Positive electrode active material, secondary battery, electronic device

Abstract

To provide a positive electrode active material in which the decrease in capacity with charge / discharge cycle is suppressed, or the crystalline structure of the positive electrode active material is not easily decomposed even after charge and discharge are repeated.SOLUTION: A positive electrode active material contains titanium, nickel, aluminum, magnesium, and fluorine. The positive electrode active material has a region where titanium, nickel, and magnesium are unevenly distributed in convex portions on a surface. It is preferable that aluminum is unevenly distributed not in the convex portions but in a surface layer portion of the positive electrode active material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One aspect of the present invention relates to an article, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[0002] In the present specification, the electronic device generally refers to all devices having a power storage device, and all electro-optical devices having a power storage device, information terminal devices having a power storage device, etc. are electronic devices.

Background Art

[0003] In recent years, various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries have been actively developed. In particular, lithium-ion secondary batteries with high output and high capacity have rapidly expanded their demand along with the development of the semiconductor industry and have become indispensable in modern information societies as a source of rechargeable energy.

[0004] Among them, for secondary batteries for mobile electronic devices, etc., there is a high demand for secondary batteries with a large discharge capacity per unit weight and excellent cycle characteristics. In order to meet these demands, improvements to the positive electrode active material of secondary batteries are actively being made (for example, Patent Documents 1 and 2). In addition, research on the crystal structure of the positive electrode active material is also being conducted (Non-Patent Documents 1 to 4).

[0005] X-ray diffraction (XRD) is one of the techniques used for analyzing the crystal structure of the positive electrode active material. By using the ICSD (Inorganic Crystal Structure Database) introduced in Non-Patent Document 5, the XRD data can be analyzed.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2018-190700 [Patent Document 2] Japanese Patent Application Publication for International Patent Application No. 2018-508116 [Non-Patent Document]

[0007] [Non-Patent Document 1] Toyoki Okumura et al, “Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3- and O2-lithium cobalt oxides from first-principle calculation”, Journal of Materials Chemistry, 2012, 22, p.17340-17348 [Non-Patent Document 2] Motohashi, T. et al, “Electronic phase diagram of the layered cobalt oxide system LixCoO2 (0.0≦x≦1.0) ”, Physical Review B, 80(16);165114 [Non-Patent Document 3] Zhaohui Chen et al, “Staging Phase Transitions in LixCoO2”, Journal of The Electrochemical Society, 2002, 149(12) A1604-A1609 [Non-Patent Document 4] W. E. Counts et al, “Fluoride Model Systems:II,The Binary Systems CaF2-BeF22, MgF2-BeF2, and LiF-MgF2” Journal of the American Ceramic Society, (1953) 36 [1] 12-17. Fig.01471 [Non-Patent Document 5] 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

Problems to be Solved by the Invention

[0008] However, there is still room for improvement in lithium-ion secondary batteries and the cathode active materials used therein in various aspects such as charge-discharge capacity, cycle characteristics, reliability, safety, or cost.

[0009] One aspect of the present invention is to provide a cathode active material that suppresses a decrease in capacity during charge-discharge cycles when used in a lithium-ion secondary battery. Or, one aspect of the present invention is to provide a cathode active material whose crystal structure is difficult to collapse even when charge-discharge is repeated. Or, one aspect of the present invention is to provide a cathode active material having a large charge-discharge capacity. Or, one aspect of the present invention is to provide a secondary battery with high safety or reliability.

[0010] Another aspect of the present invention is to provide a cathode active material, a power storage device, or a method for manufacturing them.

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

Means for Solving the Problems

[0012] Another aspect of the present invention is a cathode active material having titanium, having a concave portion on the surface, and having titanium on a part of the inner wall of the concave portion.

[0013] In the above, the concave portion preferably has a depth of 100 nm or more and a width of 20 nm or more.

[0014] Another aspect of the present invention is a positive electrode active material having titanium and magnesium, and the positive electrode active material having a region where magnesium and titanium are unevenly distributed.

[0015] In the above, the region where magnesium and titanium are unevenly distributed preferably exists on the surface of the positive electrode active material.

[0016] In the above, the positive electrode active material further has cobalt and oxygen, and cobalt and oxygen preferably exist uniformly.

[0017] In the above, the positive electrode active material preferably further has lithium.

[0018] In the above, it is preferable to have a region where magnesium and titanium are uniformly present.

[0019] In the above, the region where magnesium and titanium are uniformly present is preferably a convex portion on the surface of the positive electrode active material.

[0020] In the above, the convex portion preferably has a portion with a height of 50 nm or more.

[0021] In the above, the positive electrode active material preferably further has nickel and has a region where nickel is unevenly distributed.

[0022] In the above, the positive electrode active material further has aluminum, the positive electrode active material has a surface layer portion and an interior, and the surface layer portion preferably has a higher aluminum concentration than the interior.

[0023] In the above, the positive electrode active material preferably further has fluorine and has a region where fluorine is unevenly distributed.

[0024] Another aspect of the present invention is a secondary battery having the above-described positive electrode active material.

[0025] Another aspect of the present invention is an electronic device having the above-described secondary battery.

Advantages of the Invention

[0026] According to one aspect of the present invention, by using it in a lithium-ion secondary battery, a positive electrode active material can be provided in which a decrease in capacity during charge and discharge cycles is suppressed. Or, a positive electrode active material in which the crystal structure is hardly broken even when charge and discharge are repeated can be provided. Or, a positive electrode active material having a large charge and discharge capacity can be provided. Or, a secondary battery with high safety or reliability can be provided.

[0027] Also, according to one aspect of the present invention, a positive electrode active material, a power storage device, or a method for manufacturing them can be provided.

[0028] Note that the description of these effects does not prevent the existence of other effects. Note that one aspect of the present invention does not necessarily have to have all of these effects. Note that other effects will be apparent from the description in the specification, drawings, claims, etc., and it is possible to extract these other effects from the description in the specification, drawings, claims, etc.

Brief Description of the Drawings

[0029]

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Mode for Carrying Out the Invention

[0030] 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 is easily understood by those skilled in the art that its form and details can be variously changed. Also, the present invention is not to be construed as being limited to the description of the embodiments shown below.

[0031] In this specification and the like, Miller indices are used for the notation of crystal planes and directions. Individual planes indicating crystal planes are represented by ( ). In crystallography, notations for crystal planes, directions, and space groups are represented by numbers with an overbar, but in this specification and the like, due to the constraints of the application notation, instead of attaching an overbar to the number, a - (minus sign) may be attached before the number for expression.

[0032] In this specification and the like, segregation refers to a phenomenon in a solid composed of a plurality of elements (for example, A, B, C) in which a certain element (for example, B) is spatially non-uniformly distributed.

[0033] In this specification and the like, uniform or homogeneous refers to a phenomenon in a solid composed of a plurality of elements (for example, A, B, C) in which a certain element (for example, A) is distributed with similar characteristics in a specific region. Note that it is sufficient if the concentrations of the elements in the specific regions are substantially the same. For example, the difference in the element concentrations between the specific regions may be within 10%. Examples of the specific region include the surface, convex portion, concave portion, interior, and the like.

[0034] In this specification and the like, the layered rock salt-type crystal structure of the 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 the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as cation or anion deficiencies. Also, strictly speaking, the layered rock salt-type crystal structure may be a structure in which the lattice of the rock salt-type crystal is distorted.

[0035] In this specification and the like, the rock salt-type crystal structure refers to a structure in which cations and anions are alternately arranged. Note that there may be cation or anion deficiencies.

[0036] In this specification and the like, the pseudo-spinel type crystal structure of the composite oxide containing lithium and transition metals has a space group of R-3m, which is not a spinel type crystal structure. However, ions such as cobalt and magnesium occupy the oxygen six-coordinate positions, and the crystal structure has a symmetry similar to that of the spinel type in the arrangement of cations. Note that in the pseudo-spinel type crystal structure, light elements such as lithium may occupy the oxygen four-coordinate positions, and in this case as well, the ion arrangement has a symmetry similar to that of the spinel type.

[0037] Also, it can be said that the pseudo-spinel type crystal structure is a crystal structure similar to the CdCl2 type crystal structure although it has Li randomly between layers. The crystal structure similar to this CdCl2 type is close to the crystal structure when lithium nickelate is charged to a charge depth of 0.94 (Li 0.06 NiO2), but it is known that pure lithium cobaltate or a layered rock salt type cathode active material containing a large amount of cobalt usually does not take this crystal structure.

[0038] The anions of the layered rock salt type crystal and the rock salt type crystal take a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the pseudo-spinel type crystal also take a cubic close-packed structure. When these are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned. However, since the space groups of the layered rock salt type crystal and the pseudo-spinel type crystal are R-3m, which is different from the space groups Fm-3m (space group of a general rock salt type crystal) and Fd-3m (space group of a rock salt type crystal having the simplest symmetry) of the rock salt type crystal, the Miller indices of the crystal planes satisfying the above conditions are different between the layered rock salt type crystal and the pseudo-spinel type crystal and the rock salt type crystal. In this specification, in the case of the layered rock salt type crystal, the pseudo-spinel type crystal, and the rock salt type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are generally in agreement.

[0039] The approximate alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc. X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc. can also be used as materials for determination. In TEM images, etc., the arrangement of cations and anions can be observed as a repetition of bright and dark lines. When the orientations of the cubic close-packed structures in layered rock salt-type crystals and rock salt-type crystals are aligned, it can be observed that the angle formed by the repetition of bright and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that in TEM images, etc., light elements such as oxygen and fluorine may not be clearly observable. In such cases, the alignment can be determined by the arrangement of metal elements.

[0040] Also, in this specification, etc., the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been removed. 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.

[0041] Also, in this specification, etc., the state of charge when all the insertable and removable lithium has been inserted is defined as 0, and the state of charge when all the insertable and removable lithium in the positive electrode active material has been removed is defined as 1.

[0042] In this specification and the like, charging means moving electrons from the positive electrode to the negative electrode in an external circuit. For the positive electrode active material, removing lithium ions is defined as charging. Also, a positive electrode active material with a state of charge (SOC) of 0.74 or more and 0.9 or less, more specifically, a positive electrode active material with a SOC of 0.8 or more and 0.83 or less, is referred to as a positive electrode active material charged at a high voltage. Therefore, for example, if LiCoO2 is charged at 219.2 mAh / g, it is a positive electrode active material charged at a high voltage. Also, in LiCoO2, in an environment of 25 °C, constant current charging is performed with a charging voltage of 4.525 V or more and 4.65 V or less (in the case of a lithium counter electrode), and then constant voltage charging is performed until the current value becomes 0.01C, or about 1 / 5 to 1 / 100 of the current value during constant current charging. The resulting positive electrode active material is also referred to as a positive electrode active material charged at a high voltage.

[0043] Similarly, discharging means moving electrons from the negative electrode to the positive electrode in an external circuit. For the positive electrode active material, inserting lithium ions is defined as discharging. Also, a positive electrode active material with a SOC of 0.06 or less, or a positive electrode active material that has discharged 90% or more of its charge capacity from a state charged at a high voltage, is referred to as a fully discharged positive electrode active material. For example, if the charge capacity of LiCoO2 is 219.2 mAh / g, it is in a state charged at a high voltage. After discharging 197.3 mAh / g or more, which is 90% of the charge capacity, the resulting positive electrode active material is a fully discharged positive electrode active material. Also, in LiCoO2, in an environment of 25 °C, after constant current discharging until the battery voltage becomes 3 V or less (in the case of a lithium counter electrode), the resulting positive electrode active material is also referred to as a fully discharged positive electrode active material.

[0044] In this specification and the like, as an example of a secondary battery using the positive electrode and the positive electrode active material of one aspect of the present invention, a case where lithium metal is used as the counter electrode may be shown. However, the secondary battery of one aspect of the present invention is not limited to this. Other materials may be used for the negative electrode, such as graphite, lithium titanate, and the like. The properties such as the crystal structure being difficult to collapse even when the charge and discharge are repeated, and good cycle characteristics can be obtained for the positive electrode and the positive electrode active material of one aspect of the present invention, and are not affected by the material of the negative electrode. Also, for the secondary battery of one aspect of the present invention, a case may be shown where charging and discharging are performed at a relatively high voltage such as a charging voltage of 4.6 V with lithium as the counter electrode, but charging and discharging may be performed at a lower voltage. When charging and discharging are performed at a lower voltage, it is expected that the cycle characteristics will be even better than those shown in this specification and the like.

[0045] (Embodiment 1) In this embodiment, the positive electrode active material of one aspect of the present invention will be described with reference to FIGS. 1 to 6.

[0046] FIG. 1(A) is an example of a top view of the positive electrode active material 101 which is one aspect of the present invention. The schematic cross-sectional view taken along A - B in FIG. 1(A) is shown in FIG. 1(B).

[0047] <Contained elements and distribution> The positive electrode active material 101 has lithium, a transition metal M, oxygen, and impurities. The positive electrode active material 101 may be said to be a composite oxide represented by LiMO2 to which impurities are added.

[0048] As the transition metal M included in the positive electrode active material 101, it is preferable to use a metal capable of forming 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, only cobalt may be used as the transition metal included in the positive electrode active material 101, only nickel may be used, two types of cobalt and manganese, or two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. That is, the positive electrode active material 101 can have a composite oxide containing lithium and the transition metal M, such as lithium cobaltate, lithium nickelate, lithium cobaltate in which part of cobalt is substituted with manganese, lithium cobaltate in which part of cobalt is substituted with nickel, and lithium nickel-manganese-cobaltate. When the transition metal M has nickel in addition to cobalt, the crystal structure may be more stable in the charged state at a high voltage, which is preferable.

[0049] As the impurity included in the positive electrode active material 101, it is preferable to use at least one of magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron. These elements may stabilize the crystal structure of the positive electrode active material 101 as described later. That is, the positive electrode active material 101 can have lithium cobaltate added with magnesium and fluorine, lithium cobaltate added with magnesium, fluorine, and titanium, lithium nickel-cobaltate added with magnesium and fluorine, lithium cobalt-aluminate added with magnesium and fluorine, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate added with magnesium and fluorine, lithium nickel-manganese-cobaltate added with magnesium and fluorine, and the like. Note that in this specification and the like, the impurity does not impair the properties of the positive electrode active material 101. Therefore, instead of the impurity, it may be referred to as an additive, a mixture, a part of a raw material, or the like.

[0050] As shown in Fig. 1(B), the positive electrode active material 101 has a surface layer portion 101a and an interior 101b. It is preferable that the surface layer portion 101a has a higher impurity concentration than the interior 101b. Also, as shown by the gradation in Fig. 1(B), it is preferable that the impurity has a concentration gradient that increases from the interior toward the surface. In this specification and the like, the surface layer portion 101a refers to a region up to about 10 nm from the surface of the positive electrode active material 101. A surface formed by a crack or crack may also be referred to as the surface. Further, a region deeper than the surface layer portion 101a of the positive electrode active material 101 is defined as the interior 101b.

[0051] In the positive electrode active material 101 according to one aspect of the present invention, even when lithium is removed from the positive electrode active material 101 upon charging, the surface layer portion 101a having a high impurity concentration, that is, the outer peripheral portion of the positive electrode active material 101, reinforces the layer structure composed of the octahedron of the transition metal M such as cobalt and oxygen so that the layer structure does not break.

[0052] Also, it is preferable that the impurity concentration gradient is similar throughout the surface layer portion 101a of the positive electrode active material 101. It may be said that it is preferable that the reinforcement due to the high impurity concentration is uniformly present in the surface layer portion 101a. This is because if there is a part of the surface layer portion 101a with reinforcement and a part without reinforcement, stress may concentrate on the non-reinforced part, which is not preferable. When stress concentrates on a part of the particle, defects such as cracks may occur therefrom, leading to cracking of the positive electrode active material and a decrease in charge / discharge capacity.

[0053] Magnesium has a divalent valence and is more stable in the lithium site than in the transition metal site in the layered rock salt type crystal structure, so it is likely to enter the lithium site. By having magnesium present in the lithium sites of the surface layer portion 101a at an appropriate concentration, the layered rock salt type crystal structure of the positive electrode active material 101 can be easily maintained. Magnesium is preferable as long as it is at an appropriate concentration and does not adversely affect the insertion and removal of lithium during charge and discharge. However, if it is excessive, it may adversely affect the insertion and removal of lithium. As will be described later, it is preferable that the surface layer portion 101a has a higher concentration of transition metal than magnesium, for example.

[0054] Aluminum has a trivalent valence and a strong binding force with oxygen. Therefore, when aluminum is present as an impurity, changes in the crystal structure can be suppressed when it enters the lithium sites. Therefore, by adding aluminum, a cathode active material 101 can be obtained that is less likely to have its crystal structure collapse even when charge and discharge are repeated.

[0055] As the charging voltage of the secondary battery increases, the voltage of the positive electrode generally increases. The cathode active material of one aspect of the present invention has a stable crystal structure even at high voltages. By having a stable crystal structure of the cathode active material in the charged state, a decrease in capacity associated with repeated charge and discharge can be suppressed.

[0056] In addition, a short circuit in the secondary battery not only causes problems in the charging operation and discharging operation of the secondary battery, but also has a risk of causing heat generation and ignition. In order to realize a safe secondary battery, it is preferable that the short-circuit current is suppressed even at a high charging voltage. The cathode active material 101 of one aspect of the present invention suppresses the short-circuit current even at a high charging voltage. Therefore, a secondary battery with both high capacity and safety can be achieved.

[0057] The concentration gradient of the impurity can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, the measurement while scanning within a region and evaluating the region two-dimensionally is called EDX surface analysis. Also, the measurement while linearly scanning the region and evaluating the distribution of atomic concentration inside the cathode active material particles is called line analysis. Furthermore, in some cases, the data of a linear region extracted from the surface analysis of EDX is also called line analysis. Also, the measurement without scanning a certain region is called point analysis.

[0058] By EDX surface analysis (for example, elemental mapping), the concentration of impurities in the surface layer portion 101a, the interior 101b, and the vicinity of the crystal grain boundaries of the cathode active material 101, as well as the embedded portion 102, the convex portion 103, etc. to be described later, can be quantitatively analyzed. Also, by EDX line analysis, the concentration distribution and the maximum value of the impurity can be analyzed.

[0059] When the positive electrode active material 101 has magnesium as an impurity, when performing EDX analysis, the peak of the magnesium concentration in the surface layer portion 101a preferably exists up to a depth of 3 nm from the surface of the positive electrode active material 101 toward the center, more preferably up to a depth of 1 nm, and even more preferably up to a depth of 0.5 nm.

[0060] When the positive electrode active material 101 has fluorine in addition to magnesium as an impurity, the distribution of fluorine preferably overlaps with the distribution of magnesium. Therefore, when performing EDX analysis, the peak of the fluorine concentration in the surface layer portion 101a preferably exists up to a depth of 3 nm from the surface of the positive electrode active material 101 toward the center, more preferably up to a depth of 1 nm, and even more preferably up to a depth of 0.5 nm.

[0061] Note that not all impurities need to have the same concentration distribution. For example, when the positive electrode active material 101 has aluminum as an impurity, it preferably has a distribution slightly different from that of magnesium and fluorine. For example, when performing EDX analysis, it is preferable that the peak of the magnesium concentration is closer to the surface than the peak of the aluminum concentration in the surface layer portion 101a. For example, the peak of the aluminum concentration preferably exists at a depth of 0.5 nm or more and 20 nm or less from the surface of the positive electrode active material 101 toward the center, and more preferably at a depth of 1 nm or more and 5 nm or less.

[0062] When performing line analysis or surface analysis on the positive electrode active material 101, the ratio (I / M) of the number of atoms of impurity I to transition metal M in the surface layer portion 101a is preferably 0.05 or more and 1.00 or less. Further, when the impurity is titanium, the ratio (Ti / M) of the number of atoms of titanium to transition metal M is preferably 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less. When the impurity is magnesium, the ratio (Mg / M) of the number of atoms of magnesium to transition metal M is preferably 0.4 or more and 1.5 or less, more preferably 0.45 or more and 1.00 or less. When the impurity is fluorine, the ratio (F / M) of the number of atoms of fluorine to transition metal M is preferably 0.05 or more and 1.5 or less, more preferably 0.3 or more and 1.00 or less.

[0063] When performing line analysis or surface analysis on the positive electrode active material 101, the ratio (I / M) of the number of atoms of impurity I to transition metal M in the vicinity of the crystal grain boundary is preferably 0.020 or more and 0.50 or less. Further, it is preferably 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less. For example, when the impurity is magnesium and the transition metal is cobalt, the ratio (Mg / Co) of the number of atoms of magnesium to cobalt is preferably 0.020 or more and 0.50 or less. Further, it is preferably 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less.

