Secondary battery, vehicle having secondary battery, and method for producing positive electrode active material

Abstract

One mode of the present invention provides a positive electrode active material having a large charge / discharge capacity. Also provided is a positive electrode active material having a high charge / discharge voltage. Also provided is a positive electrode active material that is not susceptible to deterioration. To improve the reliability of the positive electrode active material, there is used a structure that prevents reduction caused by a positive electrode active material surface reacting with an electrolyte. Due to provision of projections on a portion of the positive electrode active material surface, reduction caused by the positive electrode active material surface reacting with the electrolyte is decreased, and cycle characteristics are improved.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery using a positive electrode active material and a method for manufacturing the same, or to a mobile information terminal, a vehicle, etc. that has a secondary battery.

[0002] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[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.

[0004] In this specification, the term "power storage device" refers to elements and devices in general that have a power storage function, including, for example, power storage devices such as lithium ion secondary batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors. [Background technology]

[0005] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, as they are used in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, and next-generation clean-energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs), making them indispensable in today's information society as a rechargeable energy source.

[0006] Therefore, improvements in the positive electrode active material have been investigated in order to improve the cycle characteristics and capacity of lithium ion secondary batteries (for example, Patent Document 1, Non-Patent Document 1).

[0007] Research is also being conducted on the crystalline structure of positive electrode active materials (Non-Patent Documents 2 to 4). Furthermore, the physical properties of fluorides such as fluorite (calcium fluoride) have long been studied (Non-Patent Document 5). Furthermore, research is being conducted on X-ray diffraction (XRD) analysis of the crystalline structure of positive electrode active materials using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 6.

[0008] 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]

[0009] [Patent Document 1] WO2015-163356 [Non-patent literature]

[0010] [Non-Patent Document 1] Suppression of Cobalt Dissolution from the LiCoO▲2▼ Cathodes with Various Metal-Oxide Coatings, Yong Jeong Kim et.,al.,Journal of The Electrochemical Society,150(12)A1723-A1725(2003) [Non-patent document 2] 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 3] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO▲2▼(0.0≦x≦1.0)”, Physical Review B, 80(16), 2009, 165114 [Non-patent document 4] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO▲2▼”, Journal of The Electrochemical Society, 2002, 149(12)A1604-A1609 [Non-patent document 5] WECounts et al,Journal of the American Ceramic Society,1953,36[1]12-17.Fig.01471 [Non-patent document 6] Belsky, A. et al., “New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design”, Acta Cryst., 2002, B58 364-369. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of one embodiment of the present invention is to provide a positive electrode active material having a large charge / discharge capacity. Another object is to provide a positive electrode active material having a high charge / discharge voltage. Another object is to provide a positive electrode active material that is less prone to deterioration. Another object is to provide a novel positive electrode active material. Another object is to provide a secondary battery having a large charge / discharge capacity. Another object is to provide a secondary battery having a high charge / discharge voltage. Another object is to provide a secondary battery that is safe or highly reliable. Another object is to provide a secondary battery that is less prone to deterioration. Another object is to provide a secondary battery with a long life. Another object is to provide a novel secondary battery.

[0012] Another object of one embodiment of the present invention is to provide a novel substance, an active material, a power storage device, or a manufacturing method thereof.

[0013] 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]

[0014] One embodiment of the present invention is a secondary battery including a composite oxide having a layered crystal structure and containing at least lithium, and an oxide containing zirconium on at least a portion of the surface of the composite oxide. The configuration disclosed herein is a secondary battery including a positive electrode and a negative electrode, in which the positive electrode has a positive electrode active material containing lithium and cobalt, and the positive electrode active material contains at least one of fluorine, zirconium, nickel, magnesium, aluminum, titanium, lanthanum, and calcium, and the positive electrode active material has a plurality of protrusions, and the protrusions contain a zirconium compound. The protrusions contain polycrystalline zirconium oxide.

[0015] In the above configuration, the protrusions are a zirconium compound, such as zirconium dioxide or lithium zirconate. Zirconium oxide, typified by zirconium dioxide, is also called zirconia. The protrusions are crystalline and contain polycrystalline zirconium oxide. The positive electrode active material disclosed herein may also be considered a granular material in which the surfaces of mother particles are unevenly coated with daughter particles (zirconium oxide). The coverage of the daughter particles is less than 50%, leaving the uncoated mother particle surfaces exposed. In this specification, even though the protrusions do not have the function of inserting or extracting lithium ions during charging or discharging, they are believed to reduce degradation due to many charge / discharge cycles and contribute to maintaining the overall structure of the positive electrode active material. Therefore, the protrusions are considered to be part of the positive electrode active material, and are also referred to as part of the positive electrode active material.

[0016] In each of the above configurations, the fluorine concentration in the positive electrode active material is higher in the surface layer than in the center of the positive electrode active material. This fluorine concentration distribution is due to the two-stage process of preparing the positive electrode active material, i.e., the process of preparing particles containing lithium and cobalt and then adding fluorine.

[0017] In each of the above-described configurations, the positive electrode active material containing fluorine, lithium, zirconium, and cobalt is preferably obtained by a solid phase method or a sol-gel method.

[0018] Furthermore, a manufacturing method for obtaining the above-mentioned configuration is also one aspect of the present invention, and one of the configurations includes a first step of manufacturing a first mixture by mixing a first material, a second material, and a third material; a second step of heating the first mixture under a first temperature condition to manufacture a second mixture; a third step of manufacturing a third mixture by mixing the second mixture and a fourth material; a fourth step of manufacturing a fourth mixture by mixing the third mixture, a fifth material, and a sixth material; and a fifth step of heating the fourth mixture under a second temperature condition to manufacture a fifth mixture. the first material is a halide compound containing lithium, the second material contains magnesium, the third material is a metal oxide containing lithium and cobalt, and the fourth material contains nickel; in the second step and the fifth step, heating is performed in an atmosphere containing oxygen, the first temperature condition is in the temperature range of 600°C to 950°C and for 1 hour to 100 hours, and the second temperature condition is in the temperature range of 600°C to 900°C and for 1 hour to 100 hours.

[0019] In the above manufacturing method, the fifth material includes aluminum, and the sixth material includes zirconium. Also, in the above manufacturing method, the first mixture, the second mixture, the third mixture, the fourth mixture, or the fifth mixture can be obtained by one or more of dry mixing, wet mixing, a solid-phase method, a sol-gel method, a sputtering method, a mechanochemical method, and a CVD method. [Effects of the Invention]

[0020] According to one embodiment of the present invention, a positive electrode active material having a high energy density and a large charge / discharge capacity can be provided. Alternatively, a positive electrode active material having a high energy density and a high charge / discharge voltage can be provided. Alternatively, a positive electrode active material with little deterioration can be provided. Alternatively, a novel positive electrode active material can be provided. Alternatively, a secondary battery with a large charge / discharge capacity can be provided. Alternatively, a secondary battery with a high charge / discharge voltage can be provided. Alternatively, a secondary battery with high safety or reliability can be provided. Alternatively, a secondary battery with little deterioration can be provided. Alternatively, a secondary battery with a long life can be provided. Alternatively, a novel secondary battery can be provided.

[0021] According to one embodiment of the present invention, a novel substance, an active material, a power storage device, or a manufacturing method thereof can be provided.

[0022] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

[0023] FIG. 1A is an SEM photograph, and FIG. 1B is a schematic diagram thereof. FIG. 2A is a partially enlarged STEM photograph of the active material, FIG. 2B is a mapping image of Zr, FIG. 2C is a mapping image of oxygen, FIG. 2D is a mapping image of aluminum, and FIG. 2E is a mapping image of cobalt. 3A and 3B are diagrams showing electron beam diffraction of cross-sectional STEM images. FIG. 4 is a diagram illustrating a method for producing a positive electrode active material. FIG. 5 is a diagram illustrating a method for producing a positive electrode active material. FIG. 6 is a diagram illustrating a method for producing a positive electrode active material. FIG. 7 is a diagram illustrating a method for producing a positive electrode active material. FIG. 8 illustrates a crystal structure of a positive electrode active material of one embodiment of the present invention. FIG. 9 shows the XRD pattern calculated from the crystal structure. FIG. 10 is a diagram illustrating the crystal structure of the positive electrode active material of the comparative example. FIG. 11 shows the XRD pattern calculated from the crystal structure. 12A to 12D are cross-sectional views illustrating examples of the positive electrode of a secondary battery. 13A is an exploded perspective view of the coin-type secondary battery, FIG. 13B is a perspective view of the coin-type secondary battery, and FIG. 13C is a cross-sectional perspective view thereof. Fig. 14A is a diagram showing an example of a cylindrical secondary battery. Fig. 14B is a diagram showing an example of a cylindrical secondary battery. Fig. 14C is a diagram showing an example of a plurality of cylindrical secondary batteries. Fig. 14D is a diagram showing an example of a power storage system having a plurality of cylindrical secondary batteries. 15A and 15B are diagrams illustrating an example of a secondary battery, and Fig. 15C is a diagram showing the internal state of the secondary battery. 16A to 16C are diagrams illustrating an example of a secondary battery. 17A and 17B are diagrams showing the external appearance of a secondary battery. 18A to 18C are diagrams illustrating a method for manufacturing a secondary battery. Fig. 19A is a diagram showing an example of the configuration of a battery pack, Fig. 19B is a diagram showing an example of the configuration of a battery pack, and Fig. 19C is a diagram showing an example of the configuration of a battery pack. 20A and 20B are diagrams illustrating an example of a secondary battery. 21A to 21C are diagrams illustrating an example of a secondary battery. 22A and 22B are diagrams illustrating an example of a secondary battery. Fig. 23A is a perspective view of a battery pack showing one embodiment of the present invention, Fig. 23B is a block diagram of the battery pack, and Fig. 23C is a block diagram of a vehicle having a motor. 24A to 24D are diagrams illustrating an example of a transportation vehicle. 25A and 25B illustrate a power storage device according to one embodiment of the present invention. Fig. 26A is a diagram showing an electric bicycle, Fig. 26B is a diagram showing a secondary battery of the electric bicycle, and Fig. 26C is a diagram explaining an electric motorcycle. 27A to 27D are diagrams illustrating an example of an electronic device. Fig. 28A is a diagram showing an example of a wearable device, Fig. 28B is a diagram showing a perspective view of a wristwatch-type device, and Fig. 28C is a diagram illustrating a side view of the wristwatch-type device. 29A and 29B are graphs showing the cycle characteristics shown in Example 1. 30A and 30B are graphs showing the cycle characteristics shown in Example 1. FIG. 31 is a graph showing the powder resistance shown in Example 1. FIG. 32 is a graph showing the cycle characteristics (discharge capacity retention rate) shown in Example 2. 33A and 33B are diagrams showing the results of XPS analysis. 34A and 34B are diagrams showing the results of XPS analysis. FIG. 35A is an SEM photograph, and FIG. 35B is a schematic diagram thereof. FIG. 36 is a graph showing the cycle characteristics shown in Example 3. FIG. 37 is a diagram illustrating a method for producing a positive electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may partially contain a substance that does not contribute to the charge / discharge capacity.

[0026] In this specification and the like, the positive electrode active material of one embodiment of the present invention may be referred to as a positive electrode material, a positive electrode material for a secondary battery, a composite oxide, or the like. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a compound. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composition. Furthermore, in this specification and the like, the positive electrode active material of one embodiment of the present invention preferably includes a composite.

[0027] In this specification and the like, uneven distribution refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of multiple elements (for example, A, B, and C).

[0028] In this specification, the surface layer of particles of active material or the like refers to, for example, a region within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm from the surface toward the interior. Surfaces caused by cracks or fissures may also be considered the surface. Regions deeper than the surface layer are referred to as the interior. In this specification, the term "grain boundary" refers to, for example, a region where particles adhere to each other, a region within a particle (including the center) where the crystal orientation changes, a region containing many defects, or a region where the crystal structure is disordered. A grain boundary can be considered a type of planar defect. The term "vicinity of a grain boundary" refers to a region within 10 nm from the grain boundary. In this specification, the term "particle" is not limited to spherical shapes (circular cross-sectional shape), but may also refer to cross-sectional shapes such as oval, rectangular, trapezoidal, conical, square with rounded corners, and asymmetrical shapes. Furthermore, individual particles may also have an irregular shape.

[0029] In this specification and elsewhere, Miller indices are used to represent crystal planes and directions. Individual planes indicating crystal planes are represented in parentheses. In crystallography, crystal planes, directions, and space groups are represented by placing a superscript bar above the numbers, but in this specification and elsewhere, due to limitations on application notation, numbers may be represented by placing a - (minus sign) before them instead of placing a bar above them.

