal light, 8604: Under-seat storage, 9600: Tablet terminal, 9625: Switch, 9626: Switch, 9627: Power switch, 9628: Operation switch, 9629: Fastener, 9630: Housing, 9630a: Housing, 9630b: Housing, 9631: Display unit, 9633: Solar cell, 9634: Charge / discharge control circuit, 9635: Power storage unit, 9636: DCDC converter, 9637: Converter, 9640: Moving part,

Claims

1. forming a first mixture having a fluorine source and a magnesium source; a first container containing the first mixture and the lithium cobalt oxide is covered with a lid, and then the first container is placed in a heating furnace; After the inside of the heating furnace is made into an oxygen-containing atmosphere, the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

2. forming a first mixture having a fluorine source and a magnesium source; a first container containing the first mixture and the lithium cobalt oxide is covered with a lid, and then the first container is placed in a heating furnace; the inside of the heating furnace is evacuated, oxygen gas is introduced, and then the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

3. placing a lid on a first container containing a first mixture having lithium cobalt oxide, a fluorine source, and a magnesium source in a furnace; After the inside of the heating furnace is made into an oxygen-containing atmosphere, the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

4. placing a lid on a first container containing a first mixture having lithium cobalt oxide, a fluorine source, and a magnesium source in a furnace; the inside of the heating furnace is evacuated, oxygen gas is introduced, and then the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

5. forming a first mixture having lithium fluoride and magnesium fluoride; a first container containing the first mixture and the lithium cobalt oxide is covered with a lid, and then the first container is placed in a heating furnace; After the inside of the heating furnace is made into an oxygen-containing atmosphere, the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

6. forming a first mixture having lithium fluoride and magnesium fluoride; a first container containing the first mixture and the lithium cobalt oxide is covered with a lid, and then the first container is placed in a heating furnace; the inside of the heating furnace is evacuated, oxygen gas is introduced, and then the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

7. placing a lid on a first container containing a first mixture having lithium cobalt oxide, lithium fluoride, and magnesium fluoride, and then placing the first container in a heating furnace; After the inside of the heating furnace is made into an oxygen-containing atmosphere, the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

8. placing a lid on a first container containing a first mixture having lithium cobalt oxide, lithium fluoride, and magnesium fluoride, and then placing the first container in a heating furnace; the inside of the heating furnace is evacuated, oxygen gas is introduced, and then the inside of the heating furnace is heated to form a composite oxide; a method for preparing a positive electrode active material, the method comprising heating a second mixture containing the composite oxide, a nickel source, and an aluminum source, the temperature to which the second mixture is heated is lower than the temperature to which the interior of the heating furnace is heated; a space defined by the first container and the lid has an atmosphere containing a fluoride; the lid does not contact the outer side surface of the first container in a cross-sectional view.

9. 9. The method for producing a positive electrode active material according to claim 1, wherein the inside of the heating furnace is heated to 735°C or more and 1000°C or less.

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