[0064] As described above, if the impurities contained in the positive electrode active material 101 are excessive, it may have an adverse effect on the insertion and extraction of lithium. When the positive electrode active material 101 is used in a secondary battery, it may also cause an increase in resistance, a decrease in capacity, etc. On the other hand, if the impurities are insufficient, they may not be distributed throughout the surface layer portion 101a, and the effect of maintaining the crystal structure may be insufficient. Thus, although the impurities need to be present in an appropriate concentration in the positive electrode active material 101, it is not easy to adjust them.

[0065] Therefore, for example, the positive electrode active material 101 may have a region where impurities are unevenly distributed. Due to the existence of such a region, excessive impurities are removed from the interior 101b, and an appropriate impurity concentration can be achieved in the interior 101b. By achieving an appropriate impurity concentration in the interior 101b, an increase in resistance, a decrease in capacity, etc. when the secondary battery is formed can be suppressed. The ability to suppress an increase in the resistance of the secondary battery is an extremely favorable characteristic particularly in high-rate charging and discharging.

[0066] Moreover, in the positive electrode active material 101 having a region where impurities are unevenly distributed, it is allowed to mix impurities to some extent in excess during the manufacturing process. Therefore, the margin in production becomes wider, which is preferable.

[0067] In this specification and the like, uneven distribution means that the concentration of an element in a certain region is different from that in other regions. It may also be described as segregation, precipitation, non-uniformity, bias, high concentration or low concentration, etc.

[0068] Examples of the positive electrode active material 101 having a region where impurities are unevenly distributed, which is one aspect of the present invention, are shown using FIGS. 2(A) to 3(C). Note that the impurities in the region where impurities are unevenly distributed exist, for example, as a compound. Therefore, when it is stated that titanium is unevenly distributed as an impurity, it means that a titanium compound such as titanium oxide is unevenly distributed. It does not necessarily mean that metallic titanium is unevenly distributed. Similarly, when it is stated that an impurity metal is unevenly distributed, it means that a compound of the impurity metal such as an oxide or fluoride of the impurity metal is unevenly distributed.

[0069] FIG. 2(A) is a top view of the positive electrode active material 101 having an embedded portion 102 as a region where impurities are unevenly distributed, which is one aspect of the present invention. The cross-sectional view taken along C-D in FIG. 2(A) is shown in FIG. 2(B).

[0070] As shown in FIGS. 2(A) and (B), the positive electrode active material 101 may have a concave portion 101c. The concave portion 101c may be a region having a different height from others, and may be, for example, a crack, a depression, a V-shaped cross section, or the like. The concave portion is, for example, 10 nm or more in depth, and further 100 nm or more. Also, for example, the depth is 5 μm or less, 1 μm or less. At this time, the positive electrode active material 101 preferably has an embedded portion 102 that fills a part of the concave portion 101c. The embedded portion 102 is attached to at least a part of the inner wall of the concave portion 101c. It may also be said that the embedded portion 102 is provided on at least a part of the inner wall of the concave portion 101c. The embedded portion 102 may be referred to as the space within the concave portion. In the embedded portion 102, it is preferable that the concentration of at least one of impurities, such as titanium, magnesium, and fluorine, is higher than that of the inside 101b.

[0071] Titanium is preferably present in the embedded portion 102 as a titanium compound, such as titanium oxide.

[0072] The concave portion 101c is one of the defects in the positive electrode active material 101, and when charging and discharging are repeated, elution of transition metals, collapse of the crystal structure, cracks in the surface layer portion and the inside, etc. may occur. However, due to the presence of the embedded portion 102, elution of transition metals and the like can be suppressed. Therefore, the positive electrode active material 101 with excellent reliability and cycle characteristics can be obtained.

[0073] FIG. 3(A) is a top view of the positive electrode active material 101 having a convex portion 103 as a region where impurities are unevenly distributed, which is one aspect of the present invention. The cross-sectional view taken along E-F in FIG. 3(A) is shown in FIG. 3(B) or FIG. 3(C). The convex portion may be a portion having a different height from others, and may be referred to as a water droplet-shaped portion, a colony-shaped portion, a mound-shaped portion, a bulge, or the like. Also, when having a plurality of convex portions, the shapes do not have to be uniform. The convex portion 103 preferably has a portion 50 nm or more in height, and further 100 nm or more in height. The height of the convex portion 103 is the height from the interface between the surface layer portion 101a and the convex portion 103. The height of the convex portion 103 can be measured from microscope images such as SEM images and TEM images.

[0074] The convex portion 103 preferably exists on the surface of the positive electrode active material 101. When the positive electrode active material 101 has both fluorine and a metal compound such as magnesium and titanium as impurities, as shown in Fig. 3(B), the convex portion 103 preferably has a high-fluorine concentration region 103a and a high-metal impurity concentration region 103b. The high-fluorine concentration region 103a has a higher fluorine concentration than the interior 101b and the high-metal impurity concentration region 103b. The high-metal impurity concentration region 103b has a higher metal impurity concentration than the interior 101b and the high-fluorine concentration region 103a. The positive electrode active material 101 preferably has a high-metal impurity concentration region 103b that covers the high-fluorine concentration region 103a on the positive electrode active material 101.

[0075] And in the surface layer portion 101a of the positive electrode active material 101, it is preferable that impurities such as titanium, magnesium, and fluorine with appropriate concentrations are present. The impurities preferably have a concentration gradient that increases from the inside to the surface of the positive electrode active material 101.

[0076] When the positive electrode active material 101 has nickel as the transition metal M, a part of the nickel may be present in the high-metal impurity concentration region 103b. At this time, the high-metal impurity concentration region 103b may have a higher nickel concentration than the interior 101b and the high-fluorine concentration region 103a.

[0077] Furthermore, as shown in Fig. 3(C), a high-nickel concentration region 101d may exist in a part of the surface layer portion 101a and the interior 101b that overlaps with the convex portion 103. The high-nickel concentration region 101d can be considered as a trace where nickel dissolved in the interior of the positive electrode active material 101 was attracted to the convex portion 103. The high-nickel concentration region 101d has a higher nickel concentration than the portions of the surface layer portion 101a and the interior 101b other than the high-nickel concentration region 101d, and a lower nickel concentration than the high-metal impurity concentration region 103b.

[0078] Moreover, not all impurities need to have the above-described distribution. For example, when the positive electrode active material 101 contains aluminum as an impurity, it is preferable that the distribution of aluminum is different from that of magnesium or titanium. For example, it is preferable that aluminum is scarcely present in the convex portions 103 and is present in the surface layer portion 101a of the positive electrode active material 101. That is, it is preferable that the aluminum concentration in the surface layer portion 101a is higher than the aluminum concentration in the convex portions 103.

[0079] In this specification and the like, regions where impurities in the positive electrode active material 101 are unevenly distributed, such as the embedded portions 102 and the convex portions 103, refer to regions having a composition different from that of the positive electrode active material 101. The positive electrode active material 101 and the regions where impurities are unevenly distributed may have different crystal structures. For example, the positive electrode active material 101 may have a layered rock salt-type crystal structure, and the regions where impurities are unevenly distributed may have a rock salt-type, spinel-type, rutile-type, anatase-type, or perovskite-type crystal structure. Further, the regions where impurities are unevenly distributed may be amorphous. It is possible to determine that they are regions having different compositions or crystal structures by various analyses including EDX, cross-sectional TEM, surface SEM, and electron beam diffraction.

[0080] Furthermore, it is more preferable that the dielectric constants of the embedded portions 102 and the convex portions 103 are higher than those of the surface layer portion 101a and the interior 101b. For example, when the dielectric constant of the convex portion 103 is high, the convex portion 103 is polarized during charge and discharge. Then, lithium ions, which are positive ions, easily move to the interface between the convex portion 103 close to the negatively charged negative electrode and the surface layer portion 101a. As a result, the insertion / desorption reaction rate of lithium ions is increased. Therefore, it is preferable because the rate characteristics are improved when the positive electrode active material 101 is used in a secondary battery.

[0081] For example, when the embedded portions 102 and the convex portions 103 contain magnesium-titanium oxide, it may be preferable because the dielectric constant becomes higher than that of lithium cobaltate.

[0082] In the positive electrode active material 101, it is preferable that lithium, transition metal, and oxygen, which are not contained in impurities, are uniformly distributed. In this specification and the like, "uniform" means substantially uniform, for example, the difference in element concentration may be within 10%.

[0083] In FIGS. 2 and 3, the embedded portion 102 and the convex portion 103 are described as regions where impurities are unevenly distributed. However, the region where impurities are unevenly distributed in the positive electrode active material 101 of one aspect of the present invention is not limited to this. Any region having a composition different from that of the positive electrode active material 101 may be used, and it is not limited to a shape such as embedding or bulging.

[0084] Regarding the impurity concentration gradient and the like in the surface layer portion 101a of the positive electrode active material 101 in FIGS. 2 and 3, the description in FIG. 1 can be referred to.

[0085] <Crystal structure> Materials having a layered rock salt-type crystal structure such as lithium cobalt oxide (LiCoO2) are known to have a high discharge capacity and be excellent as a positive electrode active material for secondary batteries. Examples of materials having a layered rock salt-type crystal structure include composite oxides represented by LiMO2.

[0086] It is known that the Jahn-Teller effect in transition metal compounds varies in strength depending on the number of electrons in the d orbitals of the transition metal.

[0087] In compounds containing nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charge and discharge are performed at a high voltage in LiNiO2, there is a concern that the crystal structure may collapse due to distortion. It is suggested that the influence of the Jahn-Teller effect is small in LiCoO2, and it may be more excellent in resistance to charge and discharge at a high voltage, which is preferable.

[0088] The positive electrode active material will be described with reference to FIGS. 4 and 5. FIGS. 4 and 5 describe the case where cobalt is used as the transition metal M included in the positive electrode active material.

[0089] <Conventional positive electrode active material> The positive electrode active material shown in Fig. 5 is lithium cobaltate (LiCoO2) to which halogen and magnesium are not added by the production method described later. As described in Non-Patent Document 1, Non-Patent Document 2, etc., the crystal structure of the lithium cobaltate shown in Fig. 5 changes depending on the depth of charge.

[0090] As shown in Fig. 5, lithium cobaltate at a charge depth of 0 (discharged state) has a region with a crystal structure of space group R-3m, and there are three CoO2 layers in the unit cell. Therefore, this crystal structure may be referred to as an O3-type crystal structure. Note that the CoO2 layer refers to a structure in which octahedral structures in which oxygen is six-coordinated to cobalt are continuous in a plane in a state of sharing edges.

[0091] When the charge depth is 1, it has a crystal structure of space group P-3m1, and there is one CoO2 layer in the unit cell. Therefore, this crystal structure may be referred to as an O1-type crystal structure.

[0092] Also, lithium cobaltate when the charge depth is about 0.88 has a crystal structure of space group R-3m. This structure can also be said to be a structure in which structures of CoO2 such as P-3m1 (O1) and structures of LiCoO2 such as R-3m (O3) are alternately stacked. Therefore, this crystal structure may be referred to as an H1-3 type crystal structure. In reality, in the H1-3 type crystal structure, the number of cobalt atoms per unit cell is twice that of other structures. However, in this specification including Fig. 5, for easy comparison with other structures, it will be shown in a figure in which the c-axis of the H1-3 type crystal structure is set to 1 / 2 of the unit cell.

[0093] As an example, as described in Non-Patent Document 3, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150 ± 0.00016), O1(0, 0, 0.27671 ± 0.00045), and O2(0, 0, 0.11535 ± 0.00045). O1 and O2 are oxygen atoms respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, as will be described later, the pseudo-spinel type crystal structure of one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen. This indicates that in the case of the pseudo-spinel structure and the H1-3 type structure, the symmetry between cobalt and oxygen is different, and the change of the pseudo-spinel structure from the O3 structure is smaller than that of the H1-3 type structure. The choice of which unit cell is more preferable for representing the crystal structure of the positive electrode active material may be made, for example, so that the value of GOF (goodness of fit) is smaller in the Rietveld analysis of XRD.

[0094] When high-voltage charging such that the charging voltage becomes 4.6 V or more based on the redox potential of lithium metal, or deep charging such that the charging depth becomes 0.8 or more, and discharging are repeated, lithium cobaltate repeats a change in crystal structure (i.e., non-equilibrium phase change) between the H1-3 type crystal structure and the structure of R-3m(O3) in the discharged state.

[0095] However, the shift of the CoO2 layer is large between these two crystal structures. As shown by the dotted line and arrow in FIG. 5, in the H1-3 type crystal structure, the CoO2 layer is largely shifted from R-3m(O3). Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0096] Furthermore, the volume difference is also large. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.0% or more.

[0097] In addition, a structure in which CoO2 layers such as P-3m1(O1) having an H1-3 type crystal structure are continuous is likely to be unstable.

[0098] Therefore, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is considered to be because, when the crystal structure collapses, the sites where lithium can exist stably decrease, and it becomes difficult for lithium to be inserted and removed.

[0099] <The positive electrode active material of one aspect of the present invention> ≪Inside≫ The positive electrode active material 101 of one aspect of the present invention can reduce the shift of the CoO2 layer in the repeated high-voltage charge and discharge. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one aspect of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material of one aspect of the present invention can have a stable crystal structure in the high-voltage charged state. Therefore, when the positive electrode active material of one aspect of the present invention holds a high-voltage charged state, a short circuit is less likely to occur. In such a case, the safety is further improved, which is preferable.

[0100] In the positive electrode active material of one aspect of the present invention, the change in the crystal structure and the volume difference per the same number of transition metal atoms in the fully discharged state and the state charged at a high voltage are small.

[0101] The crystal structure of the positive electrode active material 101 before and after charge and discharge is shown in FIG. 4. The positive electrode active material 101 is a composite oxide having lithium, cobalt as a transition metal M, and oxygen. In addition to the above, it preferably has magnesium as an impurity. It also preferably has halogens such as fluorine and chlorine as impurities.

[0102] The crystal structure at a charge depth of 0 (discharged state) in FIG. 4 is the same R-3m (O3) as in FIG. 5. On the other hand, the positive electrode active material 101 has crystals with a structure different from the H1-3 type crystal structure when fully charged. This structure belongs to the space group R-3m and is not a spinel-type crystal structure. However, ions such as cobalt and magnesium occupy the oxygen six-coordinate positions, and the cation arrangement has symmetry similar to that of the spinel type. Therefore, this structure is referred to as a pseudo-spinel-type crystal structure in this specification and the like. In the diagram of the pseudo-spinel-type crystal structure shown in FIG. 4, the display of lithium is omitted for the purpose of explaining the symmetry of cobalt atoms and oxygen atoms. However, in reality, for example, lithium of 20 atomic% or less relative to cobalt exists between the CoO2 layers. Also, in both the O3-type crystal structure and the pseudo-spinel-type crystal structure, it is preferable that magnesium exists thinly between the CoO2 layers, that is, at the lithium site. Further, it is preferable that halogens such as fluorine exist randomly and thinly at the oxygen site.

[0103] Note that in the pseudo-spinel-type crystal structure, light elements such as lithium may occupy the oxygen four-coordinate positions. In this case as well, the ion arrangement has symmetry similar to that of the spinel type.

[0104] Also, it can be said that the pseudo-spinel-type crystal structure is a crystal structure similar to the CdCl2-type crystal structure although it has Li randomly between the layers. This crystal structure similar to the CdCl2 type is close to the crystal structure when lithium nickelate is charged to a charge depth of 0.94 (Li 0.06 NiO2), but it is known that pure lithium cobaltate or a layered rock salt-type positive electrode active material containing a large amount of cobalt usually does not take this crystal structure.

[0105] In the positive electrode active material 101 according to one aspect of the present invention, the change in the crystal structure when charging at a high voltage and a large amount of lithium is detached is suppressed more than that of the conventional positive electrode active material. For example, as shown by the dotted line in FIG. 4, there is almost no shift in the CoO2 layer in these crystal structures.

[0106] More specifically, the positive electrode active material 101 of one embodiment of the present invention has high structural stability even when the charging voltage is high. For example, a conventional positive electrode active material has an H1-3 type crystal structure at a voltage of about 4.6 V based on the potential of lithium metal. On the other hand, the positive electrode active material 101 of one embodiment of the present invention has a region of charging voltage in which the crystal structure of R-3m (O3) can be maintained even at a voltage of about 4.6 V, and further in a region where the charging voltage is increased, for example, at a voltage of about 4.65 V to 4.7 V based on the potential of lithium metal, there is a region where a pseudo-spinel type crystal structure can be adopted. When the charging voltage is further increased, an H1-3 type crystal may be observed. In addition, when graphite is used as the negative electrode active material in a secondary battery, for example, there is a region of charging voltage in which the crystal structure of R-3m (O3) can be maintained even when the voltage of the secondary battery is 4.3 V or more and 4.5 V or less, and further in a region where the charging voltage is increased, for example, at a voltage of 4.35 V or more and 4.55 V or less based on the potential of lithium metal, there is a region where a pseudo-spinel type crystal structure can be adopted.

[0107] Therefore, in the positive electrode active material 101 of one embodiment of the present invention, the crystal structure is difficult to collapse even when charging and discharging are repeated at a high voltage.

[0108] The pseudo-spinel type crystal structure can be represented by the coordinates of cobalt and oxygen in the unit cell within the range of Co(0, 0, 0.5), O(0, 0, x), and 0.20 ≤ x ≤ 0.25.

[0109] Impurities such as magnesium that are randomly and thinly present in the CoO2 layer, that is, in the lithium site, have the effect of suppressing the displacement of the CoO2 layer when charged at a high voltage. Therefore, when magnesium is present in the CoO2 layer, it is likely to form a pseudo-spinel type crystal structure. Therefore, it is preferable that magnesium is distributed throughout the particles of the positive electrode active material 101 of one embodiment of the present invention. In addition, in order to distribute magnesium throughout the particles, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 101 of one embodiment of the present invention.

[0110] However, if the heat treatment temperature is too high, cation mixing may occur, increasing the likelihood of impurities such as magnesium entering the cobalt sites. Magnesium present in the cobalt sites has no effect on maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0111] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobaltate before the heat treatment for distributing magnesium throughout the particles. Adding the halogen compound causes a melting point depression of lithium cobaltate. By lowering the melting point, it becomes easier to distribute magnesium throughout the particles at a temperature where cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolyte will be improved.

[0112] Note that if the magnesium concentration is increased to a value equal to or higher than the desired value, the effect on stabilizing the crystal structure may become small. This is presumably because magnesium also enters the cobalt sites in addition to the lithium sites. The number of magnesium atoms in the positive electrode active material according to one aspect of the present invention is preferably 0.001 times or more and 0.1 times or less, more preferably more than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times the number of atoms of the transition metal M. 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 (Inductively Coupled Plasma Mass Spectrometry) or the like, or may be based on the value of the raw material formulation in the process of manufacturing the positive electrode active material.

[0113] Lithium cobaltate may be added with one or more metals selected from, for example, nickel, aluminum, manganese, titanium, vanadium, and chromium as metals other than cobalt (hereinafter referred to as metal Z), and it is particularly preferable to add one or more of nickel and aluminum. Manganese, titanium, vanadium, and chromium may tend to stably take a tetravalent state and may contribute highly to structural stability. By adding metal Z, in the positive electrode active material of one embodiment of the present invention, for example, the crystal structure may become more stable in a charged state at a high voltage. Here, in the positive electrode active material of one embodiment of the present invention, metal Z is preferably added at a concentration that does not significantly change the crystallinity of lithium cobaltate. For example, it is preferably an amount that does not exhibit the aforementioned Jahn-Teller effect or the like.

[0114] As shown in the legend in FIG. 4, transition metals such as nickel and manganese and aluminum preferably exist at cobalt sites, but a part of them may exist at lithium sites. Also, magnesium preferably exists at lithium sites. A part of oxygen may be substituted with fluorine.

[0115] As the magnesium concentration of the positive electrode active material of one embodiment of the present invention increases, the capacity of the positive electrode active material may decrease. As a factor, for example, it is conceivable that the amount of lithium contributing to charge and discharge may decrease when magnesium enters the lithium site. Also, excessive magnesium may sometimes generate a magnesium compound that does not contribute to charge and discharge. When the positive electrode active material of one embodiment of the present invention has nickel as metal Z in addition to magnesium, the capacity per unit weight and per unit volume may be increased. Also, when the positive electrode active material of one embodiment of the present invention has aluminum as metal Z in addition to magnesium, the capacity per unit weight and per unit volume may be increased. Also, when the positive electrode active material of one embodiment of the present invention has nickel and aluminum in addition to magnesium, the capacity per unit weight and per unit volume may be increased.

[0116] The concentrations of elements such as magnesium and metal Z in the positive electrode active material of one embodiment of the present invention are represented using the number of atoms.