[0030] In this specification, the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0031] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0032] Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have a high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock-salt crystal structure is a composite oxide represented by LiMO2. The amount of lithium remaining in the positive electrode active material that can be inserted and removed can be determined by the x in the composition formula, for example, Li x x in CoO2, or Li x In this specification, Li x CoO2 is appropriately Li x In the case of the positive electrode active material in a secondary battery, x can be expressed as charge capacity / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2mAh / g, Li 0.8 CoO2 or x=0.8. x A small value of x in CoO2 is, for example, 0.1 <x≦0.24をいう。

[0033] It is known that the strength of the Jahn-Teller effect in transition metal compounds varies depending on the number of electrons in the d orbital of the transition metal.

[0034] In compounds containing nickel, distortion may occur due to the Jahn-Teller effect. xWhen NiO2 is charged and discharged so that x becomes small, there is a concern that the crystal structure may collapse due to strain. In LiCoO2, it is suggested that the influence of the Jahn-Teller effect is small, and Li x When x in CoO2 is small, the resistance may be better, which is preferable.

[0035] The positive electrode active material will be described with reference to Figures 8 to 10. Figures 8 to 10 describe the case where cobalt is used as the transition metal contained in the positive electrode active material.

[0036] <Conventional positive electrode active materials> Lithium cobalt oxide (LiCoO2) can have different crystal structures depending on the occupancy rate x of Li at the lithium site. The change in the crystal structure of a conventional positive electrode active material is shown in Figure 10. The conventional positive electrode active material shown in Figure 10 is lithium cobalt oxide (LiCoO2) that does not contain any additional element A. The change in the crystal structure of lithium cobalt oxide that does not contain any additional element A is described in Non-Patent Documents 1 to 3, etc.

[0037] Figure 10 shows R-3m O3 and Li x This shows the crystal structure of lithium cobalt oxide with x=1 in CoO2. In this crystal structure, lithium occupies octahedral sites, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and these structures are connected in a plane with edge sharing. This is sometimes called a layer consisting of octahedra of cobalt and oxygen.

[0038] Conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when x=0.5, increasing the symmetry of lithium. This structure has one CoO2 layer in the unit cell. For this reason, it is sometimes called the O1 type or monoclinic O1 type. When x=0, the positive electrode active material has a crystal structure in the space group P-3m1, with one CoO2 layer in the unit cell. For this reason, this crystal structure is sometimes called the O1 type crystal structure.

[0039] Furthermore, conventional lithium cobalt oxides with x = approximately 0.24 have a crystal structure of the space group R-3m. This structure can be thought of as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes referred to as the 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, the c-axis of the H1-3 crystal structure is shown as half the unit cell to facilitate comparison with other structures.

[0040] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 crystal structure can be expressed as Co(0, 0, 0.42150±0.00016), O1(0, 0, 0.27671±0.00045), and O2(0, 0, 0.11535±0.00045). O1 and O2 are each an oxygen atom. Thus, the H1-3 crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the O3' crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' crystal structure and the H1-3 structure, and that the O3' crystal structure exhibits smaller changes from the O3 structure than the H1-3 structure. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of XRD. In this case, the unit cell that results in the smallest goodness of fit (GOF) value should be used.

[0041] Li x When charging and discharging are repeated so that x in CoO2 becomes 0.24 or less, lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0042] 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.

[0043] 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%.

[0044] 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.

[0045] Therefore, when charging and discharging is repeated so that x becomes 0.24 or less, the crystalline structure of lithium cobalt oxide breaks down. This break in the crystalline structure causes a deterioration in cycle characteristics. This is because the number of sites where lithium can exist stably decreases and it becomes difficult for lithium to be inserted and extracted.

[0046] The anions in layered rock salt crystals and rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in the O3'-type crystal structure also have a cubic close-packed structure. When these crystals contact, there is a crystal plane where the cubic close-packed structure formed by the anions is oriented in the same direction. However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which is different from the space groups Fm-3m (the space group of general rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry) of rock salt crystals. Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and O3'-type crystals and rock salt crystals. In this specification, when the cubic close-packed structure formed by the anions is oriented in the same direction in layered rock salt crystals, O3'-type crystals, and rock salt crystals, it may be said that the crystal orientations are approximately the same.

[0047] The general alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope), STEM (scanning transmission electron microscope), HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope), and ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, and neutron diffraction can also be used. In TEM images, the arrangement of cations and anions can be observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure of the layered rock salt crystal and the rock salt crystal is aligned, the angle between the repeated bright and dark lines between the crystals can be observed to be less than 5 degrees, and more preferably less than 2.5 degrees. Light elements such as oxygen and fluorine may not be clearly visible in TEM images, but in such cases, the alignment of the orientations can be determined from the arrangement of metal elements.

[0048] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0049] When properly synthesized lithium cobalt oxide is used in the positive electrode, it is LiCoO2 and x = 1 when it approximately satisfies the stoichiometric ratio. Secondary batteries that have finished discharging can also be said to be LiCoO2 or x = 1. Here, "finished discharging" refers to a state where the voltage is 3.0V or 2.5V or less at a current of 100mAh / g or less. x It is preferable to measure the charge and / or discharge capacity used to calculate x in CoO2 under conditions where there is little or no influence of short circuit and / or electrolyte decomposition. For example, data from a secondary battery that has experienced a sudden change in capacity that may be due to a short circuit should not be used to calculate x.

[0050] Discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). When discharging at a current of 2X (A), it is said to have been discharged at 2C, and when discharging at a current of X / 5 (A), it is said to have been discharged at 0.2C. The same is true for charge rate; when charging at a current of 2X (A), it is said to have been charged at 2C, and when charging at a current of X / 5 (A), it is said to have been charged at 0.2C.

[0051] Constant current charging, for example, refers to a method of charging at a constant charge rate. Constant voltage charging, for example, refers to a method of charging at a constant voltage once the upper voltage limit is reached. Constant current discharging, for example, refers to a method of discharging at a constant discharge rate.

[0052] In this specification, a value close to a certain value A refers to a value between 0.9 A and 1.1 A.

[0053] Although this specification and the like may show examples of secondary batteries using a positive electrode and a positive electrode active material of one embodiment of the present invention, the secondary battery of one embodiment of the present invention is not limited to this example. Other materials, such as graphite and lithium titanate, may also be used for the negative electrode. The properties of the positive electrode and positive electrode active material of one embodiment of the present invention, such as their resistance to crystal structure collapse even after repeated charge and discharge and their excellent cycle characteristics, are not affected by the material of the negative electrode. Although examples of secondary batteries of one embodiment of the present invention using a lithium counter electrode and charging and discharging at a voltage higher than the typical charging voltage of about 4.7 V, may also be used for charging and discharging at a lower voltage. Charging and discharging at a lower voltage is expected to result in even better cycle characteristics than those shown in this specification and the like.

[0054] (Embodiment 1) In this embodiment, a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0055] To improve the reliability of the positive electrode active material, the positive electrode active material surface is designed to prevent reaction with the electrolyte and reduction. By forming protrusions on part of the surface of the positive electrode active material using a sol-gel method, the reaction area between the positive electrode active material and the electrolyte is reduced, suppressing decomposition of the electrolyte or reduction of the positive electrode active material and improving cycle characteristics.

[0056] FIG. 1 is a TEM photograph of one particle of the positive electrode active material produced by the sol-gel method shown in this embodiment.

[0057] A single particle of positive electrode active material 100 has multiple protrusions, and although the shapes vary, a schematic diagram of a single particle of positive electrode active material 100 having protrusions 101, 102, and 103 is shown in FIG. 1B.

[0058] FIG. 2A shows a STEM image of the vicinity of the protrusion 103. FIG. 2A is a STEM image measured at an acceleration voltage of 200 kV using an HD-2700 manufactured by Hitachi High-Technologies Corporation. FIG. 2B shows a mapping image of Zr in the vicinity of the region (Area 1) of the protrusion 103 in FIG. 2A. FIG. 2C shows a mapping image of oxygen in the vicinity of the region (Area 1) of the protrusion 103. FIG. 2D shows a mapping image of aluminum in the vicinity of the region (Area 1) of the protrusion 103. FIG. 2E shows a mapping image of cobalt in the vicinity of the region (Area 1) of the protrusion 103. These mapping images suggest that there may be a grain boundary between Area 1 and Area 2.

[0059] For comparison, the quantitative values ​​of each element (carbon, nitrogen, oxygen, fluorine, Zr, Al, Si, Ti, Co, Ni, Cu, and Ga) detected in Area 1 and Area 2 inside the positive electrode active material particle in Figure 2A are shown in Table 1 below. Note that carbon, oxygen, and silicon include elements derived from the collodion film. Cu also includes elements scattered by the mesh, etc.

[0060] [Table 1]

[0061] These results indicate that the protrusions 103 contain zirconium oxide. The protrusions 103 also contain cobalt. The protrusions 103 contain greater amounts of fluorine, silicon, and Cu than Area 2, an area inside the positive electrode active material particle. In Area 2, an area inside the positive electrode active material particle, cobalt and aluminum are detected in greater amounts than Area 1. As can be seen from FIG. 2D , the protrusions 103 also contain aluminum. In Area 1 and Area 2, the concentrations of nitrogen, titanium, nickel, and gallium are approximately the same.

[0062] Electron beam diffraction was also performed using a Hitachi High-Technologies Corporation HD-2700. The results for Area 1 are shown in Figure 3A. The results for Area 2 are shown in Figure 3B. In Figure 3A, multiple crystal planes are observed, indicating that protrusions 103 contain polycrystals. The protrusions are also monoclinic. Note that zirconium oxide is most stable in the monoclinic system at room temperature. Providing protrusions (such as zirconium oxide) on a portion of the surface of the positive electrode active material reduces the reaction area between the positive electrode active material and the electrolyte, suppressing decomposition of the electrolyte or reduction of the positive electrode active material, and improving cycle characteristics.

[0063] The XPS analysis results of the obtained positive electrode active material are shown in Figures 33A, 33B, 34A, and 34B. Note that in these XPS analysis results, each peak may appear at a lower position than the actual position due to the influence of charging.

[0064] The results in FIG. 33A show that zirconium is present as ZrO2 in the protrusions on the surface of the positive electrode active material.

[0065] X-ray photoelectron spectroscopy (XPS) can analyze the region from the surface to a depth of 2 to 8 nm (usually about 5 nm), making it possible to quantitatively analyze the concentration of each element in about half of the surface layer. Narrow scan analysis also makes it possible to analyze the bonding state of elements. The quantitative accuracy of XPS is often about ±1 atomic %, and the lower detection limit is about 1 atomic %, although this depends on the element.

[0066] When performing XPS analysis, for example, monochromated aluminum can be used as the X-ray source. The output can be, for example, 1486.6 eV. The take-off angle can be, for example, 45°. Under these measurement conditions, it is possible to analyze a region from the surface to a depth of 2 nm to 8 nm (usually about 5 nm), as mentioned above. The XPS analysis was performed using a Quantera 2 manufactured by PHI Corporation.

[0067] Furthermore, when the positive electrode active material of one embodiment of the present invention is analyzed by XPS, the peak representing the binding energy of fluorine with other elements is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably approximately 684.3 eV, as shown in FIG. 33B. This value is different from both the binding energy of lithium fluoride (685 eV) and the binding energy of magnesium fluoride (686 eV). In other words, when the positive electrode active material of one embodiment of the present invention contains fluorine, the binding energy is preferably a value other than that of lithium fluoride or magnesium fluoride.

[0068] Furthermore, when the positive electrode active material of one embodiment of the present invention was analyzed by XPS, as shown in FIG. 34A , the peak representing the bond energy between magnesium and another element was preferably greater than or equal to 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is closer to the bond energy of magnesium oxide. In other words, when the positive electrode active material of one embodiment of the present invention contains magnesium, the bond is preferably other than that of magnesium fluoride.

[0069] Furthermore, when the positive electrode active material of one embodiment of the present invention was subjected to XPS analysis, data regarding aluminum is shown in FIG. 34B.

[0070] The concentrations of additive elements that are preferably present in large amounts in the surface layer, such as magnesium, aluminum, and titanium, measured by XPS or the like, are preferably higher than the concentrations measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0071] When a cross section of magnesium, aluminum, titanium, etc. is exposed by processing and analyzed using TEM-EDX, it is preferable that the concentration in the surface layer is higher than the concentration in the interior. For example, in TEM-EDX analysis, it is preferable that the magnesium concentration at a point 1 nm deep from the peak top decays to 60% or less of the peak. It is also preferable that the magnesium concentration at a point 2 nm deep from the peak top decays to 30% or less of the peak. Processing can be performed, for example, using a FIB (focused ion beam) device.