[0117] The number of atoms of nickel in the positive electrode active material of one embodiment of the present invention is preferably 7.5% or less of the number of atoms of cobalt, more preferably 0.05% or more and 4% or less, and even more preferably 0.1% or more and 2% or less. The nickel 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 formulation in the process of producing the positive electrode active material.

[0118] The number of atoms of aluminum in the positive electrode active material of one embodiment of the present invention is preferably 0.05% or more and 4% or less of the number of atoms of cobalt, and more preferably 0.1% or more and 2% or less. The aluminum 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 formulation in the process of producing the positive electrode active material.

[0119] The positive electrode active material of one embodiment of the present invention preferably has element X, and it is preferable to use phosphorus as element X. Further, the positive electrode active material of one embodiment of the present invention more preferably has a compound containing phosphorus and oxygen.

[0120] When the positive electrode active material of one embodiment of the present invention has a compound containing element X, short circuits may be less likely to occur when maintaining a high voltage charged state.

[0121] When the positive electrode active material of one embodiment of the present invention has phosphorus as element X, hydrogen fluoride generated by the decomposition of the electrolytic solution may react with phosphorus, and the hydrogen fluoride concentration in the electrolytic solution may decrease.

[0122] When the electrolyte contains LiPF6, hydrogen fluoride may be generated by hydrolysis. In addition, hydrogen fluoride may also be generated by the reaction of PVDF used as a component of the positive electrode with an alkali. By reducing the concentration of hydrogen fluoride in the electrolyte, corrosion of the current collector and peeling of the film may be suppressed in some cases. In addition, a decrease in adhesiveness due to gelation or insolubilization of PVDF may be suppressed in some cases.

[0123] When the positive electrode active material of one embodiment of the present invention contains magnesium in addition to element X, the stability in a charged state at a high voltage is extremely high. When element X is phosphorus, the number of phosphorus atoms is preferably 1% or more and 20% or less, more preferably 2% or more and 10% or less, still more preferably 3% or more and 8% or less of the number of cobalt atoms. In addition, the number of magnesium atoms is preferably 0.1% or more and 10% or less, more preferably 0.5% or more and 5% or less, still more preferably 0.7% or more and 4% or less of the number of cobalt atoms. The concentrations of phosphorus and magnesium shown here may be values obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, ICP-MS or the like, or may be based on the values of the raw material formulation in the process of producing the positive electrode active material.

[0124] When the positive electrode active material has cracks, the progress of the cracks may be suppressed by the presence of phosphorus, more specifically, a compound containing, for example, phosphorus and oxygen, inside the positive electrode active material.

[0125] ≪Surface layer portion 101a≫ Magnesium is preferably distributed throughout the particles of the positive electrode active material 101 of one embodiment of the present invention. In addition, it is preferable that the magnesium concentration in the surface layer portion 101a is higher than the average of the entire particles. For example, it is preferable that the magnesium concentration in the surface layer portion 101a measured by XPS (X-ray photoelectron spectroscopy) or the like is higher than the average magnesium concentration of the entire particles measured by ICP-MS or the like.

[0126] In addition, when the positive electrode active material 101 of one aspect of the present invention contains one or more metals selected from elements other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal in the surface layer portion 101a is higher than the average of the entire particle. For example, it is preferable that the concentration of elements other than cobalt in the surface layer portion 101a measured by XPS or the like is higher than the average concentration of the element in the entire particle measured by ICP-MS or the like.

[0127] The particle surface can be said to be entirely crystal defects, and during charging, lithium is removed from the surface, making it a part where the lithium concentration is likely to be lower than that inside. Therefore, it is a part that is prone to instability and where the crystal structure is likely to collapse. If the magnesium concentration in the surface layer portion 101a is high, changes in the crystal structure can be more effectively suppressed. Also, when the magnesium concentration in the surface layer portion 101a is high, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution will be improved.

[0128] Also, for halogens such as fluorine, it is preferable that the concentration in the surface layer portion 101a of the positive electrode active material 101 of one aspect of the present invention is higher than the average of the entire particle. The presence of halogen in the surface layer portion 101a, which is the region in contact with the electrolytic solution, can effectively improve the corrosion resistance against hydrofluoric acid.

[0129] Thus, it is preferable that the surface layer portion 101a of the positive electrode active material 101 of one aspect of the present invention has a different composition from the inside 101b, with a higher concentration of impurities, such as magnesium and fluorine. Also, it is preferable that the composition has a crystal structure that is stable at room temperature. Therefore, the surface layer portion 101a may have a crystal structure different from that of the inside 101b. For example, at least a part of the surface layer portion 101a of the positive electrode active material 101 of one aspect of the present invention may have a rock salt-type crystal structure. Also, when the surface layer portion 101a and the inside 101b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 101a and the inside 101b are substantially the same.

[0130] The fact that the crystal orientations of the surface layer portion 101a and the interior 101b are substantially consistent means that the surface layer portion 101a and the interior 101b have a stable bond. Therefore, when the positive electrode active material 101 is used in a secondary battery, changes in the crystal structure of the interior 101b caused by charge and discharge can be effectively suppressed. Also, even when lithium has been removed from the interior 101b due to charging, it is possible to suppress the detachment of cobalt and / or oxygen from the interior 101b by the stable surface layer portion 101a having the bond. Furthermore, the region in contact with the electrolytic solution can be made of a chemically stable material. Therefore, a secondary battery with excellent cycle characteristics can be obtained.

[0131] However, if the surface layer portion 101a consists only of MgO or only of a structure in which MgO and CoO(II) are in solid solution, the insertion and desorption of lithium will become difficult. Therefore, the surface layer portion 101a needs to have at least cobalt, have lithium in the discharged state, and have a path for the insertion and desorption of lithium. Also, it is preferable that the concentration of cobalt is higher than that of magnesium.

[0132] Also, it is preferable that the element X is located in the surface layer portion 101a of the particles of the positive electrode active material 101 according to one aspect of the present invention. For example, the positive electrode active material 101 according to one aspect of the present invention may be covered with a film having the element X.

[0133] ≪Grain boundary≫ The impurities that the positive electrode active material 101 according to one aspect of the present invention has may be randomly and thinly present inside, but it is more preferable that some are segregated at the grain boundaries.

[0134] In other words, it is preferable that the impurity concentration at the crystal grain boundaries of the positive electrode active material 101 according to one aspect of the present invention and in the vicinity thereof is also higher than that in other regions inside.

[0135] Similar to the particle surface, the crystal grain boundaries are also plane defects. Therefore, they tend to become unstable and the change in the crystal structure tends to start. Therefore, if the magnesium concentration at the crystal grain boundaries and in the vicinity thereof is high, the change in the crystal structure can be more effectively suppressed.

[0136] Also, when the impurity concentration at the grain boundaries and in the vicinity thereof is high, even if cracks occur along the grain boundaries of the particles of the positive electrode active material 101 according to one embodiment of the present invention, the impurity concentration increases in the vicinity of the surface generated by the cracks. Therefore, the corrosion resistance against hydrofluoric acid can be enhanced even in the positive electrode active material after cracks occur.

[0137] In this specification and the like, the vicinity of the grain boundary shall refer to a region up to about 10 nm from the grain boundary.

[0138] ≪Particle size≫ If the particle size of the positive electrode active material 101 according to one embodiment of the present invention is too large, there are problems such as difficulty in lithium diffusion and the surface of the active material layer becoming too rough when coated on the current collector. On the other hand, if it is too small, problems such as difficulty in supporting the active material layer during coating on the current collector and excessive progress of the reaction with the electrolyte solution occur. Therefore, the average particle diameter (D50: also referred to as the median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0139] <Analysis method> Whether a certain positive electrode active material is the positive electrode active material 101 according to one embodiment of the present invention that exhibits a pseudo-spinel type crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt possessed by the positive electrode active material with high resolution, can compare the crystallinity and crystal orientation, can analyze the periodic strain of the lattice and the crystallite size, and sufficient accuracy can be obtained even by measuring the positive electrode obtained by disassembling the secondary battery as it is.

[0140] The positive electrode active material 101 according to one aspect of the present invention is characterized in that there is little change in the crystal structure between the state of being charged at a high voltage and the discharge state as described above. A material in which a crystal structure with a large change from the discharge state occupies 50 wt% or more when charged at a high voltage is not preferable because it cannot withstand the charge and discharge at a high voltage. It should be noted that the desired crystal structure may not be obtained only by adding impurity elements. For example, even when common in terms of lithium cobaltate having magnesium and fluorine, there are cases where the pseudo-spinel type crystal structure becomes 60 wt% or more and the H1-3 type crystal structure occupies 50 wt% or more in the state of being charged at a high voltage. Also, at a predetermined voltage, the pseudo-spinel type crystal structure may become almost 100 wt%, and when the predetermined voltage is further increased, the H1-3 type crystal structure may occur. Therefore, in order to determine whether or not it is the positive electrode active material 101 according to one aspect of the present invention, analysis of the crystal structure including XRD is necessary.

[0141] However, the positive electrode active material in the state of being charged or discharged at a high voltage may cause a change in the crystal structure when exposed to the atmosphere. For example, it may change from a pseudo-spinel type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0142] <<Charging method>> For the high voltage charging to determine whether or not a certain composite oxide is the positive electrode active material 101 according to one aspect of the present invention, for example, a coin cell (CR2032 type, diameter 20 mm height 3.2 mm) can be produced with a counter electrode lithium and charged.

[0143] More specifically, as the positive electrode, a slurry obtained by mixing a positive electrode active material, a conductive assistant, and a binder can be used by coating it on a positive electrode current collector made of an aluminum foil.

[0144] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode are different. The voltage and potential in this specification and the like are the potential of the positive electrode unless otherwise specified.

[0145] As the electrolyte for the electrolytic solution, lithium hexafluorophosphate (LiPF6) at 1 mol / L is used. For the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) can be used in a mixture of EC:DEC = 3:7 (volume ratio), and vinylene carbonate (VC) at 2 wt%.

[0146] As the separator, polypropylene with a thickness of 25 μm can be used.

[0147] As the positive electrode can and negative electrode can, those made of stainless steel (SUS) can be used.

[0148] The coin cell fabricated under the above conditions is charged at a constant current of 4.6 V and 0.5 C, and then charged at a constant voltage until the current value reaches 0.01 C. Here, 1 C is taken as 137 mA / g, and the temperature is 25°C. After charging in this way, if the coin cell is disassembled in a glove box under an argon atmosphere to take out the positive electrode, a positive electrode active material charged at a high voltage can be obtained. When performing various analyses thereafter, it is preferable to seal it in an argon atmosphere to suppress the reaction with external components. For example, XRD can be performed by enclosing it in a sealed container under an argon atmosphere.

[0149] ≪XRD≫ The ideal powder XRD patterns calculated from the models of the pseudo-spinel type crystal structure and the H1-3 type crystal structure using CuKα1 line are shown in Fig. 6. Also shown for comparison are the ideal XRD patterns calculated from the crystal structures of LiCoO2 (O3) with a charge depth of 0 and CoO2 (O1) with a charge depth of 1. The patterns of LiCoO2 (O3) and CoO2 (O1) were created using Reflex Powder Diffraction, which is one of the modules of Materials Studio (BIOVIA), from the crystal structure information obtained from ICSD (see Non-Patent Document 5). The range of 2θ is from 15° to 75°, Step size = 0.01, and wavelength λ1 = 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 3. The pattern of the pseudo-spinel type crystal structure was estimated from the XRD pattern of the positive electrode active material of one aspect of the present invention, and was fitted using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0150] As shown in Fig. 6, in the pseudo-spinel type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° or more and 19.50° or less), and 2θ = 45.55 ± 0.10° (45.45° or more and 45.65° or less). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° or more and 19.40° or less), and 2θ = 45.55 ± 0.05° (45.50° or more and 45.60° or less). However, in the H1-3 type crystal structure and CoO2 (P-3m1, O1), peaks do not appear at these positions. Therefore, it can be said that the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in the state charged at a high voltage is a feature of the positive electrode active material 101 of one aspect of the present invention.

[0151] This can also mean that in the crystal structure at a charge depth of 0 and the crystal structure when charged at a high voltage, the positions where the XRD diffraction peaks appear are close. More specifically, it can be said that the difference in the positions where peaks appear is 2θ = 0.7 or less, more preferably 2θ = 0.5 or less, in two or more, more preferably three or more, of the main diffraction peaks of both.

[0152] Note that the cathode active material 101 according to one embodiment of the present invention has a pseudo-spinel crystal structure when charged at a high voltage, but not all of the particles need to have a pseudo-spinel crystal structure. It may contain other crystal structures or some may be amorphous. However, when performing Rietveld analysis on the XRD pattern, it is preferable that the pseudo-spinel crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the pseudo-spinel crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a cathode active material with sufficiently excellent cycle characteristics can be obtained.

[0153] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when performing Rietveld analysis, it is preferable that the pseudo-spinel crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0154] Also, the crystallite size of the pseudo-spinel crystal structure possessed by the particles of the cathode active material only decreases to about 1 / 10 of that of LiCoO2(O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the cathode before charge and discharge, a clear peak of the pseudo-spinel crystal structure can be confirmed after high-voltage charging. On the other hand, in simple LiCoO2, even if a part has a structure similar to the pseudo-spinel crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0155] In the cathode active material according to one embodiment of the present invention, as described above, it is preferable that the influence of the Jahn-Teller effect is small. The cathode active material according to one embodiment of the present invention preferably has a layered rock salt crystal structure and mainly contains cobalt as a transition metal. Further, in the cathode active material according to one embodiment of the present invention, within a range where the influence of the Jahn-Teller effect is small, in addition to cobalt, it may have the metal Z described above.

[0156] In the positive electrode active material, the range of lattice constants where the influence of the Jahn-Teller effect is presumed to be small is considered using XRD analysis.

[0157] Figure 7 shows the results of estimating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material of one embodiment of the present invention has a layered rock salt-type crystal structure and contains cobalt and nickel. Figure 7(A) shows the results of the a-axis, and Figure 7(B) shows the results of the c-axis. The XRD patterns used for these calculations are powders after synthesizing the positive electrode active material and before being incorporated into the positive electrode. The nickel concentration on the horizontal axis indicates the nickel concentration when the sum of the atomic numbers of cobalt and nickel is 100%. The positive electrode active material was prepared by mixing a lithium source, a cobalt source, and a nickel source and then heating.

[0158] Figure 8 shows the results of estimating the lattice constants of the a-axis and c-axis using XRD when the positive electrode active material of one embodiment of the present invention has a layered rock salt-type crystal structure and contains cobalt and manganese. Figure 8(A) shows the results of the a-axis, and Figure 8(B) shows the results of the c-axis. The XRD patterns used for these calculations are powders after synthesizing the positive electrode active material and before being incorporated into the positive electrode. The manganese concentration on the horizontal axis indicates the manganese concentration when the sum of the atomic numbers of cobalt and manganese is 100%. The positive electrode active material was prepared by mixing a lithium source, a cobalt source, and a manganese source and then heating.

[0159] Figure 7(C) shows the value (a-axis / c-axis) obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis for the positive electrode active material whose lattice constant results are shown in Figures 7(A) and 7(B). Figure 8(C) shows the value (a-axis / c-axis) obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis for the positive electrode active material whose lattice constant results are shown in Figures 8(A) and (B).

[0160] From FIG. 7(C), it is found that when the nickel concentration is 5% and 7.5%, the a-axis / c-axis shows a tendency to change significantly, and it is considered that the strain of the a-axis increases. This strain may be the Jahn-Teller strain. It is suggested that when the nickel concentration is less than 7.5%, an excellent positive electrode active material with small Jahn-Teller strain can be obtained.

[0161] Next, from FIG. 8(A), when the manganese concentration is 5% or more, the behavior of the change in the lattice constant is different, suggesting that it does not follow Vegard's law. Therefore, it is suggested that the crystal structure is different when the manganese concentration is 5% or more. Thus, the manganese concentration is preferably, for example, 4% or less.

[0162] Note that the above ranges of nickel concentration and manganese concentration do not necessarily apply to the surface layer portion 101a of the particles. That is, in the surface layer portion 101a of the particles, it may be higher than the above concentrations.

[0163] From the above, when considering the preferable range of the lattice constant, in the positive electrode active material of one embodiment of the present invention, in the layered rock salt type crystal structure of the particles of the positive electrode active material in the state of not performing charge and discharge or in the discharged state, which can be estimated from the XRD pattern, the lattice constant of the a-axis is larger than 2.814×10 -10 m and smaller than 2.817×10 -10 m, and the lattice constant of the c-axis is larger than 14.05×10 -10 m and smaller than 14.07×10 -10 m. The state of not performing charge and discharge may be, for example, the powder state before manufacturing the positive electrode of the secondary battery.

[0164] Alternatively, in the layered rock salt type crystal structure of the particles of the positive electrode active material in the state of not performing charge and discharge or in the discharged state, the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is preferably larger than 0.20000 and smaller than 0.20049.

[0165] Alternatively, when XRD analysis is performed on the layered rock salt-type crystal structure of the particles of the positive electrode active material in a state where charge and discharge are not performed or in a discharged state, a first peak may be observed at 2θ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2θ of 38.00° or more and 38.80° or less.

[0166] Note that the peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 101b of the positive electrode active material 101, which occupies the majority of the volume of the positive electrode active material 101. The crystal structures of the surface layer portion 101a, the embedded portion 102, the convex portion 103, etc. can be analyzed by electron beam diffraction or the like of the cross section of the positive electrode active material 101.

[0167] ≪XPS≫ In X-ray photoelectron spectroscopy (XPS), since analysis of a region from the surface to a depth of about 2 to 8 nm (usually about 5 nm) is possible, the concentration of each element can be quantitatively analyzed for a region about half the depth of the surface layer portion 101a. Also, the bonding state of the elements can be analyzed by performing narrow scan analysis. Note that the quantitative accuracy of XPS is often about ±1 atomic %, and the detection limit is about 1 atomic % depending on the element.

[0168] When XPS analysis is performed on the positive electrode active material 101 of one aspect of the present invention, the number of impurity atoms is preferably 1.6 times or more and 6.0 times or less, more preferably 1.8 times or more and less than 4.0 times, the number of atoms of the transition metal M. When the impurity is magnesium and the transition metal M is cobalt, the number of magnesium atoms is preferably 1.6 times or more and 6.0 times or less, more preferably 1.8 times or more and less than 4.0 times, the number of cobalt atoms. Also, the number of atoms of a halogen such as fluorine is preferably 0.2 times or more and 6.0 times or less, more preferably 1.2 times or more and 4.0 times or less, the number of atoms of the transition metal M.

[0169] When performing XPS analysis, for example, monochromatized aluminum can be used as the X-ray source. Also, the take-off angle may be, for example, 45°.

[0170] When the positive electrode active material 101 of one embodiment of the present invention is analyzed by XPS, the peak indicating the binding energy of fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This is a value different from both 685 eV, which is the binding energy of lithium fluoride, and 686 eV, which is the binding energy of magnesium fluoride. That is, when the positive electrode active material 101 of one embodiment of the present invention contains fluorine, it is preferably a bond other than lithium fluoride and magnesium fluoride.

[0171] Furthermore, when the positive electrode active material 101 of one embodiment of the present invention is analyzed by XPS, the peak indicating the binding energy of magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably about 1303 eV. This is a value different from 1305 eV, which is the binding energy of magnesium fluoride, and is a value close to the binding energy of magnesium oxide. That is, when the positive electrode active material 101 of one embodiment of the present invention contains magnesium, it is preferably a bond other than magnesium fluoride.

[0172] Impurities that preferably exist in a large amount in the surface layer portion 101a, such as magnesium and aluminum, preferably have a concentration measured by XPS or the like that is higher than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0173] When magnesium and aluminum are processed to expose their cross-sections and the cross-sections are analyzed using TEM-EDX, the concentration of the surface layer portion 101a is preferably higher than the concentration of the internal portion 101b. The processing can be performed, for example, by FIB (Focused Ion Beam).

[0174] In the analysis of XPS (X-ray photoelectron spectroscopy), the atomic number of magnesium is preferably 0.4 times or more and 1.5 times or less the atomic number of cobalt. On the other hand, the ratio of the atomic number of magnesium Mg / Co by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.

[0175] On the other hand, it is preferable that nickel contained in the transition metal M is not unevenly distributed in the surface layer portion 101a but is distributed throughout the entire positive electrode active material 101. However, this is not the case when the above-described high-concentration metal impurity region 103b exists.

[0176] ≪Surface roughness and specific surface area≫ For example, as follows, the smoothness of the surface can be quantified from the cross-sectional SEM image of the positive electrode active material 101.