[0072] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms, while the ratio of the number of magnesium atoms Mg / Co in ICP-MS analysis is preferably 0.001 to 0.06.

[0073] On the other hand, it is preferable that nickel is not concentrated in the surface layer portion but is distributed throughout the positive electrode active material.

[0074] The positive electrode active material 100 has an O3' type crystal structure.

[0075] In the positive electrode active material 100 of one embodiment of the present invention shown in FIG. xThe change in the crystal structure between the discharge state where x in CoO2 is 1 and the state where x is 0.24 or less is smaller than that of conventional positive electrode active materials. More specifically, the deviation of the CoO2 layer between the state where x is 1 and the state where x is 0.24 or less can be reduced. Furthermore, the change in volume compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to collapse in crystal structure even when repeatedly charged and discharged so that x is 0.24 or less, and excellent cycle characteristics can be achieved. Furthermore, the positive electrode active material 100 of one embodiment of the present invention has a low crystalline structure even when repeatedly charged and discharged so that x is 0.24 or less. x When x in CoO2 is 0.24 or less, the positive electrode active material 100 can have a more stable crystal structure than conventional positive electrode active materials. x When x in CoO2 is kept at 0.24 or less, short circuits are less likely to occur, which is preferable because it further improves safety.

[0076] In the positive electrode active material of one embodiment of the present invention, the change in crystal structure and the difference in volume per the same number of transition metal atoms between a fully discharged state and a high-voltage charged state are small.

[0077] Li x The crystal structure of the positive electrode active material 100 when x in CoO2 is approximately 1 or 0.2 is shown in Figure 8. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal, and oxygen. In addition to the above, it preferably contains magnesium as an additive element. It also preferably contains a halogen such as fluorine or chlorine as an additive element.

[0078] In Figure 8, when x = 1, the cathode active material 100 has the same R-3m O3 crystal structure as the conventional lithium cobalt oxide shown in Figure 10. However, when x is 0.24 or less, such as approximately 0.2 or 0.15, the cathode active material 100 has a different crystal structure from the conventional lithium cobalt oxide, which has an H1-3 crystal structure. When x = approximately 0.2, the cathode active material 100 of one embodiment of the present invention has a crystal structure belonging to the trigonal space group R-3m. This has the same symmetry as the O3 type CoO2 layer. Therefore, this structure is referred to herein as the O3' type crystal structure (or pseudospinel type crystal structure). This crystal structure is shown in Figure 8 with the R-3m O3' designation.

[0079] In the O3' crystal structure, ions of cobalt, nickel, magnesium, etc. occupy the hexacoordinated oxygen positions. Light elements such as lithium may occupy the tetracoordinated oxygen positions.

[0129] In addition, in the O3' type crystal structure of FIG. 8, lithium is shown to exist at all lithium sites with equal probability, but this is not limited to this. It may exist unevenly at some lithium sites, for example, in the monoclinic O1(Li 0.5 The lithium distribution can be analyzed, for example, by neutron diffraction.

[0080] It can also be said that the O3' type crystal structure has random Li between the layers, but is similar to the CdCl2 type crystal structure. This CdCl2 type-like crystal structure is obtained by dissolving lithium nickel oxide in Li 0.06 Although the crystal structure is similar to that when charged to NiO2, 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 a CdCl2 type crystal structure.

[0081] In the positive electrode active material 100 according to one embodiment of the present invention, Li xWhen x in CoO2 is 0.24 or less, the change in the crystal structure when a large amount of lithium is released is suppressed compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 8, there is almost no deviation in the CoO2 layers between the R-3m(O3) in the discharged state and the O3'-type crystal structure. Furthermore, the difference in volume per the same number of cobalt atoms between the R-3m(O3) in the discharged state and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0082] Thus, the positive electrode active material 100 according to one embodiment of the present invention is Li x When x in CoO2 is small, that is, when a large amount of lithium is released, the change in the crystal structure is suppressed compared to conventional positive electrode active materials. In addition, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the crystal structure of the positive electrode active material 100 is not easily broken even when repeatedly charged and discharged so that x is 0.24 or less. Therefore, the decrease in charge / discharge capacity during charge / discharge cycles is suppressed in the positive electrode active material 100. Furthermore, since more lithium can be stably used than in conventional positive electrode active materials, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be produced. The positive electrode active material 100 does not contain Li x It has been confirmed that when x in CoO2 is between 0.15 and 0.24, it may have an O3' type crystal structure, and it is also presumed that when x is between 0.24 and 0.27, it also has an O3' type crystal structure. However, the crystal structure is Li x The x range is not necessarily limited to the above range because it is affected not only by the x in CoO2 but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc. Therefore, the positive electrode active material 100 is Li x When x in CoO2 is more than 0.1 and not more than 0.24, the entire interior 100b of the positive electrode active material 100 does not have to have an O3'-type crystal structure. It may contain other crystal structures, or may be partially amorphous. x To make the x in CoO2 small, it is generally necessary to charge at a high charging voltage. xA state in which x in CoO2 is small can be rephrased as a state in which the material is charged at a high charging voltage. For example, when conventional positive electrode active materials are charged at a voltage of 4.6 V or higher relative to the potential of lithium metal in a 25°C environment under CC / CV charging, an H1-3 crystal structure appears. Therefore, a charging voltage of 4.6 V or higher relative to the potential of lithium metal can be considered a high charging voltage. Furthermore, unless otherwise specified, charging voltages are expressed relative to the potential of lithium metal. Therefore, the positive electrode active material 100 of one embodiment of the present invention can be rephrased as being preferable because it can maintain a crystal structure with R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or higher at 25°C. Alternatively, it can be rephrased as being preferable because it can adopt an O3' crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or higher and 4.7 V or lower at 25°C.

[0083] In some cases, the H1-3 type crystal is finally observed when the charge voltage is further increased, even in the positive electrode active material 100. Furthermore, as described above, the crystal structure is affected by the number of charge / discharge cycles, the charge / discharge current, the electrolyte, and the like. Therefore, even when the charge voltage is lower, for example, even when the charge voltage is 4.5 V or higher but lower than 4.6 V at 25° C., the positive electrode active material 100 of one embodiment of the present invention may be able to adopt the O3′ type crystal structure.

[0084] In addition, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above by the potential of the graphite. The potential of graphite is approximately 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystalline structure is maintained at a voltage obtained by subtracting the potential of graphite from the above voltage.

[0085] In the positive electrode active material 100, the difference in volume per the same number of cobalt atoms between the O3 type crystal structure and the O3' type crystal structure in a discharged state is 2.5% or less, more specifically 2.2% or less, typically 1.8%.

[0086] As shown in Figure 7, the O3'-type crystal structure can have the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25. Regarding the lattice constant of the unit cell, the a-axis is preferably 2.797≦a≦2.837 (Å), more preferably 2.807≦a≦2.827 (Å), typically a=2.817 (Å). The c-axis is preferably 13.681≦c≦13.881 (Å), more preferably 13.751≦c≦13.811 (Å), typically c=13.781 (Å).

[0087] Additives such as magnesium, which exist randomly and dilutely between the CoO2 layers, i.e., at the lithium sites, have the effect of suppressing the displacement of the CoO2 layers. Therefore, when magnesium exists between the CoO2 layers, the O3'-type crystal structure is easily formed.

[0088] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that additives, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site will be converted into Li x When x in CoO2 is 0.24 or less, there is no effect of maintaining the R-3m structure. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0089] 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 in the surface layer. 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 in the surface layer at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance against hydrofluoric acid produced by decomposition of the electrolyte.

[0090] However, if the magnesium concentration is increased above a desired value, the effect on stabilizing the crystal structure may be reduced. This is thought to be due to the incorporation of magnesium into the cobalt site in addition to the lithium site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of transition metal 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 production process of the positive electrode active material.

[0091] Lithium cobalt oxide may contain one or more metals other than cobalt (hereinafter referred to as metal Z), such as nickel, aluminum, manganese, titanium, vanadium, and chromium. Adding one or more of nickel and aluminum is particularly preferred. Manganese, titanium, vanadium, and chromium may easily assume a stable tetravalent state, which may contribute significantly to structural stability. Adding metal Z to the positive electrode active material of one embodiment of the present invention may result in, for example, Li x The crystal structure may become more stable when x in CoO2 is 0.24 or less. In the positive electrode active material of one embodiment of the present invention, the metal Z is preferably added at a concentration that does not significantly change the crystallinity of the lithium cobalt oxide. For example, the amount is preferably such that the aforementioned Jahn-Teller effect is not exhibited.

[0092] As shown in the legend in Figure 8, transition metals such as nickel and manganese and aluminum are preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0093] As is clear from the oxygen atoms in Figure 8, the symmetry of the oxygen atoms is slightly different between the O3 and O3' crystal structures. Specifically, in the O3 crystal structure, the oxygen atoms are aligned along the (-102) plane indicated by the dotted line, whereas in the O3' crystal structure, the oxygen atoms are not strictly aligned along the (-102) plane. This is because, in the O3' crystal structure, as lithium decreases, tetravalent cobalt increases, increasing Jahn-Teller distortion and distorting the octahedral structure of CoO6. Another factor is that as lithium decreases, the repulsion between oxygen atoms in the CoO2 layer becomes stronger.

[0094] <XRD> The XRD measurement equipment and conditions are not particularly limited. For example, a Bruker D8 ADVANCE can be used as the measurement equipment. Measurement conditions include a CuKα X-ray source and powder setting, sprinkling the sample on a greased silicone anti-reflection plate, and adjusting the measurement surface to match the measurement surface required by the equipment.

[0095] Figures 9 and 11 show the ideal powder XRD patterns calculated from the O3'-type crystal structure and H1-3-type crystal structure models using CuKα1 radiation. x The ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) with x = 1 in CoO2, H1-3 type, and CoO2(O1) with x = 0 are also shown. The LiCoO2(O3) and CoO2(O1) patterns were created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 6). The 2θ range was 15° to 75°, the step size was 0.01, and the wavelength λ1 was 1.540562 × 10 -10m and λ2 were not set, and the monochromator was set to single. The pattern of the H1-3 type crystal structure was similarly created from the crystal structure information described in Non-Patent Document 4. The crystal structure pattern of the O3' type crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and an XRD pattern was created in the same way as the others.

[0096] As shown in Figure 9, the O3'-type crystal structure exhibits diffraction peaks at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 11, the H1-3-type crystal structure and CoO2(P-3m1, O1) do not exhibit peaks at these positions. Therefore, the appearance of peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0097] This means that the positions at which XRD diffraction peaks appear are close between the crystal structures with x = 1 and x ≦ 0.24. More specifically, the difference in the positions at which two or more, preferably three or more, of the main diffraction peaks between the crystal structures with x = 1 and x ≦ 0.24 appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less.

[0098] Although the positive electrode active material 100 of one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage, the entire particle does not necessarily have to have the O3'-type crystal structure. Other crystal structures may be included, or a portion may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. When the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, the positive electrode active material can have sufficiently excellent cycle characteristics.

[0099] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0100] In addition, the crystallite size of the O3'-type crystal structure of the positive electrode active material particles is reduced to only about 1 / 20 of that of LiCoO2(O3) in the discharged state. x When x in CoO2 is small, a clear peak of the O3'-type crystal structure can be confirmed. On the other hand, in simple LiCoO2, even if a part of it can adopt a structure similar to the O3'-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.

[0101] As described above, the positive electrode active material of one embodiment of the present invention preferably has a small influence of the Jahn-Teller effect. The positive electrode active material of one embodiment of the present invention preferably has a layered rock salt crystal structure and contains cobalt as a transition metal. Furthermore, the positive electrode active material of one embodiment of the present invention may contain the aforementioned metal Z in addition to cobalt, as long as the influence of the Jahn-Teller effect is small.

[0102] (Embodiment 2) In this embodiment, an example of a method for manufacturing a positive electrode active material of one embodiment of the present invention will be described with reference to FIGS.

[0103] <Step S11> In step S11 of FIG. 4, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen.

[0104] As the lithium source, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, etc. can be used.

[0105] The transition metal M is preferably a metal that can form a layered rock-salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, as the source of the transition metal M, only cobalt may be used, only nickel may be used, or two types of cobalt and manganese, or two types of cobalt and nickel, or three types of cobalt, manganese, and nickel may be used.

[0106] When using metals capable of forming a layered rock-salt complex oxide, it is preferable to mix cobalt, manganese, and nickel in a ratio that allows a layered rock-salt crystal structure to be formed. Aluminum may also be added to these transition metals in a ratio that allows a layered rock-salt crystal structure to be formed.

[0107] As the transition metal M source, oxides, hydroxides, etc. of the metals exemplified above as the transition metal M can be used. As the cobalt source, for example, cobalt oxide, cobalt hydroxide, etc. can be used. As the manganese source, manganese oxide, manganese hydroxide, etc. can be used. As the nickel source, nickel oxide, nickel hydroxide, etc. can be used. As the aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0108] <Step S12> Next, in step S12, the lithium source and the transition metal M source are mixed. Mixing can be performed by a dry method or a wet method. 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 grinding media.

[0109] <Step S13> Next, in step S13, the mixed materials are heated. This step is sometimes referred to as calcination or first heating to distinguish it from subsequent heating steps. Heating is preferably performed at a temperature of 800°C or higher but lower than 1100°C, more preferably 900°C or higher but 1000°C or lower, and even more preferably around 950°C. Alternatively, a temperature of 800°C or higher but 1000°C or lower is preferred. Alternatively, a temperature of 900°C or higher but 1100°C or lower is preferred. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal used as the transition metal M, which is responsible for the redox reaction, or lithium evaporation. For example, if cobalt is used as the transition metal M, defects may occur due to the cobalt becoming divalent.

[0110] The heating time can be, for example, from 1 hour to 100 hours, preferably from 2 hours to 20 hours. Alternatively, from 1 hour to 20 hours is preferred. Alternatively, from 2 hours to 100 hours is preferred. Firing is preferably carried out in an atmosphere with little water, such as dry air (for example, a dew point of -50°C or less, more preferably -100°C or less). For example, heating is preferably carried out at 1000°C for 10 hours, with a temperature increase rate of 200°C / h and a flow rate of the dry atmosphere of 10 L / min. The heated material can then be cooled to room temperature (25°C). For example, the cooling time from the specified temperature to room temperature is preferably from 10 hours to 50 hours.

[0111] However, cooling to room temperature in step S13 is not essential, and cooling to a temperature higher than room temperature may be performed if there is no problem in carrying out the subsequent steps S41 to S43.

[0112] <Step S14> Next, in step S14, the calcined material is recovered to obtain a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen. Specifically, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is substituted with manganese, lithium cobalt oxide in which some of the cobalt is substituted with nickel, or lithium nickel-manganese-cobalt oxide is obtained.

[0113] Alternatively, a composite oxide containing lithium, a transition metal M, and oxygen that has been synthesized in advance may be used in step S14, in which case steps S11 to S13 can be omitted.

[0114] For example, lithium cobalt oxide particles (product name: Cellseed C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used as a pre-synthesized composite oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) 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.

[0115] Alternatively, lithium cobalt oxide particles (product name: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. can also be used. This is lithium cobalt oxide with an average particle size (D50) of approximately 6.5 μm, and in impurity analysis by GD-MS, the concentrations of elements other than lithium, cobalt, and oxygen are similar to or lower than those of C-10N.

[0116] In this embodiment, cobalt is used as the metal M, and pre-synthesized lithium cobalt oxide particles (Cellseed C-10N manufactured by Nippon Chemical Industry Co., Ltd.) are used.

[0117] <Step S21> Next, in step S21, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared as materials for the mixture 902. It is also preferable to prepare a lithium source.

[0118] Examples of fluorine sources include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4, TiF3), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride (MnF2, MnF3), iron fluoride (FeF2, Examples of fluorine sources that can be used include FeF3, chromium fluoride (CrF2, CrF3), niobium fluoride (NbF5), zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), and sodium aluminum hexafluoride (Na3AlF6). A mixture of multiple fluorine sources may also be used. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the annealing process described below.

[0119] As the chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used.

[0120] As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used.

[0121] Examples of lithium sources that can be used include lithium fluoride and lithium carbonate. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0122] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The melting point is most effectively lowered when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, excessive lithium fluoride can lead to excessive lithium, which can degrade cycle characteristics. Therefore, the molar ratio of lithium fluoride (LiF) to magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0 ≦ x ≦ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≦ x ≦ 0.5), and even more preferably LiF:MgF2 = x:1 (near x = 0.33). In this specification, "near" refers to a value greater than 0.9 times but less than 1.1 times the value.

[0123] 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, ethers such as diethyl 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.

[0124] <Step S22> Next, in step S22, the materials for the mixture 902 are pulverized and mixed. 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 pulverization media. It is preferable to thoroughly perform this mixing and pulverization process to finely pulverize the mixture 902.

[0125] <Step S23> Next, in step S23, the mixed and crushed materials are collected to obtain a mixture 902.

[0126] The D50 (median diameter) of the mixture 902 is preferably, for example, 600 nm to 20 μm, more preferably 1 μm to 10 μm, or more preferably 600 nm to 10 μm, or more preferably 1 μm to 20 μm. If the mixture 902 is finely powdered in this manner, when it is mixed with a composite oxide containing lithium, a transition metal M, and oxygen in a later step, the mixture 902 can be easily distributed uniformly on the surfaces of the composite oxide particles.

[0127] <Step S41> Next, in step S41, the LiMO obtained in step S14 is mixed with mixture 902. The ratio of the number of transition metal atoms M in the composite oxide containing lithium, transition metal, and oxygen to the number of magnesium atoms Mg in mixture 902 is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0128] The mixing in step S41 is preferably performed under milder conditions than those in step S12 so as not to destroy the composite oxide particles. For example, it is preferable to perform the mixing under conditions with a lower rotation speed or shorter time than those in step S12. It can also be said that a dry method is less likely to destroy particles than a wet method. For example, a ball mill, a bead mill, etc. can be used for mixing. When using a ball mill, it is preferable to use zirconia balls as the grinding media.

[0129] <Step S42> Next, in step S42, the mixed materials are collected to obtain a mixture 903.

[0130] Although this embodiment describes a method of adding a mixture of lithium fluoride and magnesium fluoride to lithium cobalt oxide with few impurities, one embodiment of the present invention is not limited thereto. Instead of the mixture 903 in step S42, a lithium cobalt oxide starting material to which a magnesium source, a fluorine source, and the like are added and then fired may be used. In this case, there is no need to separate steps S11 to S14 from steps S21 to S23, which simplifies the process and increases productivity.

[0131] Alternatively, lithium cobalt oxide to which magnesium and fluorine have been added in advance may be used. If lithium cobalt oxide to which magnesium and fluorine have been added is used, the steps up to step S42 can be omitted, which is simpler.

[0132] Alternatively, a magnesium source and a fluorine source may be further added to lithium cobalt oxide to which magnesium and fluorine have been added in advance.

[0133] <Step S43> Next, in step S43, the mixture 903 is heated in an atmosphere containing oxygen. This step is sometimes referred to as the first annealing (first temperature conditions) to distinguish it from other heating steps. It is more preferable that this heating be performed under conditions that have an adhesion suppression effect so that the particles of the mixture 903 do not adhere to each other.

[0134] Examples of heating that has the effect of suppressing adhesion include heating while stirring the mixture 903, heating while vibrating the container containing the mixture 903, and the like.

[0135] The heating temperature in step S43 must be equal to or higher than the temperature at which the reaction between LiMO2 and the mixture 902 proceeds. The temperature at which the reaction proceeds here is any temperature at which mutual diffusion of elements contained in LiMO2 and the mixture 902 occurs. Therefore, it may be lower than the melting temperature of these materials. For example, in the case of salts and oxides, the melting temperature T m 0.757 times (Tanman temperature T d) solid-state diffusion occurs.

[0136] However, the reaction proceeds more easily if the annealing temperature is equal to or higher than the temperature at which at least a portion of mixture 903 melts. Therefore, the annealing temperature is preferably equal to or higher than the eutectic point of mixture 902. When mixture 902 contains LiF and MgF2, the temperature in step S43 is preferably equal to or higher than the eutectic point of 742°C.

[0137] Furthermore, in the mixture 903, which is mixed so that the molar ratio of LiCoO2:LiF:MgF2 is 100:0.33:1, an endothermic peak is observed around 830°C in differential scanning calorimetry (DSC measurement). Therefore, an annealing temperature of 830°C or higher is more preferable. The mixture 903 contains at least fluorine, lithium, cobalt, and magnesium. The mixture 903 also has an O3'-type crystal structure.

[0138] A higher annealing temperature is preferable because the reaction proceeds more easily, the annealing time is shorter, and productivity is increased.

[0139] However, the annealing temperature must be below the decomposition temperature of LiMO2 (1130°C for LiCoO2). At temperatures close to the decomposition temperature, there is concern that LiMO2 may decompose, albeit in trace amounts. Therefore, the annealing temperature is preferably 1130°C or lower, more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0140] Therefore, the annealing temperature is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, it is preferably 742°C to 1130°C, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, it is preferably 830°C to 1130°C, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.

[0141] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride in the atmosphere within an appropriate range.

[0142] In the fabrication method described in this embodiment, some materials, such as LiF, a fluorine source, function as a flux. This function allows the annealing temperature to be lowered to a temperature below the decomposition temperature of LiMO, for example, between 742°C and 950°C, and allows additives such as magnesium to be distributed more highly in the surface layer than in the center, resulting in a positive electrode active material with excellent properties.

[0143] However, because LiF is lighter than oxygen molecules, it can volatilize and dissipate when heated. In this case, the amount of LiF in the mixture 903 decreases, weakening its function as a flux. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, Li and F on the LiMO2 surface may react to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0144] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, the volatilization of LiF in the mixture 903 can be suppressed.

[0145] The annealing is preferably performed for an appropriate time, which varies depending on conditions such as the annealing temperature, the size and composition of the LiMO2 particles in step S14, etc. If the particles are small, a lower temperature or shorter time may be more preferable than if the particles are large.

[0146] For example, when the average particle size (D50) of the particles in step S14 is about 12 μm, the annealing temperature is preferably, for example, 600° C. or more and 950° C. or less. The annealing time is, for example, preferably 3 hours or more, more preferably 10 hours or more, and even more preferably 60 hours or more.

[0147] On the other hand, when the average particle size (D50) of the particles in step S24 is about 5 μm, the annealing temperature is preferably, for example, 600° C. to 950° C. The annealing time is preferably, for example, 1 hour to 10 hours, more preferably about 2 hours.

[0148] The temperature drop time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0149] <Step S31> Next, in step S31, an additive source is prepared. The additive source may contain one or more elements selected from the group consisting of zirconium, aluminum, nickel, manganese, titanium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. FIG. 4 illustrates an example in which a zirconium source is used as the additive source.

[0150] The source of each additive is preferably an oxide, hydroxide, fluoride, alkoxide, or the like.

[0151] <Step S61> Next, in step S61, the annealed mixture 903 is mixed with an additive source. It can be said that the additive is contained in the surface of the annealed mixture 903.

[0152] Examples of the mixing method that can be used include a solid phase method, a sol-gel method, a sputtering method, a mechanochemical method, a CVD method, etc. The solid phase method and the sol-gel method are preferable because they allow the additive to be easily incorporated into the surface of the mixture 903 after annealing at atmospheric pressure and room temperature.

[0153] In this specification, the sol-gel method refers to a method in which a solution of an organic metal compound is used as a starting material, and the solution is converted into a sol in which fine particles of metal oxide or hydroxide are dissolved by hydrolysis and polymerization of the compound in the solution, and the reaction is further advanced to gel, and the resulting amorphous porous gel is heated to produce a film or crystals.

[0154] When the sol-gel method is used, first, alkoxide as an additive source dissolved in alcohol is mixed with the annealed mixture 903 .

[0155] For example, when zirconium is used as the additive source, zirconium (IV) tetrapropoxide can be used, and the alcohol can be isopropanol (2-propanol).

[0156] Next, the mixture of the isopropanol solution of zirconium (IV) tetrapropoxide and the annealed mixture 903 is stirred. Stirring can be performed, for example, with a magnetic stirrer. The stirring time may be long enough to cause the water in the atmosphere and the zirconium (IV) tetrapropoxide to undergo hydrolysis and polycondensation reactions, and can be performed for, for example, 60 hours at room temperature.

[0157] The precipitate is recovered from the mixed solution after the above treatment. The recovery method can be filtration, centrifugation, evaporation to dryness, or the like. In this embodiment, the precipitate is recovered by evaporation to dryness. In this embodiment, the precipitate is dried by ventilation at 95°C.

[0158] <Step S62> Next, in step S62, the dried material is collected to obtain a mixture 904.

[0159] <Step S63> Next, the mixture 904 synthesized in step S62 is heated. (If S43 is called the first annealing, the heating in S63 may be called the second annealing (second temperature conditions).) The heating time is preferably maintained at the specified temperature for 50 hours or less, more preferably 2 to 10 hours, and even more preferably 1 to 3 hours.

[0160] The temperature range of the specified temperature is preferably 500°C or higher and 1200°C or lower, and more preferably 800°C or higher and 1000°C or lower.

[0161] It is also preferable to heat in an atmosphere containing oxygen.