[0177] First, the positive electrode active material 101 is processed by FIB or the like to expose a cross section. At this time, it is preferable to cover the positive electrode active material 101 with a protective film, a protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the positive electrode active material 101 is taken. Noise processing is performed on the SEM image with image processing software. For example, after performing Gaussian blur (σ = 2), binarization is performed. Further, interface extraction is performed with image processing software. Further, an interface line between the protective film or the like and the positive electrode active material 101 is selected with an automatic selection tool or the like, and the data is extracted into spreadsheet software or the like. Using the functions of spreadsheet software or the like, correction is performed from a regression curve (quadratic regression), a parameter for calculating roughness is obtained from the data after slope correction, and the root mean square surface roughness (RMS) obtained by calculating the standard deviation is obtained. Further, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm on the outer periphery of the particles.

[0178] On the particle surface of the positive electrode active material 101 of the present embodiment, the roughness (RMS: root mean square surface roughness), which is an index of roughness, is preferably less than 3 nm, more preferably less than 1 nm, and even more preferably less than 0.5 nm in terms of root mean square surface roughness (RMS).

[0179] Note that the image processing software for performing noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. Also, the spreadsheet software or the like is not particularly limited, but for example, Microsoft Office Excel can be used.

[0180] For example, the actual specific surface area A measured by the gas adsorption method using the constant volume method R and the ideal specific surface area A i From the ratio with, the smoothness of the surface of the positive electrode active material 101 can be quantified.

[0181] The ideal specific surface area A i is calculated and obtained on the assumption that the diameter of all particles is the same as D50, the weight is the same, and the shape is an ideal sphere.

[0182] The median diameter D50 can be measured by a particle size distribution meter using the laser diffraction / scattering method or the like. The specific surface area can be measured by a specific surface area measuring device using, for example, the gas adsorption method by the constant volume method.

[0183] The positive electrode active material 101 according to one aspect of the present invention has an ideal specific surface area A obtained from the median diameter D50 i and the actual specific surface area A R The ratio A of R / A i is preferably 2 or less.

[0184] This embodiment can be used in combination with other embodiments.

[0185] (Embodiment 2) An example of a method for producing a positive electrode active material according to one aspect of the present invention will be described with reference to FIGS. 9 and 10. In this embodiment, an example of a method for producing the positive electrode active material 101 shown in FIG. 1, which has cobalt and nickel as transition metals M and has magnesium, aluminum, and fluorine as impurities, will be described.

[0186] <Step S11> First, as materials for the mixture 902, a halogen source such as a fluorine source or a chlorine source and a magnesium source are prepared.

[0187] As the fluorine source, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), sodium hexafluoroaluminate (Na3AlF6), etc. can be used. Also, the fluorine source is not limited to solids. For example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. can be used and mixed into the atmosphere in the heating process described later. Also, a plurality of fluorine sources may be mixed and used. Among them, lithium fluoride is preferable because its melting point is relatively low at 848 °C and it is easily melted in the annealing process described later.

[0188] As the chlorine source, for example, lithium chloride, magnesium chloride, etc. can be used.

[0189] As the magnesium source, for example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc. can be used.

[0190] As the lithium source, for example, lithium fluoride, lithium carbonate can be used. That is, lithium fluoride can be used as both a lithium source and a fluorine source. Also, magnesium fluoride can be used as both a fluorine source and a magnesium source.

[0191] In this embodiment, lithium fluoride LiF is prepared as the fluorine source and the lithium source, and magnesium fluoride MgF2 is prepared as the fluorine source and the magnesium source (step S11 in FIG. 9).

[0192] When lithium fluoride LiF and magnesium fluoride MgF₂ are mixed at about LiF:MgF₂ = 65:35 (molar ratio), the effect of lowering the melting point is the highest (Non-Patent Document 4). On the other hand, when the amount of lithium fluoride increases, there is a concern that lithium becomes excessive and the cycle characteristics deteriorate. 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 (x is in the vicinity of 0.33).

[0193] Also, when the following mixing and pulverization steps are performed wet, a solvent is prepared. As the solvent, ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that hardly reacts with lithium. In this embodiment, acetone is used (see step S11 in FIG. 9).

[0194] <Step S12> Next, the materials of the above mixture 902 are mixed and pulverized (step S12 in FIG. 9). The mixing can be performed dry or wet, but wet is preferred because it can pulverize more finely. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the media, for example. It is preferable to perform this mixing and pulverization step sufficiently to pulverize the mixture 902 into fine powder.

[0195] As the mixing means, mixing by a blender, a mixer, or a ball mill is suitable.

[0196] <Step S13, Step S14> The materials mixed and pulverized above are recovered (step S13 in FIG. 9) to obtain a mixture 902 (step S14 in FIG. 9).

[0197] Mixture 902 preferably has a D50 of 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. When the thus micronized mixture 902 is mixed with a composite oxide containing lithium, a transition metal, and oxygen in a subsequent step, it is easy to uniformly adhere the mixture 902 to the surface of the composite oxide particles. When the mixture 902 is uniformly adhered to the surface of the composite oxide particles, it is preferable because it is easy to uniformly distribute halogen and magnesium in the surface layer portion of the composite oxide particles after heating. If there is a region in the surface layer portion that does not contain halogen and magnesium, there is a possibility that it is difficult to form the aforementioned pseudo-spinel type crystal structure in the charged state.

[0198] <Step S15, Step S16, Step S17> Also, prepare micronized nickel hydroxide (Ni(OH)2) for mixing in Step S31. For the micronized nickel hydroxide, perform Step S15 of mixing nickel hydroxide and acetone in advance and Step S16 of recovery. By Step S16, micronized nickel hydroxide is obtained (Step S17).

[0199] <Step S18, Step S19, Step S20> Also, prepare micronized aluminum hydroxide (Al(OH)3) for mixing in Step S31. For the micronized aluminum hydroxide, perform Step S18 of mixing aluminum hydroxide and acetone in advance and Step S19 of recovery. By Step S19, micronized aluminum hydroxide is obtained (Step S20).

[0200] In this embodiment, a production method of micronizing and mixing nickel and aluminum in Steps S15 to S20 will be described, but one aspect of the present invention is not limited to this. Other impurity elements such as titanium may be mixed. When mixing titanium, it is preferable to micronize and mix it in the same manner as in Steps S15 to S17. As the titanium source, titanium hydroxide, titanium oxide, etc. can be used.

[0201] <Step S25> Also, a lithium source is prepared for mixing in step S31. As step S25, a composite oxide having lithium, a transition metal, and oxygen, which has been synthesized in advance, is used.

[0202] When using a composite oxide having lithium, a transition metal, and oxygen, which has been synthesized in advance, it is preferable to use one with less impurities. In this specification and the like, for the composite oxide having lithium, a transition metal, and oxygen, and the positive electrode active material, the main components are lithium, cobalt, nickel, manganese, aluminum, and oxygen, and elements other than the above main components are regarded as impurities. For example, when analyzed by glow discharge mass spectrometry, the total impurity concentration is preferably 10,000 ppm wt or less, more preferably 5000 ppm wt or less. In particular, the total impurity concentration of transition metals such as titanium and arsenic is preferably 3000 ppm wt or less, more preferably 1500 ppm wt or less.

[0203] For example, as the lithium cobaltate (LiCoO2) synthesized in advance, lithium cobaltate particles (trade name: Celsid C-10N) manufactured by Nippon Chemical Industry Co., Ltd. can be used. This has an average particle size (D50) of about 12 μm, and in impurity analysis by glow discharge mass spectrometry (GD-MS), the magnesium concentration and fluorine concentration are 50 ppm wt or less, the calcium concentration, aluminum concentration, and silicon concentration 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 concentration of elements other than lithium, cobalt, and oxygen is 150 ppm wt or less. It is lithium cobaltate.

[0204] The composite oxide containing lithium, transition metal, and oxygen in step S25 preferably has a layered rock salt-type crystal structure with few defects and strains. Therefore, it is preferably a composite oxide with few impurities. If the composite oxide containing lithium, transition metal, and oxygen contains a large amount of impurities, it is highly likely to have a crystal structure with many defects or strains.

[0205] <Step S31> Next, the mixture 902, the composite oxide containing lithium, transition metal, and oxygen, the pulverized aluminum hydroxide, and the pulverized nickel hydroxide are mixed (step S31 in FIG. 9). The ratio of the number of atoms M of the transition metal in the composite oxide containing lithium, transition metal, and oxygen to the number of atoms Mg of magnesium in the mixture 902 is preferably M:Mg = 100:y (0.1 ≦ y ≦ 6), and more preferably M:Mg = 100:y (0.3 ≦ y ≦ 3).

[0206] The mixing in step S31 is preferably carried out under milder conditions than the mixing in step S12 so as not to break the particles of the composite oxide. For example, it is preferable to use conditions with a lower rotation speed or a shorter time than the mixing in step S12. Also, it can be said that the dry method is milder than the wet method. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the media, for example.

[0207] The materials mixed above are recovered (step S32 in FIG. 9) to obtain a mixture 903 (step S33 in FIG. 9).

[0208] Next, the mixture 903 is heated (step S34 in FIG. 9). This step may be referred to as annealing or firing.

[0209] Annealing is preferably performed at an appropriate temperature and for an appropriate time. The appropriate temperature and time vary depending on conditions such as the particle size and composition of the composite oxide particles containing lithium, transition metal, and oxygen in step S25. When the particles are small, a lower temperature or a shorter time may be more preferable than when they are large.

[0210] For example, when the average particle diameter (D50) of the particles in step S25 is about 12 μm, the annealing temperature is preferably, for example, 700°C or higher and 950°C or lower. The annealing time is preferably, for example, 3 hours or longer, more preferably 10 hours or longer, and even more preferably 60 hours or longer.

[0211] The temperature reduction time after annealing is preferably, for example, 10 hours or longer and 50 hours or shorter.

[0212] When the mixture 903 is annealed, first, the material with a low melting point in the mixture 903 (for example, lithium fluoride, melting point 848°C) melts and is considered to be distributed in the surface layer portion of the composite oxide particles. Next, due to the presence of this melted material, the melting point of other materials drops, and it is presumed that other materials melt. For example, magnesium fluoride (melting point 1263°C) melts and is considered to be distributed in the surface layer portion of the composite oxide particles.

[0213] The diffusion of the elements contained in this mixture 903 is faster in the surface layer portion and near the grain boundaries than in the interior of the composite oxide particles. Therefore, magnesium and halogen have a higher concentration in the surface layer portion and near the grain boundaries than in the interior. As will be described later, when the magnesium concentration in the surface layer portion and near the grain boundaries is high, the change in the crystal structure can be more effectively suppressed.

[0214] Recover the material annealed above (step S35 in FIG. 9). Further, it is preferable to sieve the particles. In the above steps, the positive electrode active material 101 according to one embodiment of the present invention can be produced (step S36 in FIG. 9).

[0215] Next, with reference to FIG. 10, another example of a method for producing a positive electrode active material according to an aspect of the present invention will be described. Since FIG. 10 is the same as FIG. 9 except for a part, the same parts will be omitted for simplification.

[0216] <Steps S11 to S20> In Steps S11 to S20, each element source is prepared. FIG. 10 illustrates an example in which lithium fluoride, magnesium fluoride, nickel hydroxide, and aluminum hydroxide are prepared, but an aspect of the present invention is not limited thereto. The element sources to be prepared may be one or more of these. For example, only lithium fluoride may be used.

[0217] <Step S26> Next, in Step S26, a composite oxide is prepared. Different from Step S25 in FIG. 9, a composite oxide having some impurities may be used at this stage. For example, using a composite oxide containing magnesium and titanium can reduce the types of impurities mixed in the subsequent process, which is preferable.

[0218] <Steps S31 to S36> Then, in Steps S31 to S36, each element source and the composite oxide are mixed, and the mixture 903 is annealed. In the above steps, the positive electrode active material 101 can be produced.

[0219] (Embodiment 3) With reference to FIG. 11, another example of a method for producing a positive electrode active material according to an aspect of the present invention will be described. Since this embodiment is the same as Embodiment 2 except for a part, the same parts will be omitted for simplification.

[0220] <Steps S11 to S36> Similar to Embodiment 2, various impurity elements and a composite oxide having lithium, a transition metal, and oxygen are mixed and annealed to obtain a mixture 904 (Step S36).

[0221] <Steps S42, S43, S44> Next, through Steps S42 to S44, metal Z is added as one of the impurities to the positive electrode active material according to one embodiment of the present invention. For adding the impurity metal Z, methods such as a liquid phase method including a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (chemical vapor deposition) method, a PLD (pulsed laser deposition) method, etc. can be applied.

[0222] As shown in FIG. 11, first, in Step S42, a metal source is prepared. As the metal source, metal alkoxides, metal hydroxides, metal oxides, etc. can be used. Further, when applying the sol-gel method, a solvent used in the sol-gel method is prepared. As this solvent, alcohol is preferable, and it is particularly preferable to use the same alcohol as the alkoxyl group of the alkoxide of the additive source. The water contained in the solvent is preferably 3% by volume or less, and more preferably 0.3% by volume or less. By using alcohol as the solvent, deterioration of LiCoO2 in the manufacturing process can be suppressed compared to the case of using water. When metal Z is aluminum, for example, taking the number of cobalt atoms in lithium cobaltate as 1, the number of aluminum atoms in the metal source may be 0.001 times or more and 0.02 times or less. When metal Z is titanium, for example, taking the number of cobalt atoms in lithium cobaltate as 1, the number of titanium atoms in the metal source may be 0.001 times or more and 0.02 times or less. When metal Z is aluminum and titanium, for example, taking the number of cobalt atoms in lithium cobaltate as 1, the number of aluminum atoms in the metal source may be 0.001 times or more and 0.02 times or less, and the number of titanium atoms in the metal source may be 0.001 times or more and 0.02 times or less.

[0223] Here, as an example, an example of applying the sol-gel method and using titanium(IV) tetraisopropoxide (TTIP) as the metal source and 2-propanol as the solvent is shown (Step S42 in FIG. 11).

[0224] Next, dissolve the above titanium alkoxide in 2-propanol, and further mix lithium cobaltate particles (step S43 in FIG. 11).

[0225] The required amount of the metal alkoxide varies depending on the particle size of lithium cobaltate. For example, when using titanium isopropoxide and the particle size (D50) of lithium cobaltate is about 20 μm, it is preferable to add it so that the number of cobalt atoms in lithium cobaltate is 1 and the number of titanium atoms in titanium isopropoxide is 0.001 times or more and 0.02 times or less.

[0226] Next, stir the mixed solution of the alcohol solution of the metal alkoxide and the particles of lithium cobaltate in an atmosphere containing water vapor. Stirring can be performed, for example, with a magnetic stirrer. The stirring time may be a time sufficient for water and the metal alkoxide in the atmosphere to undergo hydrolysis and polycondensation reactions. For example, it can be performed under the conditions of 4 hours, 25 °C, and 90% RH (Relative Humidity). Also, stirring may be performed in an atmosphere where humidity control and temperature control are not performed, for example, in the atmospheric atmosphere in a draft chamber. In such a case, it is preferable to make the stirring time longer, for example, 12 hours or more at room temperature.

[0227] By gradually incorporating water vapor in the atmosphere and gradually volatilizing the alcohol, water and the metal alkoxide can react, and the sol-gel reaction can proceed gently. Also, by reacting the metal alkoxide and water at room temperature, the sol-gel reaction can proceed more gently than when heating at a temperature exceeding the boiling point of the alcohol, which is the solvent, for example.

[0228] Also, water may be added actively. When it is desired to react gently, the reaction time may be controlled by gradually adding water diluted with alcohol, adding a stabilizer, etc. By gently proceeding with the sol-gel reaction, a coating layer with uniform thickness and good quality can be formed.

[0229] Recover the precipitate from the mixed solution after the above treatment (step S44 in Fig. 11). As the recovery method, filtration, centrifugation, evaporation to dryness, etc. can be applied. The precipitate can be washed with the same alcohol as the solvent in which the metal alkoxide was dissolved. When evaporation to dryness is applied, it is not necessary to separate the solvent and the precipitate in this step. For example, in the drying step of the next step (step S44), the precipitate may be recovered.

[0230] Next, dry the recovered residue to obtain mixture 904 (step S44 in Fig. 11). The drying process can be, for example, vacuum or ventilation drying at 80°C for 1 hour or more and 4 hours or less.

[0231] <Step S45> Next, heat the obtained mixture (step S45 in Fig. 11).

[0232] The heating time is preferably 1 hour or more and 80 hours or less as the holding time within the range of the heating temperature, and more preferably 1 hour or more and 20 hours or less considering productivity.

[0233] The heating temperature is less than 1000°C, preferably 700°C or more and 950°C or less, and more preferably about 850°C.

[0234] Also, the heating is preferably performed in an atmosphere containing oxygen.

[0235] In this embodiment, the heating temperature is set to 850°C and held for 2 hours, the temperature increase rate is 200°C / h, and the oxygen flow rate is 10 L / min.

[0236] The heating temperature in step S45 is preferably lower than the heating temperature in step S34.

[0237] <Steps S46, S47> Next, the cooled particles are collected (step S46 in FIG. 11). Further, it is preferable to sieve the particles. In the above steps, the positive electrode active material 101 of one aspect of the present invention can be produced (step S47 in FIG. 11).

[0238] This embodiment can be used in combination with other embodiments.

[0239] (Embodiment 4) In this embodiment, another example of the method for producing the positive electrode active material of one aspect of the present invention will be described. Since this embodiment is the same as Embodiments 2 and 3 except for being partially different, the same parts will be omitted for simplification.

[0240] In the previous embodiment, the method of mixing impurity elements in step S31 or step S43 was described, but one aspect of the present invention is not limited to this. With reference to FIG. 12, the timing and method for adding impurity elements will be described.

[0241] <Step S01> As step S01 in FIG. 12, first, a lithium source and a transition metal M source are prepared as materials for a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. At this time, that is, a first impurity element source may be prepared as one of the raw materials when firing the composite oxide.

[0242] As the first impurity element, at least one of magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. As the first impurity element source, these oxides, hydroxides, fluorides, etc. can be used.

[0243] As the lithium source, for example, lithium carbonate, lithium fluoride, etc. can be used.

[0244] As the transition metal M, it is preferable to use 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, only cobalt may be used as the transition metal M source, only nickel may be used, two types of cobalt and manganese, or two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used.

[0245] When using a metal that can form a layered rock salt-type composite oxide, it is preferable to use a mixing ratio of cobalt, manganese, and nickel within the range that can take on the layered rock salt-type crystal structure. Also, within the range that can take on the layered rock salt-type crystal structure, aluminum may be added to these transition metals.

[0246] As the transition metal M source, oxides, hydroxides, etc. of the above-mentioned metals exemplified 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.

[0247] <Step S02> Next, as step S02, the above lithium source, transition metal M source, and first impurity element source are mixed. The mixing can be carried out dry or wet. For mixing, for example, a ball mill, a bead mill, etc. can be used. When using a ball mill, it is preferable to use zirconia balls as the media, for example.

[0248] <Step S03> Next, as step S03, heat the material mixed above. This step may be referred to as firing or first heating for the purpose of distinguishing it from subsequent heating steps. The heating is preferably carried out at a temperature of 800 °C or higher and less than 1100 °C, more preferably at 900 °C or higher and 1000 °C or lower, and even more preferably about 950 °C. If the temperature is too low, there is a risk that the decomposition and melting of the lithium source, transition metal M source, and first impurity element source will be insufficient. On the other hand, if the temperature is too high, defects may occur due to excessive reduction of the metal responsible for the oxidation-reduction reaction used as transition metal M, evaporation of lithium, etc. For example, when cobalt is used as transition metal M, defects may occur in which cobalt becomes divalent.

[0249] The heating time can be, for example, 1 hour or more and 100 hours or less, and preferably 2 hours or more and 20 hours or less. The firing is preferably carried out in an atmosphere with little water such as dry air (for example, dew point of -50 °C or lower, more preferably -100 °C or lower). For example, it is preferable to heat at 1000 °C for 10 hours, with a heating rate of 200 °C / h and a flow rate of the dry atmosphere of 10 L / min. Thereafter, the heated material can be cooled to room temperature. For example, it is preferable that the cooling time from the specified temperature to room temperature is 10 hours or more and 50 hours or less.

[0250] However, the cooling to room temperature in step S03 is not essential. If there is no problem in performing the subsequent steps, the cooling may be to a temperature higher than room temperature.

[0251] <Step S04> Next, as step S04, recover the material fired above to obtain a composite oxide (LiMO2) having lithium, transition metal M, the first impurity element, and oxygen.

[0252] <Steps S11 to S13 and Step S31> Also, similar to the method described in the previous embodiment, as shown in steps S11 to S13 and step S31, after synthesizing a composite oxide having lithium, transition metal M, and oxygen, a second impurity element source may be mixed. As the second impurity element, at least one of magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. As the second impurity element source, these oxides, hydroxides, fluorides, etc. can be used.

[0253] <Steps S42 and S43> Also, similar to the method described in the previous embodiment, as shown in steps S42 and S43, after mixing the second impurity element and annealing, a third impurity element source may be mixed. As the third impurity element, at least one of magnesium, fluorine, aluminum, titanium, zirconium, vanadium, iron, chromium, niobium, cobalt, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. As the third impurity element source, these oxides, hydroxides, fluorides, etc. can be used.

[0254] Also, although not shown in the figure, after mixing the third impurity element source and further annealing, a fourth impurity element source may be mixed.

[0255] In this way, the impurity element sources can be mixed at multiple timings in the process of manufacturing the positive electrode active material 101.

[0256] As the mixing method of each impurity element source, methods such as the sol-gel method and other liquid phase methods, solid phase methods, sputtering methods, vapor deposition methods, CVD (chemical vapor deposition) methods, PLD (pulsed laser deposition) methods, etc. can be applied.

[0257] The first impurity element source, the second impurity element source, and the third impurity element source may each be a different element, or some of them may be the same element. For example, magnesium may be used for both the first impurity element source and the second impurity element source.

[0258] Among the respective impurity element sources, it is preferable to mix magnesium and fluorine simultaneously. By adding magnesium and fluorine simultaneously, the function of the fluorine source as a flux is sufficiently exerted, and the distribution of magnesium in the surface layer portion of the positive electrode active material 101 becomes favorable.

[0259] Also, depending on the impurity element, the optimal timing for mixing may be different. For example, magnesium and fluorine are preferably mixed as impurity element sources after the second one rather than as the first impurity element source.

[0260] Note that in the manufacturing method of one aspect of the present invention, any one or more of the first to third impurity element sources may be mixed. That is, one or more of the timings of mixing the impurity element sources shown in FIG. 12 may be adopted, and it is not necessarily required to mix the impurity elements at all timings.

[0261] This embodiment can be used in combination with other embodiments.

[0262] (Embodiment 5) In this embodiment, an example of a secondary battery of one aspect of the present invention will be described with reference to FIGS. 13 to 16.

[0263] <Configuration Example 1 of Secondary Battery> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be described as an example.

[0264] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material and may have a conductive material and a binder. As the positive electrode active material, the positive electrode active material produced by using the production method described in the previous embodiment is used.

[0265] Further, the positive electrode active material described in the previous embodiment may be mixed with other positive electrode active materials and used.

[0266] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0267] Further, as another positive electrode active material, lithium-containing materials having a spinel-type crystal structure containing manganese such as LiMn2O4 are 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.

[0268] Further, as another positive electrode active material, the composition formula Li a Mn b M c O dA lithium manganese composite oxide represented by [the formula] can be used. Here, 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. Note that 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 determined by using valence evaluation of melting gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. Note that 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.

[0269] Hereinafter, as an example, a cross-sectional configuration example when a graphene compound is used as a conductive material in the active material layer 200 will be described.

[0270] FIG. 13(A) shows a longitudinal sectional view of the active material layer 200. The active material layer 200 includes granular positive electrode active material 101, graphene and graphene compound 201 as a conductive material, and a binder (not shown).

[0271] In this specification and the like, the graphene compound includes multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-layer graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-layer graphene oxide, graphene quantum dots, etc. The graphene compound refers to a substance that contains carbon, has a flat or sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may be referred to as a carbon sheet. The graphene compound may have a functional group. Also, the graphene compound preferably has a bent shape. Further, the graphene compound may be curled to be like a carbon nanofiber.

[0272] In this specification and the like, graphene oxide refers to a graphene compound that contains carbon and oxygen, has a sheet-like shape, and has a functional group, particularly an epoxy group, a carboxy group, or a hydroxy group.

[0273] In this specification and the like, reduced graphene oxide refers to a substance that contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. It may be referred to as a carbon sheet. Reduced graphene oxide can function even when there is a single sheet, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting such carbon and oxygen concentrations, it can function as a highly conductive material even in small amounts. Also, reduced graphene oxide preferably has an intensity ratio G / D of the G band and the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0274] In the longitudinal section of the active material layer 200, as shown in FIG. 13(B), sheet-like graphene and graphene compound 201 are dispersed approximately uniformly inside the active material layer 200. In FIG. 13(B), graphene and graphene compound 201 are schematically represented by thick lines, but actually they are thin films having a thickness of a single layer or multiple layers of carbon molecules. A plurality of graphene and graphene compound 201 are formed so as to partially cover a plurality of granular positive electrode active materials 101 or adhere onto the surfaces of a plurality of granular positive electrode active materials 101, and thus are in surface contact with each other. Note that it is preferable that graphene and graphene compound 201 adhere to at least a part of the active material. Also, it is preferable that graphene and graphene compound 201 overlap at least a part of the active material. Also, it is preferable that the shape of graphene and graphene compound 201 coincides with at least a part of the shape of the active material. The shape of the active material refers to, for example, the unevenness of a single active material particle or the unevenness formed by a plurality of active material particles. Also, it is preferable that graphene and graphene compound 201 surround at least a part of the active material. Also, graphene and graphene compound 201 may have holes.

[0275] Here, by bonding a plurality of graphene compounds to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is covered with the graphene net, the graphene net can also function as a binder that binds the active materials to each other. Therefore, the amount of the binder can be reduced or the binder can be not used, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the capacity of the secondary battery can be increased.

[0276] Here, it is preferable to use graphene and graphene compound 201 as graphene oxide, mix it with the active material to form a layer that becomes the active material layer 200, and then reduce it. That is, the completed active material layer preferably has reduced graphene oxide. By using graphene oxide with extremely high dispersibility in a polar solvent for the formation of graphene and graphene compound 201, graphene and graphene compound 201 can be dispersed substantially uniformly inside the active material layer 200. In order to volatilize and remove the solvent from the dispersion medium containing uniformly dispersed graphene oxide and reduce the graphene oxide, the graphene and graphene compound 201 remaining in the active material layer 200 partially overlap and are dispersed to the extent of surface contact with each other, so that a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or using a reducing agent.

[0277] Therefore, unlike granular conductive materials such as acetylene black that make point contact with the active material, graphene and graphene compound 201 enable surface contact with low contact resistance. Thus, the electrical conductivity between the granular positive electrode active material 101 and graphene and graphene compound 201 can be improved with a smaller amount than that of ordinary conductive materials. Therefore, the ratio of the positive electrode active material 101 in the active material layer 200 can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

[0278] Also, by using a spray dryer in advance, a graphene compound, which is a conductive material, can be formed as a coating covering the entire surface of the active material, and a conductive path can also be formed between the active materials with the graphene compound.

[0279] [Negative electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. Also, the negative electrode active material layer may have a conductive material and a binder.

[0280] [Negative electrode active material] As the negative electrode active material, for example, an alloy-based material, a carbon-based material, or the like can be used.

[0281] As the negative electrode active material, an element capable of performing a charge-discharge reaction by an alloying / dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. Such elements have a larger capacity compared to carbon, and in particular, silicon has a high theoretical capacity of 4200 mAh / g. Therefore, it is preferable to use silicon as the negative electrode active material. Also, compounds containing these elements may be used. For example, there are SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. Here, elements capable of performing a charge-discharge reaction by an alloying / dealloying reaction with lithium, and compounds containing such elements, etc. may be referred to as alloy-based materials.

[0282] In this specification, etc., SiO refers to, for example, silicon monoxide. Alternatively, SiO can also be represented as SiO x where x preferably has a value near 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.

[0283] As the carbon-based material, graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0284] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which may be preferable. Examples of natural graphite include flake graphite, spheroidized natural graphite, etc.

[0285] Graphite exhibits a potential as low as that of lithium metal (0.05 V or more and 0.3 V or less vs. Li / Li + ) when lithium ions are inserted into the graphite (when a lithium-graphite intercalation compound is formed). As a result, a lithium-ion secondary battery can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal, and thus is preferable.

[0286] In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0287] In addition, as the negative electrode active material, Li 3-x M x N (M = Co, Ni, Cu) which is a complex nitride of lithium and a transition metal and has an Li3N-type structure can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable.

[0288] When using a complex nitride of lithium and a transition metal, since the negative electrode active material contains lithium ions, it can be preferably combined with materials such as V2O5 and Cr3O8 that do not contain lithium ions as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, a complex nitride of lithium and a transition metal can be used as the negative electrode active material by previously desorbing the lithium ions contained in the positive electrode active material.

[0289] In addition, a material in which a conversion reaction occurs can also be used as the negative electrode active material. For example, transition metal oxides that do not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Materials in which a conversion reaction occurs further include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, 0.89 sulfides such as CoS, NiS, and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0290] As the conductive material and binder that the negative electrode active material layer can have, the same materials as those of the conductive material and binder that the positive electrode active material layer can have can be used.

[0291] [Negative electrode current collector] For the negative electrode current collector, the same materials as those of the positive electrode current collector can be used. It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0292] [Electrolyte solution] The electrolyte has a solvent and an electrolyte. As the solvent of the electrolyte, an aprotic organic solvent is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc. can be used alone, or two or more of these can be used in any combination and ratio.

[0293] In addition, by using one or more ionic liquids (room temperature molten salts) that are flame retardant and hardly volatile as the solvent of the electrolyte, even if the internal temperature of the secondary battery rises due to internal short circuit, overcharge, etc., rupture and ignition of the secondary battery can be prevented. An ionic liquid consists of a cation and an anion and contains an organic cation and an anion. Examples of the organic cation 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 the anion used in the electrolyte include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions.

[0294] In addition, as the electrolyte dissolved in the above solvent, for example, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B12 Cl 12 One kind of lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc., or two or more of these can be used in any combination and ratio.

[0295] For the electrolyte used in the secondary battery, it is preferable to use a highly purified electrolyte with a low content of particulate dust and elements other than the constituent elements of the electrolyte (hereinafter also simply referred to as "impurities"). Specifically, it is preferable that the weight ratio of impurities to the electrolyte is 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0296] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive material may be, for example, 0.1 wt% or more and 5 wt% or less based on the entire solvent.

[0297] Also, a polymer gel electrolyte in which the polymer is swollen with the electrolyte may be used.

[0298] By using the polymer gel electrolyte, the safety against liquid leakage and the like is enhanced. Also, the secondary battery can be made thinner and lighter.

[0299] As the polymer to be gelled, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, fluorine-based polymer gel, etc. can be used.

[0300] As the polymer, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the formed polymer may have a porous shape.

[0301] Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide-based or oxide-based material, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide)-based material can be used. When using a solid electrolyte, it is not necessary to install a separator or a spacer. Further, since the entire battery can be solidified, there is no risk of liquid leakage and the safety is dramatically improved.

[0302] 〔Separator〕 Moreover, the secondary battery preferably has a separator. As the separator, for example, those formed of paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into an envelope shape and arranged to wrap either the positive electrode or the negative electrode.

[0303] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0304] Coating with a ceramic-based material improves oxidation resistance, suppresses deterioration of the separator during high-voltage charge and discharge, and can improve the reliability of the secondary battery. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere, and can improve the output characteristics. Coating with a polyamide-based material, particularly aramid, improves heat resistance, and thus can improve the safety of the secondary battery.

[0305] For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Also, a mixed material of aluminum oxide and aramid may be coated on the surface of the polypropylene film that contacts the positive electrode, and a fluorine-based material may be coated on the surface that contacts the negative electrode.

[0306] When using a separator with a multilayer structure, even if the overall thickness of the separator is thin, the safety of the secondary battery can be maintained, so the capacity per unit volume of the secondary battery can be increased.

[0307] 〔Outer package〕 As the outer package of the secondary battery, for example, a metal material such as aluminum or a resin material can be used. Also, a film-shaped outer package can be used. As the film, for example, on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., a metal thin film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided, and further, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the outer package on the metal thin film, and a three-layer structure film can be used.

[0308] <Configuration Example 2 of Secondary Battery> Hereinafter, as an example of the configuration of a secondary battery, the configuration of a secondary battery using a solid electrolyte layer will be described.

[0309] As shown in FIG. 14(A), a secondary battery 400 according to an aspect of the present invention includes a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0310] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material layer 414 may also have a conductive assistant and a binder.

[0311] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that has neither the positive electrode active material 411 nor the negative electrode active material 431.

[0312] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive assistant and a binder. When metallic lithium is used for the negative electrode 430, as shown in FIG. 14(B), the negative electrode 430 without the solid electrolyte 421 can be used. When metallic lithium is used for the negative electrode 430, it is preferable because the energy density of the secondary battery 400 can be improved.

[0313] As the solid electrolyte 421 included in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. can be used.

[0314] The sulfide-based solid electrolytes include thiophosphosilicate-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.), and sulfide crystallized glasses (Li7P3S 11 、Li 3.25 P 0.95 S4 etc.). Sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft so that the conductive path is easily maintained even after charge and discharge.

[0315] Oxide-based solid electrolytes include materials having a perovskite crystal structure (such as La 2 / 3-x Li 3x TiO3), materials having a NASICON crystal structure (such as Li 1+X Al X Ti 2-X (PO4)3), materials having a garnet crystal structure (such as Li7La3Zr2O 12 ), materials having a LISICON crystal structure (such as Li 14 ZnGe4O 16 ), oxide glasses (such as Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3), and oxide-crystallized glasses (such as Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3). Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0316] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can be used as solid electrolytes.

[0317] Also, a plurality of solid electrolytes may be mixed and used.

[0318] Among them, Li having a NASICON crystal structure 1+x Al x Ti 2-x(PO4)3(0 ≦ x ≦ 1) (hereinafter referred to as LATP) contains elements such as aluminum and titanium, which may be included in the positive electrode active material used in the secondary battery 400 of one aspect of the present invention. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. In addition, an improvement in productivity due to the reduction of processes can also be expected. 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 share vertices and are three-dimensionally arranged.

[0319] <> 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, various materials and shapes can be used, but it preferably has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0320] For example, FIG. 15 shows an example of a cell for evaluating the materials of an all-solid-state battery.

[0321] FIG. 15(A) is a schematic cross-sectional view of the evaluation cell. The evaluation cell has a lower member 761, an upper member 762, and fixing screws and wing nuts 764 for fixing them. By rotating the pressing screw 763, the electrode plate 753 is pressed to fix the evaluation material. An insulator 766 is provided between the lower member 761 and the upper member 762, both of which are made of stainless steel. Also, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0322] The evaluation material is placed on the electrode plate 751, surrounded by an insulating tube 752 around it, and is in a state of being pressed by the electrode plate 753 from above. A perspective view of the periphery of this evaluation material is shown in FIG. 15(B).

[0323] As an example of the evaluation material, a stack of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in FIG. 15(C). The same reference numerals are used for the same parts in FIGS. 15(A), (B), and (C).

[0324] The electrode plate 751 and the lower member 761 that are electrically connected to the positive electrode 750a can be said to correspond to the positive electrode terminal. The electrode plate 753 and the upper member 762 that are electrically connected to the negative electrode 750c can be said to correspond to the negative electrode terminal. Electrical resistance and the like can be measured while applying pressure to the evaluation material via the electrode plate 751 and the electrode plate 753.

[0325] Also, for the exterior body of the secondary battery according to one aspect of the present invention, it is preferable to use a package having excellent airtightness. For example, a ceramic package or a resin package can be used. Further, when sealing the exterior body, it is preferable to perform the sealing in an atmosphere where the outside air is blocked and sealed, for example, inside a glove box.

[0326] FIG. 16(A) shows a perspective view of a secondary battery according to one aspect of the present invention having an exterior body and a shape different from those in FIG. 15. The secondary battery in FIG. 16(A) has external electrodes 771 and 772 and is sealed with an exterior body having a plurality of package members.

[0327] An example of a cross-section cut along the dashed line in FIG. 16(A) is shown in FIG. 16(B). The laminate having the positive electrode 750a, the solid electrolyte layer 750b, and the negative electrode 750c is surrounded and sealed by a package member 770a provided with an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c provided with an electrode layer 773b on a flat plate. For the package members 770a, 770b, and 770c, an insulating material, for example, a resin material or a ceramic, can be used.

[0328] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. Also, the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0329] This embodiment can be used in appropriate combination with other embodiments.

[0330] (Embodiment 6) In this embodiment, an example of the shape of a secondary battery having a positive electrode described in the previous embodiment will be described. The materials used for the secondary battery described in this embodiment can refer to the description of the previous embodiment.

[0331] <Coin-shaped secondary battery> First, an example of a coin-shaped secondary battery will be described. FIG. 17(A) is an external view of a coin-shaped (single-layer flat type) secondary battery, and FIG. 17(B) is a cross-sectional view thereof.

[0332] In the coin-shaped secondary battery 300, a positive electrode can 301 also serving as a positive electrode terminal and a negative electrode can 302 also serving as a negative electrode terminal are insulated and sealed with a gasket 303 formed 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 therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

[0333] Note that for the positive electrode 304 and the negative electrode 307 used in the coin-shaped secondary battery 300, the active material layer may be formed only on one side.

[0334] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolyte, or alloys thereof or alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolyte, it is preferable to coat with nickel, aluminum, or the like. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0335] These negative electrode 307, positive electrode 304, and separator 310 are impregnated with an electrolyte, and as shown in FIG. 17(B), with the positive electrode can 301 facing down, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are pressure-bonded via the gasket 303 to manufacture the coin-shaped secondary battery 300.

[0336] By using the positive electrode active material described in the previous embodiment for the positive electrode 304, a coin-type secondary battery 300 with high capacity and excellent cycle characteristics can be obtained.

[0337] Here, the flow of current during charging of the secondary battery will be described with reference to Fig. 17(C). When a secondary battery using lithium is regarded as a single closed circuit, the movement of lithium ions and the flow of current are in the same direction. In a secondary battery using lithium, the anode and cathode are reversed during charging and discharging, and the oxidation reaction and reduction reaction are also reversed. Therefore, the electrode with a higher reaction potential is called the positive electrode, and the electrode with a lower reaction potential is called the negative electrode. Thus, in this specification, whether during charging, discharging, when applying a reverse pulse current, or when applying a charging current, the positive electrode will be referred to as the "positive electrode" or the "+ electrode (plus electrode)", and the negative electrode will be referred to as the "negative electrode" or the "- electrode (minus electrode)". Using terms such as anode and cathode related to oxidation and reduction reactions would result in them being reversed during charging and discharging, which could cause confusion. Therefore, the terms anode and cathode will not be used in this specification. If the terms anode and cathode are used, it is necessary to specify whether it is during charging or discharging, and also indicate which one corresponds to the positive electrode (plus electrode) and the negative electrode (minus electrode).

[0338] A charger is connected to the two terminals shown in Fig. 17(C), and the secondary battery 300 is charged. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0339] <Cylindrical secondary battery> Next, an example of a cylindrical secondary battery will be described with reference to FIG. 18. An external view of the cylindrical secondary battery 600 is shown in FIG. 18(A). FIG. 18(B) is a diagram schematically showing a cross section of the cylindrical secondary battery 600. As shown in FIG. 18(B), the cylindrical secondary battery 600 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0340] Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof or alloys of these and other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with nickel, aluminum, or the like. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. The non-aqueous electrolytic solution can be the same as that used in the coin-type secondary battery.

[0341] Since the positive and negative electrodes used in the cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. A positive electrode terminal (positive current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can use a metal material such as aluminum. The positive electrode terminal 603 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602. The safety valve mechanism 612 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. Also, the PTC element 611 is a thermal sensing resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO3)-based semiconductor ceramics or the like can be used.

[0342] Also, as shown in Fig. 18(C), a module 615 may be configured by sandwiching a plurality of secondary batteries 600 between a conductive plate 613 and a conductive plate 614. The plurality of secondary batteries 600 may be connected in parallel, in series, or in parallel and then further in series. By configuring a module 615 having a plurality of secondary batteries 600, a large amount of power can be extracted.

[0343] FIG. 18(D) is a top view of module 615. The conductive plate 613 is shown by a dotted line for clarity. As shown in FIG. 18(D), module 615 may have a conductive wire 616 that electrically connects a plurality of secondary batteries 600. A conductive plate can be superimposed and provided on the conductive wire 616. Further, a temperature control device 617 may be provided between the plurality of secondary batteries 600. When the secondary battery 600 is overheated, it can be cooled by the temperature control device 617, and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617. Therefore, the performance of module 615 is less likely to be affected by the outside air temperature. The heat medium of the temperature control device 617 preferably has insulation and incombustibility.

[0344] By using the positive electrode active material described in the previous embodiment for the positive electrode 604, a cylindrical secondary battery 600 with high capacity and excellent cycle characteristics can be obtained.