[0162] In this embodiment, the specified temperature is set to 800° C. and is maintained for two hours, the temperature is increased at a rate of 200° C. / h, and the flow rate of the dry atmosphere is set to 10 L / min.

[0163] <Step S64> In step S64, crushing is carried out, and mixing is carried out if necessary.

[0164] <Step S66> Next, in step S66, the crushed material is recovered to produce the positive electrode active material 100. At this time, it is preferable to further sieve the recovered particles. By sieving, if any positive electrode active material particles are stuck together, this can be resolved.

[0165] Next, a manufacturing method different from that shown in FIG. 4 will be described with reference to FIGS. 5 to 7. Note that since there are many commonalities with FIG. 4, the different parts will be mainly described. For the commonalities, the explanation for FIG. 4 can be referred to. Note that although the manufacturing flows shown in FIGS. 4, 5, 6, and 7 indicate that a positive electrode active material 100 is ultimately obtained, this does not mean that the same structure and components will be obtained. If the manufacturing process is different, at least some of the characteristics will be different, such as particle size, protrusions, concentration distribution, and particle appearance.

[0166] 4, the production method in which the annealed mixture 903 is mixed with a zirconium source as an additive source in step S61 has been described, but this is not a limitation of one embodiment of the present invention. As shown in steps S32 and S33 of FIGS. 5 to 7, other additives may be further mixed. Crushing may be performed before the mixing in steps S32 and S33 of FIGS. 5 to 7.

[0167] The additive may be, for example, one or more selected from nickel, aluminum, manganese, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. 5 to 7 show an example in which two additives are further used: an aluminum source in step S32 and a nickel source in step S33.

[0168] The additives can be mixed by, for example, a solid phase method, a sol-gel method, a sputtering method, a mechanochemical method, a CVD method, etc. A combination of several methods may also be used.

[0169] As shown in FIG. 5, a nickel source can be mixed in step S61-1, and then a zirconium source and an aluminum source can be mixed in step S61-2. Mixing can be performed by a dry method or a wet method. In this case, for example, step S61-1 can be performed by a solid-phase method, and step S61-2 can be performed by a sol-gel method. When the sol-gel method is used, an aluminum alkoxide is used as the aluminum source, and a zirconium alkoxide is used as the zirconium source. The subsequent steps S62, S63, and S64 can be performed in the same procedure to obtain the positive electrode active material 100.

[0170] As shown in FIG. 6, various additive sources may be mixed with mixture 902 in step S41. Alternatively, annealing may be performed multiple times in steps S53 and S55, with the adhesion suppression operation step S54 being performed between them. The annealing conditions in steps S53 and S55 can be determined by referring to the description of step S43. Examples of the adhesion suppression operation include crushing with a pestle, mixing using a ball mill, mixing using a planetary mixer, sieving, and vibrating the container containing the composite oxide. After annealing in the subsequent step S55, crushing is performed in step S55-2, and the resulting mixture is recovered to obtain positive electrode active material 100.

[0171] 7, LiMO2 and mixture 902 may be mixed and annealed in step S41, and then various additive sources may be mixed in step S61. Mixing may be performed by either a dry or wet method. The annealing conditions may refer to the description of step S43. The subsequent steps S62, S63, and S64 may be performed in the same manner to obtain positive electrode active material 100.

[0172] In this way, by separating the steps of introducing the transition metal M and the additive, it may be possible to change the depth profile of each element. For example, the concentration of the additive can be increased in the surface layer portion compared to the center portion of the particle. Furthermore, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of the additive element to this reference can be made higher in the surface layer portion than in the center portion. The additive element is particularly concentrated in the convex portion.

[0173] This embodiment can be used in combination with other embodiments.

[0174] (Embodiment 3) In this embodiment, a lithium-ion secondary battery including a positive electrode active material according to one embodiment of the present invention will be described. The secondary battery includes at least an outer casing, a current collector, an active material (a positive electrode active material or a negative electrode active material), a conductive additive, and a binder. The secondary battery also includes an electrolyte solution containing a lithium salt or the like dissolved therein. In the case of a secondary battery using an electrolyte solution, a positive electrode, a negative electrode, and a separator are provided between the positive electrode and the negative electrode.

[0175] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer preferably includes the positive electrode active material described in Embodiment 1, and may further include a binder, a conductive additive, and the like.

[0176] FIG. 12A shows an example of a schematic cross-sectional view of a positive electrode.

[0177] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry onto the metal foil and drying it. After drying, the metal foil may be further pressed. The positive electrode is formed by forming an active material layer on the current collector 550.

[0178] The slurry is a material liquid used to form an active material layer on the current collector 550, and refers to a material containing at least an active material, a binder, and a solvent, and preferably further mixed with a conductive additive. The slurry is also called an electrode slurry or an active material slurry, and is sometimes called a positive electrode slurry when forming a positive electrode active material layer, and a negative electrode slurry when forming a negative electrode active material layer.

[0179] The conductive additive, also called a conductivity-imparting agent or conductive material, is made of a carbon material. By attaching the conductive additive between multiple active materials, the active materials are electrically connected to each other, thereby increasing their conductivity. Note that "attachment" does not only refer to physical adhesion between the active material and the conductive additive, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covering part of the surface of the active material, the conductive additive fitting into the surface irregularities of the active material, and electrical connection even when not in contact with each other.

[0180] Carbon black (furnace black, acetylene black, graphite, etc.) is a typical carbon material used as a conductive additive.

[0181] FIG. 12A illustrates acetylene black 553 as a conductive additive. FIG. 12A also illustrates an example in which a second active material 562 having a particle size smaller than that of the positive electrode active material 100 shown in Embodiment 1 is mixed. Mixing particles of different sizes can provide a high-density positive electrode active material layer, thereby increasing the charge / discharge capacity of the secondary battery. The positive electrode active material 100 shown in Embodiment 1 corresponds to the active material 561 in FIG. 12A.

[0182] A binder (resin) is mixed to bond the active material to a current collector 550 such as a metal foil as the positive electrode of a secondary battery. The binder is also called a binding agent. The binder is a polymer material, and if a large amount of binder is added, the proportion of active material in the positive electrode decreases, thereby reducing the discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum. In FIG. 12A, the areas not filled with the active material 561, second active material 562, and acetylene black 553 indicate voids or binder.

[0183] 12A shows an example in which active material 561 is spherical, but the shape is not particularly limited and various shapes are possible. The cross-sectional shape of active material 561 may be elliptical, rectangular, trapezoidal, conical, quadrangular with rounded corners, or asymmetrical.

[0184] 12B shows an example in which the active material 561 has various shapes. FIG 12B shows an example different from FIG 12A.

[0185] In the positive electrode in FIG. 12B, graphene 554 is used as a carbon material used as a conductive additive.

[0186] Graphene is a carbon material that has amazing electrical, mechanical, and chemical properties and is expected to be applied in a variety of fields, including field-effect transistors and solar cells.

[0187] In FIG. 12B, a positive electrode active material layer including an active material 561, graphene 554, and acetylene black 553 is formed on a current collector 550.

[0188] In the step of mixing graphene 554 and acetylene black 553 to obtain electrode slurry, the weight of the carbon black to be mixed is preferably 1.5 to 20 times, more preferably 2 to 9.5 times, that of graphene.

[0189] Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, the dispersion stability of acetylene black 553 is excellent and aggregation is unlikely to occur during slurry preparation. Furthermore, when the mixture of graphene 554 and acetylene black 553 is within the above range, a higher electrode density can be achieved than a positive electrode using only acetylene black 553 as a conductive additive. Increasing the electrode density can increase the capacity per unit weight. Specifically, the density of the positive electrode active material layer measured by weight can be increased to more than 3.5 g / cc. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is within the above range, a synergistic effect can be expected in terms of increasing the capacity of the secondary battery, which is preferable.

[0190] Although the electrode density is lower than that of a positive electrode using only graphene as a conductive additive, rapid charging can be achieved by mixing the first carbon material (graphene) and the second carbon material (acetylene black) in the above range. Furthermore, when the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode and the mixture of graphene 554 and acetylene black 553 is in the above range, the secondary battery is more stable and a synergistic effect of being able to handle even faster charging can be expected, which is preferable.

[0191] These features are effective for use as a secondary battery for vehicles.

[0192] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0193] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0194] By using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and setting the mixture ratio of acetylene black and graphene in an optimal range, it is possible to achieve both high electrode density and creation of appropriate gaps necessary for ion conduction, and a secondary battery for vehicle use having high energy density and favorable output characteristics can be obtained.

[0195] This configuration is also effective in a portable information terminal, and the secondary battery can be miniaturized and have a high capacity by using the positive electrode active material 100 described in Embodiment 1 for the positive electrode and by setting the mixture ratio of acetylene black and graphene in an optimal range. In addition, by setting the mixture ratio of acetylene black and graphene in an optimal range, the portable information terminal can be rapidly charged.

[0196] 12B, the regions not filled with the active material 561, graphene 554, and acetylene black 553 indicate voids or binders. The voids are necessary for the electrolyte to penetrate, but if there are too many voids, the electrode density decreases, and if there are too few voids, the electrolyte cannot penetrate, and if the voids remain even after the secondary battery is fabricated, the energy density decreases.

[0197] By using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode and by adjusting the mixture ratio of acetylene black and graphene to an optimal range, it is possible to achieve both high electrode density and the creation of appropriate gaps necessary for ion conduction, thereby obtaining a secondary battery with high energy density and good output characteristics.

[0198] 12C illustrates an example of a positive electrode in which carbon nanotubes 555 are used instead of graphene. Fig. 12C shows an example different from Fig. 12B. The use of carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and improve dispersibility.

[0199] In FIG. 12C, the regions not filled with active material 561, carbon nanotubes 555, and acetylene black 553 indicate voids or binders.

[0200] Another example of a positive electrode is shown in Fig. 12D. Fig. 12C shows an example in which carbon nanotubes 555 are used in addition to graphene 554. Using both graphene 554 and carbon nanotubes 555 can prevent aggregation of carbon black such as acetylene black 553 and further improve dispersibility.

[0201] In FIG. 12D, the regions not filled with the active material 561, the carbon nanotubes 555, the graphene 554, and the acetylene black 553 indicate voids or binders.

[0202] A secondary battery can be produced by using any one of the positive electrodes shown in Figures 12A to 12D, placing a separator on the positive electrode, and placing the laminate in a container (such as an exterior body or a metal can) that houses the laminate, with the negative electrode on the separator, and filling the container with an electrolyte.

[0203] Although the above configuration shows an example of a secondary battery using an electrolytic solution, the present invention is not particularly limited.

[0204] For example, the positive electrode active material 100 shown in the first embodiment can be used to fabricate a semi-solid battery or an all-solid battery.

[0205] In this specification, a semi-solid battery refers to a battery that has a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. The term "semi-solid" does not mean that the ratio of solid material is 50%. Semi-solid means that the battery has solid properties, such as small volume change, while also possessing some liquid-like properties, such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, the battery may be made by infiltrating a porous solid material with a liquid material.

[0206] In this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between a positive electrode and a negative electrode. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries. Polymer electrolyte secondary batteries may also be called semi-solid batteries.

[0207] When a semi-solid battery is fabricated using the positive electrode active material 100 described in Embodiment 1, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, the semi-solid battery can have a high charge / discharge voltage. Alternatively, a semi-solid battery with high safety or reliability can be realized.

[0208] The positive electrode active material described in the first embodiment may be mixed with other positive electrode active materials.

[0209] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. Examples of such compounds include LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, MnO2, and the like.

[0210] In addition, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0211] In addition, as another positive electrode active material, a lithium manganese composite oxide represented by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particles of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≦ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particles of the lithium manganese composite oxide can be measured using, for example, ICP-MS (inductively coupled plasma mass spectrometer). Also, the oxygen composition of the entire particles of the lithium manganese composite oxide can be measured using, for example, EDX (energy dispersive X-ray analysis method). Further, it can be obtained by using valence evaluation of melting gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0212] <Binder> As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0213] 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.

[0214] Alternatively, it is preferable to use materials such as polystyrene, polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.

[0215] The binder may be used in combination with two or more of the above.

[0216] 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.

[0217] 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.

[0218] 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.

[0219] 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.

[0220] <Positive electrode current collector> The current collector can be made of a highly conductive material, such as a metal such as stainless steel, gold, platinum, aluminum, or titanium, or an alloy thereof. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, can also be used. The current collector may also be made of a metal element that reacts with silicon to form a silicide. Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate, sheet, mesh, punched metal, expanded metal, or the like. It is preferable that the current collector have a thickness of 5 μm to 30 μm.

[0221] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and may further include a conductive additive and a binder.

[0222] <Negative electrode active material> As the negative electrode active material, for example, an alloy-based material or a carbon-based material can be used.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries using graphite to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and higher safety compared to lithium metal.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0232] 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.

[0233] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, or may be made of copper, etc. It is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0234] [Separator] A separator is placed between the positive electrode and the negative electrode. The separator can be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0235] 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).

[0236] 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.

[0237] 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.

[0238] 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.

[0239] [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.

[0240] 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.

[0241] 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 , Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalato)borate (Li(C2O4)2, LiBOB), etc. can be used alone or in any combination and ratio of two or more of these.

[0242] 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.

[0243] The electrolyte may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % relative to the solvent.

[0244] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0245] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0246] 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.

[0247] 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.

[0248] Therefore, the positive electrode active material 100 obtained in the first embodiment can be applied to an all-solid-state battery. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and excellent characteristics can be obtained.

[0249] [Exterior body] The exterior body of the secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like exterior body can be used. Examples of the film include a three-layer structure film in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body.

[0250] This embodiment can be used in combination with other embodiments.

[0251] (Fourth embodiment) In this embodiment mode, examples of a plurality of shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0252] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 13A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 13B is an external view, and Fig. 13C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices.

[0253] 13A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 13A and 13B are not completely identical corresponding views.

[0254] In Fig. 13A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked together. These are sealed between a negative electrode can 302 and a positive electrode can 301. Note that the gasket used for sealing is not shown in Fig. 16A. The spacer 322 and the washer 312 are used to protect the interior or to fix the position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0255] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 .

[0256] To prevent short-circuiting between the positive electrode and the negative electrode, a separator 310 and a ring-shaped insulator 313 are arranged so as to cover the side and top surfaces of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0257] FIG. 13B is a perspective view of the completed coin-type secondary battery.

[0258] In the coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector. The negative electrode 307 is not limited to a laminated structure, and may be made of lithium metal foil or a lithium-aluminum alloy foil.

[0259] 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.

[0260] 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, etc., it is preferable to coat them with nickel, aluminum, etc. Positive electrode can 301 is electrically connected to positive electrode 304, and negative electrode can 302 is electrically connected to negative electrode 307.

[0261] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in FIG. 13C, positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with positive electrode can 301 facing downwards, and positive electrode can 301 and negative electrode can 302 are crimped together via gasket 303 to produce coin-type secondary battery 300.

[0262] By using it as a secondary battery, it is possible to obtain a coin-type secondary battery 300 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that when a secondary battery is formed between the negative electrode 307 and the positive electrode 304, the separator 310 may not be necessary.

[0263] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 14A. As shown in Fig. 14A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface, and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0264] 14B is a schematic diagram showing the cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 14B 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.

[0265] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals or alloys of these metals with other metals (e.g., stainless steel). To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0266] Since the positive and negative electrodes used in a cylindrical storage battery are wound up, it is preferable to form active materials on both sides of the current collector.

[0267] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0268] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases with an increase in temperature. This increase in resistance limits the amount of current and prevents abnormal heat generation. The PTC element can be made of a barium titanate (BaTiO3)-based semiconductor ceramic or the like.

[0269] 14C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via wiring 626. The control circuit 620 may be a charge / discharge control circuit that performs charging and discharging, or a protection circuit that prevents overcharging or overdischarging.

[0270] 14D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel, in series, or in series after being connected in parallel. By configuring the power storage system 615 to have a plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0271] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0272] A temperature control device may be provided between the multiple secondary batteries 616. When the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes the performance of the power storage system 615 less susceptible to the outside temperature.

[0273] 14D, the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 600 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 600 via a conductive plate 614.

[0274] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0275] A secondary battery 913 shown in Fig. 15A has a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in Fig. 15A, 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.

[0276] 15B, the housing 930 shown in Fig. 15A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 15B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0277] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking effect of the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0278] 15C shows the structure of wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the stacked sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0279] Alternatively, a secondary battery 913 may be provided having a wound body 950a as shown in Fig. 16. The wound body 950a shown in Fig. 16A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0280] By using the positive electrode active material 100 obtained in Embodiment 1 for the positive electrode 932, the secondary battery 913 can have a large capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0281] The separator 933 has a width wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable because of its high safety and productivity.

[0282] 16B, negative electrode 931 is electrically connected to terminal 951 by ultrasonic bonding, welding, or crimping. Terminal 951 is electrically connected to terminal 911a. Positive electrode 932 is electrically connected to terminal 952 by ultrasonic bonding, welding, or crimping. Terminal 952 is electrically connected to terminal 911b.

[0283] 16C, wound body 950a and the electrolyte are covered by casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of casing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0284] As shown in Fig. 16B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a allows the secondary battery 913 to have a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 16A and 16B, the descriptions of the secondary battery 913 shown in Figs. 15A to 15C can be referred to.

[0285] <Laminated secondary battery> 17A and 17B show examples of external views of a laminated secondary battery, which includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0286] FIG. 18A 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. 18A.

[0287] <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. 17A will be described with reference to FIGS. 18B and 18C.

[0288] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 18B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five negative electrodes and four positive electrodes are used. This can also be called a laminate consisting of a negative electrode, separator, and positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0289] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0290] Next, as shown in Fig. 18C, 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.

[0291] Next, electrolyte 508 (not shown) is introduced into the inside of exterior body 509 through an inlet provided in exterior body 509. The introduction of electrolyte 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, laminated secondary battery 500 can be produced.

[0292] By using the positive electrode active material 100 obtained in the first embodiment for the positive electrode 503, the secondary battery 500 can be made to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics.

[0293] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be described with reference to FIG.

[0294] FIG. 19A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (which can also be called a thick flat plate shape). FIG. 19B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is attached to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0295] The inside of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0296] 19B, for example, a secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to a terminal 514. The circuit board 540 is also electrically connected to an antenna 517, one 551 of a positive electrode lead and a negative electrode lead of a secondary battery 513, and the other 552 of a positive electrode lead and a negative electrode lead of the secondary battery 513.

[0297] Alternatively, as shown in FIG. 19C, the circuit system 590 may include a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via the terminal 514.

[0298] The antenna 517 is not limited to a coil shape, and may be, for example, a wire or plate shape. Also, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

[0299] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field caused by the secondary battery 513. The layer 519 can be made of, for example, a magnetic material.

[0300] This embodiment mode can be freely combined with other embodiment modes.

[0301] (Embodiment 5) In this embodiment, an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in the first embodiment will be described.

[0302] As shown in FIG. 20A, a secondary battery 400 according to one embodiment of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0303] Positive electrode 410 includes positive electrode current collector 413 and positive electrode active material layer 414. Positive electrode active material layer 414 includes positive electrode active material 411 and solid electrolyte 421. Positive electrode active material 411 is made of positive electrode active material 100 obtained in Embodiment 1. Positive electrode active material layer 414 may also include a conductive additive and a binder.

[0304] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0305] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive additive and a binder. When metallic lithium is used for the negative electrode 430, the negative electrode 430 may not include the solid electrolyte 421, as shown in FIG. 20B . Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0306] As the solid electrolyte 421 of the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0307] Sulfide-based solid electrolytes include thiosilicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0308] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON-type crystal structure (Li 1-Y Al Y Ti 2-Y (PO4)3, etc.), materials with garnet-type crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON-type crystal structure (Li 14 ZnGeO 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide glass-ceramics (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0309] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as solid electrolytes.

[0310] Also, different solid electrolytes may be mixed and used.

[0311] Among them, Li with NASICON type crystal structure 1+x Al x Ti 2-x Since (PO4)3(0[x[1]) (hereinafter referred to as LATP) contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, a synergistic effect in improving cycle characteristics can be expected, which is preferable. In addition, improved productivity can be expected due to a reduction in the number of steps. In this specification and the like, the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), which has a structure in which MO6 octahedra and XO4 tetrahedra are arranged three-dimensionally with vertices shared.

[0312] [Shapes of exterior body and secondary battery] The exterior of the secondary battery 400 of one embodiment of the present invention can be made of various materials and in various shapes, but preferably has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

[0313] For example, Figure 21 shows an example of a cell for evaluating materials for all-solid-state batteries.

[0314] 21A is a cross-sectional schematic diagram of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw and wing nut 764 that fix them in place, and electrode plate 753 is pressed by rotating a holding screw 763 to fix the evaluation material. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is provided between upper member 762 and holding screw 763 to provide a tight seal.

[0315] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 21B.

[0316] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 21C. Note that the same reference numerals are used for the same parts in Figs. 21A to 21C.

[0317] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be said to correspond to a positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be said to correspond to a negative electrode terminal. Electrical resistance and the like can be measured by applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0318] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0319] Fig. 22A shows a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 21. The secondary battery in Fig. 22A has external electrodes 771 and 772 and is sealed in an exterior body having multiple package members.

[0320] An example of a cross section taken along the dashed line in Figure 22A is shown in Figure 22B. A laminate including positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is enclosed and sealed within package member 770a, which is a flat plate with electrode layer 773a provided thereon, frame-shaped package member 770b, and package member 770c, which is a flat plate with electrode layer 773b provided thereon. Package members 770a, 770b, and 770c can be made of an insulating material, such as a resin material or ceramic.

[0321] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal, while the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0322] By using the positive electrode active material 100 obtained in the first embodiment, an all-solid-state secondary battery having high energy density and good output characteristics can be realized.

[0323] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0324] (Embodiment 6) This embodiment is an example different from the cylindrical secondary battery shown in Fig. 14D, and an example of application to an electric vehicle (EV) is shown using Fig. 23C.

[0325] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0326] The internal structure of the first battery 1301a may be a wound type as shown in Fig. 15A or 16C, or a stacked type as shown in Fig. 17A or 17B. The first battery 1301a may use the all-solid-state battery of Embodiment 5. Using the all-solid-state battery of Embodiment 5 for the first battery 1301a allows for a high capacity, improved safety, and reduction in size and weight.

[0327] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0328] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0329] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0330] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0331] The first battery 1301a will be described with reference to FIG. 23A.

[0332] FIG. 23A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to vibrations or shaking from the outside (such as the road surface), it is preferable to fix multiple secondary batteries using fixing portions 1413 and 1414 or a battery housing box. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0333] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor.

[0334] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used as the oxide 530. In particular, the In-M-Zn oxide that can be used as the oxide 530 is preferably a C-Axls Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In-Ga oxide or an In-Zn oxide may be used as the oxide 530. A CAAC-OS is an oxide semiconductor that has multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface where the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region is also a region with a uniform lattice arrangement. Furthermore, the CAAC-OS has a region where multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a location where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with a different uniform lattice arrangement in the region where multiple crystalline regions are connected. In other words, the CAAC-OS is an oxide semiconductor that is c-axis oriented but not clearly oriented in the ab-plane direction. The CAC-OS is, for example, a material in which elements constituting a metal oxide are unevenly distributed within a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof. In the following, a state in which one or more metal elements are unevenly distributed in a metal oxide and regions containing the metal elements are mixed in a size of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a size close to this size, is also referred to as a mosaic or patch state.

[0335] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0336] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0337] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0338] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0339] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0340] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0341] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0342] Furthermore, because the control circuit unit 1320 can be used in high-temperature environments, it is preferable to use transistors using oxide semiconductors. To simplify the process, the control circuit unit 1320 may be formed using unipolar transistors. Transistors using oxide semiconductors in the semiconductor layer have a wider operating ambient temperature range than single-crystal silicon, from -40°C to 150°C, and their characteristics change less when the secondary battery is heated than single-crystal silicon. The off-current of transistors using oxide semiconductors is below the lower limit of measurement regardless of temperature, even at 150°C, whereas the off-current characteristics of single-crystal silicon transistors are highly temperature-dependent. For example, at 150°C, the off-current of single-crystal silicon transistors increases, and the current on / off ratio is not sufficiently large. The control circuit unit 1320 can improve safety. Furthermore, combining the control circuit unit 1320 with a secondary battery using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode can achieve a synergistic effect in terms of safety. A secondary battery using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode and the control circuit unit 1320 can significantly contribute to eliminating accidents, such as fires, caused by secondary batteries.

[0343] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for secondary batteries to address 10 causes of instability, such as micro-short circuits. The functions for addressing the 10 causes of instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of degradation, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits. The control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for secondary batteries can be miniaturized.

[0344] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0345] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0346] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0347] FIG. 23B shows an example of a block diagram of the battery pack 1415 shown in FIG. 23A.

[0348] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside and the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0349] The switch unit 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch unit 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, facilitating integration. Furthermore, OS transistors can be fabricated using the same manufacturing equipment as Si transistors, allowing for low-cost fabrication. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The control circuit unit 1320 occupies a smaller volume, enabling miniaturization.