[0345] <Structural Example of Secondary Battery> Another structural example of the secondary battery will be described with reference to FIGS. 19 to 23.

[0346] FIGS. 19(A) and 19(B) are views showing the external appearance of a battery pack. The battery pack has a secondary battery 913 and a circuit board 900. The secondary battery 913 is connected to an antenna 914 via the circuit board 900. A label 910 is attached to the secondary battery 913. Further, as shown in FIG. 19(B), the secondary battery 913 is connected to a terminal 951 and a terminal 952. The circuit board 900 is fixed with a seal 915.

[0347] The circuit board 900 has a terminal 911 and a circuit 912. The terminal 911 is connected to the terminal 951, the terminal 952, the antenna 914, and the circuit 912. Note that a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

[0348] The circuit 912 may be provided on the back surface of the circuit board 900. Note that the antenna 914 is not limited to a coil shape, and may be, for example, linear or plate-shaped. Also, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 914 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. That is, the antenna 914 may function as one of the two conductors of the capacitor. Thereby, power exchange can be performed not only by electromagnetic fields and magnetic fields but also by electric fields.

[0349] The battery pack has a layer 916 between the antenna 914 and the secondary battery 913. The layer 916 has a function of, for example, shielding the electromagnetic field generated by the secondary battery 913. As the layer 916, for example, a magnetic material can be used.

[0350] Note that the structure of the battery pack is not limited to that shown in FIG. 19.

[0351] For example, as shown in FIGS. 20(A) and 20(B), antennas may be provided on each of a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 19(A) and 19(B). FIG. 20(A) is an external view showing one of the pair of surfaces, and FIG. 20(B) is an external view showing the other of the pair of surfaces. Note that for the same parts as the secondary battery shown in FIGS. 19(A) and 19(B), the description of the secondary battery shown in FIGS. 19(A) and 19(B) can be appropriately incorporated.

[0352] As shown in FIG. 20(A), the antenna 914 is provided with the layer 916 interposed between one of the pair of surfaces of the secondary battery 913, and as shown in FIG. 20(B), the antenna 918 is provided with the layer 917 interposed between the other of the pair of surfaces of the secondary battery 913. The layer 917 has a function of, for example, shielding the electromagnetic field generated by the secondary battery 913. As the layer 917, for example, a magnetic material can be used.

[0353] By adopting the above structure, the sizes of both the antenna 914 and the antenna 918 can be increased. The antenna 918 has a function capable of performing data communication with an external device, for example. An antenna having a shape applicable to the antenna 914 can be applied to the antenna 918, for example. As a communication method between the secondary battery and other devices via the antenna 918, a response method or the like that can be used between the secondary battery and other devices, such as NFC (Near Field Communication), can be applied.

[0354] Alternatively, as shown in FIG. 20(C), a display device 920 may be provided on the secondary battery 913 shown in FIGS. 19(A) and 19(B). The display device 920 is electrically connected to the terminal 911. Note that a label 910 may not be provided at the portion where the display device 920 is provided. Regarding the same portions as the secondary battery shown in FIGS. 19(A) and 19(B), the description of the secondary battery shown in FIGS. 19(A) and 19(B) can be appropriately incorporated.

[0355] The display device 920 may display, for example, an image indicating whether charging is in progress, an image indicating the remaining charge amount, or the like. As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (EL) display device, or the like can be used. For example, by using an electronic paper, the power consumption of the display device 920 can be reduced.

[0356] Alternatively, as shown in FIG. 20(D), a sensor 921 may be provided on the secondary battery 913 shown in FIGS. 19(A) and 19(B). The sensor 921 is electrically connected to the terminal 911 via the terminal 922. Regarding the same portions as the secondary battery shown in FIGS. 19(A) and 19(B), the description of the secondary battery shown in FIGS. 19(A) and 19(B) can be appropriately incorporated.

[0357] As the sensor 921, for example, it may have a function capable of measuring displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays. By providing the sensor 921, for example, data (such as temperature) indicating the environment where the secondary battery is placed can be detected and stored in the memory within the circuit 912.

[0358] Furthermore, a structural example of the secondary battery 913 will be described with reference to FIGS. 21 and 22.

[0359] The secondary battery 913 shown in FIG. 21(A) has a wound body 950 provided with a terminal 951 and a terminal 952 inside a housing 930. The wound body 950 is impregnated with an electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 21(A), for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (such as aluminum) or a resin material can be used.

[0360] Note that, as shown in FIG. 21(B), the housing 930 shown in FIG. 21(A) may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 21(B) has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the region surrounded by the housing 930a and the housing 930b.

[0361] As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna such as the antenna 914 may be provided inside the housing 930a. As the housing 930b, for example, a metal material can be used.

[0362] Furthermore, the structure of the wound body 950 is shown in FIG. 22. The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0363] The negative electrode 931 is connected to the terminal 911 shown in FIG. 19 via one of the terminals 951 and 952. The positive electrode 932 is connected to the terminal 911 shown in FIG. 19 via the other of the terminals 951 and 952.

[0364] By using the positive electrode active material described in the previous embodiment for the positive electrode 932, a secondary battery 913 with high capacity and excellent cycle characteristics can be obtained.

[0365] <Laminated secondary battery> Next, an example of a laminated secondary battery will be described with reference to FIGS. 23 to 27. If the laminated secondary battery has a flexible configuration and is mounted on an electronic device having at least a part of a flexible portion, the secondary battery can also be bent in accordance with the deformation of the electronic device.

[0366] The laminated secondary battery 980 will be described with reference to FIG. 23. The laminated secondary battery 980 has a wound body 993 shown in FIG. 23(A). The wound body 993 includes a negative electrode 994, a positive electrode 995, and a separator 996. Similar to the wound body 950 described in FIG. 22, the wound body 993 is formed by laminating the negative electrode 994 and the positive electrode 995 with the separator 996 interposed therebetween and winding the laminated sheet.

[0367] Note that the number of layers of the laminate composed of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and the element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrodes 997 and 998, and the positive electrode 995 is connected to a positive electrode current collector (not shown) via the other of the lead electrodes 997 and 998.

[0368] As shown in FIG. 23(B), the wound body 993 described above is housed in a space formed by thermocompression bonding or the like of a film 981 serving as an exterior body and a film 982 having a concave portion, whereby a secondary battery 980 as shown in FIG. 23(C) can be manufactured. The wound body 993 has lead electrodes 997 and 998 and is impregnated with an electrolytic solution inside the film 981 and the film 982 having a concave portion.

[0369] For the film 981 and the film 982 having a concave portion, a metal material such as aluminum or a resin material can be used. If a resin material is used as the material of the film 981 and the film 982 having a concave portion, the film 981 and the film 982 having a concave portion can be deformed when an external force is applied, and a flexible storage battery can be manufactured.

[0370] Also, although FIGS. 23(B) and 23(C) show an example using two films, a space may be formed by bending a single film, and the wound body 993 described above may be housed in the space.

[0371] By using the positive electrode active material described in the previous embodiment for the positive electrode 995, a secondary battery 980 with high capacity and excellent cycle characteristics can be obtained.

[0372] Also, although FIG. 23 describes an example of the secondary battery 980 having a wound body in a space formed by a film serving as an exterior body, for example, as shown in FIG. 24, a secondary battery having a plurality of strip-shaped positive electrodes, separators, and negative electrodes in a space formed by a film serving as an exterior body may be used.

[0373] The laminated secondary battery 500 shown in Fig. 24(A) includes a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an electrolytic solution 508, and an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. Also, the interior of the exterior body 509 is filled with the electrolytic solution 508. As the electrolytic solution 508, the electrolytic solution shown in Embodiment 3 can be used.

[0374] In the laminated secondary battery 500 shown in Fig. 24(A), the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, a part of the positive electrode current collector 501 and the negative electrode current collector 504 may be arranged to be exposed outside the exterior body 509. Alternatively, without exposing the positive electrode current collector 501 and the negative electrode current collector 504 outside the exterior body 509, a lead electrode may be ultrasonically bonded to the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 so that the lead electrode is exposed outside.

[0375] In the laminated secondary battery 500, the exterior body 509 may be made of a three-layer laminated film in which a metal thin film with excellent flexibility 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-based resin or a polyester-based resin is provided as the outer surface of the exterior body on the metal thin film.

[0376] Also, an example of the cross-sectional structure of the laminated secondary battery 500 is shown in Fig. 24(B). In Fig. 24(A), for simplicity, an example composed of two current collectors is shown, but actually, as shown in Fig. 24(B), it is composed of a plurality of electrode layers.

[0377] In Fig. 24(B), as an example, the number of electrode layers is 16. Even when the number of electrode layers is 16, the secondary battery 500 has flexibility. Fig. 24(B) shows a structure with a total of 16 layers, where the negative electrode current collector 504 has 8 layers and the positive electrode current collector 501 has 8 layers. Note that Fig. 24(B) shows a cross-section of the extraction part of the negative electrode, and the 8-layer negative electrode current collector 504 is ultrasonically bonded. Of course, the number of electrode layers is not limited to 16, and it may be more or less. When the number of electrode layers is large, a secondary battery with a larger capacity can be obtained. Also, when the number of electrode layers is small, it can be thinned and a secondary battery with excellent flexibility can be obtained.

[0378] Here, an example of the external view of the laminate-type secondary battery 500 is shown in Figs. 25 and 26. Figs. 25 and 26 have a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0379] Fig. 27(A) shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. Also, the positive electrode 503 has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. Also, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the examples shown in Fig. 27(A).

[0380] <Manufacturing method of laminate-type secondary battery> Here, an example of the manufacturing method of the laminate-type secondary battery whose external view is shown in Fig. 25 will be described with reference to Figs. 27(B) and (C).

[0381] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 27(B) shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown where five sets of negative electrodes and four sets of positive electrodes are used. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab area of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like may be used. Similarly, the tabs of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab area of the outermost negative electrode.

[0382] Next, the negative electrode 506, the separator 507, and the positive electrode 503 are arranged on the exterior body 509.

[0383] Next, as shown in FIG. 27(C), the exterior body 509 is bent at the portion indicated by the dashed line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, an area that is not joined (hereinafter referred to as the inlet) is provided in a part (or one side) of the exterior body 509 so that the electrolytic solution 508 can be introduced later.

[0384] Next, the electrolytic solution 508 (not shown) is introduced into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolytic solution 508 is preferably performed under a reduced-pressure atmosphere or an inert atmosphere. And finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

[0385] By using the positive electrode active material described in the previous embodiment for the positive electrode 503, a secondary battery with high capacity and excellent cycle characteristics can be obtained.

[0386] In an all-solid-state battery, by applying a predetermined pressure in the stacking direction of the stacked positive and negative electrodes, the contact state of the interfaces inside can be kept good. By applying a predetermined pressure in the stacking direction of the positive and negative electrodes, it is possible to suppress the expansion in the stacking direction due to charge and discharge of the all-solid-state battery, and the reliability of the all-solid-state battery can be improved.

[0387] This embodiment can be used in appropriate combination with other embodiments.

[0388] (Embodiment 7) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described.

[0389] First, an example of mounting the bendable secondary battery described in the previous embodiment on an electronic device is shown in FIGS. 28(A) to 28(G). Examples of electronic devices to which the bendable secondary battery is applied include, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or a mobile phone device), a portable game machine, a portable information terminal, an audio playback device, and a large game machine such as a pachinko machine.

[0390] In addition, it is also possible to incorporate a secondary battery having a flexible shape along the inner wall or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

[0391] FIG. 28(A) shows an example of a mobile phone. The mobile phone 7400 includes, in addition to a display unit 7402 incorporated in a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. Note that the mobile phone 7400 has a secondary battery 7407. By using the secondary battery of one aspect of the present invention for the secondary battery 7407, a lightweight and long-life mobile phone can be provided.

[0392] FIG. 28(B) shows the state in which the mobile phone 7400 is bent. When the mobile phone 7400 is deformed by an external force and bent as a whole, the secondary battery 7407 provided therein is also bent. At that time, the state of the bent secondary battery 7407 is shown in FIG. 28(C). The secondary battery 7407 is a thin rechargeable battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode electrically connected to a current collector. For example, the current collector is a copper foil, which is alloyed with a part of gallium to improve the adhesion to the active material layer in contact with the current collector, and the secondary battery 7407 has a high reliability in a bent state.

[0393] FIG. 28(D) shows an example of a bangle-type display device. The portable display device 7100 includes a housing 7101, a display unit 7102, operation buttons 7103, and a secondary battery 7104. Further, FIG. 28(E) shows the state of the bent secondary battery 7104. When the secondary battery 7104 is bent and worn on the user's arm, the housing deforms and the curvature of part or all of the secondary battery 7104 changes. The value representing the degree of bending at an arbitrary point on the curve by the radius value of the corresponding circle is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature. Specifically, part or all of the main surface of the housing or the secondary battery 7104 changes within the range where the radius of curvature is 40 mm or more and 150 mm or less. If the radius of curvature of the main surface of the secondary battery 7104 is in the range of 40 mm or more and 150 mm or less, high reliability can be maintained. By using the secondary battery according to one aspect of the present invention for the above secondary battery 7104, a lightweight and long-life portable display device can be provided.

[0394] FIG. 28(F) shows an example of a wristwatch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, operation buttons 7205, input / output terminals 7206, and the like.

[0395] The portable information terminal 7200 can execute various applications such as mobile phones, e-mails, text viewing and creation, music playback, Internet communication, and computer games.

[0396] The display unit 7202 is provided with a curved display surface and can perform displays along the curved display surface. Further, the display unit 7202 is provided with a touch sensor and can be operated by touching the screen with a finger, a stylus, or the like. For example, an application can be launched by touching an icon 7207 displayed on the display unit 7202.

[0397] In addition to time setting, the operation button 7205 can be provided with various functions such as power on / off operations, wireless communication on / off operations, execution and cancellation of a silent mode, and execution and cancellation of a power saving mode. For example, the functions of the operation button 7205 can be freely set by an operating system incorporated in the portable information terminal 7200.

[0398] Further, the portable information terminal 7200 can execute short-range wireless communication conforming to a communication standard. For example, it can also make a hands-free call by communicating with a wireless communication-capable headset.

[0399] Further, the portable information terminal 7200 is provided with an input / output terminal 7206 and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminal 7206. Note that the charging operation may be performed by wireless power supply without using the input / output terminal 7206.

[0400] The display unit 7202 of the portable information terminal 7200 has a secondary battery according to one aspect of the present invention. By using the secondary battery according to one aspect of the present invention, a lightweight and long-life portable information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 28(E) can be incorporated inside the housing 7201 in a curved state or in a state where it can be curved inside the band 7203.

[0401] The portable information terminal 7200 preferably has a sensor. As the sensor, for example, it is preferable to mount a human body sensor such as a fingerprint sensor, a pulse sensor, or a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0402] Figure 28(G) shows an example of a wristband-type display device. The display device 7300 has a display unit 7304 and has a secondary battery according to one aspect of the present invention. Further, the display device 7300 can be provided with a touch sensor on the display unit 7304 and can also function as a portable information terminal.

[0403] The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. Further, the display device 7300 can change the display status by means of communication-standardized short-range wireless communication or the like.

[0404] Further, the display device 7300 is provided with input / output terminals and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input / output terminals. Note that the charging operation may be performed by wireless power supply without using the input / output terminals.

[0405] By using the secondary battery according to one aspect of the present invention as the secondary battery of the display device 7300, a lightweight and long-life display device can be provided.

[0406] An example of mounting a secondary battery with good cycle characteristics shown in the previous embodiment on an electronic device will be described with reference to FIGS. 28(H), 29, and 30.

[0407] By using the secondary battery according to one aspect of the present invention as the secondary battery of a consumer electronic device, a lightweight and long-life product can be provided. For example, consumer electronic devices include an electric toothbrush, an electric shaver, an electric beauty device, etc. As the secondary battery for these products, considering the ease of use by the user, a secondary battery having a stick shape, being small, lightweight, and having a large capacity is desired.

[0408] FIG. 28(H) is a perspective view of a device also called a tobacco-containing smoking device (electronic cigarette). In FIG. 28(H), the electronic cigarette 7500 includes an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle, a sensor, and the like. To enhance safety, a protection circuit that prevents overcharging and over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504. The secondary battery 7504 shown in FIG. 28(H) has external terminals so that it can be connected to a charging device. Since the secondary battery 7504 becomes the tip portion when held, it is desirable that the total length is short and the weight is light. Since the secondary battery according to one aspect of the present invention has a high capacity and good cycle characteristics, it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long time over a long period.

[0409] Next, FIGS. 29(A) and 29(B) show an example of a foldable tablet terminal. The tablet terminal 9600 shown in FIGS. 29(A) and 29(B) includes a housing 9630a, a housing 9630b, a movable part 9640 that connects the housing 9630a and the housing 9630b, a display unit 9631 including a display unit 9631a and a display unit 9631b, switches 9625 to 9627, a fastener 9629, and an operation switch 9628. By using a flexible panel for the display unit 9631, a tablet terminal having a wider display unit can be obtained. FIG. 29(A) shows the tablet terminal 9600 in an open state, and FIG. 29(B) shows the tablet terminal 9600 in a closed state.

[0410] Further, the tablet terminal 9600 has a power storage body 9635 inside the housing 9630a and the housing 9630b. The power storage body 9635 is provided across the housing 9630a and the housing 9630b through the movable part 9640.

[0411] The display unit 9631 can have all or part of its area as the touch panel area, and data can be input by touching an icon, character, input form, etc. displayed in the area. For example, keyboard buttons may be displayed on the entire surface of the display unit 9631a on the housing 9630a side, and information such as characters and images may be displayed and used on the display unit 9631b on the housing 9630b side.

[0412] Alternatively, a keyboard may be displayed on the display unit 9631b on the housing 9630b side, and information such as characters and images may be displayed and used on the display unit 9631a on the housing 9630a side. Also, a keyboard display switch button for the touch panel may be displayed on the display unit 9631, and the keyboard may be displayed on the display unit 9631 by touching the button with a finger or a stylus.

[0413] Also, touch input can be simultaneously performed on the touch panel areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side.

[0414] Also, the switches 9625 to 9627 may be interfaces not only for operating the tablet terminal 9600 but also for switching various functions. For example, at least one of the switches 9625 to 9627 may function as a switch for turning on and off the power of the tablet terminal 9600. Also, for example, at least one of the switches 9625 to 9627 may have a function of switching the display orientation such as vertical or horizontal display, or a function of switching between black and white display and color display. Also, for example, at least one of the switches 9625 to 9627 may have a function of adjusting the brightness of the display unit 9631. Also, the brightness of the display unit 9631 can be optimized according to the amount of external light detected by the optical sensor built into the tablet terminal 9600 during use. Note that the tablet terminal may incorporate other detection devices such as a gyro and an acceleration sensor for detecting inclination in addition to the optical sensor.

[0415] In addition, FIG. 29(A) shows an example in which the display areas of the display unit 9631a on the housing 9630a side and the display unit 9631b on the housing 9630b side are substantially the same. However, the respective display areas of the display unit 9631a and the display unit 9631b are not particularly limited, and the size of one may be different from that of the other, and the display quality may also be different. For example, one may be a display panel capable of performing a higher-definition display than the other.

[0416] FIG. 29(B) shows a state in which the tablet-type terminal 9600 is closed in a two-fold manner. The tablet-type terminal 9600 has a charging / discharging control circuit 9634 including a housing 9630, a solar cell 9633, and a DCDC converter 9636. Further, as the power storage body 9635, a power storage body according to one aspect of the present invention is used.

[0417] As described above, since the tablet-type terminal 9600 can be folded in two, the housing 9630a and the housing 9630b can be folded so as to overlap each other when not in use. By folding, the display unit 9631 can be protected, and thus the durability of the tablet-type terminal 9600 can be enhanced. In addition, since the power storage body 9635 using the secondary battery according to one aspect of the present invention has a high capacity and good cycle characteristics, a tablet-type terminal 9600 that can be used for a long time over a long period can be provided.

[0418] In addition, the tablet-type terminal 9600 shown in FIGS. 29(A) and 29(B) can also have functions such as a function of displaying various information (still images, moving images, text images, etc.), a function of displaying a calendar, a date, or a time on the display unit, a touch input function of touch-inputting or editing the information displayed on the display unit, and a function of controlling processing by various software (programs).

[0419] Power can be supplied to a touch panel, a display unit, a video signal processing unit, etc. by a solar cell 9633 mounted on the surface of the tablet-type terminal 9600. Note that the solar cell 9633 can be provided on one or both sides of the housing 9630, and can be configured to efficiently charge the power storage body 9635. As the power storage body 9635, using a lithium ion battery has advantages such as enabling miniaturization.