[0350] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle devices, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle devices. Lead-acid batteries are often used as the second battery 1311 due to their cost advantages. Lead-acid batteries have a higher self-discharge rate than lithium-ion secondary batteries and are prone to degradation due to a phenomenon called sulfation. Using a lithium-ion secondary battery as the second battery 1311 offers the advantage of being maintenance-free, but after prolonged use (e.g., three years or more), there is a risk of abnormalities occurring that cannot be detected at the time of manufacture. In particular, if the second battery 1311, which starts the inverter, becomes inoperable, even if the first batteries 1301a and 1301b still have remaining capacity, the motor cannot be started. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery, and the second battery is constantly charged to maintain a fully charged state.

[0351] In this embodiment, an example in which lithium ion secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown. A lead storage battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, high capacity can be achieved, and miniaturization and weight reduction are possible.

[0352] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 or the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0353] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions according to the charging characteristics of the secondary battery used, and can perform rapid charging.

[0354] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU and a GPU.

[0355] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW. Charging is also possible by receiving power from external charging equipment using a wireless power supply system, etc.

[0356] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0357] Moreover, the secondary battery of the present embodiment described above has a high-density positive electrode by using the positive electrode active material 100 obtained in the first embodiment. Furthermore, by using graphene as a conductive additive, a secondary battery with significantly improved electrical characteristics can be realized, as a synergistic effect of suppressing capacity reduction and maintaining high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and can provide a vehicle with a long driving range, specifically, a driving range of 500 km or more per charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0358] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material 100 described in embodiment 1, and the usable capacity can be increased as the charging voltage increases. Furthermore, by using the positive electrode active material 100 described in embodiment 1 for the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0359] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0360] 14D, 16C, and 23A, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, secondary batteries can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0361] 24A to 24D illustrate examples of transportation vehicles using one embodiment of the present invention. An automobile 2001 shown in FIG. 24A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 4 is installed in one or more locations. The automobile 2001 shown in FIG. 24A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0362] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method, connector standards, or the like, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station provided in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electricity storage device mounted on automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0363] Furthermore, 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 two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0364] 24B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series for a maximum voltage of 170 V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 24A, and therefore a description thereof will be omitted.

[0365] FIG. 24C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, which is obtained by connecting in series one hundred or more secondary batteries with a nominal voltage of 3.0 V to 5.0 V. Therefore, a secondary battery with little variation in characteristics is required. By using a secondary battery in which the positive electrode active material 100 described in the first embodiment is used for the positive electrode, a secondary battery with stable battery characteristics can be manufactured, and mass production at low cost is possible from the viewpoint of yield. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those shown in FIG. 24A are provided, and therefore a description thereof will be omitted.

[0366] As an example, Fig. 24D shows an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 24D has wheels for takeoff and landing, it can also be said to be part of a transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and includes the secondary battery module and a charge control device.

[0367] The secondary battery module of the aircraft 2004 has, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in Fig. 24A, and therefore a description thereof will be omitted.

[0368] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0369] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 25A and 25B.

[0370] 25A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 through a wiring 2611 or the like. The power storage device 2612 may be electrically connected to a ground-mounted charging device 2604. The power storage device 2612 can be charged with power obtained by the solar panel 2610. The power stored in the power storage device 2612 can be charged to a secondary battery included in a vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0371] The power stored in the power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0372] 25B illustrates an example of a power storage device 700 according to one embodiment of the present invention. As illustrated in FIG. 25B, a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. The power storage device 791 may be provided with the control circuit described in Embodiment 6. A synergistic effect on safety can be obtained by using a secondary battery in which the positive electrode active material 100 obtained in Embodiment 1 is used for the power storage device 791. The control circuit described in Embodiment 6 and the secondary battery in which the positive electrode active material 100 described in Embodiment 1 is used for the positive electrode can greatly contribute to preventing accidents such as fires caused by the power storage device 791 including a secondary battery.

[0373] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also called a control device), a display 706, and a router 709 by wiring.

[0374] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via an outlet (not shown).

[0375] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0376] The power storage controller 705 has a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (for example, from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day, based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791, based on the amount of power demand predicted by the prediction unit 712.

[0377] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, or the mobile electronic device.

[0378] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0379] (Embodiment 8) In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

[0380] 26A is an example of an electric bicycle using the power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 shown in FIG. 26A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0381] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 26B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery, an example of which is shown in Embodiment 6. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. The control circuit 8704 may be provided with the small solid-state secondary battery shown in FIGS. 22A and 22B. By providing the small solid-state secondary battery shown in FIGS. 22A and 22B in the control circuit 8704, power can be supplied to retain data in a memory circuit included in the control circuit 8704 for a long period of time. Furthermore, a synergistic effect in terms of safety can be obtained by combining it with a secondary battery using, as its positive electrode, positive electrode active material 100 obtained in embodiment 1. The secondary battery using, as its positive electrode, positive electrode active material 100 obtained in embodiment 1 and control circuit 8704 can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0382] 26C is an example of a two-wheeled vehicle including a power storage device of one embodiment of the present invention. A scooter 8600 shown in FIG. 26C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602 includes a plurality of secondary batteries each using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode, and thus can have a high capacity, which can contribute to miniaturization.

[0383] 26C, the power storage device 8602 can be stored in the under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0384] (Embodiment 9) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a secondary battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0385] 27A shows an example of a mobile phone. Mobile phone 2100 includes a display unit 2102 built into housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that mobile phone 2100 also includes secondary battery 2107. By including secondary battery 2107 using positive electrode active material 100 described in Embodiment 1 as a positive electrode, high capacity can be achieved, and a configuration that can accommodate space saving associated with a smaller housing can be realized.

[0386] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0387] The operation button 2103 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.

[0388] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0389] The mobile phone 2100 also has an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Charging may also be performed by wireless power supply without using the external connection port 2104.

[0390] The mobile phone 2100 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.

[0391] FIG. 27B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be installed in the unmanned aerial vehicle 2300.

[0392] Fig. 27C shows an example of a robot. A robot 6400 shown in Fig. 27C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0393] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0394] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0395] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0396] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6409 is suitable for the robot 6400.

[0397] 27D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, multiple cameras 6303 arranged on the side, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0398] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0399] Figure 28A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. To improve water resistance for everyday use or outdoor use, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging, with the connector exposed.

[0400] For example, the secondary battery of one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 28A. The eyeglasses-type device 4000 includes a frame 4000a and a display portion 4000b. By mounting the secondary battery on temple portions of the curved frame 4000a, the eyeglasses-type device 4000 can be lightweight, well-balanced in weight, and has a long continuous use time. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[0401] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and can achieve a space-saving configuration that can be achieved by miniaturizing the housing.

[0402] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0403] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a structure that can accommodate space saving due to miniaturization of the housing can be realized.

[0404] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an inner region of the belt portion 4006a. The secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density, and a configuration that can accommodate space saving associated with miniaturization of the housing can be realized.

[0405] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on a wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided in the display portion 4005a or the belt portion 4005b. A secondary battery using the positive electrode active material 100 obtained in Embodiment 1 for its positive electrode has high energy density and can achieve a space-saving configuration that can be achieved by miniaturizing a housing.

[0406] The display unit 4005a can display not only the time but also various other information such as incoming emails and phone calls.

[0407] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0408] FIG. 28B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0409] 28C shows a side view of the display portion 4005a. FIG. 28C shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 4. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and can have high density and high capacity, and is small and lightweight.

[0410] Since the wristwatch-type device 4005 is required to be small and lightweight, by using the positive electrode active material 100 obtained in embodiment 1 for the positive electrode of the secondary battery 913, the secondary battery 913 can have a high energy density and be small.

[0411] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0412] Example 1 In this example, a positive electrode active material according to one embodiment of the present invention was prepared, and then a plurality of coin-type battery cells were fabricated, and their cycle characteristics were evaluated.

[0413] The samples prepared in this example are described below. Four samples were prepared under the same conditions and procedures except for the solvent (amount of 2-propanol) used in the sol-gel method. The amounts of 2-propanol used were 0 ml, 1 ml, 5 ml, and 10 ml.

[0414] The positive electrode active material used for each sample was the positive electrode active material obtained by the method shown in Embodiment 1. Positive electrode active material 100 was obtained according to the flow chart of FIG.

[0415] The sample produced in this example will be described with reference to the production method shown in FIG.

[0416] As LiMO2 in step S14, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M and no particular additives was prepared. Lithium fluoride and magnesium fluoride were mixed with this by a solid-phase method, as in steps S21 to S23, S41, and S42. The number of lithium fluoride molecules was 0.33 and the number of magnesium fluoride molecules was 1, assuming that the number of cobalt atoms was 100. This was designated mixture 903.

[0417] Next, annealing was performed in the same manner as in step S43. 30 g of the mixture 903 was placed in a square alumina container, a lid was placed, and the mixture was heated in a muffle furnace. The furnace was purged and oxygen gas was introduced, but no gas flow was observed during heating. The annealing temperature was 900°C and the time was 20 hours.

[0418] In step S61-1, nickel hydroxide was added to the heated composite oxide and dry mixed. The number of nickel atoms was set to 0.5 when the number of cobalt atoms was taken as 100.

[0419] Next, in step S61-2, mixing was performed using the sol-gel method. When using the sol-gel method, a solvent for the sol-gel method 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 preferable to use an aprotic solvent that is less likely to react with lithium. In this example, aluminum alkoxide was used as the metal alkoxide. For example, aluminum was added so that the number of aluminum atoms was 0.5 relative to the number of cobalt atoms (100). For zirconium, zirconium alkoxides such as zirconium isopropoxide can be used. For example, zirconium was added so that the number of zirconium atoms was 0.1 at%, 0.25 at%, 0.5 at%, and 1 at% for each sample (100 cobalt atoms). Step S63, the heat treatment after the sol-gel method, was performed at 850°C for 2 hours. The positive electrode active material 100 obtained through the above steps was used as a sample.

[0420] Acetylene black was used as the conductive additive, and the materials were mixed to prepare a slurry, which was then applied to an aluminum current collector.

[0421] After the slurry was applied to the current collector, the solvent was evaporated. After that, a pressure of 210 kN / m was applied, and then a pressure of 1467 kN / m was applied. A positive electrode was obtained through these steps. The loading amount of the positive electrode was approximately 7 mg / cm.2 It was decided.

[0422] Using the prepared positive electrode, a coin-type battery cell of the CR2032 type (diameter 20 mm, height 3.2 mm) was prepared.

[0423] Lithium metal was used as the counter electrode.

[0424] The electrolyte used for the sample was 1 mol / L lithium hexafluorophosphate (LiPF6), mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7, and vinylene carbonate (VC) was added as an additive at a concentration of 2 wt% relative to the solvent.

[0425] The separator was made of polypropylene with a thickness of 25 μm.

[0426] The positive electrode can and the negative electrode can were made of stainless steel (SUS).

[0427] In the evaluation of cycle characteristics, the charging voltage was 4.7 V. The measurement temperature was 25°C. The charging was CC / CV (0.5 C, 0.05 C cut), and the discharging was CC (0.5 C, 2.5 V cut), with a 10-minute rest period before the next charging. In this example, 1 C was 200 mA / g.

[0428] 29A and 29B show the respective cycle characteristics. In Fig. 29A, the vertical axis represents the discharge capacity retention rate, and in Fig. 29B, the vertical axis represents the discharge capacity.

[0429] As described above, the positive electrode active material of one embodiment of the present invention was shown to be a positive electrode active material in which the decrease in charge / discharge capacity was suppressed even when the sample containing 5 ml of 2-propanol and the sample containing 10 ml of 2-propanol were repeatedly charged and discharged at a high voltage of 4.7 V.

[0430] A sample was also prepared using 40 ml of 2-propanol, but good cycle characteristics were not obtained.

[0431] In addition, in Figures 29A and 29B, the comparative example is a sample in which the amount of 2-propanol is 0 ml.

[0432] 30A and 30B show the results of similar cycle characteristics tests conducted while varying the ratio of zirconium atoms to cobalt (0.1 at%, 0.25 at%, 0.5 at%, 1 at%). The vertical axis in FIG. 30A represents the discharge capacity retention rate, while the vertical axis in FIG. 30B represents the discharge capacity. After drying and solidifying using the sol-gel method in FIG. 30, annealing was performed at 850°C for 2 hours. When annealing was performed at 850°C and comparing the presence and absence of zirconium, better cycle characteristics were obtained in all conditions with zirconium than in the condition without zirconium (comparative example).

[0433] In particular, among these samples, the samples with zirconium contents of 0.1 at% and 0.25 at% were shown to be positive electrode active materials in which the decrease in charge / discharge capacity was suppressed even when repeatedly charged and discharged at a high voltage of 4.7 V.

[0434] Also, powder resistance measurements were carried out using samples prepared using the same method as the above-mentioned samples, with the ratio of zirconium atoms to cobalt changed (0.25 at %, 2 at %). The results are shown in FIG.

[0435] <Powder Resistivity Measurement> The powder resistance of the obtained positive electrode active material particles was measured using a powder resistance measurement device (MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The positive electrode active material was placed in a measurement cell, and pressure was applied from above using a compression rod to compress the powder. At this time, current was passed through the powder while measuring the pressure and volume, and the resistance value was measured using the Loresta GP using the four-probe method. Note that powder resistance varies depending on the density.

[0436] Example 2 In this example, a positive electrode active material according to one embodiment of the present invention was prepared according to the flow shown in FIG. 5 , and then a laminated battery cell having a separator, an electrolyte, and a negative electrode was fabricated, and its cycle characteristics were evaluated.

[0437] Sample 1 produced in this example will be described with reference to the production method shown in FIG.

[0438] As LiMO2 in step S14, commercially available lithium cobalt oxide (Cellseed C-10N, manufactured by Nippon Chemical Industry Co., Ltd.) containing cobalt as the transition metal M and no particular additives was prepared. Lithium fluoride and magnesium fluoride were mixed with this by a solid-phase method, as in steps S21 to S23, S41, and S42. The number of lithium fluoride molecules was 0.33 and the number of magnesium fluoride molecules was 1, assuming that the number of cobalt atoms was 100. This was designated mixture 903.

[0439] Next, annealing was performed in the same manner as in step S43. 30 g of mixture 903 was placed in a square alumina container, a lid was placed, and the container was heated in a muffle furnace. The inside of the furnace was purged, and oxygen gas was introduced and allowed to flow during heating. The annealing temperature was 850°C for 60 hours.

[0440] In step S61-1, nickel hydroxide was added to the heated composite oxide and dry mixed. The number of nickel atoms was set to 0.5 when the number of cobalt atoms was taken as 100.

[0441] Next, in step S61-2, mixing was performed using the sol-gel method. When using the sol-gel method, a solvent to be used in the sol-gel method 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 example, 10 ml of 2-propanol was used as the solvent.

[0442] In this example, aluminum alkoxide was used as the metal alkoxide. In the case of aluminum, for example, the number of aluminum atoms was added so that the number of cobalt atoms was 100, and the number of aluminum atoms was 0.5. When zirconium is used, zirconium alkoxides such as zirconium isopropoxide can be used. In the case of zirconium, for example, the number of cobalt atoms was added so that the number of zirconium atoms was 0.25, and the number of cobalt atoms was 100. The heat treatment in step S63 after the sol-gel method was performed at 850°C for 2 hours. Thereafter, in step S64, the positive electrode active material 100 obtained by crushing and recovering was used as a sample.

[0443] The cathode active material particles, which have multiple Zr-containing protrusions on their surfaces, AB (acetylene black), and PVDF (polyvinylidene fluoride) were mixed in a weight ratio of 95:3:2, and the slurry was coated onto an aluminum foil current collector. NMP (N-methyl-2-pyrrolidone) was used as the solvent for the slurry.

[0444] After the slurry was applied to the current collector, the solvent was evaporated. After that, pressure was applied at 210 kN / m, and then pressure was applied again at 1467 kN / m. A positive electrode was obtained through these steps. The loading amount of the positive electrode was approximately 20 mg / cm. 2 It was decided.

[0445] 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) at a volume ratio of EC:DEC = 3:7. For the secondary batteries used to evaluate the cycle characteristics, 2 wt% vinylene carbonate (VC) was added to the electrolytic solution.

[0446] The separator was made of polypropylene with a thickness of 25 μm.

[0447] Graphite was used for the negative electrode, and a slurry of graphite: carbon nanotubes (VGCF (registered trademark)): CMC (carboxymethyl cellulose) thickener: SBR (styrene-butadiene rubber) mixed in a ratio of 96:1:1:2 was applied to a current collector (copper foil).

[0448] The typical values ​​of the vapor-grown carbon fiber (VGCF (registered trademark): Vapor-Grown Carbon Fiber) used were a fiber diameter of 150 nm, a fiber length of 10 μm or more and 20 μm or less, and a true density of 2.1 g / cm 3 , specific surface area 13m 2 / g. The fiber diameter refers to the diameter of a perfect circle circumscribing a cross section perpendicular to the fiber axis in a two-dimensional image taken using an SEM. True density refers to the density calculated using only the volume occupied by the substance itself. Specific surface area refers to the surface area per unit mass or per unit volume of an object.

[0449] The results of the cycle test of Sample 1, a secondary battery fabricated in this manner, are shown in FIG.

[0450] The measurement temperature was 25°C. Charging was performed at 4.5 V (CCCV, 0.2 C, cutoff current 0.1 C) and discharging at 3 V (CC, 0.2 C), and 233 charge / discharge cycles were performed. The rest time between cycle tests was 1 minute. 1 C here is the current value per weight of the positive electrode active material, which is 200 mA / g.

[0451] Immediately after 233 cycles, the capacity retention rate of Sample 1 was 95.6%. The maximum capacity of Sample 1 was 192.4 mAh / g. Note that since measurements were only taken up to 233 cycles for Sample 1, only the data shown in Figure 32 is available, but it can be seen that Sample 1 exhibited good cycle characteristics up to 233 cycles.

[0452] The comparative example was the same as Sample 1 except that it used a positive electrode active material to which Zr was not added. The maximum capacity of the comparative example was 188 mAh / g, and the capacity retention rate immediately after 233 cycles was 91.5%.

[0453] Example 3 In this example, an SEM photograph of a positive electrode active material obtained under the same conditions as in Example 1 is shown in FIG. 35A, and a schematic diagram thereof is shown in FIG. 35B. Zirconium was added during the preparation of the positive electrode active material so that the number of zirconium atoms was 0.25 when the number of cobalt atoms was 100. Another difference from Example 1 is that the heating in step S43 was performed at 850°C for 60 hours. The same parts in FIG. 35B and FIG. 1B use the same reference numerals.

[0454] A half cell was prepared using this same sample, and the same cycle test as in Example 1 (cycle test at a charging voltage of 4.7 V and 25°C) was carried out as Sample 2. The obtained cycle characteristics are shown in Figure 34. Sample 2 had a maximum capacity of 223 mAh / g.

[0455] 36, Sample 3 shows the cycle characteristics when no zirconium is added. Sample 3 is a sample to which nickel and aluminum are added by the solid phase method. Sample 3 had a maximum capacity of 230 mAh / g.

[0456] In addition, in Figure 36, Sample 4 was produced according to the production flow shown in Figure 37. Figure 37 has many processes in common with Figure 4, but zirconium is added using a solid-phase method rather than a sol-gel method. The maximum capacity of Sample 4 was 231 mAh / g, the highest value among the three samples. Although Sample 4 had a lower capacity retention rate than Sample 2, it had a higher maximum capacity.

[0457] In this example, experimental results of samples produced using different manufacturing flows were shown, and although there were differences in the results, highly reliable results were obtained. [Explanation of symbols]

[0458] 100: positive electrode active material, 101: protrusion, 102: protrusion, 103: protrusion, 300: secondary battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 312: washer, 313: ring-shaped insulator, 322: spacer, 400: secondary battery, 410: positive electrode, 411: positive electrode active material, 413: positive electrode current collector, 414: positive electrode active material layer, 420: solid electrolyte layer, 421: solid electrolyte, 430: negative electrode, 431: negative electrode active material, 4 33: negative electrode current collector, 434: negative electrode active material layer, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 508: electrolyte, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 513: secondary battery, 514: terminal, 515: seal, 517: antenna, 519: layer, 529: label, 530: oxide, 531: secondary battery pack, 540: circuit board, 550: current collector, 551: one side, 552: other side, 553: acetylene black, 554 : Graphene, 555: Carbon nanotube, 561: Active material, 562: Active material, 590: Control circuit, 590a: Circuit system, 590b: Circuit system, 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, 613: Safety valve mechanism, 614: Conductive plate, 615: Energy storage system, 616: Secondary battery, 620: Control circuit, 621: Wiring, 622: Wiring, 623: Wiring, 624: Conductor, 625: Insulator , 626: Wiring, 627: Wiring, 628: Conductive plate, 700: Energy storage device, 701: Commercial power supply, 703: Distribution board, 705: Energy storage controller, 706: Display, 707: General load, 708: Energy storage load, 709: Router, 710: Lead wire attachment part, 711: Measurement part, 712: Prediction part, 713: Planning part, 750a: Positive electrode, 750b: Solid electrolyte layer, 750c: Negative electrode, 751: Electrode plate, 752: Insulating tube, 753: Electrode plate, 761: Lower part, 762: Upper part, 764: Wing nut, 765: O-ring, 766: Insulator, 770a: Package part,770b: packaging member, 770c: packaging member, 771: external electrode, 772: external electrode, 773a: electrode layer, 773b: electrode layer, 790: control device, 791: power storage device, 796: underfloor space, 799: building, 902: mixture, 903: mixture, 904: mixture, 911a: terminal, 911b: terminal, 913: secondary battery, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 931a: negative electrode active material layer, 932: positive electrode, 932a: positive electrode active material layer, 933: separator, 950: wound body, 950a: wound body, 951: terminal, 952: terminal, 1 300: rectangular secondary battery, 1301a: battery, 1301b: battery, 1302: battery controller, 1303: motor controller, 1304: motor, 1305: gear, 1306: DCDC circuit, 1307: electric power steering, 1308: heater, 1309: defogger, 1310: DCDC circuit, 1311: battery, 1312: inverter, 1313: audio, 1314: power window, 1315: lamps, 1316: tires, 1317: rear motor, 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 132 4: switch unit, 1325: external terminal, 1326: external terminal, 1413: fixed unit, 1414: fixed unit, 1415: battery pack, 1421: wiring, 1422: wiring, 2001: automobile, 2002: transport vehicle, 2003: transport vehicle, 2004: aircraft, 2100: mobile phone, 2101: housing, 2102: display unit, 2103: operation button, 2104: external connection port, 2105: speaker, 2106: microphone, 2107: secondary battery, 2200: battery pack, 2201: battery pack, 2202: battery pack, 2203: battery pack, 2300: unmanned aerial vehicle, 230 1: Secondary battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Power storage device, 4000: Glasses-type device, 4000a: Frame, 4000b: Display unit, 4001: Headset-type device, 4001a: Microphone unit, 4001b: Flexible pipe, 4001c: Earphone unit, 4002: Device, 4002a: Housing, 4002b: Secondary battery, 4003: Device, 4003a: Housing, 4003b: Secondary battery, 4005: Wristwatch-type device, 4005a: Display unit,4005b: Belt part, 4006: Belt type device, 4006a: Belt part, 4006b: Wireless power supply receiving part, 6300: Cleaning robot, 6301: Housing, 6302: Display part, 6303: Camera, 6304: Brush, 6305: Operation button, 6306: Secondary battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: speaker, 6405: display unit, 6406: lower camera, 6407: obstacle sensor, 6408: moving mechanism, 6409: secondary battery, 8600: scooter, 8601: side mirror, 8602: power storage device, 8603: turn signal light, 8604: under-seat storage, 8700: electric bicycle, 8701: storage battery, 8702: power storage device, 8703: display unit, 8704: control circuit,

Claims

1. A secondary battery having a positive electrode and a negative electrode, the positive electrode has a positive electrode active material including lithium and cobalt, the positive electrode active material contains fluorine and magnesium, the fluorine concentration in the positive electrode active material is higher in a surface layer portion than in a central portion of the positive electrode active material, The positive electrode active material has a plurality of protrusions, and the protrusions contain zirconium dioxide.

2. 2. A vehicle according to claim 1, comprising the secondary battery.

3. A first step of preparing a first mixture in which a first material, a second material, and a third material are mixed; a second step of heating the first mixture at a first temperature condition to produce a second mixture; a third step of preparing a third mixture by mixing the second mixture and a fourth material; a fourth step of preparing a fourth mixture by mixing the third mixture, a fifth material, and a sixth material; a fifth step of heating the fourth mixture at a second temperature condition to produce a fifth mixture; the first material is a lithium-containing halide; the second material comprises magnesium; the third material is a metal oxide having lithium and cobalt; the fourth material comprises nickel and zirconium; In the second step and the fifth step, the heating is performed in an atmosphere containing oxygen; the first temperature condition is a temperature range of 600° C. or higher and 950° C. or lower, and a time range of 1 hour or higher and 100 hours or lower; The second temperature condition is a temperature range of 600° C. to 900° C. for 1 hour to 100 hours.

4. 4. The method for producing a positive electrode active material according to claim 3, wherein the fifth material comprises aluminum.

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