[0420] Also, the configuration and operation of the charge / discharge control circuit 9634 shown in Fig. 29(B) will be described with reference to the block diagram in Fig. 29(C). Fig. 29(C) shows the solar cell 9633, the power storage body 9635, the DCDC converter 9636, the converter 9637, the switches SW1 to SW3, and the display unit 9631. The power storage body 9635, the DCDC converter 9636, the converter 9637, and the switches SW1 to SW3 correspond to the parts of the charge / discharge control circuit 9634 shown in Fig. 29(B).

[0421] First, an example of the operation when power is generated by the solar cell 9633 due to external light will be described. The power generated by the solar cell is stepped up or down by the DCDC converter 9636 so as to be a voltage for charging the power storage body 9635. When the power from the solar cell 9633 is used for the operation of the display unit 9631, the switch SW1 is turned on, and the converter 9637 steps up or down the voltage to the voltage required for the display unit 9631. Also, when the display on the display unit 9631 is not performed, SW1 may be turned off and SW2 may be turned on to charge the power storage body 9635.

[0422] Note that although the solar cell 9633 is shown as an example of a power generation means, it is not particularly limited, and the power storage body 9635 may be charged by other power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). For example, a contactless power transmission module that wirelessly (non-contact) transmits and receives power for charging, or a configuration that combines other charging means may be used.

[0423] Fig. 30 shows an example of another electronic device. In Fig. 30, the display device 8000 is an example of an electronic device using the secondary battery 8004 according to one aspect of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving TV broadcasts and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, etc. The secondary battery 8004 according to one aspect of the present invention is provided inside the housing 8001. The display device 8000 can receive power supply from a commercial power source or use the power stored in the secondary battery 8004. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, the display device 8000 can be used by using the secondary battery 8004 according to one aspect of the present invention as an uninterruptible power supply.

[0424] The display unit 8002 can use a light-emitting device having a light-emitting element such as a liquid crystal display device or an organic EL element in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (Plasma Display Panel), an FED (Field Emission Display), etc., a semiconductor display device.

[0425] Note that the display device includes all display devices for information display such as for personal computers and for advertising display in addition to those for receiving TV broadcasts.

[0426] In Fig. 30, the installed lighting device 8100 is an example of an electronic device using the secondary battery 8103 according to one aspect of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, etc. In Fig. 30, the case where the secondary battery 8103 is provided inside the ceiling 8104 where the housing 8101 and the light source 8102 are installed is illustrated, but the secondary battery 8103 may be provided inside the housing 8101. The lighting device 8100 can receive power supply from a commercial power source or use the power stored in the secondary battery 8103. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, the lighting device 8100 can be used by using the secondary battery 8103 according to one aspect of the present invention as an uninterruptible power supply.

[0427] In addition, although FIG. 30 illustrates the installed lighting device 8100 provided on the ceiling 8104, the secondary battery according to one aspect of the present invention can be used not only for the installed lighting device provided on the ceiling 8104 but also for, for example, the installed lighting device provided on the side wall 8105, the floor 8106, the window 8107, etc., or for a desktop lighting device or the like.

[0428] Moreover, as the light source 8102, an artificial light source that artificially obtains light using electric power can be used. Specifically, an incandescent bulb, a discharge lamp such as a fluorescent lamp, and a light emitting element such as an LED or an organic EL element can be cited as an example of the above artificial light source.

[0429] In FIG. 30, an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using the secondary battery 8203 according to one aspect of the present invention. Specifically, the indoor unit 8200 has a housing 8201, an air outlet 8202, a secondary battery 8203, etc. In FIG. 30, the case where the secondary battery 8203 is provided in the indoor unit 8200 is illustrated, but the secondary battery 8203 may be provided in the outdoor unit 8204. Alternatively, the secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204. The air conditioner can receive power supply from a commercial power source or use the power stored in the secondary battery 8203. In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from the commercial power source cannot be received due to a power outage or the like, the air conditioner can be used by using the secondary battery 8203 according to one aspect of the present invention as an uninterruptible power supply.

[0430] Note that, although FIG. 30 illustrates a separate type air conditioner composed of an indoor unit and an outdoor unit, the secondary battery according to one aspect of the present invention can also be used for an integrated type air conditioner having the functions of the indoor unit and the outdoor unit in one housing.

[0431] In FIG. 30, the electric refrigerator 8300 is an example of an electronic device using a secondary battery 8304 according to an aspect of the present invention. Specifically, the electric refrigerator 8300 includes a housing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 30, the secondary battery 8304 is provided inside the housing 8301. The electric refrigerator 8300 can receive power supply from a commercial power source or use the power stored in the secondary battery 8304. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the secondary battery 8304 according to an aspect of the present invention as an uninterruptible power supply, the electric refrigerator 8300 can be used.

[0432] Among the above-described electronic devices, high-frequency heating devices such as microwave ovens and electronic devices such as electric rice cookers require high power in a short period of time. Therefore, by using a secondary battery according to an aspect of the present invention as an auxiliary power supply to supplement power that cannot be covered by the commercial power source, it is possible to prevent the breaker of the commercial power source from tripping when the electronic device is in use.

[0433] Also, during a time period when the electronic device is not in use, particularly during a time period when the ratio of the actually used power amount to the total power amount that can be supplied by the commercial power source (referred to as the power utilization rate) is low, by storing power in the secondary battery, it is possible to suppress an increase in the power utilization rate outside the above time period. For example, in the case of the electric refrigerator 8300, at night when the temperature is low and the refrigerator door 8302 and the freezer door 8303 are not opened or closed, power is stored in the secondary battery 8304. Then, during the day when the temperature rises and the refrigerator door 8302 and the freezer door 8303 are opened or closed, by using the secondary battery 8304 as an auxiliary power supply, the power utilization rate during the day can be kept low.

[0434] According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved, and the reliability can be enhanced. Further, according to one aspect of the present invention, a high-capacity secondary battery can be obtained, thus improving the characteristics of the secondary battery, and therefore, the secondary battery itself can be made smaller and lighter. Therefore, by mounting the secondary battery, which is one aspect of the present invention, in the electronic device described in this embodiment, an electronic device with a longer lifespan and lighter weight can be obtained.

[0435] This embodiment can be implemented in appropriate combination with other embodiments.

[0436] (Embodiment 8) In this embodiment, an example of an electronic device using the secondary battery described in the previous embodiment will be described with reference to FIGS. 31 to 32.

[0437] FIG. 31(A) shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Further, when the user uses it in daily life or outdoors, in order to enhance the anti-foaming performance, water resistance performance or dust-proof performance, a wearable device that can perform not only wired charging with the exposed connector part but also wireless charging is desired.

[0438] For example, a secondary battery according to one aspect of the present invention can be mounted in a glasses-type device 4000 as shown in FIG. 31(A). The glasses-type device 4000 has a frame 4000a and a display part 4000b. By mounting the secondary battery on the temple part of the frame 4000a having a curvature, a glasses-type device 4000 that is lightweight, has a good weight balance, and has a long continuous use time can be obtained. By providing a secondary battery according to one aspect of the present invention, a configuration that can cope with space saving due to the miniaturization of the housing can be realized.

[0439] In addition, a secondary battery according to one aspect of the present invention can be mounted on the headset-type device 4001. The headset-type device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A secondary battery can be provided inside the flexible pipe 4001b or inside the earphone unit 4001c. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0440] In addition, a secondary battery according to one aspect of the present invention can be mounted on the device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0441] In addition, a secondary battery according to one aspect of the present invention can be mounted on the device 4003 that can be attached to clothes. A secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0442] In addition, a secondary battery according to one aspect of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power supply / reception portion 4006b, and a secondary battery can be mounted inside the belt portion 4006a. By providing a secondary battery according to one aspect of the present invention, a configuration can be realized that can cope with space saving accompanying the miniaturization of the housing.

[0443] In addition, a secondary battery, which is one aspect of the present invention, can be mounted on the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and a secondary battery can be provided in the display unit 4005a or the belt unit 4005b. By providing the secondary battery, which is one aspect of the present invention, it is possible to realize a configuration that can cope with space saving due to downsizing of the housing.

[0444] The display unit 4005a can display not only the time but also various information such as incoming mails and phone calls.

[0445] In addition, since the wristwatch-type device 4005 is a wearable device of a type that is directly wound around the wrist, it may be equipped with sensors for measuring the user's pulse, blood pressure, etc. Data regarding the user's exercise amount and health can be accumulated and the health can be managed.

[0446] Fig. 31(B) shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0447] Also, a side view is shown in Fig. 31(C). Fig. 31(C) shows a state in which the secondary battery 913 is built inside. The secondary battery 913 is the secondary battery shown in Embodiment 5. The secondary battery 913 is provided at a position overlapping the display unit 4005a and is small and lightweight.

[0448] Fig. 32(A) shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, etc. Although not shown, the cleaning robot 6300 is equipped with tires, a suction port, etc. The cleaning robot 6300 can travel automatically, detect dust 6310, and suck dust from the suction port provided on the lower surface.

[0449] For example, the cleaning robot 6300 can analyze the image captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Also, when an object that is likely to get caught in the brush 6304, such as wiring, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one aspect of the present invention and semiconductor devices or electronic components inside it. By using the secondary battery 6306 according to one aspect of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be made into an electronic device with a long operating time and high reliability.

[0450] FIG. 32(B) shows an example of a robot. The robot 6400 shown in FIG. 32(B) 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 moving mechanism 6408, an arithmetic unit, and the like.

[0451] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user by using the microphone 6402 and the speaker 6404.

[0452] The display unit 6405 has a function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer can be enabled.

[0453] The upper camera 6403 and the lower camera 6406 have the function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the moving 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.

[0454] The robot 6400 includes a secondary battery 6409 according to one aspect of the present invention and semiconductor devices or electronic components inside thereof. By using the secondary battery according to one aspect of the present invention in the robot 6400, the robot 6400 can be made into an electronic device with a long operating time and high reliability.

[0455] FIG. 32(C) shows an example of an aircraft. The aircraft 6500 shown in FIG. 32(C) has a propeller 6501, a camera 6502, a secondary battery 6503, etc., and has the function of autonomous flight.

[0456] For example, the image data captured by the camera 6502 is stored in the electronic component 6504. The electronic component 6504 can analyze the image data and detect the presence or absence of obstacles when moving. Also, the remaining battery level can be estimated from the change in the power storage capacity of the secondary battery 6503 by the electronic component 6504. The aircraft 6500 includes a secondary battery 6503 according to one aspect of the present invention inside thereof. By using the secondary battery according to one aspect of the present invention in the aircraft 6500, the aircraft 6500 can be made into an electronic device with a long operating time and high reliability.

[0457] This embodiment can be implemented in appropriate combination with other embodiments.

[0458] (Embodiment 9) In this embodiment, an example of mounting a secondary battery which is one aspect of the present invention on a vehicle is shown.

[0459] When a secondary battery is mounted on a vehicle, next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), or plug-in hybrid electric vehicles (PHEVs) can be realized.

[0460] In FIG. 33, a vehicle using a secondary battery, which is one aspect of the present invention, is illustrated. The automobile 8400 shown in FIG. 33(A) is an electric vehicle that uses an electric motor as a power source for running. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running. By using one aspect of the present invention, a vehicle with a long cruising range can be realized. The automobile 8400 also has a secondary battery. For the secondary battery, the modules of the secondary battery shown in FIGS. 18(C) and 18(D) may be arranged and used with respect to the floor portion inside the vehicle. Alternatively, a battery pack combining a plurality of secondary batteries shown in FIG. 21 may be installed with respect to the floor portion inside the vehicle. The secondary battery can not only drive the electric motor 8406 but also supply power to a light-emitting device such as a headlight 8401 and a room light (not shown).

[0461] In addition, the secondary battery can supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has. Further, the secondary battery can supply power to semiconductor devices such as a navigation system that the automobile 8400 has.

[0462] The motor vehicle 8500 shown in FIG. 33(B) can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, or the like to the secondary battery of the motor vehicle 8500. FIG. 33(B) shows a state in which charging is being performed from a ground-mounted charging device 8021 to a secondary battery 8024 mounted on the motor vehicle 8500 via a cable 8022. When charging, the charging method, the connector standard, etc. may be appropriately performed in a predetermined method such as CHAdeMO (registered trademark) or Combo. The charging device 8021 may be a charging station provided in a commercial facility or may be a household power source. For example, by the plug-in technology, the secondary battery 8024 mounted on the motor vehicle 8500 can be charged by external power supply. The charging can be performed by converting AC power into DC power via a conversion device such as an AC-DC converter.

[0463] Also, although not shown, a power receiving device can be mounted on the vehicle, and power can be supplied non-contact from a power transmission device on the ground for charging. In the case of this non-contact power supply method, by incorporating the power transmission device into a road or an outer wall, charging can be performed not only while the vehicle is stopped but also while it is running. Further, power can be transmitted and received between vehicles using this non-contact power supply method. Furthermore, a solar cell may be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped or running. For such non-contact power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0464] Also, FIG. 33(C) is an example of a two-wheeled vehicle using a secondary battery according to an aspect of the present invention. The scooter 8600 shown in FIG. 33(C) includes a secondary battery 8602, a side mirror 8601, and a direction indicator lamp 8603. The secondary battery 8602 can supply electricity to the direction indicator lamp 8603.

[0465] In addition, in the scooter 8600 shown in FIG. 33(C), the secondary battery 8602 can be stored in the under-seat storage 8604. Even if the under-seat storage 8604 is small, the secondary battery 8602 can be stored in the under-seat storage 8604. The secondary battery 8602 is removable. When charging, the secondary battery 8602 can be carried indoors, charged, and then stored before driving.

[0466] According to one aspect of the present invention, the cycle characteristics of the secondary battery can be improved, and the capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it contributes to the weight reduction of the vehicle, so the cruising range can be improved. In addition, the secondary battery mounted on the vehicle can also be used as a power supply other than the vehicle. In this case, for example, it is possible to avoid using a commercial power supply during the peak of power demand. If it is possible to avoid using a commercial power supply during the peak of power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. In addition, if the cycle characteristics are good, the secondary battery can be used for a long time, so the amount of use of rare metals such as cobalt can be reduced.

[0467] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0468] In this example, the positive electrode active material described in Embodiment 1 was prepared, its characteristics were analyzed, and its properties were evaluated.

[0469] <Fabrication and Analysis of Positive Electrode Active Material> The sample prepared in this example will be described with reference to the manufacturing method shown in FIG. 11.

[0470] As a positive electrode active material having cobalt as the transition metal M and having no particular impurities, commercially available lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Celsid C-10N) was used. This was designated as Sample 1 (comparative example).

[0471] Titanium oxide was added to Sample 1 by the sol-gel method in the same manner as Steps S42 to S44 in FIG. 11. When the number of cobalt atoms in Sample 1 was set to 100, TTIP was added so that the number of titanium atoms became 0.5. Then, it was heated in the same manner as Step S45. The heating conditions were 850 °C, 2 hours, and an oxygen atmosphere (flow rate of 10 L / min). In this way, a positive electrode active material having cobalt as the transition metal M and titanium as an impurity was designated as Sample 2.

[0472] Lithium fluoride and magnesium fluoride were added to Sample 1 by the solid-phase method in the same manner as Steps S11 to S14 and Step S31 in FIG. 11. When the number of cobalt atoms was set to 100, they were added so that the number of lithium fluoride molecules became 0.17 and the number of magnesium fluoride molecules became 0.5. Then, it was heated in the same manner as Step S34. During heating, the raw materials were placed in an alumina crucible and covered with a lid. The heating conditions were 850 °C and 60 hours. In this way, a positive electrode active material having cobalt as the transition metal M and magnesium and fluorine as impurities was designated as Sample 3.

[0473] Lithium fluoride and magnesium fluoride were added to Sample 1 by the solid-phase method in the same manner as Steps S11 to S14 and Step S31 in FIG. 11. When the number of cobalt atoms was set to 100, they were added so that the number of lithium fluoride molecules became 0.17 and the number of magnesium fluoride molecules became 0.5. Then, it was heated in the same manner as Step S34. The heating conditions were 900 °C, 20 hours, and an oxygen atmosphere (flow rate of 10 L / min). Next, titanium oxide was added to it by the sol-gel method in the same manner as Steps S42 to S44. The addition amount of titanium and the heating conditions were the same as those of Sample 2. In this way, a positive electrode active material having cobalt as the transition metal M and magnesium, fluorine, and titanium as impurities was designated as Sample 4.

[0474] To Sample 1, lithium fluoride, magnesium fluoride, nickel hydroxide, and aluminum hydroxide were added by a solid-phase method in the same manner as in Steps S11 to S20 and Step S31 of FIG. 11. When the number of cobalt atoms was set to 100, they were added such that the number of lithium fluoride molecules was 0.33, the number of magnesium fluoride molecules was 1, the number of nickel atoms was 0.5, and the number of aluminum atoms was 0.5. Then, heating was performed in the same manner as in Step S34. The heating conditions were 900° C. for 10 hours. After heating, the adhesion of the particles was tapped with a mortar and broken up. This process of heating and breaking up the adhesion was repeated three times in total. Thus, a positive electrode active material having cobalt and nickel as transition metals M and having magnesium, fluorine, and aluminum as impurities was designated as Sample 5.

[0475] To Sample 5, titanium oxide was added by a sol-gel method in the same manner as in Steps S42 to S44. The addition amount of titanium and the heating conditions were the same as those of Sample 2. Thus, a positive electrode active material having cobalt and nickel as transition metals M and having magnesium, fluorine, aluminum, and titanium as impurities was designated as Sample 6.

[0476] The production conditions of Samples 1 to 6 are shown in Table 1.

[0477]

Table 1

[0478] FIG. 34(A) is a surface SEM image of Sample 2. As shown in FIG. 34(A), a state was observed in which the positive electrode active material had recesses that seemed to be cracks. An enlarged image of the recesses is shown in FIG. 34(B). The results of performing linear EDX analysis on the straight-line portion of FIG. 34(B) are shown in FIG. 34(C).

[0479] As shown in FIG. 34(C), it was confirmed that the recesses had a higher titanium concentration than other regions. That is, it was confirmed that a part of the inner wall of the recesses had titanium. It was also confirmed that oxygen was present. Therefore, it is presumed that titanium oxide is embedded in the recesses.

[0480] In addition, cobalt was detected uniformly from all regions of the positive electrode active material. Oxygen decreased slightly in the concave portions and was detected more or less uniformly from other portions.

[0481] Figure 35(A) is a cross-sectional STEM image of Sample 2. An enlarged image of the white dotted line portion in Figure 35(A) is shown in Figure 35(B). What is observed on the positive electrode active material 1000 is a protective film 1001 having C and Pt formed for STEM observation. EDX mapping images of the square portion of the white dotted line in Figure 35(B), which is the surface layer portion of the positive electrode active material 1000, are shown in Figures 36(A) to (C). Figure 36(A) is a mapping image for oxygen, Figure 36(B) is a mapping image for cobalt, and Figure 36(C) is a mapping image for titanium.

[0482] Oxygen and cobalt were uniformly distributed throughout the surface layer portion and the interior of the positive electrode active material. On the other hand, as shown by the white dotted circles in Figures 36(C) and 35(B), it was observed that titanium was present as if embedded in the concave portions.

[0483] Thus, it is considered that the titanium oxide selectively adhered to the concave portions.

[0484] From the above results, it was shown that Sample 2 is a positive electrode active material 101 having concave portions 101c and embedded portions 102, and the titanium concentration in the embedded portions 102 is higher than that in the surface layer portion.

[0485] Figure 37(A) is a surface SEM image of Sample 4. As indicated by the arrow, a positive electrode active material having convex portions was observed. A cross-sectional STEM image of the white dotted line portion in Figure 37(A) is shown in Figure 37(B). A magnified cross-sectional STEM image of the white dotted line portion, which is the convex portion, in Figure 37(B) is shown in Figure 37(C).

[0486] The EDX mapping images of the white dotted square portion in Fig. 37(C) are shown in Figs. 38(A) to 38(E). Fig. 38(A) is the mapping image for oxygen, Fig. 38(B) is for fluorine, Fig. 38(C) is for magnesium, Fig. 38(D) is for titanium, and Fig. 38(E) is for cobalt. In EDX, since the peak of fluorine is detected at a position close to cobalt, the detection accuracy is low. In this example, etc., the internal fluorine is at the background level.

[0487] From Fig. 38(B), it was confirmed that the convex portion has a fluorine high-concentration region having fluorine with a concentration different from the background. The fluorine concentration in the fluorine high-concentration region was higher than that in the high-concentration region of impurity metals.

[0488] Also, from Figs. 38(C) and 38(D), it was confirmed that the convex portion has a high-concentration region of impurity metals where the concentrations of magnesium and titanium are higher than those in the interior and the fluorine high-concentration region. Thus, it was confirmed that the convex portion has a fluorine high-concentration region and a high-concentration region of impurity metals. It is presumed that the excessive magnesium and titanium contained in the positive electrode active material aggregate in the high-concentration region of impurity metals. Also, since the fluorine high-concentration region exists near the center of the convex portion, it was suggested that the presence of the fluorine high-concentration region might be a trigger for the aggregation of impurities.

[0489] Also, in the interior and the surface layer portion of the positive electrode active material, oxygen and cobalt were uniformly present. Also, in the convex portion excluding the fluorine high-concentration region, oxygen, magnesium, and titanium were uniformly present.

[0490] Fig. 39(A) is the surface SEM image of Sample 6. As indicated by the arrow, a positive electrode active material having a large number of convex portions was observed. Fig. 39(B) shows the cross-sectional STEM image of the white dotted line portion in Fig. 39(A). Fig. 39(C) shows the magnified cross-sectional STEM image of the white dotted line portion in Fig. 39(B) which is the convex portion.

[0491] The EDX mapping images of the white dotted square portion in Fig. 39(C) are shown in Figs. 40(A) to 40(G). Fig. 40(A) is for oxygen, Fig. 40(B) is for fluorine, Fig. 40(C) is for magnesium, Fig. 40(D) is for titanium, Fig. 40(E) is for nickel, Fig. 40(F) is for aluminum, and Fig. 40(G) is for cobalt mapping images.

[0492] From Figs. 40(A) to 40(G), it was confirmed that the convex portion has a fluorine high-concentration region where the fluorine concentration is higher than that in the surface layer portion, the interior, and the impurity metal high-concentration region. Also, it was confirmed that the convex portion has an impurity metal high-concentration region where the concentrations of magnesium, titanium, and nickel are higher than those in the surface layer portion, the interior, and the fluorine high-concentration region.

[0493] From the nickel mapping image in Fig. 40(E), it was confirmed that there are nickel high-concentration regions in a part of the surface layer portion and the interior. It is presumed that the excess magnesium, titanium, and nickel in the positive electrode active material aggregate in the impurity metal high-concentration region. In particular, nickel is attracted from the interior 101b to the impurity metal high-concentration region, and it is suggested that the nickel high-concentration region existing in a part of the interior 101b may be a trace of this.

[0494] On the other hand, the concentration of aluminum in the surface layer portion was higher than that in the interior or the convex portion. It was confirmed that aluminum does not aggregate in the impurity metal high-concentration region and remains in the surface layer portion.

[0495] Fig. 41(A) shows the convergent electron beam diffraction image of the convex portion of Sample 6. This was presumed to be the incidence of

[0110] of the cubic crystal. Therefore, it was presumed that the convex portion has a spinel-type or rock salt-type crystal structure. Fig. 41(B) shows the convergent electron beam diffraction image of the interior of Sample 6. This was presumed to be a hexagonal crystal. Therefore, it was presumed that the interior has a layered rock salt-type crystal structure.

[0496] Note that no concave or convex portions were observed in Samples 1, 3, and 5.

[0497] <Fabrication and Evaluation of Secondary Battery> Secondary batteries were fabricated using the positive electrode active materials of Samples 1 to 6. First, the positive electrode active materials of Samples 1 to 6, AB, and PVDF were mixed at an active material:AB:PVDF weight ratio of 95:3:2 to prepare a slurry, and the slurry was coated on an aluminum current collector. NMP was used as the solvent for the slurry.

[0498] After coating the slurry on the current collector, the solvent was volatilized. Then, pressure was applied at 210 kN / m, and further pressure was applied at 1467 kN / m. Through the above steps, a positive electrode was obtained. The loading amount of the positive electrode was approximately 7 mg / cm 2 and the density was 3.8 g / cc or more.

[0499] Using the fabricated positive electrode, a coin-type battery cell of CR2032 type (diameter 20 mm, height 3.2 mm) was fabricated.

[0500] Lithium metal was used as the counter electrode.

[0501] For the electrolyte in the electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiPF6) was used. For the electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at an EC:DEC volume ratio of 3:7, and vinylene carbonate (VC) was added at 2 wt%.

[0502] A 25-μm-thick polypropylene was used as the separator.

[0503] Stainless steel (SUS)-formed positive and negative cans were used.

[0504] The charge-discharge cycle characteristics of the secondary batteries of Sample 1 and Sample 2 are shown in FIG. 42, those of the secondary batteries of Sample 3 and Sample 4 are shown in FIG. 43, and those of the secondary batteries of Sample 5 and Sample 6 are shown in FIG. 44. All were measured at 45°C. Charging was CC / CV (0.5C, 4.6V, 0.05C cut-off), discharging was CC (0.5C, 2.5V cut-off), and a 10-minute rest time was provided before the next charging. In this example, 1C was 200 mA / g.

[0505] Samples 3 to 6 having magnesium and fluorine as impurities showed good cycle characteristics despite the relatively high temperature of 45°C.

[0506] Samples 2, 4, and 6, each having a concave or convex portion as a region where impurities were unevenly distributed, all had an increased discharge capacity compared to samples under the same conditions without these features. For example, while the discharge capacity of Sample 1 was 215.5 mAh / g, the discharge capacity of Sample 2 was 221.1 mAh / g. While the discharge capacity of Sample 3 was 228.9 mAh / g, the discharge capacity of Sample 4 was 232.7 mAh / g. While the discharge capacity of Sample 5 was 221.5 mAh / g, the discharge capacity of Sample 6 was 227.2 mAh / g.

[0507] In Samples 2, 4, and 6 having titanium as an impurity, titanium oxide is present on the surface of the positive electrode active material. Therefore, it is considered that the wettability at the interface between the electrolyte and the positive electrode active material was improved due to the presence of titanium oxide. As a result, it was considered that the solvation and desolvation of lithium ions became easier, and the resistance of the secondary battery was suppressed.

[0508] In Sample 2, due to the presence of regions where impurities were unevenly distributed, elution of transition metals from cracks, collapse of the crystal structure, cracking of the interior 101b, etc. were suppressed, and as a result, it was considered that the discharge capacity increased. Also, in Samples 4 and 6, due to the presence of regions where impurities were unevenly distributed, excessive impurities including magnesium were removed from the interior 101b, and the interior 101b was brought to an appropriate impurity concentration. Therefore, it was considered that the resistance when used as a secondary battery was suppressed and the discharge capacity increased.

Example

[0509] In this example, a positive electrode active material was produced using the method described in Embodiment 2, its characteristics were analyzed, and its properties were evaluated.

[0510] <Production and Analysis of Positive Electrode Active Material> The samples produced in this example will be described with reference to the production methods shown in FIGS. 9 and 10.

[0511] Sample 1 (comparative example) same as in Example 1 was prepared as a positive electrode active material having cobalt as transition metal M and having no particular impurities.

[0512] Lithium fluoride, magnesium fluoride, nickel hydroxide, and aluminum hydroxide were added to Sample 1 by the solid phase method in the same manner as in Steps S11 to S20 and Step S25 in FIG. 9. When the number of cobalt atoms was 100, they were added so that the number of lithium fluoride molecules was 0.33, the number of magnesium fluoride molecules was 1, the number of nickel atoms was 0.5, and the number of aluminum atoms was 0.5. Then, heating was performed in the same manner as in Step S34. The heating conditions were 850°C for 60 hours. In this way, a positive electrode active material having cobalt and nickel as transition metal M and having magnesium, fluorine, and aluminum as impurities was designated as Sample 11.

[0513] In the same solid-phase method as steps S11 to S14 and step S26 in FIG. 10, lithium fluoride was added to the composite oxide containing impurities. As the composite oxide containing impurities, one having titanium, aluminum, and magnesium as impurities was used. Lithium fluoride was added so that the number of moles of lithium fluoride became 0.17 when the number of cobalt atoms in the composite oxide containing impurities was 100. Then, it was heated in the same manner as in step S34. The heating conditions were 850 °C for 20 hours. In this way, a positive electrode active material having cobalt as the transition metal M and having magnesium, fluorine, aluminum, and titanium as impurities was designated as Sample 12.

[0514] A positive electrode active material prepared in the same manner as Sample 12 except that lithium fluoride was added so that the number of moles of lithium fluoride became 1.17 when the number of cobalt atoms in the composite oxide containing impurities was 100 was designated as Sample 13.

[0515] A positive electrode active material prepared in the same manner as Sample 12 except that lithium fluoride was added so that the number of moles of lithium fluoride became 2.33 when the number of cobalt atoms in the composite oxide containing impurities was 100 was designated as Sample 14.

[0516] In the same solid-phase method as steps S11 to S14 and step S26 in FIG. 10, lithium fluoride and magnesium fluoride were added to the composite oxide containing impurities. As the composite oxide containing impurities, one having titanium, aluminum, and magnesium as impurities was used. Lithium fluoride was added so that the number of moles of lithium fluoride became 0.17, and magnesium fluoride was added so that the number of moles of magnesium fluoride became 0.5 when the number of cobalt atoms in the composite oxide containing impurities was 100. Then, it was heated in the same manner as in step S34. The heating conditions were 900 °C for 10 hours in an oxygen atmosphere (flow rate of 10 L / min). In this way, a positive electrode active material having cobalt as the transition metal M and having magnesium, fluorine, aluminum, and titanium as impurities was designated as Sample 15.

[0517] In the same solid-phase method as steps S11 to S20 and step S26 in FIG. 10, lithium fluoride, magnesium fluoride, nickel hydroxide, and aluminum hydroxide were added to the composite oxide containing impurities. As the composite oxide containing impurities, one having titanium, aluminum, and magnesium as impurities was used. When the number of cobalt atoms in the composite oxide containing impurities was set to 100, the number of lithium fluoride molecules was 0.33, the number of magnesium fluoride molecules was 1, the number of nickel atoms was 0.5, and the number of aluminum atoms was 0.5. Then, it was heated in the same manner as in step S34. The heating conditions were 900 °C for 10 hours. Thus, a positive electrode active material having cobalt and nickel as transition metals M and having magnesium, fluorine, aluminum, and titanium as impurities was designated as sample 16.

[0518] A positive electrode active material prepared in the same manner as sample 13 except that the heating time was 2 hours was designated as sample 17.

[0519] A positive electrode active material prepared in the same manner as sample 13 except that the heating time was 60 hours was designated as sample 18.

[0520] A positive electrode active material prepared in the same manner as sample 13 except that nickel hydroxide and aluminum hydroxide were added to the composite oxide containing impurities in addition to lithium fluoride. When the number of cobalt atoms in the composite oxide containing impurities was set to 100, the number of nickel atoms was 0.5 and the number of aluminum atoms was 0.5.

[0521] The preparation conditions of samples 1, 11 to 19 are shown in Table 2.

[0522]

Table 2

[0523] FIG. 45 is a surface SEM image of sample 13. No cracks were observed, and it was confirmed that the shape was smooth with few irregularities.

[0524] Figure 46(A) is a surface SEM image of another part of Sample 13. Figures 46(B) to 46(G) are EDX mapping images of the same region as Figure 46(A). Figure 46(B) is for cobalt, Figure 46(C) is for titanium, Figure 46(D) is for oxygen, Figure 46(E) is for magnesium, Figure 46(F) is for carbon, and Figure 46(G) is for aluminum mapping images.

[0525] From Figures 46(B) to 46(G), it was confirmed that Sample 13 is a positive electrode active material having regions where titanium, magnesium, and aluminum are unevenly distributed. The regions where titanium and magnesium were unevenly distributed partially overlapped.

[0526] Figure 47(A) is a surface SEM image of Sample 19. Here too, cracks were not observed, and it was confirmed that the shape is smooth with few irregularities.

[0527] Figures 47(B) to (H) are SEM-EDX mapping images of the same region as Figure 47(A). Figure 47(B) is for nickel, Figure 47(C) is for cobalt, Figure 47(D) is for titanium, Figure 47(E) is for oxygen, Figure 47(F) is for magnesium, Figure 47(G) is for carbon, and Figure 47(H) is for aluminum mapping images. The nickel in Figure 47(B) was at the background level. Since carbon was used for the conductive tape to fix the sample, there is a possibility that this was detected. Also, although not shown, fluorine was at the background level.

[0528] As shown in Figures 47(B) to 47(H), cobalt and oxygen were detected in almost all regions. On the other hand, regions where titanium, magnesium, and aluminum were unevenly distributed were observed. Titanium and magnesium were present in the same region, while aluminum was observed in another region. Thus, it was also confirmed that Sample 19 is a positive electrode active material having regions where titanium, magnesium, and aluminum are unevenly distributed.

[0529] Also, although nickel hydroxide was added to Sample 19 in the same manner as in Steps S13 to S17, the nickel concentration was at the background level in SEM-EDX. It was presumed that nickel was more likely to dissolve in the interior 101b of the positive electrode active material 101 than other impurity elements.

[0530] <Fabrication of Secondary Battery> Using the positive electrode active materials of Sample 1, Sample 11 to Sample 18 fabricated above, a secondary battery was fabricated in the same manner as in Example 1. However, pressure was not applied in the fabrication process of the positive electrode. The loading amount of the positive electrode was 20 mg / cm 2 to 21 mg / cm 2 as follows.

[0531] <Crystal Structure after Charging> For the secondary batteries of Sample 11, Sample 13, and Sample 15, the crystal structure after charging was analyzed by XRD. First, one charge-discharge cycle was performed for capacity confirmation. Charging was carried out with CC / CV (0.2C, 4.5V, 0.05C cut-off), and discharging was carried out with CC (0.2C, 3.0V cut-off). Next, charging was performed at 4.50V, 4.55V, or 4.6V for analysis of the structure after charging. Charging was carried out with CC / CV (0.2C, each voltage, 0.02C cut-off). In the measurement of the crystal structure after charging in this Example etc., 1C was taken as 191 mA / g. Charge-discharge and XRD measurements were carried out at 25°C.

[0532] The charging capacities for analysis of the structure after charging are shown in Table 3.

[0533]

Table 3

[0534] The charged secondary battery was then disassembled in an argon-filled glove box, the positive electrode removed, and washed with DMC (dimethyl carbonate) to remove the electrolyte. Powder XRD analysis was then performed using CuKα1 radiation. The XRD instrument used was a Bruker D8 Advance, set up for powder samples, with the sample height adjusted to fit the required measurement surface. The sample was also set flat, without any curvature.

[0535] Figure 48 shows the powder XRD patterns of Sample 11, Sample 13, and Sample 15 after charging. Figure 49(A) shows an enlarged pattern near 2θ=20°, Figure 49(B) shows an enlarged pattern near 2θ=38°, Figure 50(A) shows an enlarged pattern near 2θ=45°, and Figure 50(B) shows an enlarged pattern near 2θ=61°. For comparison, the XRD patterns of pseudospinel, H1-3, and CoO2 are also shown.

[0536] It was confirmed that Samples 11 and 13, which were charged at 4.6 V, had a pseudospinel crystal structure. In addition, the peaks were sharp, suggesting high crystallinity.

[0537] The lattice constants of sample 11 at 4.6 V charging calculated from these XRD patterns were 2.818 Å for the a-axis and 13.79 Å for the c-axis. The lattice constants of sample 13 were 2.816 Å for the a-axis and 13.74 Å for the b-axis. Note that 1 Å is 10 -10 m.

[0538] Sample 15, charged at 4.6 V, had a different crystal structure from pseudospinel and H1-3. The main peaks in Sample 15 occurred at 2θ values of 19.27°, 37.37°, 45.11°, 66.37°, and 69.64°.

[0539] <Cycle characteristics> Figure 51(A) is a graph of the cycle characteristics of Sample 1, Samples 11 to 14. Figure 51(B) is a graph of the cycle characteristics of Sample 1, Sample 11, Sample 15, and Sample 16. Figure 52 is a graph of the cycle characteristics of Sample 1, Sample 11, Sample 13, Sample 17, and Sample 18. Figures 53(A) and (B) are graphs of the cycle characteristics of Sample 1, Sample 13, and Sample 19.

[0540] All were measured at 45°C. Charging was CC / CV (0.5C, 4.6V, 0.05C cut-off), and discharging was CC (0.5C, 2.5V cut-off). In the measurement of the cycle characteristics of this example etc., 1C was 200 mA / g.

[0541] As shown in Figure 51(A), Samples 11 to 14 having impurities such as titanium, magnesium, and fluorine showed extremely good cycle characteristics rather than Sample 1 having no impurities in particular. Although the cycle characteristics of Sample 14 could only be evaluated up to 28 cycles due to defects caused by the manufacturing process of the secondary battery, it showed good characteristics before the defects occurred.

[0542] Samples 12 to 14 in which the number of lithium fluoride molecules was changed from 0.17 to 2.33 when the number of cobalt atoms was set to 100 all had good cycle characteristics. Among them, Sample 13 with a value of 1.17 showed the best characteristics.

[0543] As shown in Figure 51(B), Samples 15 and 16 having impurities such as magnesium and fluorine showed better cycle characteristics rather than Sample 1 having no impurities in particular.

[0544] As shown in Figure 52, Samples 11, Sample 13, Sample 17, and Sample 18 having impurities such as titanium, magnesium, aluminum, and fluorine showed better cycle characteristics rather than Sample 1 having no impurities in particular.

[0545] Samples 13, 17, and 18, with the heating time changed from 2 hours to 60 hours, all had good cycle characteristics. Among them, Sample 13 with a heating time of 20 hours showed the best characteristics.

[0546] Figure 53(A) is a graph of discharge capacity, and Figure 53(B) is a graph of discharge capacity retention rate. In particular, Samples 13 and 19 with impurities such as titanium, magnesium, and fluorine showed better cycle characteristics than Sample 1 without impurities. In particular, Sample 19 with the addition of lithium fluoride, nickel source, and aluminum source showed the best characteristics.

[0547] The initial discharge capacity was 215.5 mAh / g for Sample 1, 226.6 mAh / g for Sample 13, and 226.5 mAh / g for Sample 19. The discharge capacity retention rate after 30 cycles was 61.3% for Sample 1, 91.3% for Sample 13, and 93.9% for Sample 19.

Explanation of symbols

[0548] 101 Positive electrode active material 101a Surface layer part 101b Inside 101c Concave part 101d High nickel concentration region 102 Embedded part 103 Convex part 103a High fluorine concentration region 103b High metal impurity concentration region 1000 Positive electrode active material 1001 Protective film

Claims

1. A positive electrode active material comprising particles having lithium cobaltate, magnesium, titanium, nickel, aluminum, and fluorine, wherein: the particles have a surface layer portion, an interior, a concave portion, and a convex portion on the surface layer portion; the particles have a region where the concentration of titanium in the concave portion is higher than the concentration of titanium in the surface layer portion; the particles have a region where the concentration of titanium in the convex portion is higher than the concentration of titanium in the surface layer portion; the particles have a region where the concentration of magnesium in the convex portion is higher than the concentration of magnesium in the surface layer portion; the particles have a region where the concentration of nickel in the convex portion is higher than the concentration of nickel in the surface layer portion; the particles have a region where the concentration of fluorine in the convex portion is higher than the concentration of fluorine in the surface layer portion; the particles have a region where the concentration of aluminum in the surface layer portion is higher than the concentration of aluminum in the convex portion, the positive electrode active material.

2. A positive electrode active material comprising particles having lithium cobaltate, magnesium, titanium, nickel, aluminum, and fluorine, wherein: the particles have a surface layer portion, an interior, a concave portion, and a convex portion on the surface layer portion; the particles have a region where the concentration of titanium in the concave portion is higher than the concentration of titanium in the interior; the particles have a region where the concentration of titanium in the convex portion is higher than the concentration of titanium in the interior; the particles have a region where the concentration of magnesium in the convex portion is higher than the concentration of magnesium in the interior; the particles have a region where the concentration of nickel in the convex portion is higher than the concentration of nickel in the interior; the particles have a region where the concentration of fluorine in the convex portion is higher than the concentration of fluorine in the interior; the particles have a region where the concentration of aluminum in the surface layer portion is higher than the concentration of aluminum in the convex portion, the positive electrode active material.

3. In Claim 1 or Claim 2, the concave portion has a portion with a depth of 100 nm or more and a width of 20 nm or more, the positive electrode active material.

4. In any one of Claims 1 to 3, the convex portion has a portion with a height of 50 nm or more, the positive electrode active material.

5. In any one of Claims 1 to 4, the particles have a region where the concentration of cobalt in the convex portion is lower than the concentration of cobalt in the interior, the positive electrode active material.

6. A secondary battery having the positive electrode active material according to any one of Claims 1 to 5.

7. An electronic device having the secondary battery according to Claim 6.

Images